NATGEOASTROPHYSICS0001

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first galaxes. Researchers studyng mages fromthe Hubble Space Telescope have dscovered thebreathtakng dversty of the galaxes that sur-round us today-from gant pnwheels blazngwth the blue lght of newborn stars, to ms-shapen footballs glowng with the ruddy hue ofstars bom bllons of years ago, to tattered gal-axies trailing long streamers of stars tom out bycollsons wth ntruder galaxies.Less than a century ago astronomers knewonly about our own galaxy, the M1kyWay, whchthey believed held about 100 million stars. Thenobservers dscovered that some of the fuzzy blobsn the sky weren't in our own galaxy, but weregalaxies n ther own right-collectons of stars,gas, and dust bound together by gravty. Todaywe know that the M1kyWay contans more than100 billon stars and that there are some 100 bil-lion galaxies n the unverse, each harboring anenormous number of stars.Our vew of the unverse s changng com-pletely, says cosmologst Carlos Frenk of the Un-versty of Durham n England, and it's largelybecause of our new understandng of galaxy for-mation: "It's no exaggeraton to say that we'regong through a perod of change analogous tothe Copernican revolution."O NE OF THE NEW cosmologists, TomAbel of Pennsylvania State Univer-sity, thinks he has figured out howthe first star was bom. One afternoonlast April he sat by a hotel pool n Cozumel,Mexico, oblivious to the squawkng blackbirdsand the whir of the poolsde blender kept busymaking pifia coladas. He was staring intently

past few years, together wth hs colleaguesMichael L. Norman of the Universty of Cal-ifornia, San Diego, and Greg L. Bryan of OxfordUnversity, Abel has created supercomputer sm-ulatons that show how stars were formed fromthese gases.The first step, according to the simulations,was when gravity gathered gases into diffuseclouds. As the gases cooled, they coalesced at thecenter of each cloud nto a clump no larger thanour sun. The clump collapsed further, whle sur-rounding gas piled on top of it. In this way tgrew into a behemoth about 100 times the massof the sun. Finally, several million years after theentire process began, the intense compressionforged a full-fledged star-and there was light.Elsewhere the same star-forming process hadbegun n other gas clouds that Abel refers to asmicrogalaxies-miniature, single-starred ver-sions of today's galaxies. Soon beacons of lightfrom massve stars permeated the darkness.These stars burned brightly and then fizzledafter only a few million years, dying n ttancexplosions called supemovae. During the breftime these first stars reigned, however, theywrought changes n the universe that had a pro-found effect on future galaxy formation. Theyheated surrounding gases and bombarded themwth ultraviolet light. And when they exploded,the stars seeded the universe, and the next gen-eration of stats, with the first supply of heavyelements, including the oxygen we breathe.The explosive demise of these stars may haveleft behind dense cinders, the first black holesin the universe. Moreover, the supernovaexplosions may have been accompanied by

The concept of dark matter has been aroundat images on his laptop computer-imagesdepicting how star formation could have hap-penedo In a few minutes he would go backinside the hotel to share the images with his col-leagues at one of the largest meetings everdevoted to the origin of galaxies.The first star was bom about 14 billion yearsago, Abel believes, in a universe that was moremysterous but also far sim pie r than our own.Smaller and denser than today, the unverse waspitch-black and contained mostly hydrogen andheliurn with a smattering of lithium. During the10 NATIONAL GEOGRAPHIC FEBRUARY 2003

flashes of energetc radiation known as gamma-ray bursts that are billons of tmes brighter thanthe sun. If so, some of the gamma-ray bursts thathave already been detected may actually havecome from the first stars."It would be the most wonderful thing," saidAbel, "if we were so lucky that the first stars thatformed were also the brightest."Abel's presentation in Cozumel was a success.Scentists consider his simulations the most con-vincing scenaro yet for how stars were born,The simulations are based on a mind-blowing


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COSMIC REVELATION, a photographic negative of the Andromeda galaxytaken in 1923 by astronomer Edwin Hubble became the first proof thatgalaxies other than the Milky Way existed. The triumphant ''VAR!'' markeda star of variable brightness, valuable as a measuring tool to show thatAndromeda resided far beyond our home galaxy.

ecades .... No one wanted to believe"crazy Fritz" was right.

tome kind of mystery material, which ~ oCo seen and has come to be known as darkoutweighs all the visible material in the~.-,.,r


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"lt would be the most wonderful thing," saicluster of galaxies, the Coma cluster, and real-ized it shouldn't existo Individual galaxies inComa were zipping around so fast that the grav-ity exerted by the visible parts of the cluster wastoa puny to keep Coma intact. But Zwicky hada solution. He proposed that all the visiblematerial in the cluster was a mere fillip. The rest,which he could not see, he dubbed dark matter.No one wanted to believe "crazy Fritz" was rightDecades later, resistance to Zwicky's ideasbegan to fade when astronomers found them-selves invoking dark matter to explain a ho tof puzzles. In 1973 Princeton cosmologists [imPeebles and Ierry Ostriker said the mysterymaterial was necessary to keep spiral galaxies,including our own Milky Way, from falling apart.A few years later, Vera Rubin of the CarnegieInstitution ofWashington concluded that spiralgalaxies she and her colleagues had examinedhad to be embedded in a halo of dark matter.That was the only way to explain, she said, whystars at the outer edge of the spiral galaxiesmoved no more slowly than stars at the core.Dark matter, moreover, answered a key riddleof galaxy formation: how the universe changedfrom a smooth, hot soup of particles into a jum-ble of galaxies and galaxy clusters. There had tobe some lumps in the first place. By itself, ordi-nary matter-protons, electrons, and neutrons--couldn't provide those lumps. There wasn'tenough of it, and it couldn't begin clumpinguntil the universe had cooled. Dark matter, bycontrast, was plentiful and alI but impervious toevery force but gravity. It could coalesce almostimmediately after the universe's birth, givingordinary matter a foothold to form galaxies, evenas cosmic expansion tried to pull them apart.Evidence backing up the lumpy soup theorycarne in 1992, when a NASA satellite called theCosmic Background Explorer detected tiny hot16 NATIONAL GEOGRAPHIC FEBRUARY 2003

and cold spots in space. This supported the ideathat the seeds of galaxy formation-the pri-mordiallumps in the early universe created bydark matter-Ieft tiny temperature variationsin the cosmic microwave background, nowcooled to a frigid 2.73 degrees above absolutezero. Famed cosmologist Stephen Hawkingpronounced the finding the "discovery of thecentury, if not of alI time."

m ~I.. HUBBLE et the stage for today'sstudies of galaxy formation when he dis-covered tbat the Milky Way was not alone.In the predawn hours of October 6,1923,at the Iount t ilson Observatory in California,he photographed a fuzzy, spiral-shaped clump ofstars known as M31, or Andromeda, which mostastronomers assumed was part of the Milky Way.He soon realized that within the clump he hadfound a tiny jewel: a star known as a Cepheid vari-able. This type of star has a wonderful property:Its brightness waxes and wanes like clockwork,and the longer it takes to vary, the greater the star'sintrinsic brightness. That means the star can beused to measure cosmic distances. By comparingthe true brightness of the Cepheid in M31 withits brightness as it appears in the sky, Hubblewas able to determine the distance between Earthand the star.He discovered that the star and the cloud, ornebula, in which it resided were a million light-years away-three times the estimated diameterof the entire universe! Clearly this clump of starsresided far beyond the confines of the MilkyWay. But if Andromeda was a separate galaxy,then maybe many of the other nebulae in thesky were galaxies as well. The known universesuddenly ballooned in size.Hubble soon recognized that galaxies come inthree varieties. Ellipticals, which converted most


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THE "BOTTOM UP" model of galaxy building(sequence above) shows how gas (red) and newstars (white) came together to form small gal-axies that kept merging and growing. The lastimage shows the universe at middle age aboutseven billion years ago when huge galaxies(yellow) spun inside dark matter halos (green).but aiso growing bigger. The most popularversion of the dark matter theory says that gal-axies began small and grew over time throughcollisions and slow accumulation of materialfrom their surroundings.And these collisions aren't just things of thepast, Navarro notes. Witness the Antennae gal-axies, two galaxies caught in a cosmic tussle 63million light-years frorn Earth. Their mutualgravity has pulled out two long streamers ofluminous matter that resemble the antennaeof a cockroach. Closer to home, the Androm-eda galaxy, now hurtling toward us at 300,000miles an hour, will merge with the Milky Wayin several billion years, theorists predict.It wasn't the orderly shapes ofmature galaxiesbut the messy shapes of baby galaxiesthat cap-tured the imagination of astroromer ChuckSteidel at the Califomia Institute ofTechnology.Ris work has led to the discovery of more than2,000 early galaxies-sometimes at a rate of ahundred a night-providing important data fortheorists likeAbel and Navarro. And it ali beganwith a trek to a remote mountaintop in Hawaii.As Steidel and three of his dosest colleaguesdrove slowly up the narrow, bumpy road tothe l3,796-foot summit of Mauna Kea, theyknew this was their chance to crack open thesecrets of the early (Continued on page 22)

el, "if we were so lucky that the firststars that formed were also the brightest."

of their gas into stars long ago,resembledistortedfootballs. Spiral galaxies, induding our ownMilkyWay,account for two-thirds of the knownalaxiesin the universe. These galaxieshavecen-tral bulges of old stars, just like an elliptical, buttheir cores are surrounded by disks containinglender, spiral arms still aglow with newbornstars. Our nearest spiral neighbor, Andromeda,resembles a Frisbee with a fried egg at its cen-ter. Finally, irregular galaxies are the plodders,apparently making stars at the same slow rateever since they were bom.This diversity of galaxiesis rooted in violence,according to Julio Navarro of the Universityof Victoria in British Columbia. Like Abel,_ avarro relieson computer simulations to studyalaxy evolution, but his work focuses on gal-axieslater in their lifecydes,when they areproneo smash into each other and are chock-full ofars. Recent studies by Navarro and Matthiasteinmetz of the Astrophysical Institute Pots-dam in Germany depict how collisions couldhave altered the appearance of a single galaxyas. made its way through some 12billion years ofcosmic history.The first galaxywas a disk, Navarro believes,consequence of the object's rapid rotationand the pull of gravity. As this disk repeatedlyran into and fused with other baby galaxies,theorbits of its stars became scrambled. The bat-rered disk puffed into a swirling, sparkly ballf gas and stars-an elliptical galaxy. Then, as

e galaxy slowly dragged in streamers of gas,~ e ball became the aging centerpiece of aigger disk with spiral arms. Another collisionerased that structure and created a larger ball.ith each collision the galaxy altered its shape,, a lump of day constantly being resculpted,IEHAEll. NOAMAN ANO BRIAN O'SHEA. UNIVERSITY DF CAUFOANrA, SAN DIEGO (UCSD), ANO OONNA cox,'ICEERT PATTEASON, ANO STUART LEVY, NeSA/Ulue. WGBH BOSTON, NOVA: ~RUNAWAY UNIVERSEH GALAXY HUNTERS 17


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universe. If the kies remained clear, they wereabout to ob erve the heavens with the largestvi ible-light telescope in the world, the Keck,It was eptember 30, 1995, and Steidel, atonlv 3_, hoped to accomplish what no one hadever done--detect in wholesale numbers galax-i 50 di tant that the light they emitted morethan 12 billion years ago was only now reachingEarth, That meant the galaxies would appear asthe did when they were infants. If Steidel andhi collaborators could find enough of them,these youngsters might reveal not only how gal-axies first formed but als o how they changedover time, and how they were distributed acrossthe universe.Until then astronomers hunting distant gal-axies hadn't made much progresso They hadfound a few oddball objects that glowedextremely brightly, but they had failed to findthe run-of-the-rnill, remote galaxies thought tobe prevalent in the cosmos. Most astronomersfigured they would need bigger telescopes to findthese faint objects. But Steidel had another idea:Maybe galaxies that hailed from the early uni-verse had already been detected but no one hadbeen able to pick them out from the thousandsof other objects on sky maps.Like a few other astronomers before him,Steidel realized that distant galaxies have theirown signposts. They contain an abundance ofhydrogen gas, as does the vast expanse of inter-galactic space between them and Earth. Whenthe ultraviolet light emitted by stars in galaxiesis above a certain energy levei, hydrogen gasabsorbs it. The light never reaches Earth. Sobefore Steidel and his collaborators ever dreamedof coming to Keck, they recorded galaxies thatshowed up brightly in red and green filters butwere absent when viewed through an ultravio-let filter. They called these galaxies Lyman breakgalaxies, after Theodore Lyman, a physicist whopioneered studies of ultraviolet light in the early20th century.According to the color criterion, the faint gal-axies Steidel's team had found prior to comingto Mauna Kea ought to be remote. But werethey? To measure distance, the astronomers hadto determine how much light from a galaxy hadbeen stretched, or reddened, by the expansionof the universe. The greater this redshift, thegreater the distance from Earth. A galaxy ata redshift of three, for instance, corresponds22 NATIONAL GEOGRAPHIC FEBRUARY 2003

to a distance of about 12 billion light-years.For faint galaxies, redshift can only be deter-mined with a telescope as powerful as Keck. NowSteidel and his colleagues Mark Dickinson,Mauro Giavalisco, and graduate student KurtAdelberger found themselves with two nightson the telescope. If they could demonstrate thattheir color method worked, they would have afoolproof way to find not just one ar two dis-tant galaxies but dozens-even hundreds.Years before, Steidel and his collaborators hadalready picked out their first target. Residing inthe constellation Eridanus, it was the brightest

Lyman break galWe figured if weit was going to brecalls. But he alsolhe starlit body r -an hour each niz -The fleeting halaxy, however,Steidel had pr .that the galaxyEarth. Steidel \ -as -ould find an ar00 the next ni'~: ~!~

l I&.AJlK THIESSEN. NG S CTO f't" _~ .:::lETITUTE OF TECHNOlOGY .g=


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- illion light-years.. - can only be deter-. 'erful as Keck. Now_fark Dickinson,uate student Kurt~~""">< with two nightsdemonstrate that

ey would have ast one or two dis-~---e


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On that night, lightly giddy from the highaltitude, teidel pla red for the first time at Keckthe dream ,lullab -like music of the alternativero ck band _ 1a zzy tar. It would soon become aroda for each night Steidel observed at Keck anda special bond between him and Dickinson,om he had met when they were both college

. jocke at Princeton in 1980.1997 Steidel's team had bagged another 250Lyman break galaxies and an intriguing patternemerged. To the surprise of the astronomers, thosedistant galaxies were strongly clustered in a waythat revealed how dark matter is distributed. The

galaxies evolved from the simple universe of darkmatter and elemental gases described by TomAbel. Without such winds we can't easily explainthe appearance of the visible universe today.Beginning where Steidel's team left off,astronomer Sandra Faber of the University ofCalifornia, Santa Cruz, is poised to break newground in the study of galaxy formation. Sheand her collaborators hope to piece together howbaby galaxies, like the ones found by Steidel,developed into the galaxies around us today.Last March, wearing a navy blue jumpsuit thatmade her look more like an auto mechanic than

"We're collecting the photo album of thelife history of the universe for

the first time: the baby pictures, theteenage pictures, the grown-up pictures."first galaxies formed in the densest regions of theuniverse, which correspond on average with thedensest regions of the cosmos today, where wefind large galaxy groups and clusters. As timewent on and gravity exerted its inexorable pull,regions of lower density also gave birth to gal-axies, blazing with newborn stars.

J UST AS IMPORTANT was another discov-ery made by Steidel and Kurt Adelbergerin 2001: Powerful winds were rushingout of the Lyman break galaxies, prov-ing that there was more to the story of galaxyformation than dark matter. The winds, drivenby supernova explosions, were so strong theyenabled ordinary matter to temporarily escapethe grasp of dark matter, which was unaffectedby the winds. Not only did the winds clear out avast bubble around their home galaxy, they car-ried hydrogen and other elements into sur-rounding space. The heavy elements, which couldonly have been forged inside stars, set the stagefor future generations of galaxies."For a few weeks I dreamed about winds andthought about winds while I was eating mycereal in the morning and while I was in theshower and while I was Rollerblading to work,"says Adelberger, now at Harvard. These windsadded a layer of complexity to the story of how24 NATIONAL GEOGRAPHIC FEBRUARY 2003

a surveyor of the heavens, Faber strode throughthe chilly rooms of the Keck II observatory,which began operating in 1996 next to the firsttelescope. She had come to Mauna Kea to instal1the state-of-the-art Deep Imaging Multi-Object .Spectrograph (DEIMOS) that she and her teamhad designed. The 20,OOO-pound device, whichhas to be slid in and out of position on metaltracks, can simultaneously analyze the light fromas many as 130 distant galaxies."We're collecting the photo album of the lifehistory of the universe for the first time;' she said."The baby pictures, the teenage pictures, thegrown-up pictures." Astronomers are even tak-ing snapshots of what the universe looked likebefore galaxies were born. If we used the birth ofgalaxies as our reference point, she said, then thehot and cold spots in the cosmic microwave back-ground would be the prenatal pictures.Faber is homing in on the process of galaxyformation from mid-childhood to earlyadult-hood. At redshift three, galaxies were blobbyandirregular. At redshift one, corresponding to atime when the universe was little more than half .its current age, the shapes of galaxies catalogedby Edwin Hubble were beginning to fali intoplace. In between is a mystery interval from12 to 8 billion years ago in which galaxies arenotoriously hard to detecto During this largely


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CLOSE ENOUGH to see in detail in visible light, the Whirlpool galaxy, 28 million light-years away,flashes tendrils of new blue stars in an image captured by an amateur's telescope. Radio emissions(far left) reveal strong magnetic fields along the galaxy's spiral arms. A mid-infrared portrait (secondfrom left) detects dust patterns and new star sites, while a near-IR image (third from !eft) shows thegalaxy's backbone of old stars. X-rays show areas of hot gas (yellow), some of it near black holes.uncharted interval galaxies matured, taking ontheir final mass and familiar shapes. A goal ofDEIMOS is to open this interval to view.

"The spectrum of the night sky is the greatenemy," she said, "an incredible picket fenceof glowing emission lines" -the bright lightemitted by atoms and molecules at sharplydefined wavelengths.This picket fence in Earth'satmosphere overwhelms the faint infrared lightfrom gaJaxies her team wants to study. There's

one saving grace, however. The emission linesare narrow, while those from distant galaxiesare much broader. With that in mind Faber'steam designed DEIMOS to great1yexpand, ordisperse, the infrared spectrum. That enablesthe team to look between the pickets and focuson the light emitted by the galaxies.That's when the fun begins. The brightnessand shapesofthe galaxiesat different redshifts-and myriad other properties that canbeobserved

TONY HAlLAS ITOP). ABDVE FROM lfFT: AAINER BECK, MPI FOR RADIO ASTRONOMY ANO NATIONAL RAOIO ASTAONOMY OBSERVATORY/ASSOCIATED UNIVERSITIES, INCJNATIONAlSCIENCE FOUNDATION; MARC SAUVAGE, EUROPEAN SfACE AGENCY (ESA)/lNFRARED SPACE OBSERVATOAY;THOMAS JA RRE IT . INFAAAED PAQCESSING ANO ANAlYSIS CENTER. CA lTEC H .2MASS PROJECT; ANDAEW WILSON ANO YUICHI TERASHIMA, UNIVERSrTY DF MARYLAND, ANO NASNCHANDAA X-RAY CENTER (CXC)


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ve s ill conceals what happened during thto DEU IOS-----canindicate how the small,scruffy Iooking galaxies in the early universe

ormed lhe familiar galaxies that Hubble- ibed in the 1920s.Perhap the most important of these proper-. mass, Faber said. By measuring the mass0-galaxies observed at different times in the uni-rer e, Faber hopes to trace the steps by whichgalaxies merge and grow larger. She wouldalso like to learn why spiral galaxies, which areeasily disturbed by collisions, are so abundant.

The answer could be that in recent times spiralshave grown by slowly drawing in material ratherthan through collisions. If her reasoning iscorrect, spiral galaxies should be forming starsat a gentle rate rather than in bursts thataccompany collisions. Over the next few years,DEIMOS should provide the answer.A few hours after Faber finished her work forthe day, the domes of the twin Keck telescopesslid open and the instruments drank in the faintlight from some of the most distant objects in

DOUBLE TROUBLE: A pair of supermassive black holes dwells deep within a single galaxy, NGC6240,400 million light-years from Earth. Astronomers believe the unusually bright, messy galaxy(opticaJ image, top left) was formed from the collision of two smaller galaxies, each containing a blackhole, Wrthin a few hundred million years the two black holes, which circle each other (x-ray image,top right), are expected to merge-one way that black holes are thought to grow. A sequence offonnations from a cluster to a large galaxy (art, above) shows how black holes vary in proportion totf1eamount of star material, reaching sizes equal to billions of times the sun's mass. Such discoveriesbring astronomers closer to deciphering the blueprint for galaxies, nature's grandest structures.28 NATIONAL GEOGRAPHIC PEBRUARY 2003


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crucial period of galaxy form ation, whichastronomers have dubbed the O ark A ges.

heavens.Down inWaimea,48milesaway,two- up of astronomers were gathered insideindustrial-style low-rise building to relayctions to operators on the mountain. Since6, a year after Steidel began his work, thepes havebeen directed from control roomsthis building.ln one room Arjun Dey of the Nationaltical Astronomy Observatory in Tucson,Dan-tem of NASA'sIet Propulsion Laboratory,eran observer Hy Spinrad of the University

= California, Berkeley, and graduate student- eve Dawson were aiming the Keck I telescopea catalog of faint galaxies, hoping to peereeper than ever before into the universe-billion years farther back in time than theaxies found bySteidel.These are galaxiesthatow brightest when they are observed through5lters that allow only certain wavelengths ofight to passoThe wavelengths correspond to aspecificultraviolet radiation emitted by hydrogentoms that has been highly redshifted by theexpansion of the universe. The filtered light, rasan indication, but not a confirmation, thatthe galaxies were located near the edge of therisible universe.In the control room next door, meanwhile,Caltech astronomer George Djorgovski was alsostudying the distant universe. Using KeckTI,heas trying to take the spectra of one of the mostdistant known quasars, the brilliant beaconsthat emanate from the cores of some galaxies.This quasar was so far away that to reach Earth,its light pierced regions so far back in time thatthey hadn't yet been blasted by radiation fromthe first generation of stars in the universe.Back at the Keck I control room, Dey and hiscoUeagues were staring at a bunch of squigglyblack lines on the computer screen. After sev-eral hours of analysis, they carne to a consen-sus.At a redshift of 5.74, the light that had fallenon the Keck telescope had left a galaxy knownas LALA Jl42546.76+352036.3 more than 13billion years ago. It appeared they had foundthe third most distant galaxy known. But aftera final check, Dey and his collaborators smiled

fives.For on this night, March 13, 2002, the as-tronomers had found the second most distantgalaxyknown in the universe (after another gal-axy discovered at Keckwith a redshift of 6.56).S o WHATDOESIT ALLMEAN?Haveastronomers finally solved the riddleof how galaxieswere bom and evolved?Not quite, saysWilliam C. Keel of theUniversity of Alabama, but astronomers arelikely to put pieces of the puzzle together overthe next decade. With mammoth new maps ofthe nearby cosmos, scientists today can study13 billion years of galaxy evolution. But a veilstill conceals what happened during the first,crucial period of galaxy formation, whichastronomers have dubbed the Dark Ages. Itbegan a few hundred thousand years after thebig bang and ended perhaps a billion yearslater. During the first chunk of that time, theuniverse was truly dark. But later on, the firstglimmers of starlight emerged and a telescopethat has enough light-gathering power and issensitive to just the right wavelengths, shouldbe able to detect them.A key task, already begun, will be to build atelescope to penetrate the veil. Keel and manyastronomers are pinning their hopes on NASA's[ames Webb SpaceTelescope,the proposed sue-cessor to the Hubble SpaceTelescope,scheduledfor launch about 2010. Equipped with a mirrorcapable of collecting six times as much light asHubble, the telescope,with its advanced infraredand visible light instruments, will be able todetect objects much dimmer and farther awaythan those observed by any other telescope.Thatshould givescientists the power for the first timeto peer into the Dark Ages and to record thefaint, warm light from some of the very firststars and galaxies, objects that can now only beseen in compute r sim-ulations like those onTom Abel's laptop.Until then the finalfrontier of galaxy for-mation awaits us, out

WEBS IT E E XC L US IV EW a t ch s im u la tions of theb irth a nd d ev elo pm e nt ofg a la x ie s a s show n in th iss to r y a t n a ti on a lg e o gr a ph ic

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