Early galaxies were more massive than previously thought

Astrophysicists at the Massachusetts Institute of Technology (MIT) have discovered a halo of abundant dark mass around the dwarf galaxy Tucana II, one of the most primitive in the universe, which has led them to conclude that the first galaxies were probably more massive than previously thought. The Magellan telescopes of Las Campanas Observatory were used to carry out the study.

The Milky Way is surrounded by dwarf galaxies that are considered vestiges of primitive constellations, one of which is Tucana II. According to a study published February 1, 2021 in "Nature Astronomy", scientists detected stars at the edge of Tucana II (163 billion light-years from Earth), far from the galaxy's center but within its gravitational orbit, suggesting the existence of a dark matter halo three to five times more massive than previously thought.

"Tucana II has much more mass than we thought, to attract those stars that are so far away. This means that other early galaxies probably had such extended halos as well," MIT researcher Anirudh Chiti said in a statement.

Dark matter is thought to account for more than 85% of the universe, and each galaxy is held together by a local concentration (or halo) of this still largely unknown matter.


Another finding of the scientists was that the stars in the periphery of Tucana II are more primitive than those in its core, which is the first evidence of something similar in analogous galaxies.

This configuration indicates, according to the MIT astrophysicists, that Tucana II may have arisen from the merger between two galaxies, one younger than the other. "We may be looking at galactic cannibalism. One galaxy could have eaten one of its smaller, more primitive neighbors and then scattered its stars around the periphery," said MIT Professor Anna Frebel.

The scientists believe that Tucana II is one of the most primitive dwarf galaxies because of the low metal content of its stars, indicating its early formation, before the universe produced heavy metals.

Chiti and Frebel tried to locate other stars in Tucana II that would explain the formation of the first galaxies, relying on observations from the SkyMapper telescope in Australia, then turned to the Magellan telescopes at Las Campanas Observatory in Chile to probe for metals in the stars.

"We had thought that the first galaxies were the tiniest and faintest. But they might actually be several times bigger than we thought and not so tiny," Frebel summarized.

Scientific publication

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