EMBARGOED FOR Sifting through ashes of the first stars, astronomers have found significant amounts of iron, which dates the initial stellar furnaces to as early as 200 million years after the universe was born.
The discovery, announced today, supports and builds upon similar evidence derived by a different method earlier this year. Combined, the findings push stellar origins back to an earlier epoch than scientists thought just a few months ago.
Researchers do not understand how the first stars and their associated galaxies formed so rapidly. The new findings won't directly help unravel that mystery, but they pin down the time frame beyond dispute.
Ironclad evidence
Iron was not present when the universe was formed, presumably in a Big Bang, according to the leading theory. It and all other elements heavier than hydrogen and helium were forged in stars, chemical factories that produce successively heavier elements, from nitrogen to carbon and finally iron.
The earliest stars were massive, theory contends, and they lived short lives and died in fiery explosions, sending their ashes into the interstellar medium where the fresh elements mixed with existing gas to fuel new star birth.
The new observations, of very distant but luminous galaxies called quasars, were made with the Hubble Space Telescope's Near Infrared Camera and Multi-Object Spectrograph (NICMOS). The instrument split the quasar light, which had spent about 12.8 billion years crossing space, into its different colors.
"Iron emits light at specific wavelengths, and so do other elements," explained study leader Wolfram Freudling of the Space Telescope-European Coordinating Facility and the European Southern Observatory. "By comparing the amount of light attributed to iron to the one from magnesium, we inferred the relative amount of iron in the quasar."
Freudling said, "We believe that the iron we detected with Hubble was created in the very first generation of stars which formed soon after the Big Bang."
Behind the discovery
The Hubble data was in hand late last year, but Freudling told SPACE.com that his research team did not know the exact age of the universe and so could not make a reliable estimate of when the first stars formed. Then earlier this year, on Feb. 11, separate results from WMAP telescope were announced. The probe examined microwave radiation leftover from the young cosmos and pinned down the age of the universe at 13.7 billion years.
"This was indeed a very exiting day for us," Freudling said of the WMAP announcement. "Only after we used the WMAP values for the age of the universe did we realized how little time there was to generate the iron we detected."
The WMAP findings also put the birth of the first stars at about 200 million years after the Big Bang.
The new Hubble results, detailed in the April 20 issue of Astrophysical Journal Letters, suggest the universe's first stars formed before supermassive black holes, Freudling and his colleagues say. These black holes, each packing the mass of perhaps billions of suns, now anchor the quasars and power their luminous output detected by Hubble. Hubble is a joint project of NASA and the European Space Agency.
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