A Supermassive Black Hole with a Case of the Hiccups

Can binary black holes, two black holes orbiting each other, influence their respective behaviors? This is what a recent study published in Science Advances hopes to address as a team of more than two dozen international researchers led by the Massachusetts Institute of Technology (MIT) investigated how a smaller black hole orbiting a supermassive black hole could alter the outbursts of the energy being emitted by the latter, essentially giving it “hiccups”. This study holds the potential to help astronomers better understand the behavior of binary black holes while producing new methods in finding more binary black holes throughout the cosmos.

“We thought we knew a lot about black holes, but this is telling us there are a lot more things they can do,” said Dr. Dheeraj “DJ” Pasham, who is a research scientist in MIT’s Kavli Institute for Astrophysics and Space Research and lead author of the study. “We think there will be many more systems like this, and we just need to take more data to find them.”

For the study, the researchers used a half dozen scientific instruments to obtain radio, ultraviolet, optical, and x-ray data on ASASSN-20qc, which is located approximately 260 megaparsecs (848,000,000 light-years) from Earth and was previously identified as a tidal disruption event (TDE) when first discovered in December 2020. The TDE responsible for astronomers first discovering ASASSN-20qc was caused by a star coming too close to the supermassive black hole and being slowly consumed over a four-month period. However, Dr. Pasham later looked over the data and found dips in energy output from the supermassive black hole occurring every 8.5 days throughout this four-month period.

Combining this data with computer models, the researchers confirmed the 8.5-day bursts of energy being emitted by supermassive black hole, which they hypothesize is caused by the smaller black orbiting around the larger one, with its own gravity influencing the gas and energy within the supermassive black hole’s disk. The researchers compare this phenomenon to an exoplanet transiting its parent star, resulting in a brief dip in starlight. These findings indicate that the disks of gas around black holes are far more chaotic than longstanding hypotheses have claimed.

“This is a different beast,” said Dr. Pasham. “It doesn’t fit anything that we know about these systems. We’re seeing evidence of objects going in and through the disk, at different angles, which challenges the traditional picture of a simple gaseous disk around black holes. We think there is a huge population of these systems out there.”

The supermassive black hole examined in this study exists at the center of its respective galaxy similar to other supermassive black holes found through the cosmos, with Sagittarius A* being the supermassive black hole at the center of our Milky Way Galaxy. However, finding another black hole orbiting the one examined in this study could help astronomers better understand the formation and evolution of supermassive black holes throughout the universe, with the study noting this research could lead to new methods in identifying binary black hole candidates, as well.

The reason astronomers are interested in learning more about binary black holes is the potential for them to teach us about gravitational waves, which were first proposed in the late 19th and early 20th century and gained traction in their existence and relevance through Albert Einstein’s general theory of relativity, as these gravitational waves have been hypothesized to create ripple in the fabric of spacetime. These gravitational waves are produced from the merging of binary black holes, with astronomers first detecting a black hole merger by the Laser Interferometer Gravitational-Wave Observatory (LIGO) and corresponding results published in Physical Review Letters in 2016.

What new discoveries will astronomers make about binary black holes in the coming years and decades? Only time will tell, and this is why we science!

As always, keep doing science & keep looking up!