An Expanded View of the Universe Science with the European Extremely Large Telescope An Expanded View of the Universe Science with the European Extremely Large Telescope Contents

Four Centuries of the Telescope — Four Centuries of Discovery 3 The European Extremely Large Telescope 6 Open Questions for the E-ELT 10 Exoplanets — Towards other Earths 15 Fundamental Physics 21 Black Holes 27 The Birth, Life and Death of Stars 31 The Stellar Content of Galaxies 35 The End of the Dark Ages — First Stars and the Seeds of Galaxies 39 The E-ELT: A Pillar in the Astronomical Landscape of 2020+ 45 Discovery Potential — Expect the Unexpected! 49

Glossary 50 Imprint 52

2 Science with the E-ELT Four Centuries of the Telescope — Four Centuries of Discovery

The year 2009 was celebrated by the Interna- tional Astronomical Union and UNESCO as the International Year of Astronomy. It marked the passing of 400 years since Galileo Galilei first used a telescope for astronomical research, making the ground-breaking observations that would finally refute the geocentric Ptolemaic worldview and establish the heliocentric Coper- nican one. In the same year, Johannes Kepler published his Astronomia Nova, in which he ­introduced his laws of planetary motion for the Solar System. The year 1609 signalled a true revolution in astronomy.

Since then, astronomical observations with tele­ scopes have increasingly become the norm, until today, when institutes around the world host giant telescopes that work every available second to collect immense quantities of data. Each technological advance has brought new, and often totally unexpected, discoveries about our Universe, enriching our cultural heritage.

Ever larger telescopes

In 1669, a few decades after the invention of the refracting telescope, a design based on lenses, Isaac Newton introduced the first practical re- flecting telescope, using mirrors. Over the fol- be constructed, and thus reflecting telescopes The refracting (top) lowing 300 years, these two telescope design finally won the day. and reflecting (bot- tom) telescopes built concepts competed and evolved into ever more by Galileo Galilei powerful research facilities. For about two cen- Reflecting telescopes in the 19th century suf- and Isaac Newton, turies, refracting telescopes were in the lead, fered from the poor reflectivity and thermal respectively. overcoming image quality problems with smart properties of their mirrors. Despite this limita- choices of optical designs and glass combina- tion, William Herschel and William Parsons, the tions. Refractor technology peaked towards the third Earl of Rosse, were able to build reflectors end of the 19th century with the big Lick and with diameters ranging from 1.25 to 1.80 metres Yerkes Refractors, which used lenses of 90 cen- around the turn of the 18th century, with which timetres and one metre in diameter, respec- they discovered more planets and moons in the tively. However, these lenses and their supports Solar System, expanding the boundaries of the proved to be the largest that could practically then known Universe further.

Science with the E-ELT 3 The mirror efficiency problem was only solved Progress has since continued. Telescopes also in the mid-19th century, when the coating of expand the observable wavelength domain. glass with silver became feasible. This paved Over the last sixty years, astronomers have de- the way for the first modern telescopes, such as veloped telescopes that are able to observe the Hooker 2.5-metre telescope (1917) and the right across the electromagnetic spectrum. Hale 5-metre telescope (1948). ­Antennas for low frequency — radio, millimetre and submillimetre — observations were con- With the new giant telescopes also came the structed, allowing many scientific break- next revolution in knowledge: the Sun, the most throughs, such as the discoveries of quasars, prominent object in the sky, was downgraded pulsars, the cosmic microwave background, to a mere dwarf star; the Milky Way was dem- and much more. onstrated to be only one galaxy among millions, and the Universe, assumed to be static and Further, space observatories have allowed eternal, was found to be expanding and to have ­observations to be pushed to shorter wave- a finite age! By the middle of the 20th century, lengths, into the ultraviolet, X-ray and gamma- our worldview had little in common with the one ray regimes. This opening up of the high energy preceding the invention of the telescope. frontier generated a further flood of discoveries such as X-ray stars, gamma-ray bursts, black

The array of 8.2- metre telescopes that makes up the ESO Very Large Telescope.

4 Science with the E-ELT  Brief history of the telescope. The star symbols mark refracting tele-

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      8D@Q hole accretion discs, and other exotic phenom- (planets orbiting other stars) were detected, and ena. Previously unknown physical processes the current generation of 8–10-metre class tele- were taking place in the Universe around us. scopes even allowed us to take the first pictures These discoveries led to a number of Nobel of a few of these objects. Our knowledge in as- Prizes in Physics (in 1974, 1978, 1993, 2002 tronomy continues to progress at an incredible and 2006) and to giant leaps in our understand- pace, answering many questions, but also rais- ing of the cosmos. ing exciting new ones.

While astronomy has expanded out into these The European Extremely Large Telescope new wavelength bands, many discoveries are ­(E-ELT) will address these new questions, and still being made in the visible and near-infrared in the following sections we seek to give a ­regimes, where stars predominantly emit their ­flavour of the kind of fundamental questions light. Technological advances in the 1980s that it will finally answer. However, just as and 1990s allowed scientists to build ever larger ­Galileo was astounded to find mountains on the telescopes and ever more sensitive cameras. Moon and moons orbiting Jupiter, the most These instruments have opened up whole new ­exciting discoveries are probably those that we areas of study. For example, the first exoplanets have not yet even imagined.

Science with the E-ELT 5 The European Extremely Large Telescope

Europe is at the forefront of all areas of contem- have been prototyped, will be completed by the porary astronomy, thanks, in particular, to the end of 2011. During this phase, the project flagship ground-based facilities operated by placed contracts with industry and institutes in ESO, the pre-eminent intergovernmental sci- Europe amounting to about 60 million euros. ence and technology organisation in astronomy. In addition to these design activities, more than The challenge is to consolidate and strengthen 30 European scientific institutes and high-tech this position for the future. This will be achieved companies studied the technological aspects with a revolutionary new ground-based tele- of large telescopes within the EU Framework scope concept, the European Extremely Large Programmes 6 and 7, partially funded by the Telescope (E-ELT). With a majestic primary mir- European Commission. Ten studies for instru- ror almost ~40 metres in diameter, it will be the ments and adaptive optics systems have also world’s biggest eye on the sky. been completed during this phase, allowing the project to build a most competitive instru- The telescope has an innovative five-mirror mentation plan for the first decade. ­design that includes advanced adaptive optics to correct for the turbulent atmosphere, giving The construction phase (phases C and D) is exceptional image quality. The main mirror will ­expected to start in 2012. The construction cost consist of almost 1000 hexagonal segments, is estimated to be close to a billion euros. The each 1.4 metres across. The gain is substantial: E-ELT is a high technology, highly prestigious the E-ELT will gather 15 times more light than science-driven project that incorporates many the largest optical telescopes operating today. innovative developments, offering numerous possibilities for technology spin-off and transfer, The basic reference design (phase A) for the together with challenging technology contract European Extremely Large Telescope was com- opportunities, and providing a dramatic show- pleted in 2006. The detailed design phase case for European industry. (phase B), during which critical components The E-ELT has already gained wide support in the European scientific community. It is the Prototypes for key only visible-light astronomy project selected in components, devel- the roadmap of the European Strategy Forum oped during the ­detailed design on Research Infrastructures. It also features as study. the top priority in ground-based astronomy in the ASTRONET European Science Vision and Infrastructure Roadmap for Astronomy.

With the start of operations planned early in the next decade, the E-ELT will address many of the most pressing unsolved questions in ­astronomy. It may, eventually, revolutionise our perception of the Universe, much as ­Galileo’s telescope did, 400 years ago.

6 Science with the E-ELT 1.4 metres

The primary mirror has ~1000 segments.

Starlight

2

Altitude cradles for inclining the tele- scope.

4 Stationary instru- ment platforms sit Five-mirror design either side of the 5 rotatable ­telescope. 1 T he ~40-metre primary mirror 1 collects light from the night 3 sky and reflects it to a smaller mirror located above it.

2 The secondary mirror reflects light back down to a still smaller mirror nestled in the primary mirror.

3 The third mirror relays light to an adaptive flat mirror directly above.

4 The adaptive mirror adjusts its shape a thousand times a second to correct for distor- tions caused by atmospheric turbulence.

5 A fifth mirror, mounted on a fast-moving stage, stabilises the image and sends the light The ~2700-tonne to cameras and other instru- telescope system ments on the stationary plat- can turn through form. 360 degrees. Lasers

Open Questions for the E-ELT

Since the invention of the telescope, genera- Are planetary systems like the Solar System tions of astronomers have expanded the common? How frequently do rocky planets set- boundaries of the known Universe ever further. tle in “habitable zones”, where water is liquid? We now think of the Universe as of a finite Do the atmospheres of exoplanets resemble the age and thus of finite observable dimension. ones in the Solar System? How is pre-biotic However, it is extremely large, and existing tele- material distributed in protoplanetary discs? Are scopes simply lack the sensitivity and angular there signs of life on any exoplanet? resolution to explore its plentiful secrets. The European Extremely Large Telescope (E-ELT) will be able to address these problems and Fundamental physics: are the laws of nature ­answer some of the most prominent open universal? questions. As far back in time and as far out in distance as we can observe, all the phenomena investi- gated so far seem to indicate that the laws of physics are universal and unchanging. Yet, un- comfortable gaps exist in our understanding: gravity and general relativity remain to be tested under extreme conditions, the amazingly rapid expansion (inflation) of the Universe after the Big Bang is not understood, dark matter seems to dominate the formation of the large scale structure but its nature remains unknown, and the recently discovered acceleration of the ex- pansion of the Universe requires a mysterious dark energy that is even less comprehensible.

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cleared region in a 2B@K nearby star’s dusty, planets exist, but we have not yet been able planet-forming disc. to detect the faint signatures of Earth-like plan- #DBDKDQ@SHNM

ets directly. The E-ELT will have the resolution !HF!@MF /QDRDMS %TSTQD to obtain the first direct images of such objects, 3HLD and even to analyse their atmospheres for the biomarker molecules that might indicate the The evolution of the Universe is presence of life. strongly dependent on dark energy.

10 Science with the E-ELT Were the physical constants indeed constant over the history of the Universe? How did the expansion history of the Universe really pro- ceed? Can we infer the nature of dark energy?

Black holes: what was their role in shaping the Universe?

Black holes have puzzled physicists and astron- omers since they were first postulated in relativ- istic form a century ago by Karl Schwarzschild. Observations have demonstrated that these bi- zarre objects really exist. And on a grand scale, too: not only have black holes been found with masses comparable to stars, but also super- massive black holes, a million or even a billion to observe the faintest, least massive stars, An artist’s impres- times heavier than the Sun, have been found at ­allowing us to close the current huge gap in our sion of a black hole accreting material the centres of many galaxies. These black holes knowledge concerning star and planet forma- from a nearby star. also seem to “know” about the galaxies they tion. Nucleocosmochronometry — the radiocar- live in, as their properties are closely correlated bon-14 method as applied to stars — will with the surrounding galaxy, with more massive ­become possible for stars right across the Milky black holes found in more massive galaxies. Way, allowing us to study galactic prehistory by dating the very first stars. And some of the Will the supermassive black hole at the centre brightest stellar phenomena, including the of the Milky Way reveal the nature of these ob- ­violent deaths of stars in supernovae and jects? Do theories of gravitation and general rel- gamma-ray bursts, will be traced out to very ativity as we know them hold near a black hole’s horizon? How do supermassive black holes grow? And what is their role in the formation of galaxies?

Stars: don’t we know all there is to know?

Stars are the nuclear furnaces of the Universe in which chemical elements, including the build- ing blocks of life, are synthesised and recycled: without stars there would be no life. Accord- The luminous blue variable star ingly, stellar astrophysics has long been a core Eta ­Carinae is activity for astronomers. But much remains to ­expected to explode be understood. With higher angular resolution as a ­supernova in and greater sensitivity astronomers will be able the ­astronomically near ­future.

Science with the E-ELT 11 large distances, offering a direct map of the star tens of millions of light-years. Even at greater formation history of the entire Universe. distances, we will be able to make the kind of observations of the structure of galaxies and What are the details of star formation, and how the motions of their constituent stars that previ- does this process connect with the formation ously have only been possible in the nearby of planets? When did the first stars form? What Universe: by taking advantage of the finite triggers the most energetic events that we speed of light, we can peer back in time to see know of in the Universe, the deaths of stars in how and when galaxies were assembled. gamma-ray bursts? What stars are galaxies made of? How many generations of stars do galaxies host and when Galaxies: how do “island universes” form? did they form? What is the star formation history of the Universe? When and how did galaxies The term “island universes” was introduced in as we see them today form? How did galaxies 1755 by Immanuel Kant, and used at the be­ evolve through time? ginning of the 20th century to define spiral neb- ulae as independent galaxies outside the Milky Way. Trying to understand galaxy formation and The Dark Ages: can we observe the earliest evolution has become one of the most active epoch of the Universe? fields of astronomical research over the last few decades, as large telescopes have reached For the first 380 000 years after the Big Bang, out beyond the Milky Way. Yet, even nearby the Universe was so dense and hot that light giant galaxies have remained diffuse nebulae and matter were closely coupled. Only once that cannot be resolved into individual stars. the Universe had expanded and cooled suffi- The unique angular resolution of the E-ELT will ciently, could electrons and protons “recom- revolutionise this field by allowing us to observe bine” to form the simplest element, neutral hy- individual stars in galaxies out to distances of drogen, and photons could decouple from matter. Only then could the first stars form and start to become organised into larger struc- tures. The E-ELT will allow scientists to look all the way back to these earliest times (dubbed the “Dark Ages”) to see how this first phase of astrophysical evolution began.

The galaxy NGC 300.

12 Science with the E-ELT What was the nature of the first stars? When did from the origins of the laws of physics to the the first galaxies assemble and what were their prevalence of life in the Universe, that it will properties? When did galaxies assemble into enable us to tackle. It will allow scientists to larger scale structures, shaping the distribution ­address some of the most fundamental current of matter as we see it today? questions, as well as opening up whole new frontiers of human understanding. The above illustrations only scratch the surface of the science that the E-ELT will carry out, but they give a flavour of the range of problems,

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Timeline of the Universe: A representation of the evolution dominated. More recently, the expansion has begun to of the Universe over 13.7 billion years. The far left depicts speed up again as the repulsive effects of dark energy have the earliest moment we can now probe, when a period come to dominate the expansion of the Universe. The after- of “inflation” produced a burst of exponential growth in the glow light seen by WMAP was emitted about 380 000 Universe. (Size is depicted by the vertical extent of the years after inflation and has traversed the Universe largely grid in this graphic.) For the next several billion years, the unimpeded since then. The conditions of earlier times ­expansion of the Universe gradually slowed down as are imprinted on this light; it also forms a backlight for later the gravitational pull of the matter in the Universe on itself developments of the Universe.

Science with the E-ELT 13

Exoplanets — Towards other Earths

Are we alone in the Universe? For millennia, lies at the limit of what can be achieved with Left: Artist’s impres- this question was not posed or was purely even the next generation of instruments on sion of the trio of ­super-Earths dis­ philosophical. Recently, astronomers have ­current telescopes. In contrast, ultra-stable covered by a Euro- started to provide an answer. With the E-ELT, spectrographs profiting from the large collect- pean team using for the first time in history, technology allows ing power of the E-ELT will achieve measure- the HARPS spec- us to observe and to characterise exoplanets ment precisions of ~1 cm/s over periods rang- trograph on ESO’s 3.6-metre telescope in habitable zones. ing from minutes to years. For the detection of at La Silla, Chile. rocky planets in habitable zones, this precision is needed in order to overcome measurement The first exoplanet orbiting a solar-type star contamination by oscillations, seismology, gran- (51 Pegasi) was discovered in 1995 by a ulation and magnetic activity of the parent star. ­European team. Since then, over 400 planetary companions with masses ranging from a few Thus, the E-ELT is essential for finding Earth Earth to several Jupiter masses have been twins in habitable zones, for determining how found. Most exoplanets are detected indirectly common they are and for understanding the by the radial velocity technique, a method that properties of their parent stars. This will allow a detects planets by the “wobble” they produce complete census of rocky Earth- to Neptune- on their parent star as they orbit it. However, mass planets around nearby stars for the first such indirect detections only allow us to infer very limited information about the planet itself, and very few direct observations of planets  have been made. With the E-ELT, we will be able to obtain direct images of some of these

systems, including planets in the “habitable H ) zones”, where a rocky planet might hold liquid HM 

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R: , LR   The radial velocity technique — reaching ,@R 1 cm/s accuracy LR

The radial velocity technique, which measures   the induced Doppler shift of features in the $ spectrum of the parent star, can only find cer-      tain kinds of planets. With the current genera- 2DLH L@INQ@WHR@: 4< tion of telescopes, this technique is limited both by the precision and the stability of the velocity More than 400 exo- measurements: current measurements have planets have been found so far. With the pushed the limit down to an already impressive E-ELT, the sensitivity ~1 m/s precision retained over several years. of the radial velocity Unfortunately, though, a planet like the Earth, method will be im- orbiting a star like the Sun, will only induce a proved by a factor of one hundred. ­radial velocity of about a tenth this size, which

Science with the E-ELT 15 time and will provide an understanding of the step in exoplanet research will be the physical architecture of planetary systems with low- characterisation of the then known planets. mass planets. These studies will lead to an un- derstanding of the formation of Solar System In order to achieve this, direct light from the twins and will provide an answer to an impor- planet must be detected and separated from tant part of the fundamental question: just how the glare of its parent star. Overcoming this dif- unique are we? ference in brightness (usually referred to as the contrast) is the main challenge for this type of observation, and requires extremely sharp im- Direct imaging — approaching 10–9 contrast aging. This capability will be a huge strength of ground-based telescopes. Planet-finder instru- By 2020, ground- and space-based facilities ments on 8-metre-class telescopes will achieve will have discovered thousands of massive similar contrasts to the James Webb Space (Neptune- and Jupiter-mass) exoplanets. The ­Telescope: around 10–5 to 10 –6 at sub-arcsec- E-ELT will start detecting Earth-twin targets in ond distances from the parent stars. habitable zones using the radial velocity tech- nique described above. By then, the statistical The detection of an Earth-twin requires a con- understanding of the properties of the parent trast of 10–9 or better within less than 0.1 arc- stars and the distributions of the masses and seconds from the star. The unprecedented orbits of exoplanets will have matured. The next light-gathering power of a 40-metre-class tele-

Direct imaging of Earth-twin planets in habitable zones is one of the main chal- lenges for the E-ELT.

16 Science with the E-ELT Using the Hubble Space Telescope astronomers have found water vapour and methane in the atmosphere of the Jupiter-sized planet HD 189733b.

scope, and the implementation of extreme self-luminous exoplanets of Jupiter-mass. The adaptive optics in the E-ELT are absolutely cru- contrast ratio between star and planet at these cial to reaching this limit. A planet-finder instru- wavelengths becomes so advantageous that, ment on the E-ELT will allow scientists not only for the nearest stars, hydrogen, helium, meth- to study young (self-luminous) and mature giant ane, water ammonia and other molecules can planets in the solar neighbourhood and out to all be detected in low resolution spectra of the the closest star-forming regions, but also to un- atmospheres of Neptune-like planets in habita- derstand the composition and structure of their ble zones. atmospheres. Around the nearest hundred stars, the E-ELT will enable the first characteri- Alternatively, exoplanet atmospheres can be sation of Neptune-like planets and rocky plan- observed during transits. Ground- and space- ets located in habitable zones, establishing a based facilities (such as the CoRoT and Kepler new frontier in astrobiology and in our under- missions) are accumulating target stars for standing of the evolution of life. which an exoplanet, as seen from Earth, transits in front of its parent star. During these events (lasting a few hours every few months or years), Characterising atmospheres spectral features of the exoplanet’s ­atmosphere, back-lit by their parent star, can be seen in With the E-ELT, the detailed study of the atmos- the spectrum of the system. Such measure- pheres of young, massive exoplanets becomes ments are challenging, but lie within reach of feasible. Indeed, with its unprecedented sensi- the E-ELT. In the case of rocky planets in the tivity and spatial resolution at mid-infrared wave- habitable zone, the spectra can be examined lengths, the E-ELT will be able to detect young, for the ­biomarker molecules that are indicative

Science with the E-ELT 17 of biological processes, offering perhaps the The E-ELT’s spatial resolution of a few to tens of best opportunity to make the first detection of milliarcseconds allows it to probe the inner few extraterrestrial life. astronomical units of these discs, out to the nearest star-forming regions (at about 500 light- years from us), allowing us to explore the re- Protoplanetary discs and pre-biotic molecules gions where Earth-like planets will form for the first time. These data will beautifully comple- The observed diversity in the properties of exo- ment observations with the new international planets must be related to the structure and ALMA submillimetre array that will look at the evolution of the discs of preplanetary material colder material further out in these systems, to from which they form. A crucial step for our un- provide a full understanding of protoplanetary derstanding of the origin of life is thus the study disc evolution. Furthermore, the inner discs of the formation of such protoplanetary discs. probed by the E-ELT are those where the key The transition from the gas-rich to the gas-poor molecules for organic chemistry, such as meth- phase of discs is of particular interest: it is ane, acetylene, and hydrogen cyanide, occur, the time when gaseous planets form and rocky and more complex, pre-biotic molecules are planets gradually accrete “planetesimals” — ­expected to form. Their study will provide ­essentially boulders — onto their cores. a further vital piece in the astrobiology puzzle.

An artist’s concept of H the environment of a young star, reveal- ing the geometry of the dust disc. O O

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Right: An artist’s H H view of the exoplanet H CoRoT-7b, the clos- est known to its host star. The role of the Glycolaldehyde E-ELT is to charac- terise similar rocky Pre-biotic molecules, planets, but in habit- like glycolaldehyde, are able zones. building blocks of life and found in dense interstellar clouds even before planet formation starts there.

18 Science with the E-ELT

Fundamental Physics

What is the Universe made of? In the stand- that this is not the case. Instead, there is now ard cosmological model, only 4 % of the en- broad consensus that the expansion must ergy density of the Universe is composed have recently begun to accelerate! This result of normal matter (gas and stars), while a fur- came as a surprise to most, but also as a ther 22 % is made up of some mysterious big challenge. It has profoundly changed cos- dark matter. For the remaining 74%, the even mology and implies a need for new physics. more enigmatic dark energy has been in- voked. The E-ELT will explore the nature of this dark energy and our theory of gravity Dark energy by probing two of its manifestations with un- precedented accuracy: the accelerated ex- Some form of dark energy, acting against grav- pansion of the Universe and the variability of ity, is invoked by many cosmologists as an ex- fundamental physical constants. planation for the accelerated expansion of the Universe. Ironically the simplest form of such a dark energy is the cosmological constant origi- How does the expansion of the Universe nally introduced by Einstein in order to explain evolve? a now-discredited static Universe, and with this addition general relativity can explain this late The revolutionary observations made by Edwin acceleration very well. Alternatively, it has been Hubble in the late 1920s were the first direct proposed that general relativity should be re- evi ­dence that the Universe was not static. The placed with a modified theory of gravity, which systematically increasing spectroscopic red- reproduces the new observational facts, but shift observed in increasingly distant galaxies preserves the success of the original theory in was a clear sign that the Universe expands. For explaining the formation of structures in the a long time this expansion was believed to be early Universe. slowing down due to the combined gravitational pull exerted by all of the matter in the Universe. The most direct way to probe the nature of the However, at the end of the 1990s the measured acceleration in order to distinguish between dimming of Type Ia supernovae (used as stand- these possibilities is to determine the expansion ard candles) with increasing redshift revealed history of the Universe. Observables that depend

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Ω t M’ /d Ω /d z v d d Λ = 0.3, 0.0 Left: The Hubble Ultra Deep Field images reveal some of the –1.5 most distant known galaxies, when the Universe was just 800 –2 million years old. The E-ELT is –2 0 1 2 34 ­expected to look even further. z

Science with the E-ELT 21 on the expansion history include cosmic dis- of the expansion of the Universe, so is the tances and the linear growth of density per­ change in this redshift with time a measure of turbations. Surveys of Type Ia supernovae, the change of the rate of expansion. However, weak gravitational lensing and the signature the estimated size of this redshift drift over a that perturbations in the primordial baryon–­ decade is only about 10 cm/s. Such a signal is photon fluid imprinted shortly after the Big Bang about 10–20 times smaller than measurements on today’s distribution of galaxies are consid- made with today’s large telescopes on such ered to be good probes of the acceleration. distant galaxies. However, the huge light-col- However, extracting information about the ex- lecting area of the E-ELT, coupled with new de- pansion from these quantities relies on assump- velopments in quantum optics to record ultra- tions about the curvature of space, depends stable spectra, means that this amazing on the adopted cosmological model, and can measurement now lies within reach: the E-ELT only estimate the averaged expansion history will be able to determine the accelerating ex- over large periods of time. pansion of the Universe directly, allowing us to quantify the nature of the dark energy responsi- ble for the acceleration. A new approach — the redshift drift

A model-independent approach that measures Are the fundamental constants of physics the expansion rate directly was proposed as ­really constant? early as the 1960s, but limitations in technology did not allow astronomers to consider making The values of fundamental constants in physics such a measurement in practice. As the redshift generally have no theoretical explanation: of the spectra of distant objects is an indication they just are what they are, and the only way we

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22 Science with the E-ELT 2 The variability of the fine structure constant is not yet proved and awaits the extreme sensitivity of the E-ELT.

1 ) –5

0 / α (in units of 10 ∆α –1

–2 0 0.5 1 1.5 2 2.5 Redshift know their values is by measuring them in the of carbon produced in the cores of stars would laboratory. These fundamental quantities be drastically reduced, making carbon-based ­include the fine structure constant, α, and the life impossible. strong interaction coupling constant, μ. The former is central to our understanding of elec- tromagnetism, and is made up from three Strings, scalar fields, dark energy… other constants: the charge on the electron, e, Planck’s constant, h, and the speed of light, c. Theoretical models have been proposed where The latter, μ, is the ratio of the mass of the pro- the variability of fundamental constants is due ton to the mass of the electron. to a scalar field that is coupled to the electro- magnetic field. We do not know whether such In the traditional understanding of physics, the scalar fields exist, but they are predicted by a laws of nature have always and everywhere whole number of theories and the Large Hadron been the same, but this is really just an as- Collider experiment at CERN could detect the sumption. If this assumption does not hold, first such scalar field very soon. String theory then the fundamental constants may vary with also suggests that fundamental constants may the epoch and location of the measurement. vary by a tiny amount, of the order of one part Such variations can have a profound impact on in 10 000 or 100 000. In this case the variability the physical properties of the Universe. An is due to the changing size scale of hidden upper limit is given by the fact that if the value space-time dimensions. Other proposed expla- of a were larger by just 4% in the early Uni- nations for a possible variability of fundamental verse, then the processes of nuclear fusion constants are related to the contribution of dark would be altered in such a way that the amount energy to the energy density of the Universe.

Science with the E-ELT 23 Astronomical observations probe much longer The reason for these conflicting results is that timescales and are therefore much more sensi- the measurements involved are very chal­ tive to possible variations of the fundamental lenging. Testing the variability of fundamental constants than laboratory experiments. By ex- constants with quasar absorption line spectra ploring the spectra of distant quasars, the is essentially a measurement of the relative ­variability can be probed over a large fraction of wavelength shifts of pairs of absorption lines the history of the Universe. A team led by Aus- whose wavelengths have different sensitivity to tralian researchers has used a method called the fundamental constants. The strength of the “many-multiplets” method, where the rela- the constraint on the variability is therefore criti- tive shifts between iron and magnesium ab- cally dependent on the accuracy of the wave- sorption lines are measured, leading to claims length calibration. The ultra-stable high resolu- of a detected variation in the value of α. The tion spectrograph proposed for the E-ELT will team measured a very small relative variation of essentially remove the systematic uncertain- Δα/α ~ –6 × 10–6. However, a European re- ties due to the wavelength calibration which search team obtained later new measurements plague current measurements. It will improve consistent with no variability. It has also been the constraints on the stability of fundamental suggested that the strong interaction coupling constants by two orders of magnitude. The ­constant varies. Studies of the vibrational and E-ELT will thus confirm or disprove the current rotational states of the hydrogen molecule in claims that fundamental constants vary and damped Lyman-α systems have been claimed that we are living in a fine-tuned location of to vary at a level of Δμ/μ ~ 2 × 10–5, although space time where the fundamental constants these measurements have also been disputed. are conveniently suitable for life.

Quasars are some of the most distant objects that could be observed.

Right: The laser comb method ­allows ultra-stable measure- ments of the redshift drift and fundamental constants varia- tions, when applied to the light collected by the E-ELT.

24 Science with the E-ELT Science with the E-ELT 25

Black Holes

Black holes are some of the most bizarre ob- level over fields of tens of arcseconds), as well Left: Very Large jects in the Universe, challenging the imagina- as radial velocity measurements with about ­Telescope (VLT) ­observations have tions of even the most creative scientists. 1 km/s precision, pushing our observations ever ­revealed that the They are places where gravity trumps all other closer to the black hole event horizon. Stars can ­supermassive black forces in the Universe, pushing our under- then be discovered at 100 Schwarzschild radii, hole closest to us is standing of physics to the limit. Even more where orbital velocities approach a tenth of located in the centre of the Milky Way. strangely, supermassive black holes seem to the speed of light. This is more than ten times play a key role in the formation of galaxies closer than can be achieved with the current and structures in the Universe. generation of telescopes. Such stellar probes will allow us to test the predicted relativistic ­signals of black hole spin and the gravitational Galactic Centre redshift caused by the black hole, and even to detect gravitational wave effects. Further out, Over the last 15 years or so, an enormous the dark matter distribution around the black amount of work has gone into improving our hole, predicted by cold dark matter cosmolo- understanding of the closest supermassive gies (LCDM), can be explored. The distance to black hole — Sagittarius A* at the centre of the Galactic Centre can be measured to 0.1%, the Milky Way. constraining in turn the size and shape of the galactic halo and the Galaxy’s local rotation Technological progress, in particular in the speed to unprecedented levels. Crucial pro- areas of adaptive optics and high angular reso- gress in our understanding of the interaction of The Milky Way’s cen- lution with ground-based 8-metre-class tele- the black hole with its surroundings will be tral supermassive scopes, has allowed impressive progress in made. The puzzling stellar cusp around the black hole has been ­understanding supermassive black holes and ­Galactic Centre, as well as the observed star weighed by meas­ uring the proper mo- their surroundings. Key progress was made ­formation in the vicinity of the black hole will be tions of stars in its in proving the very existence of a supermassive studied in detail for the first time. ­vicinity. black hole at the centre of the Milky Way, in ­refining our knowledge of how matter falls into black holes, and in identifying gas discs and S2 Orbit around SgrA* young stars in the immediate vicinity of the     black hole. The Galactic Centre was thus estab-     lished as the most important laboratory for   the study of supermassive black holes and their   surroundings.   6JU$    ǥ But its potential for progress in fundamental KHFGSC@XR physics and astrophysics is far from being fully 6 exploited. The Galactic Centre remains the   best place to test general relativity directly in a 2FQ   strong gravitational field. The E-ELT will enable     extremely accurate measurements of the po­   sitions of stars (at the 50–100 microarcsecond      

Science with the E-ELT 27 W  W 

6

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A powerful flare from the centre of the Milky Way, where a ǥ OLJKWGD\V  supermassive black hole resides.

Looking at the Galactic Centre with the collect- Intermediate-mass black holes ing power and spatial resolution of the E-ELT will truly allow us to reach new dimensions in Black hole research with the E-ELT will not be our understanding of black hole physics, their limited to the Galactic Centre. An open question surroundings and the extent of the validity of awaiting the advent of the E-ELT is the exist- general relativity. ence and the demographics of intermediate- mass (100–10 000 solar masses) black holes. These black holes represent a link currently missing between stellar-mass black holes and supermassive black holes, and they could serve as seeds in the early Universe for the formation

Messier 15 is one of the very few globular clusters thought to host an intermediate- mass black hole.

28 Science with the E-ELT of the supermassive black holes that we see today. They could plausibly form from the first ultra-massive stars, or via the same unknown mechanism that forms supermassive black holes. Their existence in the local Universe can- not unambiguously be proven with current ob- servational facilities. To date, only a few detec- tions at the centres of dwarf galaxies and massive star clusters have been reported. Their existence has been inferred either from X-ray and radio emission that is believed to originate from matter falling onto a black hole, or from the disturbance in the motions of stars and gas at the centre of these objects. The E-ELT will be able to measure accurately the three-dimen- sional velocities of stars in these star clusters and dwarf galaxies. This will allow to determine An artist’s impression of an active the masses of the intermediate-mass black galactic nucleus, powered by a supermassive black hole sur- holes that are speculated to lie at their cores. rounded by an accretion disc. The E-ELT will provide us with such detailed views of the centres Supermassive black holes and active galactic of galaxies out to 300 million light-years. nuclei

Over the past decade a correlation between the the regions immediately around the active nu- mass of a galaxy and the mass of its central cleus of galaxies and to understand the inflow black hole has been observed. For these prop- of material accreted by the central black hole. erties to be related, a number of mechanisms Furthermore, supermassive black holes will be must be at work over nine orders of magni- characterised out to large distances with the tudes in scale, from galaxy environments to the E-ELT, allowing us to trace the build up of “sphere of influence” of the black hole. The ­supermassive central objects in galaxies when E-ELT will probe scales of less than a few par- the Universe was as young as a quarter of its secs (~10 light-years) in the very central regions present age. of galaxies out to cosmological distances of hundreds of millions of light-years, allowing us to study nuclear clusters and active galactic ­nuclei in galaxies with unprecedented detail. The combination of high spatial resolution with spectroscopic capabilities available with the E-ELT will enable us to map the gas motions in

Science with the E-ELT 29

The Birth, Life and Death of Stars

Stars emit nearly all of the visible light that we With the E-ELT, see in the Universe. The details of their forma- ­astronomers will be able to study planet- tion process, coupled to the formation of pro- forming discs in toplanetary discs, but also their evolution and ­unsurpassed detail their (sometimes most energetic) death still at distances larger present some of the most interesting puzzles by a factor of ten than possible today. in astrophysics. The E-ELT is the key facility to answering many of these open fundamen- tal questions.

medium. The E-ELT will allow a close look at Star formation and the conditions for the how a star forms and to make decisive pro- ­formation of planetary systems gress in the study of the pre-main-sequence phases of star formation. The formation of a star follows a complicated route. The earliest phases of this process, dur- ing which protostellar discs start to emerge Stellar tribulations from molecular clouds, is often thought to be in the realm of longer wavelength (sub­millimetre, The path taken by a star through its lifecycle millimetre, radio) facilities, due to their ability to varies greatly with its mass. Mass determines peer into heavily dust-obscured regions. While not only a star’s lifetime and evolution but also this is partly true for present day optical/near- its final fate. Understanding the evolution of infrared telescopes, the E-ELT, with its gain in stars is critical to our understanding of the evo- sensitivity and, in particular, in angular resolu- lution of the Universe: the continuous recycling tion, will be a major player in protostellar/proto- process of matter, the energetic processes planetary disc research, even in their early shaping the interstellar medium, the feedback stages. processes in the evolution of galaxies, and the overall chemical enrichment history of the Uni- At mid-infrared wavelengths, the spatial res­ verse, all the way to the chemistry enabling life. olution limit of the E-ELT represents, at the ­distance of the closest star-forming regions High resolution spectroscopy from the optical ­(located about 150 parsecs away), a few astro- to the infrared with the E-ELT will allow unprec- nomical units (AU), i.e. a few times the mean edented progress in this field. The E-ELT will Sun–Earth distance. Thus, the E-ELT will be allow us to perform nuclear dating (“nucleocos- able to probe the innermost regions of the pro- mochronometry”) on individual stars with ages toplanetary discs, and study where rocky plan- between 1 and 12 billion years. Current facili- ets form. The closest high-mass star formation ties are limited in their collecting power and regions are a few thousand parsecs away. have performed this measurement on only a Left: In the Large At this distance, the E-ELT resolution can probe handful of stars. The E-ELT will allow measure- Magellanic Cloud, a the very inner regions (tens of AU) of the sur- ments of elements such as 232Th (mean life- part of which is pic- rounding accretion discs, allowing us to study in time 20.3 billion years) and 238U (mean lifetime tured here, astrono- mers can explore the great detail the formation of these stars, which 6.5 billion years) and their ratios to other ele- complete cycle dominate the energy budget of the interstellar ments in hundreds of stars in different regions of stellar evolution.

Science with the E-ELT 31 of the Milky Way. Combined with precise ele- ment abundance measurements in stars, and with results from space missions such as Gaia, it will allow us to determine not only the precise age of the major components of our galaxy, but also to date their assembly phases and to describe their chemical evolution. A full understanding of the assembly of the Milky Way is within reach with the E-ELT.

At the low-mass end of star formation, we enter the realm of brown dwarfs, which are not ­massive enough to have started the central nu- Free-floating planetary-mass ob- clear fusion process that powers stars. These jects, like the “planemo” twins Oph 1622, put forward some of objects are particularly interesting as they are the most intriguing questions expected to have masses and atmospheric about low-mass star and planet properties intermediate between stars and giant formation. planets. Only the E-ELT has the collecting power to reach out in distance and to study the associations (one million years old) to young faint brown dwarfs in nearby open star clusters star clusters (a few hundred million years old). in detail. In addition, the E-ELT has the spatial The study of such binary stars allows us to resolution to study brown dwarfs and planetary- ­determine precisely the masses of the stars at mass objects in so-called ultra-cool binaries different evolutionary stages. Thus, the E-ELT (with separations of only a few hundred AU) in will r­eveal the evolution of sub-stellar mass ob- nearby environments ranging from young stellar jects, supporting its work on exoplanets and

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32 Science with the E-ELT bringing us closer to a full understanding of the This supernova evolution of planets and stars over the full mass has been associated with a gamma-ray ­spectrum. burst. The E-ELT will ­explore such events up to a redshift of 15. Violent deaths and their consequences

At the high-mass end of the range of stellar properties, the most spectacular events are un- doubtedly the deaths of stars of eight or more solar masses in stellar explosions. These super- nova events seeded the early Universe with heavy chemical elements by ejecting, among others, carbon, oxygen and iron into the inter- stellar medium. These elements not only criti- cally influenced the formation of stars and gal- axies, but also were ultimately necessary for the later evolution of life. Supernova explosions are also some of the most luminous events in detected absorption line systems. Gamma-ray the Universe. As such, they can be used out to bursts represent one more route for the E-ELT great distances as signposts of the evolution of to study the Dark Ages of the Universe. the Universe. The E-ELT will be able to study supernova ex- Gamma-ray bursts have been one of the most plosions in exquisite detail. Similar to gamma- enigmatic phenomena in astronomy since their ray bursts, supernova explosions can be used discovery in the 1960s, until they were recently as cosmic probes. Indeed, supernovae provide successfully associated with the formation of the most direct evidence to date for the accel- stellar-mass black holes and highly collimated erating expansion of the Universe and hence supernovae at high redshift. Gamma-ray bursts for the existence of a dark energy driving this are the most energetic explosions observed in acceleration. With the current combination of the Universe and currently among the competi- 8-metre-class ground-based telescopes and tors for the record holders as the furthest object the Hubble Space Telescope, supernova observed. The collecting power of the E-ELT searches can reach back to only around half will allow us to use them as distant lighthouses, the age of the Universe. Infrared spectroscopy shining through billions of years of evolution with the E-ELT combined with imaging from of the Universe, similar to the way that quasars the upcoming James Webb Space Telescope have previously been used as remote beacons. will allow us to extend the search for superno- Gamma-ray bursts have a few advantages: with vae to redshifts beyond 4, a look-back time of the E-ELT, they can be detected at redshifts nearly 90% of the age of the Universe! Super- beyond 7 to 15, taking scientists into the largely nova studies with the E-ELT will thus critically unknown epoch of the reionisation of the Uni- contribute to the characterisation of the nature verse; and since they fade away, they allow us of dark energy and the investigation of the cos- to study the emission components of previously mic expansion at early epochs.

Science with the E-ELT 33

The Stellar Content of Galaxies

Galaxies are the main building blocks of the ­elements like iron and oxygen. As supernovae Left: Panorama of visible large-scale structure of the Universe. ­explode and enrich the interstellar medium the Milky Way. The galaxies themselves are made up of bil- out of which the next generation of star forms, lions of stars of all ages and chemical compo- subsequent generations will contain more of sitions. When astronomers study the light of these elements. By measuring the content of a galaxy, they are observing the diffuse light such trace elements in the stars, we can deter- emitted by all the individual stars in the gal- mine how many stars formed where and when axy. To make significant progress in our un- and thus extract the star formation history of derstanding of structure formation in the Uni- the galaxy. Current telescopes can only resolve verse, i.e. of galaxy formation and evolution, individual stars for the nearest few large galax- many of the individual stars in these distant ies, which has already yielded interesting re- galaxies need to be analysed. In this regard, sults, but does not allow us to draw any general the E-ELT is again an unprecedented facility. conclusions about galaxy formation.

By contrast, the E-ELT will allow the method to The most plausible current theory for galaxy be applied to some thousands of galaxies formation is the hierarchical assembly model, across a more representative slice of the Uni- in which all galaxies are built up from smaller verse, allowing us to compare the stellar con- pieces. This theory has been extensively ex- tents of galaxies of all types for the first time plored by numerical simulations as a theoretical and to draw the first general conclusions about experiment, and tested against the global their formation histories. ­characteristics of galaxy populations, but not against the detailed properties of individual ­galaxies. The ultimate test of this model is to   compare predictions of the stellar content of   galaxies to what we actually see in galaxies of all types, spirals, giant ellipticals, irregular and   dwarf galaxies.  :.%D<

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The billions of individual stars that make up a l l    galaxy carry information about the formation :%D'< and subsequent evolution of their host, but only The metal content of stars reveals if we can study the stars individually. If we can valuable information about the measure the amounts of the different chemical star formation history of galaxies elements in stars as a tracer of their ages and throughout the Universe. This ­figure uncovers the different for- origins, and combine such information with the mation timescales of the various current motions of these stars, we can begin components of the Milky Way. to unravel the complex formation history of the galaxy. For instance, the first generation of stars contains very low abundances of the heavier

Science with the E-ELT 35 Colours and luminosities of individual stars parts of the apparently quiescent galaxies that out to nearby galaxy clusters populate these clusters, and such measure- ments can then be compared with what we find Pushing out a little further in distance, the near- in the sparser non-cluster environments, to est galaxy clusters, located at a distance of see how a galaxy’s surroundings affect its star about 60 million light-years, are prime targets formation history. for the E-ELT. These clusters, containing thou- sands of galaxies packed in close proximity, are believed to have evolved very differently from The stellar initial mass function the more sparsely distributed “field galaxies”. Even at these distances, the E-ELT will be able The study of individual stars in nearby and dis- to resolve the individual stars, and study their tant galaxies not only reveals the history of their basic properties, such as colour and luminosity, host, but is also crucial for our understanding to obtain a measure of their ages and heavy el- of fundamental star formation and stellar evolu- ement content. Within individual galaxies, it will tion. The predominant factor determining the be possible to see whether the star formation evolution of a star is its initial mass. The initial history varies with position, as might be ex- mass function — how many stars there are pected if star formation continues in the inner of different masses — is a key ingredient in all

 

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36 Science with the E-ELT The E-ELT will be able to resolve individual stars in galaxies, very much in the same way as the VLT does for the galactic globular cluster Omega Centauri, but at a much greater distance.

interpretations of stellar populations. However, stars in a representative range of astrophysical the relative fraction of low-mass stars remains environments. unknown due to the limited abilities of current telescopes to detect low-mass, very faint stars The E-ELT will expand the portion of the even in the closest galaxies. With its unprece- ­Universe resolvable into stars by a factor of dented sensitivity, the E-ELT will be able to more than ten. It will allow scientists to obtain ­detect these low-mass stars in star-forming accurate knowledge of the present-day stellar ­regions of the Milky Way and even in other gal- populations in galaxies out to nearby galaxy axies. Any variation in the initial mass function clusters. It will return a comprehensive picture with environment is an extremely important of galaxy formation and evolution through a physical parameter for a wide variety of astro- ­detailed study of stellar populations in nearby physical investigations. The E-ELT will allow us galaxies and provide the most stringent tests to resolve this issue by, for the first time, provid- to date for current theories of galaxy formation ing us with observations of these lowest-mass and evolution.

Science with the E-ELT 37

The End of the Dark Ages – First Stars and the Seeds of Galaxies

What was the nature of the first object to The current cosmological model gives a credible Left: Image in visible shine through the Universe? How did the gas, explanation of the formation of structures in the light of the Chandra Deep Field South. dust, heavy elements and stars build up? Universe through the hierarchical assembly of The synergy be- What caused the reionisation of the Universe? dark matter halos. In contrast, very little is known tween X-ray and Were the first galaxies fundamentally differ- about the physics of formation and evolution ­optical spectroscopy ent from present ones? The E-ELT is the key of the baryonic component of gas and stars, be- has led to the dis- covery of some to establishing the physics of the first light- cause the conversion of baryons into stars is a of the most distant emitting objects in the Universe. complex and poorly understood process. As a quasars known. result, all advances in understanding galaxy for- mation and evolution over the last decade have Over the last decade significant progress in de- been essentially empirical, often based on sim- termining the processes of galaxy evolution has plified phenomenological models. Cornerstone been made using the combined power of cur- parameters in this empirical framework are the rent ground-based telescopes and the Hubble total and stellar masses of galaxies, together Space Telescope. The limits of the observable with their physical properties. They include de- Universe have been pushed to a redshift of 6, tailed knowledge about the ages and metallici- which corresponds to looking back over about ties of the underlying stellar populations, dust 90% of the age of the Universe. The global star extinction, star formation rates and morphologi- formation activity from that epoch to the pre- cal parameters. The study of well-established sent day has been estimated, and first insights scaling relations involving a number of these into the stellar mass assembly history out to a physical parameters, such as those between redshift of 3 have been acquired. However, the mass and heavy element abundance, or galaxy most uncertain issue in present day cosmology morphology and the density of the surrounding remains how and when galaxies assembled environment, are essential for understanding the across cosmic time. physical processes that drive galaxy evolution.

Map of the residual temperature fluctua- tions, imprinted on the cosmic micro- wave background by the earliest growth of structures in the Universe.

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Science with the E-ELT 39 With the current generation of telescopes, we logical timescales. With these in hand, our have been able to study these telltale correla- knowledge of galaxy evolution will make a giant tions between the properties of galaxies over a leap forward. Pushing the limits of the observa- wide range of masses in the nearby Universe. ble Universe beyond redshift of 6 by detecting However, only the brightest or most massive the first ultraviolet-emitting sources will allow us galaxies have been accessible at redshifts to probe the era a few hundred million years larger than one, and a direct measurement of right at the end of the Dark Ages, when the first masses has been almost completely out of light-emitting objects, which ionised much of reach at redshifts larger than two. Thus, our the content of the Universe, switched on. ability to explore the evolution and origin of these scaling relations has rapidly reached the Questions still to be answered are whether gal- limits of current technology telescopes, and will axies caused this reionisation, and whether only be advanced in the era of the E-ELT. they were then similar to the relatively normal galaxies that we see at somewhat lower red- shifts, or whether they were fundamentally dif- Observations beyond the limit ferent. Direct kinematics of the stars and gas in the first generation of massive galaxies, obtain- High spatial resolution, diffraction-limited imag- able with the unprecedented spatial resolution ing and spectroscopy with the E-ELT will pro- of the E-ELT, will be used to draw a con­sistent vide invaluable information about the morphol- picture of the mass assembly and star forma- ogy, dynamical state and variations in physical tion of galaxies across the entire history of the parameters across galaxies over large cosmo- Universe.

Snapshot of the evo- lution of a rotating galaxy, when the Universe was three billion years old. The E-ELT is expected to yield such velocity maps of galaxies at much earlier look- back times.

40 Science with the E-ELT Peering through the dust Thus, the migration of the peak efficiency of star formation rate from high to low masses as With E-ELT’s enhanced sensitivity in the near- galaxies evolve, known as the “downsizing infrared, it will be possible to derive dust extinc- ­effect”, will be studied through the epochs tion maps from intensity ratios of hydrogen when the effect is believed to have occurred. Balmer lines over a variety of redshifts. Star for- mation rates will be derived from the extinction- corrected emission line luminosities, using The intergalactic medium ­suitable diagnostic emission lines. These results will be combined with other indicators coming A key to further progress is a better under- from multi-wavelength observations to produce standing of the complex interplay between gal- a truly definitive measure of the star formation axies and the surrounding intergalactic medium. histories of galaxies of different types. The intergalactic medium provides the reser- voir of gas for the ongoing infall of fresh material Detailed knowledge of star formation across all into galaxies. At the same time, it acts as a cosmic epochs will allow us to explore how the ­repository for the gas driven out of galaxies by star formation histories of galaxies depend on energetic processes such as active galactic the environment in which they find themselves. ­nuclei and supernovae. The combination of

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Science with the E-ELT 41 The cosmic web of for most, if not all, aspects of the complex life- filaments and sheets        KNF- BLl " (5 cycle of gas in galaxies and the intergalactic at redshift 3 as  ­simulated­ using the medium. Measuring the widths of the absorp- ­hydrodynamical tion lines of triply ionised carbon, C iv, is a pow- code GADGET-2.  erful tool for studying this lifecycle. However, the Here, the predicted intrin ­sically low column densities of C iv make C iv column density is shown.  this cardinal test very difficult with existing tele-

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The E-ELT will directly probe the physical prop-       erties of galaxies as a function of their mass W:Gl,OB< and environment for over 90% of the age of the Universe, which, for the first time, will cover the these processes is responsible for the regula- entire epoch over which these systems formed. tion of the gas supply, which ultimately dictates With these additional observational inputs as- star formation and black hole growth as well as tronomers shall be able to directly determine the chemical and structural evolution of galax- many of the parameters currently assumed in ies. Heavy elements play a very important role models of galaxy formation.

A distant quasar is Quasar used as a beacon in the Universe. Gal- To Earth axies and intergalac- tic material that lie Intervening gas between the quasar H emission from quasar and us will reveal themselves by the H absorption ‘Metal’ absorption lines features seen in the quasar spectrum.

Right: The large- 3500 4000 4500 5000 5500 6000 scale structure of the Wavelength (Å) Universe when it was one billion years old. Galaxies are formed in the densest dark matter regions.

42 Science with the E-ELT

The E-ELT: A Pillar in the Astronomical Landscape of 2020+

When the E-ELT starts operations a decade from now, astronomy will be in a golden era. By that time, a rich heritage will have been gath- ered from today’s working facilities. In addition, new and ambitious facilities complementing the E-ELT will be deployed on the same timescale.

By 2020 observations with current telescopes will have led to a significant accumulation of knowledge and inevitably invited many new questions. Discoveries with ground-based tele- scopes such as ESO’s Very Large Telescope (VLT) and its interferometer (VLTI), and other 8–10-metre class telescopes will have prepared the scene for further fascinating discoveries with the E-ELT. For example, it is expected that in the field of exoplanets, many candidates for E-ELT follow-up will have been identified, and the first galaxies emerging from the Dark Ages wealth of synergies between these facilities: The VLT, located will have been tentatively identified and awaiting while ALMA will see the molecular gas in dis- on Cerro Paranal in Chile, is the most the E-ELT to be characterised and understood. tant galaxies, the E-ELT will reveal the ionised ­advanced and effi- gas — together ALMA and the E-ELT will revo- cient observatory in At the start of E-ELT operations, the Atacama lutionise our understanding of star formation. the world. Large Millimeter/submillimeter Array (ALMA) Similarly, the two facilities will probe different will have been exploring the cold Universe for a ­regions in nearby protoplanetary discs, ideally little less than a decade. A recent consultation complementing each other in exploring the of the ALMA and E-ELT communities revealed a early phases of planetary systems.

ALMA is the largest astronomical project in existence and will start observing the southern sky in 2011.

Science with the E-ELT 45 Several space observatories will work together with the E-ELT. Shown from left to right are Gaia, Kepler and Herschel. The James Webb Space Telescope (bottom) is expected to be launched in 2014.

The next decade will also see the advent of of years as the E-ELT starts operations. These many survey telescopes. ESO’s 2.6-metre VLT missions will have produced a major legacy Survey Telescope (VST) and the 4.1-metre Visi- for the E-ELT to exploit. For example CoRoT ble and Infrared Survey Telescope for Astron- and Kepler will reveal nearby exoplanets transit- omy (VISTA) will have been surveying the sky for ing making them perfect candidates for exo- a decade, supplemented by many similar facili- planet atmosphere studies with the E-ELT. Gaia ties worldwide. These telescopes will be com- will have studied a billion stars in the Milky Way plemented by even more powerful survey facili- in detail, revealing rare jewels such as the ties, such as the Pan-STARRS network and first stars that can be followed up with nucleo­ the 8-metre Large Synoptic Survey Telescope cosmochronometry with the E-ELT. Herschel, (LSST), which will ramp up towards the end together with ALMA, will collect a sample of of this decade. While much exciting science will galaxies in the early Universe, awaiting the come out of these surveys directly, a wealth E-ELT to be resolved and analysed. The list of understanding will follow from more detailed goes on; it is only by using the amazing power follow-up observations of targets identified by of the E-ELT to understand the detailed physics such projects, and it will only be with the larger, of the objects discovered by these missions more sophisticated E-ELT that such an under- that the benefits from the huge investment in standing can be obtained. space technology will be fully realised.

Existing or soon-to-be-launched space tele- An exciting scientific interplay can be foreseen scopes such as Hubble, Spitzer, Chandra, between the E-ELT and Hubble’s successor, XMM-Newton, Herschel, Planck, CoRoT, Kepler the James Webb Space Telescope (JWST), the and Gaia will have been working for a number ambitious optical/infrared space observatory

46 Science with the E-ELT scheduled for launch in 2018. Indeed, just as An artist’s view of the combination of 8–10-metre class telescopes the planned Square ­Kilometre Array radio and the Hubble offered two decades of discov- telescope. eries, the E-ELT and JWST complement each other perfectly. The 6.5-metre JWST, unhin- dered by the atmosphere, will be able to obtain deeper images, in particular in the infrared, while the 40-metre-class E-ELT will have over six times higher spatial resolution and will be able to collect fifty times more photons for high resolution spectroscopy and studies of rapid In summary, the E-ELT will be built on the most time variability. solid foundations. In the coming decade enor- mous progress is expected from the many Finally, the plans for the Square Kilometre Array ground-based and space observatories. While (SKA) could have it starting operations soon the E-ELT will have a sharper eye and higher after the E-ELT. Despite the very different wave- sensitivity than all of them, it will profit from their length regimes, the cosmology science drivers capabilities to observe at other wavelengths or of the E-ELT and SKA are remarkably comple- wider areas of the sky. The synergy between all mentary. Survey observations with the SKA are these facilities will enable the most fascinating likely to follow-up on the studies of the funda- discoveries with the E-ELT. mental constants and dark energy made with the E-ELT. In many other fields the SKA will probe the cold Universe, where the E-ELT can see the luminous one.

The E-ELT compared to other ELTs

GMT-project TMT-project E-ELT-project

~ 24 m ~30 m ~40 m Diameter ~400 m2 ~600 m2 ~1000 m2 Collecting area ~9 mas ~7 mas ~5 mas Diffraction limit at 1 µm

Science with the E-ELT 47

Discovery Potential ­— Expect the Unexpected!

The previous chapters presented the great sci- E-ELT will open such new frontiers in at least Left: The E-ELT entific achievements to be anticipated with the three ways. First, the E-ELT will, thanks to its ­(artist’s impression). E-ELT. These alone represent a giant leap in our immense collecting power, increase the sensi- understanding of the Universe and potentially tivity of observations by up to a factor of 600. the first step towards finding life beyond the Furthermore, the E-ELT will increase the spatial Solar System. Yet, all previous telescopes have resolution of images by an order of magnitude shown that, no matter how hard scientists have (even improving on the sharpness of future tried to predict the future, the greatest discover- space telescopes). Finally, the E-ELT will open a ies come as totally unexpected. Is this still pos- new window on time resolution, enabling obser- sible in the case of the E-ELT? vation in the nanosecond regime. These leaps forward in what a telescope can do, coupled The discovery potential of a telescope is, by with other advances such as unprecedented definition, hard to quantify. However, astrono- spectral resolution, new abilities to study polar- mer Martin Harwit pointed out in his landmark ised light, and new levels of contrast allowing book that one key indicator is the opening of us to see the very faint next to the very bright, a new parameter space: by looking somewhere mean that we will open up an entire new uni- where no one has been able to look before, verse of possibilities. It is in this great unknown one is very likely to make new discoveries. The that the ultimate excitement of the E-ELT lies.

E-ELT — the most inspiring ground- based observatory project today (artist’s impression).

Science with the E-ELT 49 Glossary

AGN — Active Galactic Nucleus: a compact re- productive astronomical observatory. ESO gion in the centre of a galaxy where luminosity ­provides state-of-the-art research facilities to is much higher than usual. It is believed that the astronomers and is supported by Austria, radiation from an AGN is due to the accretion of ­Belgium, the Czech Republic, Denmark, mass by a supermassive black hole at the cen- ­Finland, France, Germany, Italy, the Nether- tre of the host galaxy. lands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ALMA — The Atacama Large Millimeter/submil- limeter Array is the largest astronomical project Gaia — Space mission of the European Space in existence. ALMA is a partnership of Europe, Agency, whose goal is to precisely chart the North America and East Asia in cooperation positions, distances, movements of one billion with the Republic of Chile. It is currently under stars in the Milky Way, and physically character- construction at 5000 metres above sea level in ise them. To be launched in 2012. northern Chile. Composed initially of 66 high precision millimetre and submillimetre antennas, GMT — The Giant Magellan Telescope is a it is expected to start scientific observations ­project for the construction of an optical/near- with a partial array as early as 2011. infrared telescope, consisting of seven 8-metre mirrors, combined together to reach the resolv- Arcsecond — A unit of angular measurement, ing power of a 24.5-metre telescope. It is a col- corresponding to 1/3600th of a degree. laboration between US, Australian and South Korean institutions. It is expected to start oper- AU — Astronomical Unit, the mean distance ations early in the next decade in the Chilean between the Sun and the Earth, or about Andes. 150 million kilometres. HST — The Hubble Space Telescope, a joint Black hole — A region where a huge amount of project of NASA and the European Space matter is concentrated into a small space, and Agency, is a 2.4-metre ultraviolet/optical/near- where the gravitational pull is so strong that infrared telescope above the Earth’s atmos- even light cannot escape. phere. Launched in 1990.

Damped Lyman-a system — Galaxies that host JWST — The James Webb Space Telescope, a large amounts of neutral hydrogen gas and that project for the next generation, is an optical/in- are detected as they absorb the light from a frared-optimised space-based telescope with a background quasar. 6.5-metre diameter primary mirror. It is sched- uled for launch in 2018. E-ELT — The European Extremely Large Tele- scope, the world’s largest optical/near-infrared LCDM — Lambda–Cold Dark Matter model — telescope, with a diameter of ~40 m, to be built often referred to as the concordance model — by ESO. First light is foreseen early in the next is the simplest model that currently matches decade. best the observable facts about the evolution of the Universe. Lambda stands for the cosmo- ESO — The European Southern Observatory, logical constant describing the dark energy, the foremost intergovernmental astronomy which is held responsible for the current accel- ­organisation in Europe and the world’s most erated expansion of the Universe.

50 Science with the E-ELT LSST — Large Synoptic Survey Telescope, an one million square metres. It is expected to be 8.4–metre optical/near-infrared telescope to completed during the next decade in the south- be built in the Chilean Andes through a US- ern hemisphere. based public–private partnership. First light is expected at the end of this decade. With its Spitzer — An infrared, space-based 0.85-metre ability to cover the whole accessible sky twice telescope launched by NASA in 2003. Most of per week, the data from the LSST will be used the spectral window accessible to Spitzer is to create a 3D map of the Universe with un- blocked by the Earth’s atmosphere and cannot precedented depth and detail. be observed from the ground. mas — Milliarcsecond, 10–3 arcseconds. TMT — Thirty Meter Telescope, a proposed 30-metre optical/near-infrared telescope on μas — Microarcsecond, 10–6 arcseconds. Mauna Kea, Hawaii (US) project, expected to see first light early in the next decade. The TMT Parsec (pc) — A unit of distance, corresponding is a collaboration of Caltech, the University of to about 31 × 1012 km or 3.26 light-years. It is California (US), the Association of Canadian defined as the distance from which the mean Universities for Research in Astronomy, and the Earth–Sun distance is visible as 1 arcsecond on National Astronomical Observatory of Japan. the sky. VISTA — A 4.1-metre-wide field survey tele- Planetesimals — Solid objects formed during scope, equipped with a near infrared camera. the accumulation of planets whose internal Built by a consortium of UK institutions for strength is dominated by self-gravity and whose ESO, it is installed at the Paranal Observatory orbital dynamics are not significantly affected and started operations in 2010. by gas drag. This corresponds to objects larger than approximately 1 km in diameter in the solar VLT — Very Large Telescope, currently the nebula. world’s leading astronomical observatory. Oper- ated by ESO and located in the Chilean Andes Redshift — A shift towards longer wavelengths at Paranal, it comprises four 8.2-metre optical/ of the spectrum of the light emitted by astro- infrared telescopes. nomical objects. It indicates the age of the Uni- verse when the light was first emitted. A redshift VLTI — The Very Large Telescope Interferome- of zero corresponds to the current epoch; a ter is able to combine, in twos or threes and, redshift of 5 to 12.5 billion years ago. in the future, in fours, the light from the four ­8.2-metre Unit Telescopes of the VLT, or from Reionisation — Occurred when the Universe four 1.8-metre mobile Auxiliary Telescopes. was between 400 million and 1 billion years old. The neutral hydrogen then filling up space was VST — The VLT Survey Telescope is a state-of- ionised by the first light-emitting objects, mak- the-art 2.6-metre telescope equipped with ing the Universe transparent to photons. OmegaCAM, a monster 268 megapixel CCD camera with a field of view four times the area SKA — Square Kilometre Array, a proposed of the full Moon. radio telescope project with a collecting area of

Science with the E-ELT 51 Authors/Editors Image Credits

All images are copyright ESO except This document was prepared by the E-ELT ­Science Office with the help of the E-ELT Front cover: Swinburne Astronomy Productions/ESO ­Science Working Group and the science teams Page 3 top left: Reproduction of a portrait by Justus of the consortia of the E-ELT instrument S ustermans painted in 1636. National Maritime Museum, Greenwich, London ­concept studies CODEX, EAGLE, EPICS, Page 3 top right: from Singer, C. 1921, Studies in the His- ­HARMONI, METIS, MICADO, OPTIMOS, and tory and Method of Science, Vol. ii. (Oxford: Clarendon SIMPLE. Press) Page 3 bottom left: Reproduction of a portrait by Godfrey Kneller, painted in 1689 Editors: Mariya Lyubenova and Markus Kissler- Page 3 bottom right: RAS Patig Page 5: ESO/R. Gilmozzi Page 6 top: CILAS Science Working Group members: Arne Page 6 bottom: Microgate/A.D.S. International/SAGEM/ INAF team/M. Mantegazza, M. ­Tintori ­Ardeberg, Jacqueline Bergeron, Andrea Cimatti, Page 7: ESO/L. Calçada Fernando Comerón, Jose Miguel Rodriguez Page 8/9: Swinburne Astronomy Productions/ESO ­Espinosa, Sofia Feltzing, Wolfram Page 10 left: NASA/JPL-Caltech/R. Hurt (SSC) Freudling, Raffaele Gratton, Martin Haehnelt, Page 13: NASA/WMAP team Page 15: Bouchy et al. 2009, A&A 496, 527 Isobel Hook (Chair), Hans Ulrich Käufl, Page 17: NASA, ESA, G. Bacon (STScI) Matt Lehnert, ­Christophe Lovis, Piero Madau, Page 20: NASA, ESA, S. Beckwith (STScI) and the Mark ­McCaughrean, Michael Merrifield, HUDF Team Rafael ­Rebolo, Piero Rosati, Eline Tolstoy, Page 21: ESO/J. Liske Page 22: ESO/J. Liske Hans ­Zinnecker Page 28 bottom: NASA and the Hubble Heritage Team (STScI/AURA) Former Science Working Group members: Willy Page 35: ESO/Zoccali et al. 2006, A&A, 486, 177 Benz, Robert Fosbury, Marijn Franx, Vanessa Page 39: NASA/WMAP Science Team Page 42 top: Matteo Viel Hill, Bruno Leibundgut, Markus Kissler-Patig, Page 42 bottom: adapted from John Webb Didier Queloz, Peter Shaver, Stephane Udry Page 43: Springel et al. 2005, Nature, 435, 629 Page 46: Gaia: ESA/C. Carreau; Kepler: The Kepler E-ELT Science Office: Roberto Gilmozzi (E-ELT Mission; Herschel: ESA/AOES Media­lab; background: Hubble Space Telescope image (NASA/ESA/STScI); Principal Investigator), Markus Kissler-Patig JWST: NASA ­(E-ELT Project Scientist), Jochen Liske, Alex Page 47: SKA and Xilostudios Böhnert, Annalisa Calamida, Szymon Gładysz, Page 47 left: GMTO Corporation Gaël James, Maja Kazmierczak, Mariya Page 47 middle: Thirty Meter Telescope Back cover: Swinburne Astronomy Productions/ESO Lyubenova, Dominique Naef, Daniela Villegas, Aybüke Küpcü Yoldaş, Giuseppina Battaglia, Lise Christensen, Bram Venemans, Mathieu Puech, Sune Toft European Southern Observatory Karl-Schwarzschild-Straße 2 Production and Graphic Design: ESO education 85748 Garching bei München and Public Outreach Department (Henri ­Boffin, Germany Phone +498932006-0 Jutta Boxheimer, Lars Lindberg ­Christensen www.eso.org and Mafalda Martins) [email protected]