The supermassive black hole pair, located in the peculiar galaxy NGC 7727, is about 89 million light-years away from Earth, making it the record holder for the nearest dual supermassive black hole to us, with the next known dual supermassive black hole being at a distance of 470 million light-years. NGC 7727’s supermassive black holes have a separation of only 1,600 light-years (500 parsec), making them the only known pair of supermassive black holes with a sub-kiloparsec separation.
This image, taken with the MUSE instrument on ESO’s Very Large Telescope, shows two bright galactic nuclei, each housing a supermassive black hole, in NGC 7727. Image credit: ESO / Voggel et al.
NGC 7727 is a peculiar galaxy located 89 million light-years away in the constellation of Aquarius.
The galaxy was discovered by the German-born British astronomer William Herschel on November 27, 1785.
NGC 7727 is the product of the merger of two smaller spiral galaxies that took place around one billion years ago.
Astronomers suspected that the galaxy hosted two black holes, but they had not been able to confirm their presence until now.
“It is the first time we find two supermassive black holes that are this close to each other, less than half the separation of the previous record holder,” said lead author Dr. Karina Voggel, an astronomer at the Observatoire astronomique de Strasbourg.
“The small separation and velocity of the two black holes indicate that they will merge into one monster black hole, probably within the next 250 million years,” added co-author Professor Holger Baumgardt, an astronomer in the School of Mathematics and Physics at the University of Queensland.
This image, taken with ESO’s VLT Survey Telescope, shows the peculiar galaxy NGC 7727. Image credit: ESO / VST-ATLAS Team / Durham University / CASU / WFAU.
In their study, the astronomers used data gathered by the Multi-Unit Spectroscopic Explorer (MUSE), an integral-field spectrograph on ESO’s Very Large Telescope.
They were able to determine the masses of the black holes located at the core of NGC 7727 by looking at how their gravitational pull influences the motion of the stars around them.
The bigger black hole was found to have a mass almost 154 million times that of the Sun, while its companion is 6.3 million solar masses.
It is the first time the masses have been measured in this way for a supermassive black hole pair.
“Our finding implies that there might be many more of these relics of galaxy mergers out there and they may contain many hidden massive black holes that still wait to be found,” Dr. Voggel said.
“It could increase the total number of supermassive black holes known in the local Universe by 30%.”
The discovery is reported in a paper to be published in the journal Astronomy & Astrophysics.
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K.T. Voggel et al. 2021. First direct dynamical detection of a dual super-massive black hole system at sub-kpc separation. A&A, in press; doi: 10.1051/0004-6361/202140827
