Astronomers have discovered the first evidence for supermassive black holes in dwarf galaxies on a collision course. This result from NASA’s Chandra X-ray Observatory has important implications for understanding how black holes and the first wave of galaxies grew in the early universe.
Collisions between pairs of dwarf galaxies, identified in a new study, have pulled gas towards the supermassive black holes, causing the black holes to grow. Eventually they will merge into a much larger black hole due to a possible black hole collision. Pairs of galaxies will also merge into one.
Several hundred million years after the Big Bang, according to scientists, the universe was filled with smaller galaxies known as “dwarf galaxies”. Most of them combined with other galaxies in the crowded, compact early universe, beginning the process of forming the ever-larger galaxies now visible throughout the universe.
Dwarf galaxies, by definition, contain stars with masses less than about 3 billion times that of the Sun, compared to the Milky Way’s estimated total mass of about 60 billion Suns.
The earliest dwarf galaxies are impossible to see with current technology because they are exceptionally faint at their great distances. Astronomers have been able to see two in the process of merging at very close distances to Earth, but without signs of black holes in either galaxy.
“Astronomers have found many examples of black holes on collision courses in large galaxies that are relatively close,” said Marco Mick of the University of Alabama at Tuscaloosa, who led the study. “But their search in dwarf galaxies is far more challenging and had so far been unsuccessful.”
The new study overcame these challenges by implementing a systematic survey of deep lunar X-ray observations and comparing them with infrared data from NASA’s Wide Infrared Survey Explorer (WISE) and optical data from the Canada-France-Hawaii Telescope (CFHT). Found.
Chandra was particularly valuable for this study because the material surrounding a black hole can be heated to millions of degrees, producing large amounts of X-rays. The team looked for pairs of bright X-ray sources in colliding dwarf galaxies as evidence for two black holes and found two examples.
“We have identified the first two distinct pairs of black holes in colliding dwarf galaxies,” said co-author Olivia Holmes of the University of Alabama at Tuscaloosa. “Using these systems as analogs to the early universe, we can answer questions about the first galaxies, their black holes, and the collisions that led to star formation.”
A pair is in the galaxy cluster Abell 133, located 760 million light-years from Earth. The other is in the Abell 1758S galaxy cluster, about 3.2 billion light-years away. Both pairs show structures that are typical of galaxy collisions.
The pair in Abell 133 appears to be in the later stages of a merger between two dwarf galaxies, and shows a long tail due to tidal effects from the collision. The authors of the new study have named it “mirabilis” after an endangered species of hummingbird known for their exceptionally long tails. Only one name was chosen because the merger of the two galaxies into one is almost complete.
In Abel 1758S, researchers named the merging dwarf galaxies “Elstir” and “Vinteuil” after the fictional cast of Marcel Proust’s “In Search of Lost Time”. The researchers think these two were caught in the early stages of a merger, forming a bridge of stars and gas to connect the two colliding galaxies.
