Once, there was a time before stars.
In the primordial darkness, after the Big Bang, nothing drifted but a vast sea of hydrogen and helium. It wasn’t until stars came along, born from crushing densities in that clumping gas, that heavier elements emerged, forged by the fusion in their powerful hearts.
Or so scientists believe. We’ve never actually seen those first stars, known as Population III stars. A new paper may finally change that.
In a preprint submitted to The Astrophysical Journal and uploaded to arXiv, a large international team of astronomers led by Seiji Fujimoto of the University of Texas at Austin has described what they think might be a galaxy in the early Universe rich in these elusive objects.
This galaxy, called GLIMPSE-16403, is by no means confirmed as a Population III host. But the identification of even a candidate suggests that it’s only a matter of time before we finally locate the first stars in the Universe.
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“This work paves a clear path for the discovery of the first Pop III galaxies,” the researchers write. “Whatever the fate of the present candidates, the methods developed in this study will empower Pop III galaxy searches throughout the JWST era.”
The Cosmic Dawn is what we call the era that spans the first billion or so years after the Big Bang popped the Universe into existence some 13.8 billion years ago. During this time, the cosmos came together from a hot quark-gluon plasma that filled the Universe in its first moments, forming stars and galaxies that literally swept away the darkness with their blazing light.
Those first Population III stars were a vital step towards the Universe we see around us today. Elements heavier than hydrogen and helium can only be created by extreme processes such as core fusion and nova explosions. Yet previous research has only yielded second-hand traces of these first generation stars, not the objects themselves.
Astronomers believe that this is because Population III stars may have been particularly massive, larger than any stars around in the more recent Universe. Larger stars live much, much shorter lives than smaller ones, so those first stars may have long flickered out, leaving behind only the elements they fused in their cores to be taken up by subsequent stellar generations.
Cosmologists and astronomers desperately want to see what those early stars were like. They want to find out how the lights turned on in the Cosmic Dawn, clearing the neutral hydrogen fog that rendered space opaque.
Our best shot for this is JWST, the most powerful space telescope ever built, optimized for peering farther back into the early Universe than any telescope before with its infrared-sensitive eye.
Seeing into the Cosmic Dawn is hard enough, but looking for a needle in that particular haystack is even harder. Fujimoto and his colleagues figured they could expedite the search by looking very, very closely at only small regions of the sky, looking for the chemical fingerprints of Population III stars.
The researchers focused their efforts on galaxies with powerful hydrogen and helium emission spectra, and little evidence of other elements. Their pipeline yielded two candidates. One was only tentative; but the other, GLIMPSE-16403, hanging out in the Cosmic Dawn around 825 million years after the Big Bang, met all the criteria the researchers had specified for a Population III galaxy.
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This makes the galaxy the best candidate to date for finding the stars that switched on the lights in the Universe.
More work will need to be done to determine the nature of the stars in GLIMPSE-16403, which might be tricky; we’d need a detailed spectrum, and that’s not easy to obtain across such vast gulfs of space-time.
Nevertheless, the discovery is an incredibly exciting one: the detection of Population III stars now feels like it’s right around the next corner.
“Exactly a hundred years ago, our cosmic horizon expanded past the edges of the Milky Way for the first time, with Andromeda and Triangulum marking the boundaries of our place in the Universe,” the researchers write.
“As we reflect on the profound discoveries of the last hundred years, it is intriguing to consider how those early surveyors of glass plates would view the prospect that we may soon detect the Universe’s very first stars.”
The team’s paper has been submitted to The Astrophysical Journal, and is available on arXiv.
