Evidence that this supermassive black hole may have a companion comes from observations by radio telescopes on Earth. Black holes don’t emit light, but their gravity can collect disks of hot gas around them and eject some of that material into space. These jets can span millions of light years. A jet heading toward the ground appears brighter than a jet heading away from the ground. Astronomers call supermassive black holes with jets directed toward the Earth’s beam, and at the heart of this paper is an explosion dubbed PKS 2131-021.
Located about 9 billion light-years from Earth, PKS 2131-021 is one of 1,800 plazaars that a group of researchers at the California Institute of Technology in Pasadena have been monitoring with the Owens Valley Radio Observatory in Northern California for 13 years as part of a general study of plazaar behavior. But this particular blazar exhibits strange behaviour: its brightness shows regular ups and downs, as predicted as the ticking of a clock.
Researchers now believe that this regular difference is the result of a second black hole gravitating toward the first while orbiting each other about every two years. The mass of each of the black holes in PKS 2131-021 is estimated to be a few hundred million times the mass of our Sun. To confirm the result, scientists will try to detect gravitational waves – Ripples in space – coming from the system. The first detection of gravitational waves from black hole binaries It was announced in 2016.
To make sure the oscillations weren’t random or cause a temporary effect around the black hole, the team had to look beyond the decade (2008 to 2019) of data from the Owens Valley Observatory. After learning that two other radio telescopes had studied this system as well—the University of Michigan Radio Observatory (1980 to 2012) and the Haystack Observatory (1975 to 1983)—they dug into the additional data and found that it matched expectations for how the Blazer would explode. The brightness should change over time.
“This work is a testament to the importance of perseverance,” Lazio said. It took 45 years of radio observations to come to this conclusion. It took small teams, at various observatories across the country, the data week after week, month after month, to make this possible.”
To find out more, read Caltech press release.