Astronomers find young galaxy with record-low oxygen levels

Astronomers have discovered a tiny, young, metal-poor galaxy with the lowest oxygen abundance ever recorded.

To find the tiny galaxy, researchers used machine learning algorithms to parse data collected by a pair of telescopes in Hawaii, the Subaru Telescope and W. M. Keck Observatory.

Most galaxies in the modern universe are fairly large and mature, but models suggest there are still a handful of star-forming regions hiding among the masses of mostly dormant galaxies.

Predicting their existence is one thing, but finding tiny, star-producing galaxies is another, researchers say.

"To find these very faint, rare galaxies, deep, wide-field imaging data taken with the Subaru Telescope was indispensable," lead researcher Takashi Kojima, astronomer at the University of Tokyo Institute for Cosmic Ray Research, said in a news release.

Subaru's wide-field survey has revealed 40 million objects. To process such a large set of data, researchers trained a machine learning algorithm to search for the type of spectroscopic signature -- the unique combination of light frequencies -- produced by early stages of galaxy formation.

The algorithm identified 27 candidates. Scientists used the Keck Observatory's DEep Imaging and Multi-Object Spectrograph, or DEIMOS, as well as Subaru Telescope's Faint Object Camera and Spectrograph, to study each candidate.

The follow-up observations revealed one of the candidates, HSC J1631+4426, to be extremely metal-poor and with record low levels of oxygen.

Scientists described their discovery Monday in the Astrophysical Journal. An early version of their paper was published online at arxiv.

"What's surprising is the stellar mass of the HSC J1631+4426 galaxy is very small, 0.8 million solar masses, which is only about 1/100,000 of our Milky Way, and comparable to the mass of a star cluster in our galaxy," said study co-author Masami Ouchi, a professor at the National Astronomical Observatory of Japan and the University of Tokyo.

Researchers suggest low-mass, young, metal-poor galaxies like HSC J1631+4426 can help cosmologists better understand the evolution of galaxies shortly after the Big Bang, when the cosmos was just a few hundred million years old.

Because the Big Bang generated large amounts of hydrogen and helium, oxygen was in relatively short supply among the earliest galaxies.

Astronomers suggest HSC J1631+4426 might be more than just rare-- it may mark the end of a cosmic epoch.

Models suggest that as the universe expands, matter will become too sparse to birth new galaxies, so HSC J1631+4426 could be the last of its kind, researchers say.

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