While supermassive black holes at the heart of galaxies are thought by astronomers to be fairly ubiquitous throughout the universe, researchers studying one nearby example have discovered not one, but three of these cosmic giants.
The galaxy in question, labelled NGC 6240, is actually an amalgamation of smaller galaxies on a collision course with one another. Owing to its irregular butterfly shape, it was initially thought the merger underway was between only two galaxies. Instead, after new observations by the European Southern Observatory's Very Large Telescope (VLT) in Chile, the international team research team was surprised to discover the presence of three supermassive blackholes in tight proximity to one another.
"Up until now, such a concentration of three supermassive black holes had never been discovered in the universe," Dr. Peter Weilbacher of the Leibniz Institute for Astrophysics Potsdam (AIP) and co-author of a paper published in the journal Astronomy & Astrophysics said in a statement. "The present case provides evidence of a simultaneous merging process of three galaxies along with their central black holes."
A cosmic tango of epic proportions
The irregular galaxy NGC 6240. The northern black hole (N) is active and was known before. The zoomed-in new high-spatial resolution image shows that the southern component consists of two supermassive black holes (S1 and S2). (Photo: P Weilbacher (AIP), NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University))
New insights into NGC 6240 come courtesy of the VLT's 3D MUSE Spectrograph, an advanced instrument that operates in the visible wavelength range and allowed researchers to peer deep into the galaxy's dusty heart some 300 million light-years away from Earth. Each of the supermassive black holes has a mass of more than 90 million suns and resides in a region of space less than 3000 light-years across. For comparison, the supermassive black hole at the center of our own Milky Way, Sagittarius A*, has a mass of "only" 4 million suns.
Based on the close quarters of the three supermassive black holes, it's estimated the trio will eventually merge into one sometime over the next several hundred million years.
The research team says discoveries such as this one are crucial to understanding the evolution of galaxies over time. Up until now, it was regarded as a bit of a mystery as to how some of the largest galaxies observed, such as the six million light-year-wide giant IC 1101, could have possibly formed over only 14 billion years of the universe's existence.
"If, however, simultaneous merging processes of several galaxies took place, then the largest galaxies with their central supermassive black holes were able to evolve much faster," Weilbacher adds. "Our observations provide the first indication of this scenario."