This discovery indicates that there are many more supermassive black holes in the Local Universe, as well as binary systems of such objects that have not yet been detected in sky surveys since they do not show signs of active accretion of matter.
Astronomers have found the closest pair of supermassive black holes to the Sun, located at the center of the galaxy NGC 7727, 89 million light-years away. In addition, it is the first dynamically confirmed binary system of supermassive black holes, the distance between which is less than one kiloparsec.
Merging black holes
When two galaxies containing supermassive black holes in their central zones merge, a binary system of supermassive black holes is formed, separated by distances from one to hundreds of kiloparsecs. Gradually, black holes are getting closer and closer, losing energy due to the radiation of gravitational waves. After they merge together, the resulting bursts of gravitational waves become the main targets of observations for gravitational wave observatories.
The search for binary systems
Thus, the search for binary systems of supermassive black holes is aimed at solving three problems. One is confirming the formation of very massive black holes due to the merger of central black holes in the evolutionary models of galaxies. The second one is compiling a catalog of interesting candidates for existing and future gravitational-wave observatories.
The search for even tighter systems, where the distance between black holes is several kiloparsecs, at redshifts z> 2 is also important for solving the mystery of the mechanisms of formation and rapid growth of supermassive black holes in the early Universe. Until now, there had not been a single confirmed binary system at z> 2, where the distance between black holes would be less than 10 kiloparsecs (about 33 thousand light-years).
Closest pair of black holes to the Sun
A group of astronomers led by Karina Voggel of the Strasbourg Observatory in France reported the discovery of the closest known pair of supermassive black holes to the Sun. The discovery was made on the basis of observational data from the MUSE (Multi-Unit Spectroscopic Explorer) spectrograph installed on the VLT telescope complex and the Hubble Space Telescope behind the peculiar galaxy NGC 7727.
NGC 7727 is located in the constellation Aquarius, about 89 million light-years from the Sun, and has a partially distorted shape, indicating a recent merger with another galaxy. At its center are two galactic nuclei, the distance between which is estimated at 1600 light-years (500 parsecs).
In the course of observations, it was possible to determine the masses of supermassive black holes trapped in the nuclei, which amounted to 154 and 6.3 million solar masses. The smaller black hole is thought to have been part of a central star cluster – the remnant of a gas-rich disk galaxy that was five times lighter than it before merging with NGC 7727.
This discovery, according to scientists, indicates that there are many more supermassive black holes in the Local Universe, as well as binary systems of such objects that have not yet been detected in sky surveys since they do not show signs of active accretion of matter. The number of such discoveries is expected to increase with the introduction of new generation large telescopes such as the Extremely Large Telescope.
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• ESO. (n.d.). ESO telescope uncovers closest pair of supermassive black holes yet.
• Phys.org. (2021, November 30). Very large telescope uncovers closest pair of supermassive black holes yet.
• Pultarova, T. (2021, November 30). This pair of merging black holes is the closest to earth we’ve ever found. Space.com.
• Voggel, K. T., Seth, A. C., Baumgardt, H., Husemann, B., Neumayer, N., Hilker, M., Pechetti, R., Mieske, S., Dumont, A., & Georgiev, I. (2021, November 30). First direct dynamical detection of a dual super-massive black hole system at sub-kpc separation. Astronomy & Astrophysics.