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Star Factories at the End of the World

When the came into being 13.7 billion years ago, there was initially only radiation. A few hundred million years later, however, the space was filled with galaxies – tremendously productive factories that don’t fit quite so well with the image of a gradual cosmic evolution. Researchers like Fabian Walter from the Max Planck Institute for in Heidelberg are attempting to illuminate a dark of the universe.

TEXT ALEXANDER STIRN FOCUS_Cosmology

A deeper view into the cosmos: This section from the Hubble Ultra Deep Field shows the galaxies at the edge of space and time. Huge numbers of are born in these young Milky Ways.

inding catchy designations But this is slowly changing: “Because It’s still detective work – a laborious for incomprehensible pro- our telescopes are continually improv- search that has practically nothing to cesses has never been a prob- ing and becoming more sensitive, we do with the colorful photos that astron- lem for : They see things today that we couldn’t have omy otherwise produces. Many of these call the era that begins just observed ten years ago,” says Fabian typical, vivid photographs are hanging F 380,000 years after the birth of the uni- Walter, an at the Max in the stairwell of the Heidelberg-based verse the Dark Ages. At that time, the Planck Institute for Astronomy in Hei- institute, a concrete structure located positively charged ions emerging from delberg. There, the 41-year-old investi- on the Königstuhl promontory high the set about catching the free gates how and when the first stars above the city. They show planetary electrons buzzing around – and the af- emerged, how productive the early gal- nebulae, star clusters and spiral galax- terglow of the Big Bang fades. Howev- axies were, and where exactly the stel- ies. In between all these stellar images er, no stars that could bring light to the lar nurseries were located. hangs an unspectacular photograph, sudden darkness had formed yet. Time and time again throughout mostly black with many pixelated dabs This distant age isn’t only a dark pe- this process, he and his co-theoreticians of color. Hubble Ultra Deep Field is writ- riod cosmologically; science, too, has have encountered unforeseen problems ten below. had a difficult time illuminating the pro- – and will probably continue to do so. It is a view into the deepest depths cesses of that time. There are hardly any “The study of galaxies in the early of space. For many hundreds of hours, observations surrounding the birth of phase of the universe will develop into the directed its the first stars. Researchers must thus rely a main area of research for astronomers eyes to a region of the sky that would

Photo: NASA, ESA, R. Ellis (Caltech) and the HUDF 2012 Team on simulations and theoretical ideas. in the coming years,” says Walter. be only one square millimeter in size

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» Especially molecular is necessary for a star to be born. However, hydrogen can’t be directly observed.

on a thumbnail at arm’s length. Ex- twice as large as for a stationary object, axies that can be seen in the Hubble Deep tremely old objects, themselves glow- and with a value of 2, it has tripled, and Field (HDF). This light largely originates ing extremely weakly, can still be made so on. Because astronomers continual- from fully formed stars. The birth of new out on it. “Many of these galactic imag- ly see distant objects at the point in happens elsewhere – in the interi- es are made up of only a couple hun- time when the light began its journey, or of dense clouds of dust and gas. dred photons,” says Walter and points the redshift additionally serves as a “Without gas, no stars,” says Walter. to a reddish, shimmering spot. metric for the age of a galaxy. The light Especially molecular hydrogen is The color is no accident: the uni- from an object with z = 10 started its necessary for the stellar offspring to be verse has been continuing to expand trip at about the time when the uni- born; however, hydrogen can’t be di- since the Big Bang. In the process, the verse was just 500 million years old. rectly observed. It is only possible particles of light called photons have With an assumed age of the universe of through an indirect route of a gas that been stretched as well. Their wave- around 13.7 billion years, the light was is closely related to the amounts of hy- lengths were forced to extend – and all thus under way for 13.2 billion years. drogen: monoxide. Its mole- the more so the farther away the ob- “Very remote objects quickly be- cule emits a characteristic signal that ject that once sent them out was from come dramatically dark due to redshift normally lies in the infrared region of the Earth. – most especially in the visible light the spectrum. Astronomers call this effect “red- range,” says Fabian Walter. However, the Due to the redshift, it arrives at shift.” Its magnitude is described by the Heidelberg-based astronomer is only Earth with wavelengths of a few milli- “z value.” At z = 1, the wavelength is marginally interested in the light of gal- meters – that is, just below the micro-

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0 2012 1

CO(6–5) Nature 0.5

0

1.5 CO(5–4) 1 0.5 Flow (mJy) density Flow 0 -0.5 0.5 CO(2–1) A galaxy pops up: The object known as HDF850.1 can’t be seen at all in the Hubble Deep Field (photo left). In contrast, this distant galaxy becomes visible 2012; photos: STScI/NASA, F. Walter (MPIA), in the submillimeter wavelength region (light contour lines, photo right). 0 The light from HDF850.1 took 12.5 billion years to reach us and is extremely weak. Nevertheless, a team of astronomers headed by Fabian Walter Nature -2000 0 2000 succeeded in analyzing the emissions of the galaxy. The spectra (left) show Speed (km/s) characteristic lines of carbon that indicate a high stellar birth rate. Graphic:

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wave range. At the very least, the

brightest of these ancient regions of ) -1 -16

star formation can be found by modern m μ

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millimeter-wavelength telescopes, such 2 x 10 as the observatory of the Institut de Ra- dioastronomie Millimétrique (IRAM) in the French Alps (see box on page 31). -16

A BLACK SPOT ON A Flow density (W m density Flow

BLACK BACKGROUND 010

With the help of those regions, astron- 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 omers have discovered an entire series Wavelength (μm) of such sources over the past years. One of the most important of these is sim- Keys to the early developmental phase of the universe: Quasars are some of first objects ply called HDF850.1. The galaxy is no formed a few hundred million years after the Big Bang. In the heart of these young galaxies are gigantic black holes that spew in the form of jets into space (illustration above). more than a black spot on a black back- The spectra of these objects reveal a great deal about their internal workings, especially 2011 (bottom) ground in the classic Hubble Deep Field, about the processes of stellar formation. Here the spectrum of the record holder (z = 7.1), but it lights up strongly in the submil- which looks just like any quasar in the vicinity of Earth. Nature limeter wavelength region. Carbon monoxide molecules that once ab- sorbed radiation, converted it into ro- bian Walter succeeded in determining However, the study, which was pub- tational oscillations, and finally emitted the redshift of HDF850.1 in 2012. It lished in the journal NATURE, reveals it at clearly defined frequencies (spec- lies at a z-value of 5.2. Accordingly, the even more: characteristic spectral lines tral lines) are especially visible there. light of the galaxy was on its way to of carbon – particularly of atoms that Together with researchers from the Earth for 12.5 billion years, and permits are missing an electron – indicate high Max Planck Institute for Radio Astron- a glimpse into a time when the uni- stellar activity. These spectral lines not

Graphic: ESO – M. Kornmesser (top), omy in Bonn and other colleagues, Fa- verse was a mere 1.2 billion years old. only reveal that new stars are being

1 | 13 MaxPlanckResearch 29 In the labor ward of suns: The Orion Nebula produced hidden behind thick clouds ments formed in the Big Bang needed (above) is one of the most picturesque of dust and gas deep in the distant many hundreds of thousands of years subjects in our firmament. You can see a faint Milky Way, but they also provide clues to slowly agglomerate – supported by spot in the sword hilt of Orion even with the unaided eye. about the course of this process. a force that astronomers call dark mat- A telescope reveals a majestic cloud of dust ter and about whose nature they still and gas where stars are born. In the Orion KL A GALAXY WITH AN AMAZINGLY can say hardly anything. The gaseous region of the formation (black rectangle), HIGH BIRTH RATE elements – primarily hydrogen, heli- located about 1,350 light-years away, the um and – collected in the disks stellar birthrate is close to that of Galaxy According to this, a galaxy like HDF850.1 of the first galaxies, condensed under J1148+5251 (below), though calculated over a much greater volume. After all, this remote produces a trillion times as much ener- the influence of their mutual gravita- star factory in the early universe is as large as gy as our . That is possible only if tional force, and began to collapse. At a hundred million Orion regions together. stars with around a thousand solar - some point, the molecular clouds were es form there, year after year. By con- finally dense enough to ignite the fire trast, a normal galaxy like our Milky of . Way manages only one one-thousandth These first suns – theoreticians of this amount. “Galaxies must have al- speak of Population III stars – must ready existed shortly after the Big Bang have been immense. They burned out, that were able to produce incredible exploded and, in the process, hurled numbers of stars,” says Fabian Walter. the heavier elements that they had pro- However, this contradicts the con- duced during nuclear fusion out into ventional models, according to which space. The components from which to- the first stars and galaxies should form day’s stars and galaxies are made ac- rather more leisurely: Until now, the- crued in this manner, bit by bit – a slow,

oreticians have assumed that the ele- continuous process, actually. Photos: NASA, ESA, Robberto (STScI/ESA), Orion Treasury Project Team (top), NRAO/AUI/NSF (bottom)

30 MaxPlanckResearch 1 | 13 Photo: IRAM – Rebus That an enormous star factory like That anenormousstarfactory studying physicalprocesses andthe makes themidealresearch toolsfor ally brightestobjectsinspace. “That lights upbrightly. disappears intothecosmic chasm,it ed intensely. Shortlybeforethematter spiraling orbits,accelerated,andheat- matter in.Gasanddustareforced into most galaxiesandcontinuouslydraw black holesthatsitinthecenterof comes fromquasars,aswell–active of theearlyuniverse.Surprisingdata model only riskforthecontemporary with theirsimulations.” then thetheoreticianshaveaproblem however, thousandsofthemexist, ed oneindetailsofar,” saysWalter. “If, there are.We’ve reallyonlyinvestigat- how manyofthesekindsobjects hood. “Ifwe’rehonest,wehavenoidea conditions oftheuniverseinitschild- conclusions tobedrawnaboutthetrue the datapossiblydoesn’t allowforany outliers, orperhapsjustluckyhits.And Theseareperhaps easiest toobserve. est andmostactive–thereforethe ter hascapturedthosethatarebright- ies, itisquitepossiblethatFabianWal- his search for especiallyremotegalax- sufficient foradefinitivededuction.In andpractice. theory says Walter aboutthedilemmabetween much morequicklythanwethought,” universe musthaveruntheircourse several thingsatthebeginningof of astronomy, wearediscoveringthat well withthispicture.“Inmanyareas years aftertheBigBangdoesn’t fitvery HDF850.1 musthaveexistedabillion Galaxies likeHDF850.1aren’t the datastillisn’tThe observational Quasars representsomeofthe visu- » of the early universe. early of the Surprising comes well. fromquasars, data as Galaxies like HDF 850.1 aren’t the only risk the aren’t model for contemporary the the Max Planck Society. Planck Max the side by German the on funded telescopes, 12 to expanded and modernized will be Bure de Plateau the on observatory the 2018, Until telescope. asingle with sible pos- be would than cosmos into the deeply more and focus sharper with look can way, Inthis astronomers observed. objects the for differences the from image tion ahigh-resolu- compute and superposed subsequently signals are The time. different ataslightly space deep from waves radio the –receiving locations individualized dish their to –due telescope individual in each (photo). results This eter of 15 meters adiam- and having each project, connected joint German-French-Spanish in the telescopes radio together in what six are There short. for is IRAM or Millimétrique, Radioastronomie known de Institut the of as an interferometer observatory the radiation: millimeter for telescopes highest-performance the of one stands Alps French in the Bure de Plateau the on 2,550 of At analtitude meters THE IRAMINTERFEROMETER 1 | 13 MaxPlanckResearch MaxPlanckResearch FOCUS _Cosmology 31 FOCUS_Cosmology

» ALMA, an unsurpassed millimeter-wavelength telescope, will soon go into operation in Chile. The facility will comprise 66 antennas.

chemical composition in remote re- “In our Milky Way, these extreme con- porary galaxies. “There’s hardly a dif- gions,” says Walter. Even a few hours’ ditions are found only in much small- ference between a quasar that we see observation time with IRAM is suffi- er regions around parts of the Orion 800 million years after the Big Bang cient to coax the secrets from quasars. nebula,” says Walter. However, and one that we see in the today’s uni- The brightly glowing objects have J1148+5251 is as large as a hundred verse,” says Walter. one great disadvantage, though: they million Orion regions together – and occur extremely rarely – at least during that not even a billion years after the SIMPLE MEASUREMENTS RUIN the early periods of the universe – and birth of the universe. MODELS are correspondingly difficult to find. And yet another observation that Walter and his colleagues are therefore Walter and his colleagues have made However, that also means that the char- relying on a systematic scrutiny of the in relation to quasars shortly after the acteristic spectral lines of metals like sky with the aid of a telescope in Ha- Big Bang is an enigma: Although the or magnesium can be found even waii: Pan-STARRS (Panoramic Survey objects are extremely young, their in the early quasars – elements that Telescope & Rapid Response System) au- is already similar in mass to cannot form in the Big Bang, but in- tomatically sifts through the entire fir- today’s galaxies. The dynamic mass stead must first be produced by the mament above the Pacific island for that is distributed all around it, how- stars, bit by bit. One of the convention- points of light whose signatures could ever, is miniscule by comparison, to- al models of stellar formation indeed match that of quasars. “We have taling merely twenty or thirty times predicts that iron, as the heaviest ele- already found two quasars this way,” that of the center. With contemporary ment, could be formed solely in stars says Walter. “That’s not great, but it galaxies, this value is significantly that were at least two billion years old. demonstrates that the method works, higher and lies at around one thou- “With simple measurements, these and we can continue with a sense of sand times. models have been thrown into disar- confidence.” This could suggest that, in the early ray,” says Walter. But he isn’t disap- universe, the black holes originated pointed because of this – just the oppo- TELESCOPE PROBES right away. They drew in more and site: “I find it fascinating.” THE CHILDHOOD OF SPACE more dust and gas, which ultimately Nevertheless, as previously with the led to the birth of the first stars in the galaxies in the Hubble Deep Field, the One cosmic beacon that has long been immediate vicinity of the galactic cen- number of quasars that have been in- known is called J1148+5251. It provides ter. “That is very speculative though,” vestigated is still too few to allow a sta- insight into a time less than a billion warns Fabian Walter. He thus concen- tistically valid prediction about the pro- years after the Big Bang. In 2009, the trates on taking the measurements. His cesses in the young universe. That astronomers in Heidelberg and Bonn theoretical astronomy colleagues are could soon change: ALMA, an unsur- were already able to demonstrate, with the ones who have to wrack their brains passed millimeter-wavelength tele- the aid of IRAM, that an extremely over what it all means. scope, will soon go into operation in large number of stars are being formed Nor is that the only challenge that Chile. Instead of six antennas like in this galaxy as well. The rate even lies Walter and his colleagues are con- IRAM, ALMA has 66 at its disposal. And at the upper limit of what is physically fronting the theoreticians with: The instead of being at an altitude of 2,550 possible – even more stars, and the light that the astronomers have cap- meters in the French Alps, it stands at energy of the large number of births tured from the ancient quasars is more than 5,000 meters in the Atacama would blow up the 5,000-light-year spread over the various wavelengths Desert, one of the driest and clearest diameter nursery. very similarly to the light of contem- regions on Earth.

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1 Scout above a sea of clouds: The telescope of the Pan-STARRS on Maui (Hawaii) sifts through the firmament for points of light and searches for the fingerprints of quasars, among other objects. 2 Journey in space: Astronomer Fabian Walter has worked for many years on the Very Large Array in Socorro, New Mexico.

Fabian Walter becomes very excited when he thinks about it: “ALMA is ab- solutely gigantic,” says the astronomer. TO THE POINT “This is a telescope that overshadows ● The universe was born about 13.7 billion years ago in the Big Bang. Just a few hundred everything that has gone before it. It’s million years later, there were already stars and galaxies.

a great leap, like going from the human ● Several of the first galaxies were unimaginably productive: stars on the order of about eye to Galileo’s telescope.” a thousand solar apparently formed year after year within them. In contrast, a Compared to its predecessors, ALMA normal galaxy like our Milky Way manages a mere one one-thousandth of this amount. combines several qualities at once: the ● The high rate of production doesn’t match up with the theoretical models. Astronomers telescope isn’t only significantly more are attempting to collect as much data as possible about the early period of the cosmos. sensitive, its individual dishes can be ● Observations of young galaxies and remote quasars should help us understand what separated from one another by up to six- processes ran their course in the interior of the first gigantic star factories. teen kilometers. Submillimeter sources from the extremely young universe can be found more easily this way and the GLOSSARY distribution of their light and their Redshift: For objects receding from Earth at high speed, this is a metric for the shift of masses can be observed in greater detail. the wavelengths toward the red region of the spectrum and is represented by the value z. That much progress will take five to Look-back time: At very large distances, the redshift depends not only on the speed of ten years, though. “We are therefore a receding object (Doppler effect). The expansion of all of space lengthens the light much still dependent on models and simula- more. Nor can the distance to the object therefore be deduced simply from this cosmo- tions,” says Fabian Walter. With every logical redshift; it depends on the respective cosmological model applied, among other new observation, regardless of whether things. Astronomers prefer to speak of the look-back time – the time that the light from it is made now with IRAM or in the fu- the object took to reach us and that indicates the age of the universe when the light started its journey. ture with ALMA, a new opportunity Big Bang: Cosmologists’ preferred model for the birth of the universe. Accordingly, the opens up for the astronomers to adapt cosmos originated 13.7 billion years ago from an unimaginably dense and hot initial their models to the realities of that time singularity that can’t be described physically. Today, the classical Big Bang model has a little bit better – and to bring more been extended by – the sudden expansion of the extremely young cosmos.

Photos: Rob Ratkowski (left), private (right) light to a dark age of the universe.

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