(ORDO NEWS) — Astronomers first discovered an extended halo of dark matter in a small and very ancient dwarf galaxy. According to the authors, this suggests that the first galaxies in the Universe were more massive than previously thought. The results of the study are published in the journal Nature Astronomy.
The Milky Way is surrounded by dozens of dwarf galaxies that are considered relics of the very first star clusters in the universe. Among them is the ultra-thin dwarf galaxy Toucan II, located about 163 thousand light years from Earth.
It is believed that stars with low metal abundances formed very early, when the universe was not yet producing heavy elements. Toucan II is one of the most chemically primitive galaxies known, judging by the metal content of its stars.
American astrophysicists from the Massachusetts Institute of Technology (MIT), along with colleagues from the UK and Australia, discovered several stars on the edge of Toucan II that are extremely distant from the center, and, nevertheless, are in the zone of gravitational attraction of a tiny galaxy. According to the researchers, with such a configuration of stars, Toucan II should have a dark matter halo, which is three to five times more massive than previously assumed.
“Without dark matter, the galaxy would simply fly apart. Dark matter is an essential ingredient in creating and holding galaxies,” the first author of the article, MIT graduate student Anirudh Chiti, said in a press release. “Toucan II has much more mass than we thought to tie such distant stars.”
Dark matter, the nature of which is still unknown, according to scientists, makes up more than 85 percent of the universe. It is believed that the local concentration of dark matter holds the galaxies as a whole.
The researchers also determined that the stars on the outskirts of Tucana II are more primitive than the stars in its core. This is the first evidence of stellar imbalance in dwarf galaxies. The authors suggest that this is a consequence of one of the first mergers in the universe between two infant galaxies, one of which was less primitive than the other.
“We may be seeing one of the earliest signs of galactic cannibalism,” said study author Anna Frebel, assistant professor of physics at MIT. “The galaxy may have swallowed up one of its smaller and more primitive neighbors, which then scattered its stars on the outskirts of Toucan II”.
To detect more ancient stars in the dwarf galaxy, the authors used the SkyMapper ground-based optical telescope, located in Australia, which allows you to shoot wide panoramas of the southern hemisphere of the starry sky.
To detect more primitive, metal-poor stars outside the galactic core, the researchers first applied a filter and then processed the filtered data using an algorithm developed by Chiti. As a result, they identified more ancient stars, both several previously known stars in the center, and nine new ones located on the outskirts of Toucan II.
“We thought the first galaxies were the smallest, dimmest galaxies. But in fact, they could be several times larger than we thought. This also means that the earliest galaxies formed in halos of dark matter much larger than previously thought. earlier,” notes Froebel.
The authors suggest that other ancient relict galaxies may have the same extended dark matter halos.
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