BEGIN:VCALENDAR VERSION:2.0 CALSCALE:GREGORIAN PRODID:UW-Madison-Physics-Events BEGIN:VEVENT SEQUENCE:0 UID:UW-Physics-Event-1784 DTSTART:20100216T213000Z DTEND:20100216T230000Z DTSTAMP:20260506T063145Z LAST-MODIFIED:20100201T180028Z LOCATION:3425 Sterling Hall SUMMARY:A Life for Stars\, Astronomy Colloquium\, Alexander Heger\, Un iversity of Minnesota - Twin Cities DESCRIPTION:A few hundred thousand years after the Big Bang the primor dial gas recombined\, became transparent - the last light from that we now see as Cosmic Microwave Background. There was very little structu re in the universe at that time\, no source of light - we call it now the Cosmic Dark Ages. It would take several hundred million years befo re the first stars in the universe would form\, making the first sourc e of light after the big bang\, when the "\;dark"\; matter cou ld clump\, collecting up baryonic matter that could cool down\, and co ndense into the first stars. Still\, the gas was quite warm\, so it wo uld take massive\, big clouds to collapse under their own gravity\, ma king big stars. At least\, this is what out best theories tell us. But no one actually has ever observed this to date. So\, is that story tr ue? How big were the first star actually? What can we do to find out? Looking at the current universe\, we do see that some quite big stars are still formed today\, but they shed mass in massive winds and in gi ant eruptions and will die not quite as big as they were born. Is the same true for the first stars if born as big as the biggest stars we s ee today? Or were there even bigger stars\, and how would the evolve a nd die? Could these latter once be the predecessors of the super-massi ve black holes harbored in the centers of even some of the earliest ga laxies we see? So\, how can we find out? At least part of the story we may be able to uncover now by looking at ashes of the first stars\, t he pattern of elements that made and that were incorporated in subsequ ent generations of stars. Observes now have found some very old stars in the halo of our galaxy\, one of its oldest constituents\, that like ly have formed very early in the universe. These stars have only minus cule traces of heavy elements\, they almost exclusively consist of the matter made by the big bang. We now believe that many of those likely have been polluted\; only by a few\, maybe a single star. But the rat io of heavy elements that a star makes depends a lot on how massive is was\, and how it died. So looking at the ashes of these first stars\, as incorporated in the old stars we have found\, may tell the story o f the lives of those first stars. What will we discover?
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