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First stars may have been supergiants, researchers say

Jan. 3, 2007
Special to World Science  

New tel­e­scope ob­ser­va­tions have bol­stered a claim that as­tro­no­mers have seen the uni­verse’s first lu­mi­nous ob­ject­s—pos­sib­ly gar­gan­tu­an stars, re­search­ers say.

If the find­ings prove cor­rect, sci­en­tists add, they might fit with a the­o­ry that such stars seeded the growth of the big­gest, so-called su­per­mas­sive, black holes. Black holes are ob­jects so heavy and com­pact that their grav­i­ty sucks in eve­ry­thing near­by, in­clud­ing light.

The bot­tom pan­el is an im­age from NASA's Spitzer Space Tel­e­scope, of stars and galax­ies in the Ur­sa Ma­jor con­stel­la­tion. This in­fra­red im­age co­vers a re­gion of space so large that light would take up to 100 mil­lion years to trav­el across it. The top pan­el is the same im­age af­ter stars, galax­ies and oth­er sources were masked out. The re­main­ing back­ground light, ac­cord­ing to some as­tro­no­mers, is from a time when the uni­verse was less than a bil­lion years old, and prob­a­bly orig­i­nat­ed from the uni­verse's first groups of ob­jects. Darker shades in the top im­age cor­re­spond to dim­mer parts of the glow; yel­low and white show the bright­est.


But some re­search­ers said they’re not con­vinced the find­ings are cor­rect.

Ac­cord­ing to those who reached them, their new ob­ser­va­tions, from NASA’s Spitzer Space Tel­e­scope, strongly sug­gest clumps of the pri­mord­ial ob­jects—pos­sib­ly stars or black holes—are res­pon­si­ble for in­fra­red light seen in an ear­li­er stu­dy. 

In­fra­red is a form of light too low in en­er­gy to be di­rect­ly vis­i­ble, but de­tect­a­ble with suit­a­ble in­stru­ments.

The new da­ta show this patchy light is splat­tered sky-wide and comes from clus­ters of bright, mon­s­trous ob­jects more than 13 bil­lion light-years away, the as­t­ro­no­mers said. A light-year is the dis­tance light trav­els in a year. 

This would mean the light from those bo­dies has been tra­v­el­ing 13 bil­lion years, im­ply­ing in turn that we see them as they were that many years ago.

“We are push­ing our tel­e­scopes to the lim­it and are tan­ta­liz­ing­ly close to get­ting a clear pic­ture of the ve­ry first col­lec­tions of ob­jects,” said Al­ex­an­der Ka­sh­lin­s­ky of NA­SA’s God­dard Space Flight Cen­ter in Green­belt, Md. 

“What­ever these ob­jects are, they are in­t­rin­si­cal­ly in­c­red­i­bly bright and very dif­fer­ent from an­y­thing in ex­is­t­ence to­day,” added Ka­sh­lin­s­ky, the lead au­thor of two re­ports on the work to ap­pear in As­t­ro­phys­i­cal Jour­nal Let­ters, a re­search pub­li­ca­tion.

The ob­jects, he argued, are ei­ther the first stars—ti­tanic ones weigh­ing more than 1,000 times our sun—or black holes vo­ra­cious­ly con­sum­ing gas, a pro­cess that would al­so pro­duce in­tense light in their area.

If they’re stars, the clus­ters might be the first mini-galax­ies, weigh­ing less than about one mil­lion suns, he added; merg­ers of such galax­ies prob­a­bly made big­ger ones like our Milky Way, which holds the equi­v­a­lent of some 100 bil­lion suns.

The ear­li­er stu­dy, al­so by Ka­sh­lin­sky’s team, ap­peared in the jour­nal Na­ture in No­v­em­ber 2005.

Sci­en­tists es­ti­mate that the uni­verse be­gan 13.7 bil­lion years ago in an ex­plo­sion, the “Big Bang.” Stars formed a few hun­dred mil­lion years lat­er, end­ing the so-called cos­mic dark age. Kash­lin­sky’s group stud­ied the “cos­mic in­fra­red back­ground” light, a dif­fuse glow that they said comes from this ear­ly ep­och.

“There’s on­go­ing de­bate about what the first ob­jects were and how galax­ies formed,” said God­dard’s Har­vey Mose­ley, a co-au­thor of the pa­pers. “We are on the right track to fig­ur­ing this out.”

If the ob­jects are stars, they could be a first gen­er­a­tion of stars long sought by as­tro­no­mers and termed “Pop­u­la­tion III” stars. Some the­o­rize that their burnt-out rem­nants gave rise to the su­per­mas­sive black holes, which lurk at the hearts of most galax­ies. The stars, once spent, would col­lapse in­to smaller “seed” black holes, which then swell in­to huge ones by eat­ing up other mat­ter near­by. 

In or­der to form black holes big enough and fast enough to fit with ob­ser­va­tions, these the­o­ries re­ly on the in­i­tial stars them­selves be­ing “su­per­mas­sive,” weigh­ing hun­dreds of suns. Those found in the new stu­dy, if they’re stars, might fit the bill, re­search­ers say.

“There would be quite a link” to the black hole the­o­ry, said Mar­tin Haehnelt, a cos­mol­o­gist with the Uni­ver­si­ty of Cam­bridge, U.K. But he said this would de­pend on Kash­lin­sky’s team hav­ing in­ter­preted its re­sults cor­rectly, and he’s far from sure of that.

Con­tam­i­nat­ing light from ob­jects in the fore­ground can be­dev­il at­tempts to meas­ure the “in­fra­red back­ground,” Haehnelt said. Al­so, he said, Kash­lin­sky’s stu­dy in­volved com­par­ing sig­nals in dif­fer­ent parts of the sky, rath­er than re­solv­ing in­di­vid­u­al ob­jects, and it’s hard to say what such cor­re­la­tions mean.

Kash­lin­sky said his team care­ful­ly erased light from fore­ground stars and galax­ies, leav­ing on­ly the most an­cient light; then stud­ied fluc­tu­a­tions in the bright­ness, re­veal­ing clus­ters of ob­jects. “Imag­ine try­ing to see fire­works at night from across a crowd­ed city,” he said. “If you could turn off the city lights, you might get a glimpse at the fire­works. We have shut down the lights of the uni­verse to see the out­lines of its first fire­works.” 

If they’re stars, they’re prob­a­bly ex­treme­ly mas­sive, Mose­ley said, as small stars shine too in­ef­fi­cient­ly to ex­plain the light seen; also, there are the­o­ret­i­cal rea­sons to be­lieve su­per­mas­sive stars would form. A fu­ture tel­e­scope planned by NASA, the James Webb Space Tel­e­scope, should be able to iden­ti­fy what the clus­ters are, ac­cord­ing to mem­bers of Kash­lin­sky’s group.


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New telescope observations have bolstered a claim that astronomers have seen the universe’s first luminous objects—possibly gargantuan stars, researchers say. If the findings prove correct, scientists say, they might help support a theory that such stars seeded the growth of the biggest, so-called “supermassive,” black holes. Black holes are objects so heavy and compact that their gravity sucks in everything nearby, including light. But researchers said it’s too early to draw this connection between supermassive black holes and primordial stars. According to those who conducted the studies, their new observations, from NASA’s Spitzer Space Telescope, strongly suggest that clumps of some of the first cosmic objects produce infrared light seen in an earlier study. Infrared is a form of light too low in energy to be directly visible, but detectable with suitable instruments. The new data show this patchy light is splattered across the sky and comes from clusters of bright, monstrous objects more than 13 billion light-years away, the astronomers added. A light-year is the distance light travels in a year. This means the light from those objects has been traveling 13 billion years, which in turn implies that we see these objects as they were that many years ago—near the beginning of time. “We are pushing our telescopes to the limit and are tantalizingly close to getting a clear picture of the very first collections of objects,” said Alexander Kashlinsky of NASA’s Goddard Space Flight Center, Greenbelt, Md. “Whatever these objects are, they are intrinsically incredibly bright and very different from anything in existence today,” added Kashlinsky, the lead author of two reports to appear in Astro physical Journal Letters, a research publication. Astronomers, he said, believe the objects are either the first stars—titanic ones weighing more than 1,000 times our sun—or voracious black holes that are consuming gas, a process that also produces intense light. If they’re stars, the clusters might be the first mini-galaxies containing a mass of less than about one million suns, he added. Mergers of such little galaxies probably produced bigger ones like our Milky Way, which holds the equivalent of some 100 billion suns, he continued. The earlier study, also by Kashlinsky’s team, appeared in the research journal Nature in November 2005. Scientists estimate that the universe began 13.7 billion years ago in an explosion, the “Big Bang.” Stars formed a few hundred million years later, ending the so-called cosmic dark age. Kashlinsky’s group studied the “cosmic infrared background” light, a diffuse glow that they said comes from this early epoch. “There’s ongoing debate about what the first objects were and how galaxies formed,” said Goddard’s Harvey Moseley, a co-author of the papers. “We are on the right track to figuring this out.” If the objects are stars, they could be a first generation of stars long sought by astronomers and termed “Population III” stars. Some theorize that these stars’ burnt-out remnants gave rise to the supermassive black holes lurking at the cores of most galaxies. The stars, once spent, would collapse into smaller “seed” black holes, which then attract enough other matter to quickly grow into huge ones. In order to form black holes big enough and fast enough, these theories rely on the initial stars being “supermassive,” weighing hundreds of suns. Those found in the new study, if they’re stars, would seem to fit the bill. “There would be quite a link” to the black hole theory, said Martin Haehnelt, a cosmologist with the University of Cambridge, U.K. But he said this would depend on Kashlinsky’s team having interpreted its results correctly, and he is far from certain of that. Contaminating light from objects in the foreground can bedevil attempts to measure the “infrared background” that Kashlinsky’s group studied, Haehnelt said. Also, he said, the group’s work involved comparing signals in different parts of the sky rather than resolving individual objects, and it’s “difficult to come to a conclusion” on what such correlations mean. Kashlinsky said the analysis involved carefully removing the light from foreground stars and galaxies, leaving only the most ancient light. The scientists then studied fluctuations in the intensity of infrared brightness. The fluctuations revealed what they said was a clustering of objects. “Imagine trying to see fireworks at night from across a crowded city,” said Kashlinsky. “If you could turn off the city lights, you might get a glimpse at the fireworks. We have shut down the lights of the Universe to see the outlines of its first fireworks.”A future telescope planned by NASA called the James Webb Space Telescope should be able to identify what the clusters are, Mather said.