An unusual light signal was reported by George Djorgovski, a professor of astronomy and director of the Center for Data-Driven Discovery at Caltech, and his colleagues, according to Caltech. The report, printed in the Jan. 7 issue of Nature, states that a repeating light signal from a quasar in the distance could be the result of two huge black holes merging. The combining of two supermassive black holes has only been theory - never observed.
Black holes are impossible to see, but the swirling band of materials it pulls in is called an accretion disk. When the spinning particles accelerate and emit gamma rays and x-rays, a quasar results. A quasar is a especially radiant object that outshines the other stars in its galaxy. Quasars are visible across the universe.
"Quasars are valuable probes of the evolution of galaxies and their central black holes," said Djorgovski. Researchers think this merger could help solve the "final parsec problem," which refers to the inability of theories of black hole mergers to actually predict the final stages.
"The end stages of the merger of these supermassive black hole systems are very poorly understood," said Matthew Graham, a senior computational scientist at Caltech. "The discovery of a system that seems to be at this late stage of its evolution means we now have an observational handle on what is going on."
"There has never been a data set on quasar variability that approaches this scope before," said Djorgovski. "In the past, scientists who study the variability of quasars might only be able to follow some tens, or at most hundreds, of objects with a limited number of measurements. In this case, we looked at a quarter million quasars and were able to gather a few hundred data points for each one."
The light from a quasar is typically bright and steady, not staccato or repetitive."You just don't expect to see a periodic signal from a quasar," Graham said. "When you do, it stands out."
Graham said that one possibility for the repeating light is "that the quasar is funneling material from its accretion disk into luminous twin plasma jets that are rotating like beams from a lighthouse," according to Caltech.
Another possibility is a distortion in the accretion disk. "If one region is thicker than the rest, then as the warped section travels around the accretion disk, it could be blocking light from the quasar at regular intervals. This would explain the periodicity of the signal that we're seeing," Graham said.
"Even though there are a number of viable physical mechanisms behind the periodicity we're seeing -either the precessing jet, warped accretion disk or periodic dumping - these are all still fundamentally caused by a close binary system," Graham said.
