Astronomers have detected what they believe is one of the first cases of “galactic cannibalism” – when a galaxy consume one of its smaller neighbors – in an ultra-thin dwarf galaxy called Tucana II. The discoveries come from the discovery of an ancient halo of dark matter, located in a galaxy 163,000 light-years from Earth.
Tucana II is just one of dozens dwarf galaxies surrounding the Milky Way. They are believed to be artifacts left over from the first galaxies in the universe – and Toucan II is among the most primitive of them.
In a new study, published Monday in the journal Nature Astronomy, astrophysicists report the detection of nine previously unknown stars at the edge of Tucana II, using the SkyMapper Telescope in Australia and the Magellan Telescope in Chile. The stars are shockingly far from its center, but remain in the gravitational pull of the small galaxy.
The configuration of the stars provides the first evidence that the galaxy contains an extensive halo of dark matter – a region of matter three to five times larger than scientists initially thought – to maintain gravitational control over its distant stars. The findings suggest that the first galaxies They were much more massive in the universe than previously thought.
“Tucana II has a lot more mass than I thought, to link these stars that are so far away,” one of the study’s authors, MIT student Anirudh Chiti, said in a statement. “This means that other relic galaxies probably have these types of extended halos.”
It is believed that each galaxy is held together by a halo of dark matter, a type of hypothetical matter that is believed to represent over 85% of the universe, MIT News explains. But the new discoveries are the first time one has been detected in an ultra-thin dwarf galaxy.
“Without dark matter, galaxies would just fly,” Chiti said. “[Dark matter] it is a crucial ingredient in creating and maintaining a galaxy. “
Anirudh Chiti, MIT
Scientists have also discovered that these distant stars are older than the stars in the core of Tucana II – the first evidence of such an imbalance in this type of galaxy. Their discovery indicates the possibility that the galaxy may be the product of one of the first mergers between two galaxies in the universe, which scientists refer to as “galactic cannibalism.”
“We may see the first signature of galactic cannibalism,” said MIT Professor Anna Frebel. “It is possible that a galaxy ate one of its smaller, more primitive neighbors, which then shed all its stars on the periphery.
Using the imaging filter of a telescope, astronomers are able to study the metal content of a galaxy’s stars to determine how primitive it is. Earlier, they had found stars in the core of Tucana II with such a low metal content that the galaxy was identified as the most chemically primitive of the known ultrafaint dwarf galaxies.
New research has found that outer stars are three times poorer in metal than those in the center, making them even more primitive.
“This also means that the first galaxies formed in much larger dark matter halos than previously thought,” Frebel said. “I thought the first galaxies were the smallest and most beautiful galaxies. But in fact, they may have been a few times bigger than I thought, and after all, not so small.”
An early galactic fusion is a likely explanation for the imbalance. Galactic cannibalism appears “constantly” in today’s universe, according to MIT News, but mergers in the early universe are less secure.
“Tucana II will eventually be eaten by the Milky Way, without mercy,” Frebel said. “And it looks like this ancient galaxy may have its own cannibalistic history.”
The team hopes to use its approach to discover even older, more distant stars in other ultra-weak dwarf galaxies.