NASA’s Chandra X-ray Observatory has detected two pairs of supermassive black holes on collision courses in dwarf galaxies, the first evidence of such an impending encounter. This discovery provides crucial information about the early universe’s black hole growth.
- NASA‘s Chandra X-ray Observatory helped identify two pairs of dwarf galaxies on their way to merge.
- Dwarf galaxies, which are at least about 20 times less massive than The Milky Wayprobably formed larger galaxies through collisions in the early universe.
- These newly discovered merging dwarf galaxies can be used as analogs for more distant galaxies that are too faint to observe.
- The dwarf galaxies are on collision courses and are found in the galaxy clusters Abell 133 and Abell 1758S.
Evidence has been found for two pairs of supermassive black holes in dwarf galaxies on collision courses with Chandra. The two pairs are shown in X-rays from Chandra and optical light from the Canada-France-Hawaii telescope. The fusion on the left wing is in a late stage and was named Mirabilis. The second merger is in the early stages and the two dwarf galaxies are named Elstir (bottom) and Vinteuil (top). Astronomers believe that dwarf galaxies – those about 20 times less massive than the Milky Way – grow through mergers with others. This is an important process for galaxy growth in the early universe, and this discovery provides examples for scientists to study in more detail. Credit: X-ray: NASA/CXC/Univ. of Alabama/M. Micic et al.; Optical: International Gemini Observatory/NOIRLab/NSF/AURA
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 evidence of such an imminent encounter, providing scientists with important information about the growth of black holes in the early universe.
By definition, dwarf galaxies contain stars with a total mass of less than 3 billion suns – or about 20 times less than the Milky Way. Astronomers have long suspected that dwarf galaxies merge, especially in the relatively early universe, to grow into the larger galaxies seen today. However, current technology cannot observe the first generation of dwarf galaxy mergers because they are extraordinarily faint at their great distances. Another tactic—looking for dwarf galaxy mergers closer—had not been successful to date.
The new study overcame these challenges by implementing a systematic examination of deep Chandra 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 particularly valuable for this study because material around black holes can be heated to millions of degrees, producing large amounts of X-rays. The team searched for pairs of bright X-ray sources in colliding dwarf galaxies as evidence of two black holes and discovered two examples.
Evidence has been found for two pairs of supermassive black holes in dwarf galaxies on collision courses with Chandra. The two pairs are shown in X-rays from Chandra and optical light from the Canada-France-Hawaii telescope. The fusion on the left wing is in a late stage and was named Mirabilis. The second merger is in the early stages and the two dwarf galaxies are named Elstir (bottom) and Vinteuil (top). Astronomers believe that dwarf galaxies – those about 20 times less massive than the Milky Way – grow through mergers with others. This is an important process for galaxy growth in the early universe, and this discovery provides examples for scientists to study in more detail. Credit: X-ray: NASA/CXC/Univ. of Alabama/M. Micic et al.; Optical: International Gemini Observatory/NOIRLab/NSF/AURA
One pair is in the galaxy cluster Abell 133 located 760 million light years from Earth, seen in the composite image on the left. Chandra X-ray data is in pink and optical data from CFHT is in blue. This pair of dwarf galaxies appears to be in the late stages of a merger, showing a long tail caused by the tidal effects of the collision. The authors of the new study have nicknamed it “Mirabilis” after an endangered species species of hummingbirds known for their unusually long tails. Only one name was chosen because the merger of two galaxies into one is almost complete. The two Chandra sources show X-rays from material around the black holes in each galaxy.
X-ray and optical composite of Mirabilis. Credit: X-ray: NASA/CXC/Univ. of Alabama/M. Micic et al.; Optical: International Gemini Observatory/NOIRLab/NSF/AURA
The other pair was discovered in Abell 1758S, a galaxy cluster about 3.2 billion light-years away. The composite image from Chandra and CFHT is on the right and uses the same colors as for Mirabilis. The researchers nicknamed the merging dwarf galaxies “Elstir” and “Vinteuil”, after fictional artists from Marcel Proust’s “In Search of Lost Time”. Vinteuil is the galaxy at the top and Elstir is the galaxy at the bottom. Both have Chandra sources associated with them, again from X-rays from material around the black holes in each galaxy. The researchers believe these two have been caught in the early stages of a merger, causing a bridge of stars and gas to connect the two colliding galaxies from their gravitational interaction.
X-ray and optical composite by Elstir & Vinteuil. Credit: X-ray: NASA/CXC/Univ. of Alabama/M. Micic et al.; Optical: International Gemini Observatory/NOIRLab/NSF/AURA
The details of merging black holes and dwarf galaxies can provide insight into our Milky Way’s own past. Scientists believe that almost all galaxies began as dwarf or other types of small galaxies and grew over billions of years through mergers. 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.
A paper detailing these findings was published in the latest issue of That Astrophysical Journal.
Reference: “Two Candidates for Dual AGN in Dwarf-Dwarf Galaxy Mergers” by Marko Mićić, Olivia J. Holmes, Brenna N. Wells and Jimmy A. Irwin, 22 Feb 2023, The Astrophysical Journal.
DOI: 10.3847/1538-4357/aca1bb
The authors of the study are Marko Micic, Olivia Holmes, Brenna Wells and Jimmy Irwin, all from the University of Alabama in Tuscaloosa.
NASA’s Marshall Space Flight Center manages the Chandra program. The Smithsonian Astrophysical Observatory’s Chandra X-ray Center controls science operations from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.