NASA's Chandra Space Telescope Discovers Massive Black Holes on a Collision Course

As detailed in our most recent press release, a new study utilizing NASA's Chandra X-ray Observatory monitored two pairs of supermassive black holes in dwarf galaxies on collision courses. This is the first evidence of such an impending collision, providing scientists with crucial knowledge regarding the early Universe's proliferation of black holes.

Dwarf galaxies, by definition, have stars with a total mass of fewer than 3 billion Suns – roughly 20 times less than the Milky Way. Scientists have long hypothesized that dwarf galaxies combine, particularly in the early Universe, to form the more giant galaxies we observe today. Current technology, however, cannot witness the initial generation of dwarf galaxy mergers because they are so weak at such enormous distances. Another strategy, hunting for dwarf galaxy mergers closer to home, had failed thus far.

The researchers overcome these obstacles by conducting a systematic examination of deep Chandra X-ray observations and comparing them to infrared data from NASA's Wide Infrared Survey Explorer (WISE) and optical data from the Canada-France-Hawaii Telescope (CFHT).

Chandra was especially useful for this investigation because the material surrounding black holes can be heated to millions of degrees, resulting in massive volumes of X-rays. The researchers looked for pairs of strong X-ray sources in colliding dwarf galaxies as evidence of two black holes and found two.

One pair may be seen in the composite image on the left in the galaxy cluster Abell 133, which is about 760 million light-years from Earth. Pink represents Chandra X-ray data, whereas blue represents CFHT optical data. This pair of dwarf galaxies appear to be merging and has a long tail created by tidal effects from the collision. The current study's authors dubbed it "Mirabilis" after an endangered species of hummingbird known for its extraordinarily long tails. Because the merging of two galaxies into one is nearly complete, just one name was chosen. The two Chandra sources show X-rays from material surrounding black holes in their respective galaxies.

The other pair was identified in Abell 1758S, a 3.2 billion light-year galaxy cluster. On the right is a composite image created by Chandra and CFHT using the same colors as Mirabilis. The researchers called the merging dwarf galaxies "Elstir" and "Vinteuil," after imaginary artists from Marcel Proust's "In Search of Lost Time". Vinteuil is the top galaxy, and Elstir is the bottom galaxy. Both have Chandra sources, which are X-rays from material surrounding black holes in each galaxy. The researchers believe these two are in the early stages of merging, causing a bridge of stars and gas to form from the gravitational attraction of the two converging galaxies.

The features of merging black holes and dwarf galaxies may reveal information about our Milky Way's past. Astronomers believe that nearly all galaxies began as dwarf or other types of tiny galaxies and developed through mergers over billions of years. Follow-up observations of these two systems will enable astronomers to investigate mechanisms critical to understanding galaxies and their black holes in the early phases of the Universe.