Two pairs of gigantic black holes, each in a different dwarf galaxy, are hurtling toward each other, and they are poised for two separate, never-before-seen collisions.
Astronomers used NASA’s Chandra X-ray Observatory to spot the dwarf galaxy’s four black holes hurtling toward each other, trailing a vast train of gas and stars. Some of this material is already being sucked into the black holes, causing them to grow larger and larger before eventually crashing down.
The first pair was spotted in galaxy cluster Abell 133, located 760 million light-years from Earth, and the other in galaxy cluster Abell 1758S, some 3.2 billion light-years away. They will collide and merge to form even larger galaxies, and studying them as they approach each other could help astronomers understand how the cosmic monsters lurk in the universe came to grow so big. The results were published in the preprint database on November 8th arXiv (opens in new tab)and they were accepted for publication in the Astrophysical Journal.
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“We have identified the first two distinct pairs of black holes in colliding dwarf galaxies,” says co-author Olivia Holmes, a physics student at the University of Alabama at Tuscaloosa. said in a statement (opens in new tab). “By using these systems as analogues to those in the early Universe, we can study questions about the first galaxies, their black holes, and star formation from the collisions.”
black holes are born from the collapse of giant stars and grow by incessantly eating gas, dust, stars and other black holes in the star-forming galaxies they contain. Where the first black holes came from is a question that has long puzzled scientists.
Previous simulations of the “cosmic dawn” – the epoch spanning the universe’s first billions of years – have suggested that billowing clouds of cold gas may have done this merged into giant stars doomed to collapse quickly and create black holes. As these black holes grew larger, the ever-expanding gas trains surrounding them collapsed into stars, eventually forming dwarf galaxies.
Astronomers suspect that as the universe grew, the first black holes in the dwarf galaxy rapidly merged with others to create even larger supermassive black holes — and with them larger galaxies — throughout the cosmos. But so far, such black hole mergers have not been observed in dwarf galaxies.
To search for these elusive black hole mergers, the researchers conducted an examination of Chandra X-ray observations before comparing them to data obtained in infrared frequencies from NASA’s Wide Infrared Survey Explorer (WISE) and in optical frequencies from Canada- France-Hawaii Telescope (CFHT). Because the gas orbiting the black holes can be heated to millions of degrees, the researchers used Chandra to look for pairs of galaxies that emit high-energy X-rays. In fact, they found not one, but two pairs.
The astronomers observed that the first pair in Abell 133 was already in the later stages of a merger, and gravitational tidal effects have spread a long tail of material around the two black holes, which the researchers named “Mirabilis” after an endangered species of long-tailed hummingbird. The two black holes in Abell 1758S — dubbed “Elstir” and “Vinteuil” after fictional artists from Marcel Proust’s In Search of Lost Time — are in the early stages of a merger and are linked by a giant bridge of stars and planets Stars associated with gas that has spread between them.
The researchers say that further study of the dwarf galaxies could provide some important clues as to how the Milky Way’s supermassive black hole grew from a tiny black hole seedling to its current gargantuan size.
“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, a physics student at the University of Alabama at Tuscaloosa, in the statement. “In a way, dwarf galaxies are our galactic ancestors, evolving over billions of years to give birth to large galaxies like our own Milky Way.”