Astronomers spot black holes on a collision course in distant dwarf galaxies
Two separate pairs of black holes in faint merging galaxies have been observed, providing new clues about the evolution of our Universe.
Astronomers have found evidence of giant black holes in distant dwarf galaxies that appear to be on a collision course with one another.
Observing the dwarf galaxies in x-ray, infrared and visible light, the team have been able to spot two separate pairs of black holes that seem destined to collide.
Dwarf galaxies are galaxies that contain a total mass less than 3 billion times that of our Sun, as opposed to the roughly 60 billion Suns’ mass of our galaxy the Milky Way.
Dwarf galaxies are thought to have been abundant in the early Universe, hundreds of millions of years after the Big Bang.
The theory is that they merged with each other over time to form the large scale galactic structures we see today.
While astronomers have previously been able to observe black holes on collision courses in larger galaxies closer to Earth, they had not been able to discover colliding black holes in distant dwarf galaxies, until now.
Using NASA’s Chandra X-ray Observatory, NASA’s Wide Infrared Survey Explorer and optical data from the Canada-France-Hawaii Telescope, they have been able to spot two pairs of black holes in colliding dwarf galaxies in two different galaxy clusters.
One pair is in galaxy cluster Abell 133, which is 760 million lightyears away, while the other pair is in galaxy cluster Abell 1758S, which is about 3.2 billion lightyears away.
The study, led by Marko Micic of the University of Alabama at Tuscaloosa, USA, shows that the pair in Abell 133 seem to be in the late stages of a merger between the two dwarf galaxies, and a long tail caused by tidal effects from the collision can be seen.
This merger has been named 'Mirabilis' after an endangered species of hummingbird known for its long tail. Just one name was given to the pair because the merger is nearly complete.
The pair in Abell 1758S - seen at the top of this article - appear to be in the early stages of the merger, and a bridge of stars and cosmic gas can been seen connecting the two.
Two names were given to this pair: 'Elstir' and 'Vinteuil', after fictional artists from Marcel Proust's novel In Search of Lost Time.
In the image, Vinteuil is at the top and Elstir is on the bottom.
"We’ve identified the first two different pairs of black holes in colliding dwarf galaxies," says 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."
"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," says 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."
The study is available to read at arxiv.org/abs/2211.04609, or find out more about this story at chandra.harvard.edu/press/23_releases/press_022223.html.
Iain Todd is BBC Sky at Night Magazine's Content Editor. He fell in love with the night sky when he caught his first glimpse of Orion, aged 10.