First stars may still shine

Analysis suggests some slow-burning remnants of the early universe may still exist

Talk about glimmers from the past. Some of the universe’s first stars may still be shining in the Milky Way 13.4 billion years after they formed, new simulations suggest.

SOME WILL SURVIVE A computer simulation shows the birth of some of the universe’s first stars, some of which may still exist today. As star embryos form over time (white crosses, left to right), the mutual gravity of the densely packed infants may have ejected the lowest-mass member before it had a chance to grow into a massive, short-lived star. P. Clark/Univ. of Heidelberg

The study, reported online February 3 in Science and posted at on January 28, contradicts the prevailing view that the first stars were all behemoths that burned brightly and died out in a few million years.

In their simulations, Paul Clark of the University of Heidelberg in Germany and his colleagues showed that gas clouds in the early universe could have forged several stellar embryos rather than just one. Clark, along with Thomas Greif of the Max Planck Institute for Astrophysics in Garching, Germany, and other collaborators confirm that finding in an article posted at on January 31.

The infant stars in each cloud were closely spaced, and the team suggests that their mutual gravity could kick the lowest-mass embryo from the tightly packed group — before that infant had a chance to grow into a massive, short-lived star.

A few of these ejected, underweight stars could have survived to the present day — if they managed to accumulate no more than the equivalent of 80 percent of the sun’s mass from their birth cloud, Clark says.

Other researchers say they have several qualms about those conclusions. “This is an interesting and tantalizing result, but it is not based on computational physics but rather an ad hoc assumption” about the evolution of disks that surrounded the birth clouds of the first stars, contends Michael Norman of the University of California, San Diego. After reviewing a companion paper submitted by the same research team to Nature, Norman says he advised the journal not to publish it.

Although Clark and his coworkers simulated a longer period of the formation of the first stars than other teams have — the first 100 to 1,000 years of a process that lasts for several hundred thousand — it’s still not long enough to determine the final weight of the primordial stars, says Tom Abel of the SLAC National Accelerator Laboratory in Menlo Park, Calif. The simulation technique used by the researchers in their Science paper is not as mathematically rigorous as other methods, even though it can probe the star formation process for longer, he adds.

If any of the first stars did survive until today, their brightness wouldn’t require an exceptionally large telescope to image them, says Simon White of the Max Planck Institute for Astrophysics, a coauthor of the arXiv paper. But making a positive ID won’t be easy, he adds. Only high-resolution spectra could distinguish primordial stars, which would contain only hydrogen and helium, from slightly younger stars containing trace amounts of heavier elements, he notes.

And in a case of hiding in plain sight, astronomers would still need to develop a strategy for determining which of the hundreds of millions of glittering stars at the center of the Milky Way are most likely to be primordial, says White.   

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