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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.

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.