A new study using NASA’s Chandra X-ray Observatory has tracked two pairs of supermassive black holes in dwarf galaxies on collision courses. This is the first indication of such an upcoming encounter, giving scientists crucial knowledge about the growth of black holes in the early universe.

Dwarf galaxies are known to merge and grow into the larger galaxies we see today. However, current technology cannot detect the first generation of dwarf galaxy mergers because they are extremely faint at great distances.

The current study overcame these hurdles by using a systematic scan of deep Chandra X-ray observations and combining them with optical data from the Canada-France-Hawaii Telescope and infrared data from NASA’s Wide Infrared Survey Explorer (WISE) (CFHT).

The team looked for pairs of bright X-ray sources in colliding dwarf galaxies as evidence of two black holes and found two examples.

The composite image on the left shows one pair in the cluster of galaxies Abell 133, 760 million light-years from Earth. Pink represents Chandra X-ray data, while blue represents optical CFHT data. This pair of dwarf galaxies has a long tail due to tidal effects of the collision and appears to be in the final stages of merging.

The authors of the current study have nicknamed it “Mirabilis,” after a critically endangered species of hummingbird known for its unusually long tails. Due to the almost complete merger of two galaxies into one, only one name was chosen. In each galaxy, the two Chandra sources reflect X-rays from the region around the black holes.

The other pair was discovered in Abell 1758S, a galaxy cluster about 3.2 billion light-years away.

The merging dwarf galaxies were named “Elstir” and “Vinteuil” by the researchers in honor of fictional artists from Marcel Proust’s “In Search of Lost Time.” The galaxy at the top is called Vinteuil and the galaxy at the bottom Elstir.

According to scientists, these two were caught in the early stages of a merger, creating a bridge of stars and gas connecting the two colliding galaxies from their gravitational interaction. Follow-up observations of these two systems will allow astronomers to study processes crucial to understanding galaxies and their black holes in the earliest stages of the Universe.

Magazine reference:

  1. Marko Mićić, Olivia J. Holmes et al. Two Candidates for Dual AGN in Dwarf-Dwarf Galaxy Mergers. The Astrophysical Journal. DOI: DOI: 10.48550/arXiv.2211.04609