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Machine learning reveals a surprisingly early galaxy

Machine learning reveals a surprisingly early galaxy

HSC J1631 + 4426 broke the record for the lowest oxygen abundance. Credit: NAOJ / Kojima et al.

New results from combining big data from the Subaru telescope and the power of machine learning have found a galaxy with an extremely low abundance of 1

.6% oxygen, breaking the previous record with the lowest abundance. The measured abundance of oxygen suggests that most of the stars in this galaxy have formed very recently.

To understand the evolution of a galaxy, astronomers must study galaxies at different stages of formation and evolution. Most of the galaxies in the modern universe are mature galaxies, but standard cosmology predicts that there may still be several galaxies in the early formation stage in the modern universe. Because these early-stage galaxies are rare, an international research team looked for them in data from large-scale images taken with the Subaru telescope. “To find very weak, rare galaxies, the deep, wide-field data taken with the Subaru telescope was indispensable,” said Dr. Takashi Kojima, team leader.

However, it is difficult to find galaxies in the early stages of formation, as data from a wide field include about 40 million objects. Thus, the research team developed a new machine learning method to detect such galaxies from the vast amount of data. They had a computer that repeatedly learned the colors of the galaxies expected from theoretical models, and then allowed the computer to select only galaxies in the early stages of galaxy formation.

Close to HSC J1631 + 4426, created using hscmap. Credit: NAOJ / HSC-SSP

The research team then made follow-up observations to determine the elementary abundance ratios of 4 of the 27 candidates selected by the computer. They found that a galaxy (HSC J1631 + 4426), located 430 million light-years in the constellation Hercules, has an oxygen abundance of only 1.6 percent of that of the Sun. This is the lowest value ever reported for a galaxy. The measured abundance of oxygen suggests that most of the stars in this galaxy have formed very recently. In other words, this galaxy is at an early stage of evolution.

“Surprisingly, the stellar mass of the galaxy HSC J1631 + 4426 is very small, 0.8 million solar masses. This stellar mass is only about 1/100,000 of our Milky Way galaxy and is comparable to the mass of a star cluster in our Milky Way, “said Prof. Ouchi of the National Astronomical Observatory of Japan and the University of Tokyo. This small mass also supports the primitive nature of the galaxy HSC J1631 + 4426.

The research team believes that there are two interesting indications of this finding. First, it is the strongest evidence for a galaxy at such an early stage of evolution. Within standard cosmology, new galaxies are thought to be born in the current universe. The discovery of the galaxy HSC J1631 + 4426 supports the picture of standard cosmology. Second, we may be witnessing a newborn galaxy in the most recent era of space history. Standard cosmology suggests that the density of matter in the universe is rapidly declining as universal expansion accelerates. In a rapidly expanding future universe, matter will not gather by gravity and no new galaxies will develop. The galaxy HSC J1631 + 4426 may represent the latest generation of galaxies to evolve in space history.

This study will be published in Astrophysical Journal,,

Image: Hubble sees a sculpted galaxy

More info:
Kojima et al., Extremely poor metal representatives studied by the Subaru study (EMPRESS). I. Successful selection of machine learning for metal-poor galaxies and galaxy discovery with M * arxiv.org / abs / 1910.08559

Provided by the National Research Institutes

Quote: Machine learning discovers a surprisingly early galaxy (2020, August 3), retrieved on August 3, 2020 from https://phys.org/news/2020-08-machine-early-galaxy.html

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