A study of the black holes titled "The Unanticipated Phenomenology of the Blazar PKS 2131-021: A Unique Supermassive Black Hole Binary Candidate" has been published in the journal The Astrophysical Journal Letters.
Researchers from the California Institute of Technology (Caltech) have observed two supermassive black holes orbiting one another every two years, nine billion light-years away. Both are hundreds of millions of times greater in mass than our Sun and are separated by about fifty times the distance between our Sun and Pluto. They are predicted to merge in approximately ten thousand years, which will send massive gravitational waves across the universe.
The black holes are found within a blazar dubbed PKS 2131-021, a type of quasar. Quasars are a type of active galactic nuclei (AGN) where the supermassive black hole(s) within siphons material from the accretion disc encircling it and shoots out massive jets. PKS 2131-021 marks the second known candidate for a pair of supermassive black holes caught merging, with the first candidate pair being the quasar OJ 287, whose black holes orbit one another every nine years instead of two.
PKS 2131-021 was detected through changes in its radio-light brightness dating back 45 years, resulting from the black holes within orbiting one another. The combination of radio data from five different observatories yielded a nearly perfect sinusoidal light curve, indicating that PKS 2131-021 comprised not one but two supermassive black holes.
"When we realized that the peaks and troughs of the light curve detected from recent times matched the peaks and troughs observed between 1975 and 1983, we knew something very special was going on," said Sandra O'Neill, lead author of the new study.
"We knew this beautiful sine wave had to be telling us something important about the system. Roger's [Blandford] model shows us that it is simply the orbital motion that does this. Before Roger worked it out, nobody had figured out that a binary with a relativistic jet would have a light curve that looked like this," said Tony Readhead, Robinson Professor of Astronomy, Emeritus.
You can read more from the study here.