Astronomers have detected a pair of massive black holes in the distant galaxy 2MASX J21240027+3409114, located one billion light-years from the Solar System in the constellation Cygnus. These black holes are generating unusual light emissions, characterized by a cyclic pattern, likely caused by their interaction with a large gas cloud.
The black holes orbit each other every 130 days, separated by 26 billion kilometers, a distance that light takes one day to traverse. The phenomenon, never previously observed, was documented in a recent article published in Astronomy & Astrophysics.
The first unusual light emission from this galaxy was detected in March 2021 by an alert system. Over the past three years, the team has monitored the region, noting that the black holes have consumed nearly two solar masses of gas. It is anticipated that the black holes will merge in approximately 70,000 years.
Initially classified as a supernova due to its sudden brightness, further emissions in 2022 prompted researchers to reconsider its origin. The event was reclassified as an active galactic nucleus (AGN), but a recurring M-shaped pattern in observations intrigued the team.
This pattern, occurring every two to three months, could not be accounted for by either a supernova or an AGN. Lorena Hernández-García, the lead author of the study and an astrophysicist at the Millennium Institute of Astrophysics in Chile, stated that she had never encountered such a phenomenon before. The pattern was also observed in X-rays and ultraviolet light in 2022.
The most likely hypothesis proposed by Hernández-García's team is that the black holes are interacting with a massive gas cloud, larger than the black holes themselves, which is being torn apart by gravitational forces. The explosions may result from gas fragments being ejected with each passage of the black holes.
While this explanation is plausible, researchers have not ruled out the possibility of a tidal disruption event (TDE). The galaxy is merging with another, potentially generating dust. This discovery indicates that gas clouds like this may be common in galaxies with binary black holes.
Due to the galaxy's distance, scientists are unable to directly observe the gas cloud or the black holes. Future investigations will focus on developing new strategies to trace the phenomenon's origin and understand its nature.