Scientists discovered two supermassive black holes in the quasar closest to Earth, Markarian 231.

The discovery of the binary black hole system was made using NASA's Hubble Space Telescope, and suggests supermassive black holes assemble their masses through violent mergers, the University of Oklahoma reported. The black hole duo was discovered in a quasar, which is an active galaxy with an illuminated center.

"We are extremely excited about this finding because it not only shows the existence of a close binary black hole in Mrk 231, but also paves a new way to systematically search binary black holes via the nature of their ultraviolet light emission," said Youjun Lu of the National Astronomical Observatories of China.

To make their findings, a team of researchers looked at ultraviolet radiation emitted from the center of the Markarian 231 taken from Hubble observations. They applied these observations to a model of the spectrum of the galaxy, allowing them to determine the existence of two black holes.

"The structure of our universe, such as those giant galaxies and clusters of galaxies, grows by merging smaller systems into larger ones, and binary black holes are natural consequences of these mergers of galaxies," said Xinyu Dai, professor in the Homer L. Dodge Department of Physics and Astronomy, OU College of Arts and Sciences.

The findings suggest that over time, the two black holes (one of which is larger than the other) will draw closer to each other and eventually collide. The dramatic collision would result in a merger, resulting in a quasar with a supermassive black hole. 

The findings were published in a recent edition of The Astrophysical Journal.