Astronomers have discovered an extremely rare group of five “dwarf” galaxies that are “interacting with each other” about 117 million light years from Earth.
Dwarf galaxies contain a few billion stars, while standard galaxies have hundreds of billions, giving them low mass and luminosity.
The newly discovered galaxies are blue, rich in gas and actively forming new stars.
They were designated D1 to D5, and D3 and D4 show signs of mutual tidal interactions, meaning that their respective gravitational forces attract each other and distort the shapes of the galaxies.
D3 and D4 have developed ‘tidal tails’, or thin, elongated regions of stars and interstellar gas that extend away from the point where the galaxies collide.
It is very rare for dwarf galaxies to appear in groups, as studies suggest that less than five percent of dwarf galaxies are neighbors of each other.
Therefore, there is less than a 0.004 percent chance that one dwarf galaxy will be so close to four others.
Despite these incredibly low probabilities, “We have identified a distinct group of dwarf galaxies, with its five members aligned along a straight line in the celestial plane and three sharing a common rotation direction,” the researchers wrote in their report. .
The discovery of this extremely unique group is forcing scientists to question the prevailing model of our universe, but it should also help scientists better understand how dwarf galaxies form and evolve.
The group of dwarf galaxies, called D1 to D5, is extremely rare
A team of researchers led by Yonsei University in Seoul, South Korea, discovered the group of dwarf galaxies by analyzing data from several astronomical surveys that continually scan space for new discoveries.
These studies use telescopes to observe millions of celestial objects in deep space, creating huge, highly detailed maps of the universe.
The researchers’ analysis revealed the presence of the group of dwarf galaxies, isolated together in deep space.
They estimated that the total dynamical mass – or the mass of an object inferred from its motion relative to other objects – of the group was about 60.2 billion times the mass of our sun, according to the study.
Their individual masses vary widely. The largest member of the group, galaxy D2, has a stellar mass of about 275 million solar masses.
The least massive, D4, has a stellar mass of only 14.7 million solar masses.
For comparison, our Milky Way galaxy has a stellar mass of about 1.5 trillion solar masses, according to NASA.
The researchers published their findings in The letters from the astrophysical diary on November 19.
They were designated D1 to D5, and two of them, D3 and D4, show signs of mutual tidal interactions, meaning that their respective gravitational forces attract each other and distort the shapes of the galaxies.
Dwarf galaxies only contain a few billion stars, while standard galaxies have hundreds of billions. This is the irregular dwarf galaxy NGC 6822, which is not part of the newly discovered group.
Finding five dwarf galaxies clustered in a nearly straight line, with most of them spinning in the same direction, is so unusual that it challenges predictions made by the prevailing model of how the universe formed.
That model, called Lambda Cold Dark Matter (LCDM), suggests that dark matter causes disordered groupings of galaxies.
By that logic, galaxies are not expected to have a preferred alignment. The five dwarf galaxies, however, are aligned in a configuration that is “not often seen in CDM simulations,” said the study’s lead author, Sanjaya Paudel, of Yonsei University in South Korea. space.com.
What’s more, the fact that three of the five galaxies share the same direction of rotation, as demonstrated by DESI observations, suggests that they formed from the same gas cloud. This further contradicts the LCDM model.
‘Why do they have the same rotation?’ Paudel said. “They must have a connection to each other; that would be a very important issue that cannot be explained by the ΛCDM model.”
For now, this discovery raises more questions than answers. But future studies could soon confirm whether the unlikely configuration of galaxies is a chance projection or a real physical arrangement, the researchers said in their report.
Additionally, studying these five dwarf galaxies could help scientists better understand how such objects form and evolve.
Astronomers believe that dwarf galaxies were created by gravitational forces in the early stages of the creation of larger galaxies, or as a result of collisions between galaxies that eject streams of material into space.
According to the European Space Agency, dwarf galaxies are believed to be important for scientific understanding of general galaxy evolution.
Those that lack a defined shape, known as “irregular” dwarf galaxies, are considered similar to the first galaxies that populated the Universe. Therefore, studying them offers insight into ancient cosmological history.
More than 20 known dwarf galaxies orbit the Milky Way. But they are geographically and gravitationally separated from each other, not grouped together.