For the first time ever, a group of astronomers has identified black hole's on a collision course within a dwarf galaxy, a scientific observation that was yet to be achieved until now.
As detailed in a February press release, a group of astronomers using NASA's Chandra X-ray Observatory identified two separate pairs of black holes and published their results in a study added to The Astrophysical Journal. The astronomers explain that dwarf galaxies on a set course to collide are expected to form a larger galaxy once the merger is complete. As for the black holes, the press release states that as gas is pulled toward the giant black holes within each of the dwarf galaxies, they grow in size.
Eventually, the black holes within each of those galaxies will grow and collide with opposing dwarf galaxies, forming an even greater black hole. Why is this important? Researchers believe studying dwarf galaxies unlocks more knowledge about the early stages of the universe, specifically several hundred million years after the Big Bang. The press release explains that scientists think that in the early stages of the universe, dwarf galaxies were in abundance, which, after millions of years, eventually collided together to form the galaxies we are observing today.
"Astronomers have found many examples of black holes on collision courses in large galaxies that are relatively close by," said Marko Micic of the University of Alabama at Tuscaloosa, who led the study. "But searches for them in dwarf galaxies are much more challenging and until now had failed."
Observing dwarf galaxies now give astronomers and researchers alike a deeper understanding of the evolutionary process of galaxies, which enables a greater understanding of our own galaxy, the Milky Way. By definition, a dwarf galaxy is a galaxy that contains stars with a total mass less than 3 billion times that of the Sun, which, by comparison, the Milky Way, contains about 60 billion Suns.
"We've identified the first two different pairs of black holes in colliding dwarf galaxies," said co-author Olivia Holmes, also of the University of Alabama at Tuscaloosa. "Using these systems as analogs for ones in the early universe, we can drill down into questions about the first galaxies, their black holes, and star formation the collisions caused."
As for these two separate pairs of black holes, one pair is located 760 million light years from Earth within the galaxy cluster called Abell 133. The other pair is located in the galaxy cluster 1758S, which is 3.2 billion light years away from Earth. According to the press release, the Abell 133 merger appears to be in its later stages, with researchers saying it's displaying telltale signs such as a long tail caused by tidal effects from the collision. Notably, researchers gave Abell 133 the nickname "Mirabilis" after an endangered species of hummingbird known for their exceptionally long tails.
"Most of the dwarf galaxies and black holes in the early universe are likely to have grown much larger by now, thanks to repeated mergers," said co-author Brenna Wells, also of the University of Alabama at Tuscaloosa. "In some ways, dwarf galaxies are our galactic ancestors, which have evolved over billions of years to produce large galaxies like our own Milky Way."
As for Abell 1758S, the press release states that researchers gave two nicknames as the merging process appears to be in the early stages, hence the decision to give only one name to Abell 133 since it's the later phase of the merging process. Abell 1758S was given the nicknames "Elstir" and "Vinteuil," after fictional artists from Marcel Proust's "In Search of Lost Time."
"Follow-up observations of these two systems will allow us to study processes that are crucial for understanding galaxies and their black holes as infants," said co-author Jimmy Irwin, also from the University of Alabama at Tuscaloosa.