Young Galaxy Holds Record for Lowest Oxygen Level Among Other Galaxies

August 2, 2020, 6:00 AM HST (Updated August 1, 2020, 4:09 PM)
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PC: NAOJ/Kojima et al.

A galaxy in the constellation Hercules that only recently started making stars has broken the record for having the lowest level of oxygen ever seen in a young galaxy.

Astronomers used two Maunakea Observatories — W. M. Keck Observatory and Subaru Telescope — combined with the power of machine learning to detect the galaxy, named HSC J1631+4426. Finding a young, star-forming galaxy in the modern universe is rare — most galaxies today are already mature, officials stated in a press release from W.M. Keck Observatory.

The researchers measured its oxygen abundance at only 1.6% that of the Sun, suggesting the galaxy only recently started making stars. The study will be published in the Aug. 3, 2020 issue of The Astrophysical Journal and is available in preprint format on arXiv.org.

Because its chemical composition is similar to the first galaxies born after the Big Bang, this newly-discovered, extremely metal-poor galaxy provides astronomers valuable insight into how the earliest galaxies in the young universe may have formed and evolved.

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“To find these very faint, rare galaxies, deep, wide-field imaging data taken with the Subaru Telescope was indispensable,” said Takashi Kojima of the University of Tokyo Institute for Cosmic Ray Research and lead author of the study.

However, the wide-field data detected 40 million objects. To comb through the vast amount of data and zero in on galaxies that are just beginning to form stars, the research team developed a new machine learning method. They ‘taught’ a computer to repeatedly learn the galaxy colors expected from theoretical models and select only galaxies in the early stage of galaxy formation.

The research team finds two interesting indications from the discovery of HSC J1631+4426. First, it provides evidence supporting the Standard Cosmology prediction that young, star-forming galaxies do in fact exist in the present universe.

Second, the study indicates this could be the latest epoch of the cosmic history where we may witness a newborn galaxy. The Standard Cosmology suggests the density of matter drops as the expansion of the universe accelerates. This would lead to a future universe where matter does not assemble by gravity, and new galaxies won’t be born. Thus, HSC J1631+4426 may be the last generation galaxy of its kind in the long cosmic history.

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