Astronomers have captured a strange phenomenon never observed until today: very distant dwarf galaxies which are about to merge, accompanied by a giant black hole in their center. Even more, it is not one but two pairs that have been detected!
Two new candidates for “double active galactic nuclei” have just been found by a team of researchers, explains a study accepted into The Astrophysical Journal and pre-published on ArXiv. The phenomenon has been theorized for a long time but still very little observed until now. More exactly, it is about a fusion of supermassive black holes, located in the center of galaxies. And not just any: dwarf galaxies, with less than a billion stars. In comparison, the Milky Way contains 200 to 400 billion!
And this type of merger is of particular interest, because the very first galaxies, far from reaching the size of the Milky Way, were dwarf galaxies. They then merged to give the galaxies we know today. “Most of the dwarf galaxies and black holes in the early universe have probably grown much larger by now, through repeated mergers, said Brenna Wells in a communiquéco-author of the study. In a way, dwarf galaxies are our galactic ancestors, which evolved over billions of years to produce large galaxies like our own Milky Way.
Captured by black hole accretion disks
Imaged by NASA’s Chandra X-ray Observatory, the two pairs of galaxies named Mirabilis and Elstir & Vinteuil are respectively 760 million light-years and 3.2 billion light-years away. It is by the accretion disc of their central black holes that they have been detected: the matter which falls towards the black hole heats up to millions of degrees, and forms a plasma disc all around the star, emitting a large amount of X-rays!
The first pair, Mirabilis, is in the late stages of the merger, and shows a long tail caused by the tidal effects of the collision. Conversely, Elstir & Vinteuil is only at its beginning, and is gradually forming a bridge of stars and gas that connects the two galaxies. “Follow-up observations of these two systems will allow us to study processes crucial to understanding galaxies and their infancy black holes.”concluded Jimmy Irwin, co-author of the study.