Kepler-452B Is Not a New Earth a Twin of the Sun-Jupiter System

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Bi-monthly magazine of scientific and technical information ✶ September-October 2015 issue astonishing PLUTO

Kepler-452b is not a new Earth A twinofthe Sun-Jupiter system

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SUMMARY

BI-MONTHLY MAGAZINE OF SCIENTIFIC AND TECHNICAL INFORMATION Astonishing Pluto FREELY AVAILABLE THROUGH A faultless mission, that of New Horizons: after a journey of nine and a half years it finally made its THE INTERNET rendezvous with Pluto one minute earlier than predicted and performed its task in the best of ways, 4 revealing a world remarkably more lively and varied than we could have imagined. In these pages... September-October 2015

Kepler-452b is not a new Earth Discovering a planet very similar to ours, at just the right distance from a star identical to the Sun, would be an important step forward in the search for extraterrestrial life. The rush to reach this goal 18 could, however, make us overly optimistic and lead us to define the same as Earth a planet that in...

First detection of lithium from an exploding star The light chemical element lithium is one of the few elements that is predicted to have been created by the Big Bang, 13.8 billion years ago. But understanding the amounts of lithium observed in stars around 26 us today in the Universe has given astronomers headaches. Older stars have less lithium than expected...

The ghost of a dying star Nicknamed the Southern Owl Nebula, this shimmering orb is a planetary nebula with a diameter of almost four light-years. Its informal name relates to its visual cousin in the northern hemisphere, the Owl Nebula. 30 ESO 378-1, which is also catalogued as PN K 1-22 and PN G283.6+25.3, is located in the constellation of... English edition of the magazine l’ASTROFILO Early black hole could upend evolutionary theory An international team of astrophysicists led by Benny Trakhtenbrot, a researcher at ETH Zurich’s Insti- Editor in chief tute for Astronomy, discovered a gigantic black hole in an otherwise normal galaxy, using W. M. Keck Michele Ferrara 32 Observatory’s 10-meter, Keck I telescope in Hawaii. The team, conducting a fairly routine hunt for... Scientific advisor Prof. Enrico Maria Corsini A twin of the Sun-Jupiter system Publisher Astro Publishing di Pirlo L. With its mass and orbital position, Jupiter has always had a decisive role in the evolution of the planetary Via Bonomelli, 106 system architecture. Not only has it fostered the birth of a planet such as Earth, but it also appears to 25049 Iseo - BS - ITALY have indirectly contributed to making it liveable. Now astronomers have discovered an almost identical... email [email protected] 38

Internet Service Provider Aruba S.p.A. Best evidence of first generation stars in the universe Loc. Palazzetto, 4 52011 Bibbiena - AR - ITALY Astronomers have long theorised the existence of a first generation of stars — known as Population III stars — that were born out of the primordial material from the Big Bang. The name Population III Copyright arose because astronomers had already classed the stars of the Milky Way as Population I (stars like... All material in this magazine is, unless 44 otherwise stated, property of Astro Publishing di Pirlo L. or included with permission of its author. Reproduction Atmosphere stripped from Neptune-sized exoplanet or retransmission of the materials, in whole or in part, in any manner, with- Astronomers using the NASA/ESA Hubble Space Telescope have discovered an immense cloud of hy- out the prior written consent of the drogen dispersing from a warm, Neptune-sized planet orbiting a nearby star. The enormous gaseous copyright holder, is a violation of tail of the planet is about 50 times the size of the parent star. A phenomenon this large has never... copyright law. A single copy of the 46 materials available through this course may be made, solely for personal, non- commercial use. Users may not distrib- ute such copies to others, whether or Fossil star clusters reveal their age not in electronic form, whether or not Using a new age-dating method and the W. M. Keck Observatory on Maunakea, an international team for a charge or other consideration, of astronomers have determined that ancient star clusters formed in two distinct epochs – the first 12.5 without prior written consent of the billion years ago and the second 11.5 billion years ago. Although the clusters are almost as old as the... copyright holder of the materials. 49 The publisher makes available itself with having rights for possible not characterized iconographic sources. Uranus-sized planet discovered through microlensing Advertising - Administration NASA's Hubble Space Telescope and the W. M. Keck Observatory in Hawaii have made independent Astro Publishing di Pirlo L. confirmations of an exoplanet orbiting far from its central star. The planet was discovered through a Via Bonomelli, 106 technique called gravitational microlensing. This finding opens a new piece of discovery space in the... 25049 Iseo - BS - ITALY 52 email [email protected] plutone EN:l'Astrofilo 28/08/15 10:18 Page 4

4 PLANETOLOGY AstonishingAstonishing PlutoPluto

by Michele Ferrara

A faultless mission, that of New Horizons: nly Pluto was still missing for complet- after a journey of nine and a half years it O ing the initial reconnaissance of the solar sys- finally made its rendezvous with Pluto one tem, and the primary goal minute earlier than predicted and perform- of NASA's New Horizons mission was precisely to fill ed its task in the best of ways, revealing a this gap. Compared to earlier world remarkably more lively and varied achievements by other space- crafts, this seemed a far minor objec- than we could have imagined. In these tive, so much so that hardly anyone ex- pages, we offer our readers a preview of the pected to see anything more than a dark globe crystallized by some billions of new face of Pluto and some of its satellites. years, at most marked by impacts of small

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PLANETOLOGY 5 inging PlutoPluto

July 2015, New Horizons 14 encounters Pluto and its satellites’ system. [JHUAPL/SwRI]

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bodies, definitely not common in that desolate part of our system. Pluto has instead turned out to be a remarkably diversified (dwarf) the planet, after having already travelled July, the sur- planet, with an atmosphere more similar more than 5 billion km in 9 and a half 11 faces of Plu- to that of Earth’s in terms of nitrogen con- years. With a resolution of 27 km/pixel, to (above) and tent percentage, but, above all, to be geo- this image allows to observe details barely Charon (below) logically active. hinted in the previous days’ recordings: clearly reveal the presence of cra- Evidence of this unexpected fact first the surface appears very varied, with large ters, chasms and emerged from a picture of Pluto taken on areas of different albedo and diverse cra- troughs. [NASA/ 9 July by the Long Range Reconnaissance tering levels. The surface structure more Johns Hopkins Imager (LORRI) of New Horizons, when University Ap- the spacecraft was still 5.4 million km from plied Physics Lab- oratory/South- west Research Institute]

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July, New Ho- markedly visible in this image is 11 rizons cap- a long dark region lying on tures, from a dis- the equator, provisionally tance of 4 million called “whale” due to its km, the best ever odd shape. Of partic- image of the op- ular scientific inter- posite hemisphere to that of the fly- est immediately ap- by. [NASA/Johns peared the tran- Hopkins Univer- sition territories sity Applied Phys- between the ics Laboratory/ “whale’s tail” and Southwest Re- the planet’s search Institute] western edge, where for the first time were noticed some unusual polygonal formations, that in the next 14 July flyby would not be possible to observe in detail, since located in the opposite hemisphere to that framed by the spacecraft’s instruments. On 11 July, at a distance of 4 million km from Pluto, LORRI photographs the hemisphere constantly facing Charon 500 km each, all arranged along the equa- (the one not visible during the flyby) and tor and adjacent to the “whale”. Already acquires the best ever picture of 4 large glimpsed during previous recordings, they areas, apparently circular and wide nearly now show a complex structure that leaves us uncertain as to their nature. That image will remain for decades the best ever image of the hemisphere not covered by the New Horizons’ flyby.

July, Pluto and Charon 13 photographed in colour, later enhanced to highlight terrains of varying composition. The distance between the two objects has been reduced. [NASA/Johns Hopkins University Applied Physics Laboratory/ Southwest Research Institute]

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Always on 11 July, the spacecraft turns its a hundred kilometres across and its bright July, the instruments also on Charon, showing a ejecta suggest that it must have formed 13 LORRI in- surface pockmarked with chasms and cra- over the last billion years. The crater’s strument takes ters, of which, among the first, the largest dark floor may indicate that it is composed the most beauti- to be framed lies in the southern hemi- of a different type of ice than that of the ful image of Plu- to’s globe. [NASA/ sphere and it is longer and deeper than surface, or that the Johns Hopkins our Grand Canyon. It is the first ice at its University Applied hint of the disintegration bot- Physics Laborato- processes affecting the ry/Southwest Re- satellite’s surface. search Institute] The largest of the visible craters is instead

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bove, 13 July, tom was initially melted by the impact et’s actual diameter, considered on more A the best pic- and then refrozen back into larger grains, than one occasion smaller than that of ture of Charon’s less effective at reflecting sunlight. another dwarf planet, Eris. New measure- globe, showing Another interesting structure clearly vis- ments indicate that Pluto has a diameter the details of a re- ible on Charon is a dark region about 320 of 2,370 km, hence appreciably larger than gion subsequent- km across, located next to ly photographed on 14 July from the north pole, whose 79,000 km away. origin is so far un- [NASA/ Johns known. Hopkins Univer- Thanks to the sity Applied Phy- images of Plu- sics Laboratory/ to’s disk taken Southwest Re- by LORRI in search Institute] the first half On the side, the of July, plan- New Horizons etary scien- team’s jubilation for the images of tists were Pluto arrived just able to defi- before closest nitely solve the approach. [NASA/ outstanding Bill Ingalls] issue on the plan-

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previously estimated, making it the big- of Pluto’s globe, in which stands out the July, photo- gest known body among the transneptu- most noticeable of all surface formations, 14 graphed, nian objects. Given its mass, a larger di- a heart-shaped, whitish region about from a distance ameter means a lower average density, 1,600 km across, close to the equator and of 77,000 km, the and thus a fraction of ice in the planetary already spotted in earlier images taken, first mountain range on Pluto, mass greater than that estimated so far. A though, at much greater distances. The Norgay Montes, larger diameter reduces also the thickness image resolution is such that for the first as high as 3,500 of the troposphere, whose outer bound- time can be clearly observed low reflec- metres. The video ary was previously known, and that re- tance regions dotted with impact craters, below shows its mains the same. In the case of Charon, and hence rather ancient (with an age of location. [NASA/ which in not having Johns Hopkins an atmosphere has in University Ap- the past permitted to plied Physics Lab- calculate its diameter oratory/South- without uncertainties, west Research the images taken by Institute] LORRI have confirmed the previous estimated value of 1,208 km. On 13 July, the picture shot from a distance of 768,000 km will be probably considered the iconic image of the entire mission, a spectacular overview

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July, the a few billion years), 14 Ralph in- set against brighter strument reveals areas which ap- a concentration pear almost cra- of frozen carbon terless and that monoxide (green should, there- area) in Tom- baugh Regio. fore, have form- Below, Sputnik ed much more Planum’s territo- recently (per- ries characterized haps a hun- by polygonal- dred million shaped features, years ago). whose nature is In several yet to be deter- places can mined. [NASA/ be observed Johns Hopkins craters par- University Ap- tially destroy- plied Physics Lab- ed, perhaps by oratory/South- west Research erosion, and al- Institute] so craters that appear invaded by layers of ligh- ter-coloured material, proving the fact that Pluto has until relatively recently been geologically active, or that maybe it still is. plutone EN:l'Astrofilo 28/08/15 11:37 Page 12

On 14 July, at 7:49 a.m. EDT bove, a pro- (USA Eastern Daylight Time), A visional map New Horizons, at a speed of Pluto. Left, the of 49,600 km/h, passes planet viewed in one minute earlier than enhanced colour to highlight areas scheduled the point with different of closest approach chemical-miner- point to Pluto, just alogical surface 12,470 km from composition. The its surface (less diagram in the than Earth’s di- next page shows ameter). In the the gas tail ex- hours just before tending from and after that mo- Pluto under the ment, the space- pressure of the craft devotes all solar wind. its energies to the [NASA/ Johns Hopkins Univer- seven scientific in- sity Applied Phy- struments fitted sics Laboratory/ aboard, which col- Southwest Re- lect such an amount search Institute] of data that it will take a full 16 months to trans- fer it all back to us, i.e. until November 2016! While New Horizons reaches the highlight

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of its endless journey, back on Earth the and the shades of the northern polar caps July, LORRI Ralph imaging instrument team presents a of the two globes, which are in high con- 14 takes this shot of Pluto and Charon with exaggerated trast with the rest of the visible surfaces. shot of a geologi- colour, emphasizing the complex chemical- The darker brown shaded areas indicate cally interesting region of Hillary mineralogical compositional diversities of the presence of simple hydrocarbons (such Montes. [NASA/ the two surfaces (still largely to be interpre- as methane) and more complex molecules Johns Hopkins ted). The differences that first stand out of the tholins class (already found some- University Applied are the sharp dichotomy between the two where else in the solar system), which are Physics Laborato- lobes forming the “heart” (of which the formed through the action of the Sun’s ul- ry/Southwest Re- easternmost appears considerably darker) traviolet radiation. search Institute]

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July, seven Al- 14 hours after ready by closest approach, 15 July the New Horizons first close-up passes behind Pluto images of Pluto's and takes this picture of the edge of surface were avail- the atmosphere back- able, which, in an equato- lit by the sun, dis- rial area at the base of the covering that it is “heart”, show a range of mountains much more extend- with peaks as high as 3,500 metres, prob- ed than previous- ably originated not more than 100 million as far ly believed. In the years ago, as further proof that Pluto's as a thousand video below, a vir- surface is one of the youngest of the en- kilometres, suggesting extensive fractur- tual flyby of Norgay tire solar system − a fact almost entirely ing of the satellite’s crust, as a result of in- Montes and Sput- unexpected. Taking into account the prop- ternal geological processes. nik Planum. [NASA/ Johns Hopkins Uni- er differences in proportion, a similar sce- In the days following the flyby, back to versity Applied nario applies to Charon, which in a very Earth also began to arrive data and im- Physics Laboratory/ detailed image released in mid-July shows ages taken by other instruments aboard Southwest Re- terrains that were formed relatively recent- the spacecraft, such as those produced search Institute] ly, dotted by cliffs and troughs stretching by the Alice spectrograph, which demon- strate how Pluto’s upper atmosphere is overall much more extended into space than previously thought: 1,600 km instead of 270 km. This new measurement is the result of a Sun-Pluto-spacecraft alignment, carefully planned in order to backlit its atmosphere to investigate it better. Observations made with the Solar Wind Around Pluto instrument have instead shown that Pluto's atmosphere is constantly being stripped of gas by the solar wind action, that with its pressure forms behind the planet a tail extending over 100,000 km. The fact that despite this phenomenon Pluto still has an atmosphere means that the gas making it up is being contin- uously replenished by geological process-

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es, probably of gons are bor- bove, a pro- the cryovolca- dered by nar- A visional map nic type − an hy- row and deep of Charon. Left, pothesis sup- troughs, some the satellite sys- ported for long of which host- tem of Pluto photographed by time by Alan ing darker de- New Horizons on Stern, principal bris and in 26 June, from investigator of some cases real 21.5 million km the New Hori- clusters of hills away. Next page, zons mission. that seem to the best available But let’s get back rise above the images of Nix to the high-reso- same poly- and Hydra. [NA- lution images of gons. The ini- SA/Johns Hopkins the planet's surface taken by LORRI du- tial working hypotheses on how these University Applied ring the flyby. Among the features that polygons may have formed are that they Physics Labora- most attracted the researchers’ attention are either the result of the contraction of icy tory/Southwest there are some flat plains extending to- surface materials (like when mud dries), or Research Institute] wards the left lobe of the “heart” (infor- the product of convective motions within mally named “Tombaugh Regio”, after a layer of surface ice rich in carbon mono- Clyde Tombaugh who discovered Pluto in xide, methane and nitrogen, which due to 1930), which appear fractionated into ir- its composition remains relatively fluid even regular polygons (similar to those already at a temperature of minus 234 degrees C, observed in the opposite hemisphere, but measured at the surface. In the first days in reduced scale), which are on average a following the flyby were also made avail- few tens of kilometres across. These poly- able good images in false colour of the sa-

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tellites Nix and Hydra, which allowed to km long and 36 km wide, while Hydra is distinguish areas of different chemical- 55 km long and 40 km wide. By mid-Octo- mineralogical composition and determine ber, New Horizons will also send images more precisely the size of the two objects, and data regarding Pluto’s two smallest whose shape is clearly irregular: Nix is 42 satellites, Styx and Kerberos. On 20 July arrives to Earth what is so far one of the most significant images trans- mitted by the spacecraft and released to the public, showing a southern portion of the Tombaugh Regio, provisionally named Sputnik Planum, on whose western edge can be clearly seen a new mountain range with peaks about 1,500 metres high, but above all can be observed the unmistak- able traces of the progression of deposits of light-coloured and likely recent materials towards more darker, definitely older terrains, something similar to a huge gla- cier of flowing hydrocarbons that in its path has also filled the bottom of some craters. This is for now the final proof that Pluto is still a geologically active world in which the heat produced by the radioactive decay of elements inside it seems to play a dominant role. n

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18 PLANETOLOGY Kepler-452bKepler-452b isis notnot aa newnew EaEarthrth

by Michele Ferrara

Discovering a planet very uring the last ten days of July, the n the back- mass media have emphasized – per- I ground, artist's similar to ours, at just the Dhaps excessively – the discovery of an interpretation of right distance from a star exoplanet, indicated by NASA as possible how Kepler-452b, Earth’s “older cousin”. In the fantasy mind the planet too hastily defined of many generalist journalists, this had turn- identical to the Sun, would by the mass ed into the discovery of a habitable planet be an important step for- media as “Earth's like ours, or even inhabited. Evidently there twin”, may ap- ward in the search for extra- is need of some clarification, and to this end pear. [NASA we can briefly go back to the spring of Ames/JPL-Cal- terrestrial life. The rush to 2014, when in the May-June issue of the tech/T. Pyle] reach this goal could, how- magazine (to which the reader can refer for further details) we featured the discovery ever, make us overly opti- of Kepler-186f, the exoplanet until then mistic and lead us to define considered the least dissimilar to Earth. Al- most identical in size and probably also in the same as Earth a planet the mass, likely rocky and almost certainly that in reality has very little with an atmosphere, Kepler-186f orbits in the habitable zone of a red dwarf, which is in common with ours. basically the only great difference with the

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he planets ap- T parently more similar to Earth discovered by Ke- pler space telescope in the last five years. Stars and planets are shown in the re- spective scales. [NASA Ames/W. Stenzel] Below, the twelve exoplanets that, among the 1,030 discovered by Kepler and confirmed to date, orbit within habitable zones and are less than twice the size of Earth (included for comparison). The planets’ sizes are magnified by 25 times compared to those of the stars. [NASA Sun-Earth system (apart from the planet’s every 384.84 days. The first transit was re- Ames/JPL-Cal- tech/R. Hurt] possible habitability or not). An unquestion- corded by Kepler space telescope in 2009, ably objective difference, but theoretically the debut year of its original science mis- irrelevant for the purposes of establishing sion, which lasted from 13 May 2009 to 11 a planet's environmental conditions. Deep May 2013. In these four years the instru- down, though, it feeds that form of anthropocentrism still embed- ded in the human race, according to which, unless a star is identical to the Sun, it cannot host a planet identical to ours. If with Kepler-186f we were just a step away from a new Earth, let us now see if with the discovery of the “older cousin” that last step has been made. The new planet, called Kepler- 452b, orbits in the habitable zone of KIC 8311864 (or Kepler- 452), a solar-type star of magnitude 13.4, laying about 1,400 light-years from Earth, in the constellation Cygnus. Kepler-452b is the only known planet of that star, and it transits on its disk kepler-452b EN:l'Astrofilo 28/08/15 10:27 Page 21

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The periodic signal revealing the likely presence of a planet finally emerges, and a pre- liminary examination of the star’s light curve during transits allows researchers to conclude that every event lasts 10.5 hours and causes a light fall of about two ten- thousandths; all phenomena compatible with the presence on the stellar disk of a planet whose diameter is 1.1 times that of the Earth (in short, as big as Kepler-186f, if the estimated size and brightness of the star are correct). With only the observations from the Kepler telescope it is not possible to progress much further and, as standard practice, very accurate follow-up observations of he above ani- ment recorded a total of 4 Kepler-452b the star-planet system must be made using T mation shows transits, the minimum number typically powerful ground-based telescopes. To this the different Earth indicated by astronomers for assigning to end, Jenkins and colleagues took spectra of and Kepler-452b’s the detected signal the planet candidate the star at the McDonald Observatory, the evolutionary status. That signal went however unno- Fred Lawrence Whipple Observatory (Mt. paths, dependent ticed, as it remained below the “sensiti- Hopkins, Arizona) and the W.M. Keck Ob- on those of their stars. Based on vity” threshold set by the assessment pro- servatory (Mauna Kea, Hawaii). The analy- how the extent cedures used by researchers until 2013. sis of the spectra showed that the star’s of habitable zones In May 2014, Kepler’s database was how- properties are somewhat different from is interpreted, the ever investigated with a new automated those previously estimated as, in fact, it is fate of the two process developed by Jeff Coughlin (of the 11% larger than the Sun, 20% brighter and planets varies con- SETI Institute in Mountain View, Califor- 60% richer in metals. The star’s mass (infer- siderably. [NASA] nia), which no longer requires subjective red on the basis of mathematical models) Right, a scaled judgments and that consults and assesses and surface temperature (and thus its spec- comparison of more quickly and uniformly the dataset, tral type) were instead found to be similar the habitable besides being more functional for finding to those of the Sun, while its age seems to zones of Kepler- smaller planets. 186, Kepler-452 This investiga- and the Sun, and of the orbits of tion is being planets residing conducted by there. The inclu- Joseph Twicken, sion of Venus and member of the Mars in this dia- McDonald Ob- gram is clearly an servatory (Uni- optimistic repre- versity of Tex- sentation of hab- as, Austin), to- itable zones. gether with a [NASA Ames/JPL- large interna- Caltech/R. Hurt] tional team of researchers, led by Jon Jenkins, of the NASA Ames Research Center (Moffett Field, Califor- nia). kepler-452b EN:l'Astrofilo 28/08/15 10:27 Page 22

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be significantly older, 6 billion years, even if this estimate is highly dependent upon the models used to derive it, with a degree of un- certainty of ± 2 billion years. The aspect that most interests us here is nonetheless that related to the stellar diameter (and consequently that of the brightness per unit area), since in being greater than previously estimated, it resul- tantly increases the one of Kepler-452b up to 1.63 times that of Earth (about 20,800 ± 2,500 km). Also the radiation flux reaching the planet is greater, but given that it is about 7 million km farther from its star than the average Earth-Sun distance, the heat it receives is only 10% greater. Once established that KIC 8311864 is not exactly identical to the Sun, but that it is probably a more evolved version, what now remains to be seen is if and how Kepler-452b resembles Earth. In order to provide an an- swer to these questions we must add to the overall picture a key parameter, the planet’s mass. Unfortu- opposite direction), Kepler-452b is too arth and Ke- nately, its value is unknown, and in fact, small and far from KIC 8311864 to produce Epler-452b face no spectroscopic observation of the star in the star’s dim light any effect detectable to face. The artist has shown lines displacements in response with the instruments currently available to who depicted large continents to whichever planetary pull. Even when astronomers. on the new plan- transiting on the disk (and behind it), and The absence of any variation in the star's et did not consid- thus being in the best position for moving radial velocity could also mean the non- er that according the star towards the observer (and in the existence of the planet, since a periodic sig- to more recent and kepler-452b EN:l'Astrofilo 28/08/15 10:27 Page 23

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on orbits whose properties are such as not to cause secondary minima in the light curve. After all tests have been completed, Jen- kins’ team concluded that there is only 1 chance in 424 that that signal is not generated by the transit of Kepler-452b, and thus the planet really exists. The fact that it does not produce effects on the radial velocity of its star pro- vides us an upper limit on the value of its mass (beyond which it would gen- erate effects detectable with current instruments). Instead, the diameter calculated for the planet and reasonable theoretical eval- uations do provide us a lower limit of that value. The two extremes are 7 and 3 Earth masses and, subse- quently, what we are facing is not exactly a twin of our planet. In the best of cases its gravity would be double that keeping us glued to the ground and, according to the experts, this implies an atmosphere considerably thicker than ours, perhaps fuelled by intense volcanic eruptions. On this last point we could express some doubts, since with the data available we do not have the certainty that Kepler-452b has a rocky surface; a scenario that Jenkins’ team consid- accurate mathe- nal such as that attributed to it may in fact ers likely at about 49-62%. For complete- matical models, have a different origin. Consequently, re- ness’ sake, it should also be pointed out bodies of this searchers needed to start ruling out all pos- that without an intervention of Kepler- size do not have sible alternative scenarios: eclipsing binary 452b in the radial velocity of KIC 8311864 more than a 40% chance to have a stars laying along the line of sight; a faint it is not possible to know the eccentricity rocky surface. companion star transited by a big planet; of the planetary orbit, and hence not even [NASA Ames/JPL- the transit of a white dwarf companion or its exact shape. This in turn has an impact Caltech/T. Pyle] the occultation of a brown dwarf, located on the effective permanence of the planet kepler-452b EN:l'Astrofilo 28/08/15 10:27 Page 24

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within the habitable zone, both in the short (annual cycle) and very long-term (billions of years). A star’s habitable zone (which by definition is that range of distances from the star that could permit liquid water to pool on a rocky surface) is a very flex- ible concept that can be interpreted according to an “optimistic” version, which substantially takes into account also relatively short liveability periods of a planet within it, or according to a “conservative” version, which considers only distances from the star suitable for ensuring the survival of possible forms of life for a very long time. As re- Let us try at this stage to summarize the iagram show- gards to Kepler-452b, with the varying of key points and see how much Kepler-452b D ing all planets the adopted stellar, orbital and planetary resembles Earth: it has a diameter greater discovered by Ke- parameters, the chances that the planet is by 63%, a mass from 3 to 7 times greater, a pler (confirmed steadily in the habitable zone go from a gravity that is at least double, a definitely or yet to be confirmed) that are maximum of more than 96% to a mini- thicker atmosphere, and thus higher tem- least dissimilar to mum of 28%. A range a bit too broad to perature and ground pressure, always as- Earth in terms of provide any certainty. suming that there is an atmosphere and a size, inclusion in ground surface. the habitable This in addition zone, flux of ener- with the fact that gy received from the planet moves the own star, and along an orbit temperature of which for calcula- the latter. Kepler- 452b seems to be tion ease is con- the most similar, sidered circular, but only in terms but whose true of the type of shape is un- star and energy known; that it flux. The graph stations in the on the left shows habitable zone that all signals by an uncertain recorded by Ke- time and that it pler were exam- will continue to ined and that almost 4,700 plan- do so for an un- et candidates certain time. have emerged. It should be not- [NASA Ames/ ed in this regard W. Stenzel and that orbiting in SETI Institute/ a habitable zone J. Coughlin] kepler-452b EN:l'Astrofilo 28/08/15 10:27 Page 25

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ight curve of L KIC 8311864 in the 60 hours cen- tred (phase 0) on the 4 transits of Kepler-425b, of 10.5 hours each. The black dots are the photo- metric observations of Kepler, the blue circles and being habitable are two very differ- tech, places the confine between super- the averaged val- ent things: if the star-planet system’s esti- Earths and mini-Neptunes precisely at 1.6 ues. The moder- mated age is correct, the evolutionary stage solar masses.) In short, Kepler-452b does ate dispersion reached by KIC 8311864 has probably al- not at all seem to be an Earth’s twin and can be attributed ready triggered an out of control green- even the “older cousin” name given to it to photospheric house effect on the planet, which re- would seem inappropriate. activity. [Jenkins searchers estimate to be underway by The chances of finding in Kepler’s database et al.] Below, in about 800 million years. Moreover, the something much more similar still however the first half of distance of the star is not known with plentiful, given that researchers are already 2015 there was a absolute precision (we will know it better examining a further 65 candidate planets significant in- within 1-2 years thanks to Gaia space tele- with diameters between one and two crease of new scope) and it could even be more far-away times that of our own planet, all orbiting planet candidates (yellow dots) in than previously estimated; in that case the in the habitable zones of their stars. Kepler’s data- planet, already classified as super-Earth, If not even among them it will be possible base, thanks to could be even bigger and belong for sure to identify a new Earth, we will have to the introduction to the mini-Neptune class. (In a very thor- wait for future observations by two new of a new assess- ough article published in The Astrophysical NASA space telescopes currently in an ad- ment procedure. Journal in March 2015, Leslie Rogers, Cal- vanced construction stage, the Transiting Exoplanet Survey Satellite and the James Webb Space Tele- scope, scheduled for launch in 2017 and 2018. Together they will discover Earth-sized planets also at relatively short distances from our own, provide direct information on their size, mass, atmosphere, colours, sea- sonal variations and weather, including the possible presence of vegetation. So far we have evidence of about 5,000 planets, 1,500 of which have already been confirmed. Almost all of them were discovered just with the transits method in a tiny corner of the heavens representing 0.28% of the entire sky. We can just imagine how many non-transiting planets there are and how many planets there are in total in the remaining 99.72% of the sky. n chronicles EN1:l'Astrofilo 28/08/15 10:29 Page 26

SPACE CHRONICLES

First detection of lithium from an exploding star

by ESO

he light chemical element lithium is one of the few elements T that is predicted to have been created by the Big Bang, 13.8 billion years ago. But understanding the amounts of lithium observed in stars around us today in the Universe has given astronomers headaches. Older stars have less lithium than expected, and some younger ones up to ten times more. (More precisely, the terms “younger” and “older” are used to refer to what astronomers call Population I and Population II stars. The Population I category includes the Sun; these stars are rich in heavier chemical elements and form the disc of the Milky Way. Population II stars are older, with a low heavy- element content, and are found in the Milky Way Bulge and Halo, and globular star clusters. Stars in the “younger” Population I class can still be several billion years old!) Since the 1970s, astronomers have speculated that much of the extra lithium found in young stars may have come from novae — stellar explosions that expel material into the space between the stars, where it his image from the New Technology Telescope at ESO’s La Silla Ob- contributes to the material that T servatory shows Nova Centauri 2013 in July 2015 as the brightest builds the next stellar generation. star in the centre of the picture. This was more than eighteen months But careful study of several novae after the initial explosive outburst. This nova was the first in which has yielded no clear result up to now. evidence of lithium has been found. [ESO] A team led by Luca Izzo (Sapienza University of Rome, and ICRANet, Pe- chronicles EN1:l'Astrofilo 28/08/15 10:29 Page 27

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scara, Italy) has now his video sequence starts from a used the FEROS in- T wide field view of the Milky Way strument on the and closes in on the bright and fa- MPG/ESO 2.2-metre mous pair of stars Alpha and Beta telescope at the La Centauri. The final image in the Silla Observatory, zoom is a closeup of the nova taken as well the PUCHE- using the New Technology Telescope ROS spectrograph at ESO’s La Silla Observatory in July on the ESO 0.5- 2015. The nova is the brightest star metre telescope at close to the centre of the picture the Observatory of and is much fainter than it was at the Pontificia Uni- maximum light, when it could be versidad Catolica seen with the naked eye. [ESO/Digi- de Chile in Santa tized Sky Survey 2/N. Risinger] Martina near San- tiago, to study the nova Nova Cen- est nova so far this century — easily first detection of the element eject- tauri 2013 (V1369 Centauri). visible to the naked eye. ed from a nova system to date. These comparatively small telesco- The very detailed new data revealed Co-author Massimo Della Valle (INAF- pes, equipped with suitable spectro- the clear signature of lithium being Osservatorio Astronomico di Capo- graphs, are powerful tools for this expelled at two million kilometres dimonte, Naples, and ICRANet, Pe- kind of research. Even in the era of per hour from the nova. This high ve- scara, Italy) explains the significance extremely large telescopes smaller locity, from the nova towards the of this finding: “It is a very important telescopes dedicated to specific tasks Earth, means that the wavelength of step forward. If we imagine the his- can remain very valuable. The star the line in the absorption in the spec- tory of the chemical evolution of exploded in the southern skies close trum due to the presence of lithium the Milky Way as a big jigsaw, then to the bright star Beta Centauri in is significantly shifted towards the lithium from novae was one of the December 2013 and was the bright- blue end of the spectrum. This is the most important and puzzling missing pieces. In addition, any model of the Big Bang can be questioned until the lithium conundrum is understood.” The mass of ejected lithium in Nova Centauri 2013 is estimated to be tiny (less than a billionth of the mass of the Sun), but, as there have been many billions of novae in the history of the Milky Way, this is enough to explain the observed and unexpectedly large amounts of lithium in our galaxy. Authors Luca Pasquini (ESO, Garch- ing, Germany) and Massimo Della Valle have been looking for evidence of lithium in novae for more than a quarter of a century. This is the satisfying conclusion to a long search for them. And for the younger lead scientist there is a different kind of thrill: "It is very excit- n this image, the southern Milky Way crosses the field at La Silla Observa- ing,” says Luca Izzo, “to find some- Itory. Within the sea of stars, a special one is shining bright (in the little yellow circle): Nova Centauri 2013, also known as V1369 Centauri. On the left is thing that was predicted before I the Swedish-ESO Submillimetre Telescope (SEST). [Y. Beletsky (LCO)/ESO] was born and then first observed on my birthday in 2013!” n chronicles EN1:l'Astrofilo 28/08/15 10:29 Page 28

our of the seven members of Fgalaxy group HCG 16.This quar- Hubble viewsa tet is composed of (from left to right) NGC 839, NGC 838, NGC 835, and NGC 833. This new image uses observations from Hubble's bizarre cosmic Wide Field Planetary Camera 2 combined with data from the ESO Multi-Mode Instrument, installed quartet on the European Southern Obser- vatory's New Technology Tele- scope in Chile. [NASA, ESA, ESO]

by NASA left to right) NGC 839, NGC 838, NGC Compact groups represent some of 835, and NGC 833 — four of the sev- the densest concentrations of gal- en galaxies that make up the entire axies known in the Universe, making his new NASA/ESA Hubble group. They shine brightly with their them perfect laboratories for study- Space Telescope image shows glowing golden centres and wispy ing weird and wonderful phenom- T a gathering of four cosmic com- tails of gas, set against a back- ena. Hickson Compact Groups in par- panions. This quartet forms part of ground dotted with much more ticular, as classified by astronomer a group of galaxies known as the distant galaxies. (A tidal tail is a thin, Paul Hickson in the 1980s, are surpris- Hickson Compact Group 16, or HCG elongated region of stars and inter- ingly numerous, and are thought to 16 — a galaxy group bursting with stellar gas that extends into space contain an unusually high number dramatic star formation, tidal tails, from a galaxy. They are a result of galaxies with strange properties galactic mergers and black holes. of the strong gravitational forces and behaviours. HCG 16 is certainly This quartet is composed of (from around interacting galaxies.) no exception. The galaxies within it chronicles EN1:l'Astrofilo 28/08/15 10:29 Page 29

are bursting with dramatic knots of Seyfert 2 galaxy and three starburst when observed at other wave- star formation and intensely bright galaxies. These three types of galaxy lengths than in the visible light, and central regions. are all quite different, and can each are home to active supermassive Within this single group, astrono- help us to explore something diffe- black holes. The X-ray emission ema- mers have found two LINERs, one rent about the cosmos. Starbursts nating from the black hole within are dynamic galaxies NGC 833 (far right) is so high that it that produce new stars suggests the galaxy has been strip- at much greater rates ped of gas and dust by past interac- than their peers. LI- tions with other galaxies. It is not NERs (Low-Ionisation alone in having a violent history — Nuclear Emission-line the morphology of NGC 839 (far Regions) contain heat- left) is likely due to a galactic merger ed gas at their cores, in the recent past, and long tails of which spew out radia- glowing gas can be seen stretching tion. In this image NGC away from the galaxies on the right 839 is a LINER-type of the image. and luminous infrared This new image uses observations his video zooms in from a view of the night galaxy and its compan- from Hubble's Wide Field Planetary T sky, through the constellation of Cetus (The ion NGC 838 is a LINER- Camera 2, combined with data from Sea Monster), to end on new NASA/ESA Hubble type galaxy with lots of the ESO Multi-Mode Instrument in- Space Telescope observations of galaxy group starburst activity and stalled on the European Southern HCG 16. The final image uses observations from no central black hole. Observatory’s New Technology Tele- Hubble’s Wide Field Planetary Camera 2, com- The remaining galax- scope in Chile. A version of this image bined with data from the ESO Multi-Mode In- ies, NGC 835 and NGC was entered into the Hubble's Hid- strument installed on the European Southern 833, are both Seyfert 2 den Treasures image processing com- Observatory’s New Technology Telescope in Chile. [NASA, ESA, Digitized Sky Survey 2. ESO] galaxies which have in- petition by contestants Jean-Chris- credibly luminous cores tophe Lambry and Marc Canale. n chronicles EN1:l'Astrofilo 28/08/15 10:29 Page 30

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The ghostof a dying star

by ESO enon, lasting only a few tens of thousands of years, compared to a typical stellar lifetime of several billion icknamed the Southern Owl years. The lifetime of a planetary Nebula, this shimmering orb nebula as a fraction of a star's life is Nis a planetary nebula with a about the same as the life of a soap diameter of almost four light-years. bubble compared to the age of the Its informal name relates to its vi- child who blows it. sual cousin in the northern hemi- Planetary nebulae are created by sphere, the Owl Nebula. ESO 378-1, the ejected and expanding gas of which is also catalogued as PN K 1- dying stars. Although they are bril- 22 and PN G283.6+25.3, is located in liant and intriguing objects in the the constellation of Hydra, the Fe- initial stages of formation, these male Water Snake. (The ESO in the bubbles fade away as their constit- name of this object refers to a cata- uent gas moves away and the cen- logue of objects compiled in the tral stars grow dimmer. 1970s and 80s from careful inspec- For a planetary nebula to form, the tion of new photographs taken aging star must have a mass less with the ESO 1-metre Schmidt tele- than about eight times that of the scope at La Silla.) Sun. Stars that are heavier than this Like all planetary nebulae, ESO 378- limit will end their lives in dramatic 1 is a relatively short-lived phenom- fashion as supernova explosions. As these less massive stars grow old they start to lose their outer layers of gas to stellar winds. After most of these outer layers have dissipated, the remaining hot stellar core starts to emit ultraviolet radiation which then ionises the surrounding gas. This ionisation causes the expanding shell of his video sequence starts from a wide field ghostly gas to begin to T of the Milky Way and closes in on a rather glow in bright colours. empty patch of sky in the huge constellation After the planetary neb- of Hydra. A strange blue disc becomes visible ula has faded away, the — the planetary nebula ESO 378-1. The final leftover stellar remnant very detailed view comes from ESO’s Very Large Telescope at the Paranal Observatory in will burn for another Chile. [ESO/Digitized Sky Survey 2/N. Risinger] billion years before con- suming all its remaining

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his extraordinary bubble, T glowing like the ghost of a star in the haunting dark- ness of space, may appear supernatural and mysterious, but it is a familiar astronomical object: a planetary nebula, the remnants of a dying star. This is the best view of the little-known object ESO 378-1 yet obtained and was captured by ESO’s Very Large Telescope in northern Chile. [ESO]

fuel. It will then become a tiny — but hot and very dense — white dwarf that will slowly cool over billions of years. The Sun will produce a planetary nebula several billion years in the future and will afterwards also spend its twilight years as a white dwarf. Planetary nebulae play a crucial role in the chemical enrichment and evolution of the Universe. Elements such as carbon and nitrogen, as well as some other heavier elements, are created in these stars and re- turned to the interstellar medium. Out of this material new stars, planets and eventually life can form. Hence astronomer Carl Sagan's famous phrase: "We are made of star stuff." This picture comes from the ESO Cosmic Gems programme, an outreach initiative to produce images of interesting, intriguing or visual- ly attractive objects using ESO telescopes for the purposes of education and public outreach. The programme makes use of telescope time that cannot be used for science observations. All data collected may also be suitable for scientific purposes, and are made available to astronomers through ESO's science archive. n

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Early black hole could upend evolutionary theory

by Keck Observatory

n international team of astrophysicists led by Benny A Trakhtenbrot, a researcher at ETH Zurich’s Institute for Astro- nomy, discovered a gigantic black hole in an otherwise normal galaxy, using W. M. Keck Observatory’s 10- meter, Keck I telescope in Hawaii. The team, conducting a fairly routine hunt for ancient, massive black holes, was surprised to find one with a mass of more than 7 billion times our Sun making it among the most massive black holes ever discovered. And because the galaxy it was discovered in was fairly typical in size, the study calls into question previous assumptions on the de- velopment of galaxies. The data, collected with Keck Observatory’s newest instrument called MOSFIRE, revealed a giant black hole in a galaxy called CID-947 that was 11 billion light years away. The incredible sensitivity of MOSFIRE coupled to the world’s largest optical/infrared telescope meant the scientists were able to observe and characterize this black hole as it was when the Universe was less than two billion years old, just 14 percent of its current age. Even more surprising than the black hole’s record mass, was the relatively ordinary mass of the galaxy that contained it. Most galaxies chronicles EN1:l'Astrofilo 28/08/15 10:30 Page 33

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host black holes with masses less laxy,” Trakhtenbrot said. “We there- during the growth of the black than one percent of the galaxy. In fore have a gigantic black hole wi- hole controlled, or even stopped, CID-947, the black hole mass is 10 thin a normal size galaxy. The result the creation of stars as the released percent that of its host galaxy. was so surprising, two of the astro- energy heated up the gas. This cu- Because of this remarkable dispa- nomers had to verify the galaxy mulative evidence led scientists to rity, the team deduced this black mass independently. Both came to assume the growth of black holes hole grew so quickly the host galaxy the same conclusion.” and the formation of stars go was not able to keep pace, calling “Black holes are objects that possess hand-in-hand. into question previous thinking on such a strong gravitational force The latest results, however, suggest the co-evolution of galaxies and that nothing – not even light – can that these processes work different- their central black holes. escape,” said Professor Meg Urry of ly, at least in the early Universe. The “The measurements of CID-947 cor- Yale University, co-author of the distant young black hole observed respond to the mass of a typical ga- study. ”Einstein’s theory of relativity by Trakhtenbrot, Urry and their colleagues had roughly 10 times less n this illustration mass than its galaxy. In today’s local a black hole I Universe, black holes typically reach emits part of the accreted matter in a mass of 0.2 to 0.5 percent of their the form of ener- host galaxy’s mass. getic radiation “That means this black hole grew (blue), without much more efficiently than its gal- slowing down star axy – contradicting the models that formation within predicted a hand-in-hand develop- the host galaxy ment,” he said. (purple regions). The researchers also concluded stars [M. Helfenbein, were still forming even though the Yale Univ./OPAC] black hole had reached the end of its growth. Contrary to previous as- describes how they sumptions, the energy and gas flow bend space-time it- propelled by the black hole did not self. The existence of stop the creation of stars. black holes can be "From the available Chandra data proven because mat- for the source, we also concluded ter is greatly acceler- that the black hole has a very low ated by the gravita- accretion rate, and is therefore tional force and thus reached the end of its growth. emits particularly high- On the other had, other data sug- energy radiation.” gests that stars were still forming Until now, observa- throughout the host galaxy," Trakh- tions have indicated tenbrot said. that the greater the The galaxy could continue to grow number of stars pres- in the future, but the relationship ent in the host gal- between the mass of the black hole axy, the bigger the and that of the stars would remain black hole. “This is unusually large. true for the local Uni- The researchers believe CID-947 verse, which merely could be a precursor of the most reflects the situation extreme, massive systems that we in the Universe’s re- observe in today’s local Universe, cent past,” Urry said. such as the galaxy NGC 1277 in the Furthermore, previ- constellation of Perseus, some 220 ous studies suggest million light years away from our the radiation emitted Milky Way. n chronicles EN1:l'Astrofilo 28/08/15 10:30 Page 34

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ALMA witnesses assembly of galaxies in the early Universe for the first time

by Keck Observatory oratory and Kavli Institute for Cos- trace the cold gas out of which stars mology, University of Cambridge, form. Specifically, the team were United Kingdom) trained ALMA on looking for the emission from singly hen the first galaxies start- galaxies that were known to be seen ionised carbon (known as [C II]). ed to form a few hundred only about 800 mil- W million years after the Big lion years after the Bang, the Universe was full of a fog Big Bang (they had of hydrogen gas. But as more and redshifts ranging more brilliant sources — both stars from 6.8 to 7.1 ). The and quasars powered by huge black astronomers were holes — started to shine they cleared not looking for the away the mist and made the Uni- light from stars, but verse transparent to ultraviolet light. instead for the faint Astronomers call this the epoch of glow of ionised car- reionisation, but little is known bon coming from about these first galaxies, and up to the clouds of gas now they have just been seen as very from which the faint blobs. But now new observa- stars were forming. ime-lapse of a whole night at the ALMA Array tions using the power of ALMA are They wanted to T Operations Site (AOS), located at 5000 metres al- titude on the Chajnantor plateau, Chile. Three anten- starting to change this. Neutral hy- study the interac- nas are pointing at the same target in the sky at any drogen gas very efficiently absorbs tion between a moment, so their movements are perfectly synchro- all the high-energy ultraviolet light young generation nised. As the sky appears to rotate clockwise around emitted by young hot stars. of stars and the cold the south celestial pole (roughly on the upper left Consequently, these stars are almost clumps that were edge of the image), the Milky Way goes down slow- impossible to observe in the early assembling into ly, until it is lying almost horizontal before sunrise. Universe. At the same time, the ab- these first galaxies. The centre of our galaxy becomes visible during the sorbed ultraviolet light ionises the Astronomers are second half of the night as a yellowish bulge crossed hydrogen, making it fully transpar- particularly inter- by dark lanes in the centre of the image, just above ent. The hot stars are therefore carv- ested in ionised car- the antennas. The flashes on the ground are the car ing transparent bubbles in the gas. bon as this partic- lights of the guards patrolling at the AOS. ALMA, Once all these bubbles merge to fill ular spectral line the Atacama Large Millimeter/submillimeter Array is the largest astronomical project in existence and is all of space, reionisation is complete carries away most a truly global partnership between the scientific and the Universe becomes trans- of the energy inject- communities of East Asia, Europe and North America parent. A team of astronomers led ed by stars and al- with Chile. [ESO/José Francisco Salgado] by Roberto Maiolino (Cavendish Lab- lows astronomers to chronicles EN1:l'Astrofilo 28/08/15 10:30 Page 35

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This radiation is detail key processes emitted at a wave- occurring within length of 158 mi- the first galaxies. crometres, and by The effects of the the time it is stret- radiation from ched by the expan- stars, the survival of sion of the Universe molecular clouds, arrives at ALMA at the escape of ion- just the right wave- ising radiation and length for it to be the complex struc- detected at a wave- ture of the inter- length of about 1.3 stellar medium can millimetres. now be calculated They were also not and compared with looking for the ex- observation. tremely brilliant BDF 3299 is likely to rare objects — such be a typical exam- as quasars and gal- ple of the galaxies axies with very high responsible for re- rates of star for- ionisation. mation — that had “We have been been seen up to trying to under- now. Instead they stand the interstel- concentrated on lar medium and the rather less dramat- formation of the re- ic, but much more ionisation sources common, galaxies for many years. Fi- that reionised the nally to be able to Universe and went test predictions and on to turn into the hypotheses on real bulk of the galaxies his view is a combination of images from ALMA and the Very data from ALMA is that we see around T Large Telescope. The central object is a very distant galaxy, la- an exciting moment us now. From one belled BDF 3299, which is seen when the Universe was less than 800 and opens up a new of the galaxies — million years old. The bright red cloud just to the lower left is the set of questions. given the label BDF ALMA detection of a vast cloud of material that is in the process of This type of obser- 3299 — ALMA could assembling the very young galaxy. [ESO/R. Maiolino] vation will clarify pick up a faint but many of the thorny clear signal from the glowing car- but as objects with internal struc- problems we have with the forma- bon. However, this glow wasn’t ture!” The astronomers think that tion of the first stars and galaxies in coming from the centre of the gal- the off-centre location of the glow the Universe,” adds Andrea Ferrara. axy, but rather from one side. Co- is because the central clouds are Roberto Maiolino concludes: “This author Andrea Ferrara (Scuola Nor- being disrupted by the harsh en- study would have simply been im- male Superiore, Pisa, Italy) explains vironment created by the newly possible without ALMA, as no other the significance of the new findings: formed stars — both their intense instrument could reach the sensitiv- “This is the most distant detection radiation and the effects of super- ity and spatial resolution required. ever of this kind of emission from a nova explosions — while the carbon Although this is one of the deepest ‘normal’ galaxy, seen less than one glow is tracing fresh cold gas that is ALMA observations so far it is still billion years after the Big Bang. being accreted from the intergalac- far from achieving its ultimate capa- It gives us the opportunity to watch tic medium. bilities. In future ALMA will image the build-up of the first galaxies. By combining the new ALMA obser- the fine structure of primordial gal- For the first time we are seeing early vations with computer simulations, axies and trace in detail the build-up galaxies not merely as tiny blobs, it has been possible to understand in of the very first galaxies.” n chronicles EN1:l'Astrofilo 28/08/15 10:30 Page 36

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Charting the slow death of the universe

by ESO

n international team of astronomers studying more than A 200,000 galaxies has measured the energy generated within a large portion of space more precisely than ever before. The study involves many of the world’s most powerful telescopes, including ESO's VISTA and VST survey telescopes at the Paranal Obser- vatory in Chile. Supporting observations were made by two orbiting space telescopes operated by NASA (GALEX and WISE) and another belonging to the European Space Agency (Herschel). The research is part of the Galaxy And Mass Assembly (GAMA) project, the largest multi-wavelength survey ever put together. “We used as many space and ground-based telescopes as we could get our hands on to measure the All the energy in the Universe was math of the Big Bang, additional energy output of over 200 000 galaxies created in the Big Bang, with some energy is constantly being generat- across as broad a wavelength range as portion locked up as mass. Stars ed by stars as they fuse elements possible,” says Simon Driver (ICRAR, shine by converting mass back into like hydrogen and helium together,” The University of Western Australia), energy, as described by Einstein’s Simon Driver says. “This new energy who heads the large GAMA team. The famous equation E=mc2. The GAMA is either absorbed by dust as it trav- survey data includes measurements of study sets out to map and model all els through the host galaxy, or es- the energy output of each galaxy at 21 of the energy generated within a capes into intergalactic space and wavelengths, from the ultraviolet to large volume of space today and at travels until it hits something, such the far infrared. This dataset will help different times in the past. “While as another star, a planet, or, very oc- scientists to better understand how dif- most of the energy sloshing around casionally, a telescope mirror.” The ferent types of galaxies form and evolve. in the Universe arose in the after- fact that the Universe is slowly fading has been known since the late he above composite picture shows how a typical galaxy appears at 1990s, but this work shows that it is T different wavelengths in the GAMA survey. This huge project has happening across all wavelengths measured the energy output of more than 200,000 galaxies and repre- from the ultraviolet to the infrared, sents the most comprehensive assessment of the energy output of the representing the most comprehen- nearby Universe. The results confirm that the energy produced in a sec- sive assessment of the energy out- tion of the Universe today is only about half what it was two billion years ago and find that this fading is occurring across all wavelengths put of the nearby Universe. The Uni- from the ultraviolet to the far infrared. [ICRAR/GAMA and ESO] verse will decline from here on in, sliding gently into old age. n

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38 PLANETOLOGY AtAtwiwinofnofthethe Sun-Jupiter Sun-Jupiter systemsystem

by Michele Ferrara

With its mass and orbital position, Jupiter has always had rtist’s view of Athe solar twin a decisive role in the evolution of the planetary system HIP 11915, and its Jupiter’s twin architecture. Not only has it fostered the birth of a planet planet, HIP 11915 b. The distance such as Earth, but it also appears to have indirectly con- between these tributed to making it liveable. Now astronomers have two bodies is almost identical to discovered an almost identical copy of Jupiter around a that between the Sun and Jupiter. twin star of the Sun. Will there be more to come? [ESO/L. Benassi]

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PLANETOLOGY 39 ee Sun-Jupiter Sun-Jupiter

ome of the most current theories on ours, and while we wait to find out to what the formation of our solar system indi- extent its architecture can be considered S cate that the presence of Jupiter has harbinger of life, the most likely path that been instrumental in shaping the system researchers can follow for finding systems that we know today, and it has therefore analogous to ours is to discover twins of Ju- probably been a determining factor also in piter, which rotate around stars identical to the appearance of life on Earth. the Sun, on orbits very similar to that of Ju- Although hundreds of other systems were piter. This kind of research is fundamental discovered in the last twenty years, whose for estimating the dissemination of systems planetary orbits and masses varied greatly, similar to ours, but it is hampered by some the only one that surely hosts life remains contingent factors that astronomers must

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take into account and that involve working at the limits of current instrumental capabilities and data analysis. The most restrictive factor implies the need to discover a planet with an orbital period of 10-11 years, and hence collect within a comparable timeframe or (better) longer, uniform data, possibly with the same instrument and appropriate temporal coverage. The fact that extrasolar planets have been monitored as a whole for two decades does not automatically mean discovering a Jupiter twin at the right distance from a Sun twin. As mentioned, it is also essential a certain level of uniformity of the data collected and it is indispens- able an extraordinary spectroscopy precision; requirements that only the HARPS (High Accuracy Radial velocity Planet Searcher) instrument on the ESO 3.6-metre Cassegrain telescope has in the past met and still continue to meet today in its hunt for extrasolar planets. HARPS has been operating since 2003 and, consequently, for some planetary systems there are recordings and documentation that – at least that of Sun-Jupiter. HARPS’ particularity bove, the his- from the temporal viewpoint – are suffi- is to be able to highlight even tiny shifts Atoric 3.6-metre cient for revealing systems analogous to toward the blue and red of certain spectral Cassegrain tele- lines (compared to scope, installed at laboratory-measured ESO in 1977. This instrument has standard positions), over the years that are interpreted benefited from sig- as light source move- nificant upgrades, ments at speeds typ- including the ically between a few HARPS spectro- km/sec and a few hun- graph, thanks to dred km/sec. which it has been For a star with a uni- possible to discover form and stable pho- and confirm nu- tosphere, such shifts merous exoplanets. are a true reflection Left, at the focal plane of the tele- of the stellar motion scope we can see with respect to the the Fibre Adapter observer, and hence (in green), which of its radial velocity. sends to HARPS the But stars, especially light collected. those of the solar [ESO/H.H. Heyer] sole-giove EN:l'Astrofilo 28/08/15 10:31 Page 41

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stellar activity, permit researchers to eliminate false planetary signals and establish whether any residual radial velocity is con- struable with the existence of one or more planets, as well as calculate their period and mass. In the case of searches for Jupi- ter’s equivalents around Sun’s equivalents, the picture is more difficult to fill in, as the planet’s revolution period could equal that of the star’s activity cycle, exactly as it happens in our system, where the two periods are both close to 11 years. Since it is true that the solar activity cycle may deviate from the average duration by a few years, that there are long solar minimums, and that in the long run the distribution of the active regions of one side and the other of the central meridian compensate itself, if we were to apply the same to a star like the Sun, it would appear relatively simple to separate a stable signal from one not equally as stable. But this is not so, because two (or more) signals he HARPS type, show magnetic activity cycles that manifesting themselves in comparable T spectrograph, generally result in a “surface" randomly time scale, with overlapping phases or not, photographed affected by active regions, with spots, fa- and providing a unique and complex sig- both closed and culae and other pheno- open during some mena. These, in turn- tests. The vessel ing towards the ob- containing the “heart” of the in- server or moving away strument is kept from him, alter the bal- under vacuum ance between blueshift during the opera- and redshift, and mimic tional phases. the presence of plan- [ESO] ets. In other words, a star can show a certain radial velocity even though its distance from the Earth remains unaffected and it is thus virtually devoid of planets. Observations over months and years and appropriate methods for interpreting the sole-giove EN:l'Astrofilo 28/08/15 10:31 Page 42

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nal, are a problem not easily solvable. colleagues realized that for two of the he ESO’s Among the teams of astronomers who three stars the radial velocity measured is T structure, at have more recently dived into this kind of apparent and that the periodicity observ- the La Silla site in research there is that of Megan Bedell ed is entirely due to photospheric activity. Chile, home to (University of Chicago) and Jorge Melén- The signal from the third sun-like star the 3.6-metre telescope and its dez (Universidade de São Paulo), which turned out instead to be more interesting. HARPS spectro- along with some colleagues carried out The star, called HIP 11915, located 186 graph. [Serge during the last four years with the use of light-years from Earth in the constellation Brunier, ESO] HARPS a series of observations of a specific of Cetus, has a visual magnitude of 8.6, Below, an anima- sample of 63 stars, selected for their re- and besides diameter, temperature and tion of the HIP markable resemblance to the Sun. On the metallicity has also in common with the 11915 system. basis of the results, the team identified Sun another important parameter, its age, [ESO/ M. Korn- three stars among those sam- messer] pled, whose variations in the radial velocities are similar to those expected in the presence of a Jupiter twin in orbit at about 5 astronomical units. By analyzing different indexes of these stars’ magnetic activity, especially the one referring to the H and K lines of ionized calcium, where the contribu- tion of active regions on the signal can be more reliably detected, Bedell, Meléndez and sole-giove EN:l'Astrofilo 28/08/15 10:32 Page 43

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he key protag- estimated at 4.0 ± T onists of the 0.6 billion years (4.6 discovery of HIP billion in the Sun’s 11915 b, Megan case). In order to Bedell and Jorge identify the “noise” Meléndez, photo- introduced in the ra- graphed from the dome of the 3.6- dial velocity of HIP metre telescope; 11915 by its photo- in the background, spheric activity, the view of the other researchers careful- facilities of La Silla ly examined nearly Observatory. [ESO] sixty high-resolution spectra recorded with HARPS (also during previous works) between 2003 and 2015. The average signal detected, corresponding to of the elements cannot be completely a radial velocity of 10-11 m/sec, is theoret- unrelated to the fact that there are rocky ically compatible with a solar type activity, planets inner to Jupiter, it is likely that also but HIP 11915 did not prove as active as between HIP 11915 and its giant planet, the Sun, to the extent that once taken into codenamed HIP 11915 b, there are rocky planets not yet discovered due to instrumental limitations. And until they are discovered (assuming that they exist), HIP 11915 may be cautiously defined only a twin of the Sun-Jupiter system. In any case, additional observations will be necessary since Bedell/Meléndez’s team has noticed a suspicious coincidence between the trend of the stellar activity phases and the gravitational pull due to the supposed “Jupiter”. In recent years, the two signals have in fact grown at an equal pace, a correlation not found in older observations and which lends itself to more than one interpretation. One could be that seeing the stellar activity reaching a maximum phase while HIP 11915 b goes to line up with star and ob- account all possible stellar activity indexes server. But the picture could also be dif- and excluded any 5 minutes oscillation pe- ferent, as the stellar activity may have un- riod, as the one affecting the Sun, what re- known peculiarities. Moreover, HIP 11915 mains to be attributed is the larger part of b may be more massive than Jupiter, since the radial velocity, a part compatible with in not knowing the inclination of its orbit, an extrasolar planet having a mass identi- its current mass estimation is in fact a cal to that of Jupiter, located on a low-ec- lower value. We will just have to wait for centricity orbit (about 0.1) with a revolu- the results of new researches, which surely tion period of about 10 years. will not take long to arrive. Nevertheless, Given that the chemical composition of HIP 11915 is to date one of the most prom- HIP 11915 is 98% similar to the Sun’s, and ising candidates for hosting a planetary that in the case of our star the abundances system similar to our own. n chronicles EN2:l'Astrofilo 28/08/15 10:33 Page 44

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Best evidence of first generation stars in the universe

by ESO

stronomers have long theorised the existence of a first A generation of stars — known as Population III stars — that were born out of the primordial material from the Big Bang. The name Popula- tion III arose because astronomers had already classed the stars of the Milky Way as Population I (stars like the Sun, rich in heavier elements and forming the disc) and Population II (older stars, with a low heavy-element content, and found in the Milky Way bulge and halo, and globular star clusters). All the heavier chemical elements — such as oxygen, nitrogen, carbon and iron, which are essential to life — were forged in the bellies of stars. This means that the first stars must have formed out of the only elements to exist prior to stars: hydrogen, helium and trace amounts of lithium. These Population III stars would have been enormous — several hundred or even a thousand times more massive than the Sun — blazing hot, and tran- sient — exploding as supernovae after only about two million years. But until now the search for physical proof of their existence had been inconclusive. Finding these stars is very difficult: they would have been extremely short-lived, and would have shone at a time when the Universe was largely opaque to their light. Previous findings include: Nagao et al., 2008, where chronicles EN2:l'Astrofilo 28/08/15 10:33 Page 45

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no ionised helium was detected; De the University of Lisbon in Portugal, pocket in the galaxy. This meant the Breuck et al., 2000, where ionised he- and Leiden Observatory in the Ne- team had discovered the first good lium was detected, but alongside car- therlands, has now used ESO’s Very evidence for clusters of Population III bon and oxygen, as well as clear Large Telescope (VLT) to peer back stars that had ionised gas within a signatures of an active galactic nu- into the ancient Universe, to a period galaxy in the early Universe. cleus; and Cassata et al., 2013, where known as reionisation, approximately “The discovery challenged our expec- ionised helium was detected, but of a 800 million years after the Big Bang. tations from the start,” said David So- very low equivalent width, or weak Instead of conducting a narrow and bral, “as we didn’t expect to find such intensity, and alongside carbon and deep study of a small area of the sky, a bright galaxy. Then, by unveiling the oxygen. they broadened their scope to pro- nature of CR7 piece by piece, we un- A team led by David Sobral, from the duce the widest survey of very distant derstood that not only had we found Institute of Astrophysics and Space galaxies ever attempted. Their expan- by far the most luminous distant gal- Sciences, the Faculty of Sciences of sive study was made using the VLT axy, but also started to realise that it had every single characteristic expec- his artist’s impression shows ted of Population III stars. Those stars T CR7, a very distant galaxy dis- were the ones that formed the first covered using ESO’s Very Large heavy atoms that ultimately allowed Telescope. It is by far the brightest us to be here. It doesn’t really get any galaxy yet found in the early Uni- more exciting than this.” verse and there is strong evidence Within CR7, bluer and somewhat red- that examples of the first generation of stars lurk within it. These der clusters of stars were found, indi- massive, brilliant, and previously cating that the formation of Popu- purely theoretical objects were the lation III stars had occurred in waves creators of the first heavy elements — as had been predicted. in history — the elements necessary What the team directly observed was to forge the stars around us today, the last wave of Population III stars, the planets that orbit them, and life suggesting that such stars should be as we know it. This newly found easier to find than previously thought: galaxy is three times brighter than they reside amongst regular stars, in the brightest distant galaxy known brighter galaxies, not just in the ear- up to now. [ESO/M. Kornmesser] liest, smallest, and dimmest galaxies, which are so faint as to be extremely with help from the W. M. Keck Obser- difficult to study. vatory and the Subaru Telescope as Jorryt Matthee, second author of the well as the NASA/ESA Hubble Space study, concluded: “I have always won- Telescope. The team discovered — dered where we come from. Even as and confirmed — a number of surpris- a child I wanted to know where the ingly bright very young galaxies. elements come from: the calcium in One of these, labelled CR7 (abbrevia- my bones, the carbon in my muscles, tion of COSMOS Redshift 7), was an the iron in my blood. I found out that exceptionally rare object, by far the these were first formed at the very be- brightest galaxy ever observed at ginning of the Universe, by the first this stage in the Universe. With the generation of stars. With this discov- discovery of CR7 and other bright ery, remarkably, we are starting to ac- galaxies, the study was already a suc- tually see such objects for the first cess, but further inspection provided time.” Further observations with the additional exciting news. VLT, ALMA, and the NASA/ESA Hub- The X-shooter and SINFONI instru- ble Space Telescope are planned to ments on the VLT found strong ion- confirm beyond doubt that what ised helium emission in CR7 but — has been observed are Population III crucially and surprisingly — no sign stars, and to search for and identify of any heavier elements in a bright further examples. n chronicles EN2:l'Astrofilo 28/08/15 10:33 Page 46

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Atmosphere stripped from Neptune-sized exoplanet

by NASA

stronomers using the NASA/ ESA Hubble Space Telescope A have discovered an immense cloud of hydrogen dispersing from a this feature before around more warm, Neptune-sized planet orbi- massive exoplanets). It may offer ting a nearby star. The enormous clues as to how hot super-Earths — gaseous tail of the planet is about 50 massive, hot versions of Earth — are Geneva in Switzerland, lead author times the size of the parent star. A born around other stars. of the study. "Although the evap- phenomenon this large has never "This cloud of hydrogen is very spec- oration rate doesn't threaten the before been seen around such a tacular!" says David Ehrenreich of planet right now, we know that the small exoplanet (Hubble observed the Observatory of the University of star, a faint red dwarf, was more

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active in the past. This means that the planet's atmosphere evaporated faster during its first billion years of existence. Overall, we estimate that it may have lost up to 10 percent of its atmosphere." The planet, named Gliese 436b, is considered to be a "warm Neptune", because it is similar in size to Nep- tune, but much closer to its star Gliese 436 than Neptune is to the Sun. Although in this case the planet is in no danger of having its atmosphere completely stripped away — leaving just a solid, rocky core — this behaviour could explain the existence of hot super-Earths, which orbit very close to their stars and are typically more massive than Earth, although smaller than the sev- enteen Earth masses of Neptune. Hot super-Earths could be the remaining cores of more massive planets that have completely lost their thick, gaseous atmospheres to the same type of evaporation that Hub- ble observed around Gliese 436b. As the Earth's atmosphere blocks most ultraviolet light, astronomers needed a space telescope with Hubble's ultraviolet capability and exquisite precision to view the cloud. "You wouldn't be able to see it at visible wavelengths," says Eh- renreich. "But when you turn the ultraviolet eye of Hubble onto the system, it's really quite a transfor- mation — the planet turns into a monstrous thing." Ehrenreich and his team suggest that such a huge cloud of gas can exist around this planet because the cloud is not rapidly heated and swept away by the radiation from the relatively cool red dwarf star.

his artist's concept shows "The Behemoth," an enormous comet-like cloud of hydrogen bleeding off of a warm, T Neptune-sized planet just 30 light-years from Earth. Also depicted is the parent star, which is a faint red dwarf named GJ 436. The hydrogen is evaporating from the planet due to extreme radiation from the star. A phenomenon this large has never before been seen around any exoplanet. [NASA, ESA, and G. Bacon (STScI)]

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his artist's diagram shows a polar view of the T GJ 436 system. The warm, Neptune-sized exoplanet GJ 436b resides very close to its star — less than 3 million miles — and whips around it in just 2.6 Earth days. A huge, comet-like cloud of hydrogen nicknamed "The Behemoth" is shown bleeding off of the planet and trailing it like the tail of a comet. The planet is just 30 light-years from Earth. [NASA, ESA, and A. Feild (STScI)]

This allows the cloud to stick around around it in for a longer time. Evaporation such just 2.6 Earth as this may also have happened in days. the earlier history of the Solar Sys- At the very tem, when the Earth had a hydro- youngest, this gen-rich atmosphere that dissipated. exoplanet is It is also possible that it could hap- at least 6 bil- pen to Earth's atmosphere at the lion years old, end of our planet's life, when the but astrono- Sun swells up to become a red giant mers suspect and boils off our remaining atmo- that it is somewhat older. About the "Finding the cloud around Gliese sphere, before engulfing our planet size of Neptune, it has a mass of 436b could be a game-changer for completely. Gliese 436b resides very around 23 Earths. At just 30 light- characterising atmospheres of the close to Gliese 436 — just about 4 years from Earth, it is one of the whole population of Neptunes and million kilometres away — and whips closest known exoplanets. Super-Earths in ultraviolet observations," explains Vincent Bourrier, also of the Observatory of the Uni- versity of Geneva in Switzerland and co-author of the study. In the coming years, Bourrier expects that astronomers will find thousands of this kind of planet. The ultraviolet technique may also spot the signatures of oceans evaporating on smaller, more Earth-like planets. It will be extremely chal- lenging for astronomers to directly see water vapour on these worlds, because the vapour would be too low in the atmosphere (and thus shielded from telescopes). However, when stellar radiation breaks water molecules up into hydrogen and oxygen, the relatively light hydrogen atoms can he unusual light curve produced when the exoplanet GJ 436b and the huge, escape the planet. If scientists T comet-like hydrogen cloud nicknamed "The Behemoth" pass in front of could spot this hydrogen evapo- the parent star. Because the planet's orbit is tilted nearly edge-on to our view rating from a planet that is a bit from Earth, the planet and cloud can be seen eclipsing its star. Astronomers see more temperate and little less the extended dip in the light caused by the enormous cloud. That dip trails massive than Gliese 436b, it is a off slowly due to the cloud's comet-like tail. [NASA, ESA, and A. Feild (STScI)] good indicator that an ocean may be present on the surface. n chronicles EN2:l'Astrofilo 28/08/15 10:33 Page 49

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Fossil star clusters reveal their age

by Keck Observatory carried out over years using the po- “We determined globular clusters werful DEIMOS multi-object spec- form on average some 1.2 and 2.2 trograph fitted on Keck II, which is billion years after the Big Bang.” sing a new age-dating meth- capable of obtaining spectra of one “Our age measurements indicate od and the W. M. Keck Obser- hundred globular clusters in a single that globular clusters managed Uvatory on Maunakea, an in- exposure. DEIMOS breaks the visible to avoid the period, called cosmic ternational team of astronomers wavelengths of objects into spectra, reionization, in which the Universe have determined that ancient star which the team used to reverse-en- was bathed in ultra-violet radiation clusters formed in which could have two distinct ep- destroyed them” ochs – the first 12.5 said fellow team billion years ago member, Professor and the second Aaron Romanow- 11.5 billion years sky. “Now that we ago. Although the have estimated clusters are almost when globular as old as the Uni- clusters form, we verse itself, these next need to tack- age measurements le the questions of show the star clus- where and how ters – called glob- they formed.” For- ular clusters – are bes said. actually slightly The SLUGGS sur- younger than pre- vey is comprised viously thought. of an internation- “We now think al team of astro- that globular clus- nomers who aim ters formed along- to understand the osmic timeline showing the birth of the Universe in a Big Bang 13.7 side galaxies rath- formation and evo- Cbillion years ago to the present day. Using the Keck Observatory, er than significant- an international team of researchers led by Professor Forbes of Swin- lution of galaxies ly before them,” burne University of Technology has determined ancient star clusters, and their globular research team lead- known as globular clusters, formed in two epochs – 12.5 and 11.5 bil- cluster systems. er, Professor Dun- lion years ago. They formed alongside galaxies, rather than prior to Globular clusters can Forbes of Swin- galaxies, as previously thought. [NASA/CXC/SAO and A. Romanowsky] are tightly bound burne University of clusters of around Technology said. The new estimates gineer the ages of the globular a million stars. Most large galaxies, of the star cluster average ages clusters by comparing their chemi- including the Milky Way, host a sys- were made possible using data cal composition with the chemical tem of globular clusters. Although obtained from the SAGES Legacy composition of the Universe as it the Universe itself, and galaxies Unifying Globulars and GalaxieS changes with time. “The Universe within it, has evolved over cosmic (SLUGGS) survey, which was carried is now well known to be 13.7 bil- time, globular clusters are very ro- out on Keck Observatory’s 10-meter, lion years old,” research team mem- bust and many have survived intact Keck II telescope. Observations were ber and Professor Jean Brodie said. for over 10 billion years. n chronicles EN2:l'Astrofilo 28/08/15 10:33 Page 50

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Biggest explosions in the universe powered by strongest magnets

by ESO The clear signature of a supernova, first time that this could not be the later named SN 2011kl, was found. case. The amount of nickel-56 mea- This is the first time that a super- sured in the supernova with the amma-ray bursts (GRBs) are nova has been found to be associat- GROND instrument is much too one of the outcomes associ- ed with an ultra-long GRB. The link large to be compatible with the Gated with the biggest explo- between supernovae and (normal) strong ultraviolet emission as seen sions to have taken place since the long-duration GRBs was established with the X-shooter instrument. Big Bang. They are detected by or- initially in 1998, mainly by observa- Other suggested sources of energy biting telescopes that are sensitive tions at ESO observatories of the su- to explain superluminous superno- to this type of high-energy radia- pernova SN 1998bw, and confirmed vae were shock interactions with tion, which cannot penetrate the in 2003 with GRB 030329. the surrounding material — possibly Earth’s atmosphere, and then ob- The lead author of a new study, Jo- linked to stellar shells ejected be- served at longer wavelengths by chen Greiner from the Max-Planck- fore the explosion — or a blue su- other telescopes both in space and Institut für extraterrestrische Physik, pergiant progenitor star. In the case on the ground. Garching, Germany explains: “Since of SN 2011kl the observations clear- GRBs usually only last a few sec- a long-duration gamma-ray burst is ly exclude both of these options. onds, but in very rare cases the gam- produced only once every 10,000– The only explanation that fitted the ma rays continue for hours. (Normal 100,000 supernovae, the star that observations of the supernova fol- long-duration GRBs last between 2 exploded must be somehow special. lowing GRB 111209A was that it and 2000 seconds. There are now Astronomers had assumed that was being powered by a mag- four GRBs known with durations these GRBs came from very massive netar — a tiny neutron star spin- between 10 000–25 000 seconds — stars — about 50 times the mass of ning hundreds of times per second these are called ultra-long GRBs. the Sun — and that they signalled and possessing a magnetic field There is also a distinct class of short- the formation of a black hole. much stronger than normal neu- er-duration GRBs that are believed But now our new observations of tron stars, which are also known as to be created by a different mecha- the supernova SN 2011kl, found radio pulsars. nism.) One such ultra-long duration after the GRB 111209A, are chang- Magnetars are thought to be the GRB was picked up by the Swift ing this paradigm for ultra-long du- most strongly magnetised objects in satellite on 9 December 2011 and ration GRBs.” the known Universe. named GRB 111209A. It was both In the favoured scenario of a mas- They are thought to develop mag-

one of the longest and brightest sive star collapse (sometimes known netic field strengths that are 100 to GRBs ever observed. as a collapsar) the week-long burst 1000 times greater than those seen As the afterglow from this burst of optical/infrared emission from in pulsars. This is the first time that faded it was studied using both the supernova is expected to come such an unambiguous connection the GROND instrument on the from the decay of radioactive nick- between a supernova and a mag- MPG/ESO 2.2-metre telescope at el-56 formed in the explosion. netar has been possible. La Silla and also with the X-shooter But in the case of GRB 111209A the Paolo Mazzali, co-author of the instrument on the Very Large Tele- combined GROND and VLT observa- study, reflects on the significance of scope (VLT) at Paranal. tions showed unambiguously for the the new findings: “The new results chronicles EN2:l'Astrofilo 28/08/15 10:33 Page 51

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provide good evidence for an unexpected relation his artist’s impression shows a supernova and associated gamma- between GRBs, very bright supernovae and mag- T ray burst driven by a rapidly spinning neutron star with a very strong magnetic field — an exotic object known as a magnetar. Obser- netars. Some of these connections were already sus- vations from ESO’s La Silla and Paranal Observatories in Chile have for pected on theoretical grounds for some years, but the first time demonstrated a link between a very long-lasting burst of linking everything together is an exciting new de- gamma rays and an unusually bright supernova explosion. The results velopment." “The case of SN 2011kl/GRB 111209A show that the supernova following the burst GRB 111209A was not forces us to consider an alternative to the collapsar driven by radioactive decay, as expected, but was instead powered by scenario. This finding brings us much closer to a the decaying super-strong magnetic fields around a magnetar. [ESO] new and clearer picture of the workings of GRBs," concludes Jochen Greiner. n chronicles EN2:l'Astrofilo 28/08/15 15:39 Page 52

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Uranus-sized planet discovered through microlensing

by NASA & Keck large majority of exoplanets cata- period of time than their host star. Observatory loged so far are very close to their The exact timing and amount of host stars because several current light amplification can reveal clues planet-hunting techniques favor to the nature of the foreground star ASA's Hubble Space Telescope finding planets in short-period or- and its accompanying planets. and the W. M. Keck Observa- bits. But this is not the case with the The system, cataloged as OGLE- Ntory in Hawaii have made in- microlensing technique, which can 2005-BLG-169, was discovered in dependent confirmations of an exo- find more distant and colder plan- 2005 by the Optical Gravitational planet orbiting far from its cen- ets in long-period orbits that other Lensing Experiment (OGLE), the Mi- tral star. The planet was discovered methods cannot detect. crolensing Follow-Up Network (Mi- through a technique called gravita- Microlensing occurs when a fore- croFUN), and members of the Micro- tional microlensing. ground star amplifies the light of a lensing Observations in Astrophysics This finding opens a new piece of background star that momentarily (MOA) collaborations — groups that discovery space in the extrasolar aligns with it. If the foreground star search for extrasolar planets through planet hunt: to uncover planets as has planets, then the planets may gravitational microlensing. far from their central stars as Jupiter also amplify the light of the back- Without conclusively identifying and Saturn are from our sun. The ground star, but for a much shorter and characterizing the foreground star, however, astronomers have had a difficult time determining the properties of the accompanying planet. Using Hubble and the Keck Ob- servatory, two teams of astronomers have now found that the system consists of a Uranus-sized planet orbiting about 370 million miles from its parent star, slightly less than the distance between Ju- piter and the Sun. The host star, however, is rtist's rendering of a about 70 percent as mas- Asuper-Earth similar sive as our Sun. "These to OGLE-2005-BLG-169 b. chance alignments are [MicroFUN Collabora- rare, occurring only about tion, CfA, NSF] once every 1 million years for a given planet, so it chronicles EN2:l'Astrofilo 28/08/15 15:39 Page 53

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his graphic illustrates T how a star can mag- nify and brighten the light of a background star when it passes in front of the distant star. If the foreground star has planets, then the planets may also mag- nify the light of the background star, but for a much shorter period of time than their host star. Astronomers use this method, called gravitational microlensing, to identify planets. [NASA, ESA, and A. Feild (STScI)]

our solar system. Astrono- mers often rely on two indi- rect techniques to hunt for extrasolar planets. The first method detects planets by the subtle gravitational tug they give to their host stars. In another method, astronomers watch for small dips in the amount of light from a star as a planet passes in front of it. Both of these techniques work best when the planets are either extremely massive or when they orbit very was thought that a very long wait can uncover planets whose host close to their parent stars. In these would be required before the plan- stars cannot be seen by most tele- cases, astronomers can reliably de- etary microlensing signal could be scopes. "It is remarkable that we termine their short orbital periods, confirmed," said David Bennett of can detect planets orbiting unseen ranging from hours to days to a cou- the University of Notre Dame, In- stars, but we'd really like to know ple years. diana, the lead of the team that something about the stars that But to fully understand the architec- analyzed the Hubble data. "Fortu- these planets orbit," explained Vir- ture of distant planetary systems, nately, the planetary signal predicts ginie Batista of the Institut d'Astro- astronomers must map the entire how fast the apparent positions of physique de Paris, France, leader of distribution of planets around a the background star and planetary the Keck Observatory analysis. "The star. Astronomers, therefore, need host star will separate, and our ob- Keck and Hubble telescopes allow to look farther away from the star − servations have confirmed this pre- us to detect these faint planetary from about the distance of Jupiter diction. The Hubble and Keck Obser- host stars and determine their pro- is from our Sun, and beyond. vatory data, therefore, provide the perties." "It's important to understand how first confirmation of a planetary mi- Planets are small and faint com- these systems compare with our crolensing signal." In fact, microlens- pared to their host stars; only a few solar system," said team member ing is such a powerful tool that it have been observed directly outside Jay Anderson of the Space Telescope chronicles EN2:l'Astrofilo 28/08/15 10:34 Page 54

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Science Institute in Baltimore, system from Earth. The fore- Maryland. "So we need a ground and background stars complete census of planets in were observed in several dif- these systems. Gravitational ferent colors with Hubble's microlensing is critical in help- Wide Field Camera 3 (WFC3), ing astronomers gain insights allowing independent confir- into planetary formation the- mations of the mass and dis- ories." The planet in the tance determinations. OGLE-2005-BLG-169 system The observations taken with is probably an example of a the Near Infrared Camera 2 "failed-Jupiter" planet, an (NIRC2) on the Keck 2 tele- object that begins to form a scope more than eight years Jupiter-like core of rock and after the microlensing event, ice weighing around 10 Earth provided a precise measure- masses, but it doesn't grow his simulation shows the 22-year journey of ment of the foreground and fast enough to accrete a sig- T a star moving through space and passing background stars' relative nificant mass of hydrogen directly in front of a more distant background motion. "It is the first time and helium. So it ends up star. All stars drift through space. Occasionally, a we were able to completely with a mass more than 20 star lines up perfectly in front of a more distant resolve the source star and star. The momentary alignment magnifies and times smaller than that of Ju- the lensing star after a micro- brightens the light from the background star, an piter. "Failed-Jupiter planets, effect called gravitational microlensing. [NASA, lensing event. This enabled us like OGLE-2005-BLG-169Lb, ESA, D. Bennett (University of Notre Dame), Wig- to discriminate between two are predicted to be more gle Puppy Productions, and G. Bacon (STScI)] models that fit the data of common than Jupiters, espe- the microlensing light curve," cially around stars less massive than ground and background stars plus a Batista said. the Sun, according to the preferred planet. But due to the blurring ef- The Hubble and Keck Observatory theory of planet formation. So this fects of our atmosphere, a number data are providing proof of concept type of planet is thought to be quite of unrelated stars are also blended for the primary method of exoplan- common," Bennett said. Microlens- with the foreground and back- et detection that will be used by ing takes advantage of the random ground stars in the very crowded NASA's planned, space-based Wide- motion of stars, which are generally star field in the direction of our gal- Field Infrared Survey Telescope too small to be noticed without pre- axy's center. (WFIRST), which will allow astrono- cise measurements. If one star, how- The sharp Hubble and Keck Obser- mers to determine the masses of ever, passes nearly precisely in front vatory images allowed the research planets found with microlensing. of a farther background star, the teams to separate out the back- WFIRST will have Hubble's sharpness gravity of the foreground star acts ground source star from its neigh- to search for exoplanets using the like a giant lens, magnifying the bors. Although the Hubble images microlensing technique. light from the background star. were taken 6.5 years after the len- The telescope will be able to ob- A planetary companion around the sing event, the source and lens star serve foreground, planetary host foreground star can produce a var- were still so close together on the stars approaching the background iation in the brightening of the sky that their images merged into source stars prior to the microlens- background star. This brightening what looked like an elongated stel- ing events, and receding from the fluctuation can reveal the planet, lar image. Astronomers can measure background source stars after the which can be too faint, in some the brightness of both the source microlensing events. cases, to be seen by telescopes. The and planetary host stars from the "WFIRST will make measurements duration of an entire microlensing elongated image. like we have made for OGLE-2005- event is several months, while the When combined with the informa- BLG-169 for virtually all the plane- variation in brightening due to a tion from the microlensing light tary microlensing events it observes. planet lasts a few hours to a couple curve, the lens brightness reveals We'll know the masses and dis- of days. The initial microlensing da- the masses and orbital separation of tances for the thousands of planets ta of OGLE-2005-BLG-169 had indi- the planet and its host star, as well discovered by WFIRST," Bennett ex- cated a combined system of fore- as the distance of the planetary plained. n Image: Saturn by NASA NASA by Saturn Image: