Astronomers have discovered what they believe to be one of the earliest examples of “galactic cannibalism” – when one galaxy eating one of its smallest neighbors – in an ultra-dwarf galaxy called Tucana II. The findings come from the discovery of an ancient dark matter, located in a galaxy of 163,000 light-years from Earth.
Tucana II is just one of dozens of dwarf galleries circling the Milk Trail. They are thought to be artifacts left over from the first galaxies in the universe – and Tucana II is one of the most important of them.
In a new study, published Monday in the journal Nature Astronomy, astronomers report finding nine previously unknown stars at the edge of Tucana II, using the SkyMapper Telescope in Australia and the Magellan Telescopes in Chile. The stars are very far from their center but are still in the orbit of the small galaxy.
The star arrangement provides the first evidence that the galaxy contains a halo of expanded dark matter – an area of matter three to five times larger than scientists originally believed – to maintain a gravitational grip on the stars. far away. The findings suggest that the earliest galaxies in the universe there was much more than they had previously believed.
“Tucana II has a lot more mass than we thought, to connect those stars that are so far away,” one of the study’s authors, MIT graduate student Anirudh Chiti, said in a statement. “This means that other first galleries also seem to have the expanded halos types as well.”
All galaxies are believed to be held together by a Halo of dark matter, a kind of hypothetical subject that is thought to make up more than 85% of the universe, MIT News explaining. But the new findings represent the first time one has been found in an ultra¹ dwarf galaxy.
“Without a dark case, galaxies would just fly apart,” Chiti said. “[Dark matter] it’s an important part of making a galaxy and keeping it together. “
Anirudh Chiti, MIT
Scientists have also found that the distant stars are older than the stars at the heart of Tucana II – the first evidence of such an imbalance in this type of galaxy. Their discovery indicates that the galaxy may have been the result of one of the first unions between two galaxies in the universe, which scientists refer to as “galactic cannibalism.”
“We may be seeing the first signature of galactic cannibalism,” said MIT Professor Anna Frebel. “One galaxy may have eaten one of its slightly smaller, more prime neighbors, which poured its stars into the periphery.”
Using telescope image filters, astronomers can examine the metal content of galaxy stars to determine their prime. They had previously discovered stars at the heart of Tucana II with such a low metal content that the galaxy was recognized as the most chemically predominant of the ultra-dense galactic galaxies.
A new study found that outer stars were three times poorer in metal than those at the center, making them even more prime.
“This may also mean that the earliest galaxies created in halos of dark matter were much larger than previously thought,” Frebel said. “We’ve always thought that the first galleries were the smallest, worst. But they were probably several times bigger than we thought, and they weren’t so tiny after all. everything. “
Early galactic unification is one most likely explanation for the imbalance. Galactic cannibalism is happening “regularly” across today’s universe, according to MIT News, but early unions in the universe are less certain.
“Tucana II will finally be eaten by the Sweet Way, without any mercy,” Frebel said. “And it turns out that this ancient galaxy may have its own cannibalistic history.”
The team hopes to use their approach to find even older, more distant stars in other dwarf galaxies.