Astronomers have come to expect to find massive black holes at the center of the universe's brightest bodies, but last week, NASA astronomers revealed a startling new finding: a pair of "furiously whirling" black holes at the heart of a galaxy called Markarian 231.
Located some 600 million light years from our solar system, Mrl 231 is the closest galaxy to Earth that hosts a quasar core. The idea that quasars host black holes is not new, but this discovery – found with the help of the Hubble Space Telescope – suggests that they may contain binary, or twin, black holes more often than originally thought.
“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,” Youjun Lu of the National Astronomical Observatories of China, Chinese Academy of Sciences, said in a statement published by NASA.
As gas and dust swirl around a quasar, the material gets sucked inward into the black hole at its core, where the black hole's gravity compresses and heats it, producing radiation.
The black hole's magnetic fields concentrate much of that radiation into jets that stretch from each pole deep into space – jets that appear as bright points far outshining the galaxies where they originated.
Scientists first observed a mysterious hole in the center of the Mrk 231 quasar’s accretion disk, or the ring of gas that spirals around the black hole. Using modeling studies, the researchers concluded that the best explanation for the hole is that the center of the disk is carved out by two black holes – one larger and one smaller – orbiting each other.
Researchers say the primary black hole in Mrk 231 is about 150 million times the mass of our sun, while its partner weighs in at about 4 million solar masses.
The duo likely fell into orbit around one another as a result of the merger between two galaxies, and together generate huge amounts of energy that causes the core of the host galaxy to outshine the rest of its stars.
“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 co-investigator Xinyu Dai of the University of Oklahoma, in NASA's statement.
The merger has also led Mrk 231 to produce stars at a rate 100 times the Milky Way.
The two black holes are predicted to spiral together and collide within a few hundred thousand years.