The first stars formed along vast filaments of dark matter that appeared relatively soon after the big bang, according to a new model of the universe. The model challenges the current paradigm of star formation and may shed light on one of the biggest mysteries of the early cosmos.
Millions of years after the big bang, the universe remained fairly dark. All that existed was hydrogen and helium gas that was very hot but scattered across such huge distances that it barely seemed to be there at all. Eventually, that gas coalesced into stars and those stars into galaxies, giving us the universe we see today. How did this happen? Cosmologists have turned to dark matter for the answer. They postulate that the mysterious, invisible, and cold substance formed clumps in the early universe and that those clumps pulled hard enough on nearby gas to condense it into the first stars.
Now theorists Liang Gao of the University of Durham in the U.K. and Durham colleague Tom Theuns, also of the University of Antwerp in Belgium, have posed a different possibility. Instead of dark matter being totally cold--that is, emitting no radiation--the team developed a supercomputer simulation that suggests a warmer form of dark matter with the ability to emit a little bit of heat. If so, instead of clumping, the researchers report in tomorrow's issue of Science, this warm dark matter would have stretched into filaments thousands of light-years long and weighing as much as millions of suns. In the process, it would have attracted enough primordial hydrogen and helium gas to ignite the first stars. It may have even provided the seeds for the supermassive black holes that seem to anchor all of the big galaxies.
The research is valuable because it shows how studying the formation of the first stars can help scientists learn more about the nature of dark matter, says astronomer Volker Bromm of the University of Texas, Austin. Confirming the warm dark matter idea is going to be tough, however, says Bromm. The universe's earliest stars comprised unique chemical compositions, but they have burnt themselves out by now, he explains, so scientists will have to look for remnants from these stars in today's suns.