Giant black holes of dwarf galaxies on a collision course

22 Feb. () –

Observations with NASA’s Chandra X-ray Telescope have provided the first evidence of the existence of giant black holes in dwarf galaxies on a collision course.

Collisions between the dwarf galaxy pairs identified in the new study have drawn gas into the giant black holes they contain, causing them to grow. Over time, the likely collision of the black holes will cause them to merge into much larger black holes. Galaxy pairs will also merge into one.

Scientists believe that the universe was awash with small galaxies, known as “dwarf galaxies”, several hundred million years after the Big Bang. Most merged with others in the small, crowded volume of the early universe, setting in motion the construction of ever larger galaxies now seen in the nearby universe.

By definition, dwarf galaxies contain stars with a total mass less than about 3 billion times that of the Sun, compared with a total mass of about 60 billion Suns estimated for the Milky Way.

The first dwarf galaxies are impossible to observe with current technology because they are extraordinarily faint at their great distances. Astronomers have been able to observe two in the process of merging at distances much closer to Earth, but no hint of black holes in both galaxies.

“Astronomers have found many examples of black holes on a collision course in relatively close large galaxies,” he explains. it’s a statement Marko Micic of the University of Alabama at Tuscaloosa, who led the study. “But looking for them in dwarf galaxies is much more difficult and has so far failed.”

The new study overcame these challenges by conducting a systematic study of Chandra’s deep 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). .

Chandra was useful in this study because the material surrounding black holes can heat up 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 of the existence of two black holes and discovered two examples.

“We have identified the first two different pairs of black holes in colliding dwarf galaxies,” says Olivia Holmes, co-author of the study and also from the University of Alabama in Tuscaloosa. “Using these systems as analogs to others in the early universe, we can delve into questions about the first galaxies, their black holes and the star formation that caused the collisions“.

One pair is found in the galaxy cluster Abell 133, located 760 million light-years from Earth. The other is in the galaxy cluster Abell 1758S, located about 3.2 billion light-years away. Both pairs show structures that are characteristic signs of galaxy collisions.

The Abell 133 partner appears to be in the late stages of a merger between the two dwarf galaxies, and shows a long tail caused by the tidal effects of the collision. The authors of the new study have nicknamed it “Mirabilis” after an endangered hummingbird species known for its exceptionally long tails. Only one name was chosen because the merger of two galaxies into one is almost complete.

In Abell 1758S, researchers nicknamed the dwarf merger galaxies “Elstir” and “Vinteuil,” after the fictional artists of Marcel Proust’s “In Search of Lost Time.” Researchers believe these two have been caught up in the early stages of a merger, which has caused a bridge of stars and gas to connect the two colliding galaxies.

Details of the merger of black holes and dwarf galaxies may shed light on our Milky Way’s past. Scientists believe that almost all galaxies began as dwarf galaxies or other types of small galaxies and grew over billions of years through mergers.

“It is likely that most of the dwarf galaxies and black holes in the early universe have grown much larger thanks to repeated mergers“, explains Brenna Wells, a co-author of the study and also from the University of Alabama in Tuscaloosa. “In a way, dwarf galaxies are our galactic ancestors, which have evolved over billions of years to produce large galaxies like our Milky Way.” .

“Follow-up observations of these two systems will allow us to study processes that are crucial to understanding galaxies and their black holes as infants,” said co-author Jimmy Irwin, also of the University of Alabama at Tuscaloosa.

In the last number of The Astrophysical Journal A paper describing these results is published, and the research is available on the arXiv preprint server.