Sky and Telescope - March 2010 - (Page 26)
Strange Denizens of the Early Universe LIGHTon Bizarre stars powered by dark matter may have been the ﬁrst Ker Than to form after the Big Bang. Shedding All Illustrations by S&T: Casey Reed The scientiﬁc version of Genesis tells us that the universe sprang into being 13.7 billion years ago and that the ﬁrst denizens of that new realm — stars — blazed into existence about 100 million years after the Big Bang. Even by stellar standards, the ﬁrst stars were titans. They were bigger, brighter, and burned faster than any stars in existence today (S&T: May 2006, page 30). But if a new theory of star formation is correct, the stellar ﬁrst born were even stranger beasts than scientists previously thought because of how they interacted with dark matter, the unseen “substance” that scientists think makes up more than 80% of the universe’s mass. Stars like our Sun rely on the fusion of light elements into heavier ones to counteract their own immense gravities and to keep them from imploding. But some of the most popular theories in physics suggest dark matter consists of particles that can act as their own antiparticles 26 March 2010 sky & telescope (S&T: April 2009, page 22). This raises the intriguing possibility that the ﬁrst stars were powered by the self-annihilation of concentrated dark matter in their cores. Such “dark stars” would have been cooler but more colossal than their fusion-driven brethren. “They’re still stars, made primarily of hydrogen and helium. Less than 1% of their mass is dark matter,” says Katherine Freese (University of Michigan). Freese, along with Paolo Gondolo (University of Utah) and Doug Spolyar (University of California, Santa Cruz), were the ﬁrst to investigate dark stars in 2006. The team says that if dark stars existed, they could have altered the chemistry of the early universe by delaying the birth of “normal” ﬁrst-generation stars — called Population III stars — by up to a billion years. Dark stars could also explain why supermassive black holes appear to have formed so soon after the Big Bang.
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