A Black Hole has Fallen Asleep

By Laura Boness

This supermassive black hole was feeding on gas when it was first spotted nearly 10 years ago, but new observations suggest that it isn’t sucking in material right now. In other words, it has gone to sleep.

The snoozing black hole is approximately five million times the mass of our sun and lies in the middle of the Sculptor Galaxy, 13 million light years away from the Milky Way. The Sculptor Galaxy, also known as NGC 253, is actively giving birth to new stars, so it’s a surprise to find that the black hole has gone dormant.

“Black holes feed off surrounding accretion disks of material. When they run out of this fuel, they go dormant,” says Ann Hornschemeier from NASA’s Goddard Space Flight Center, one of the authors of a study in the Astrophysical Journal. “NGC 253 is somewhat unusual because the giant black hole is asleep in the midst of tremendous star-forming activity all around it.”

Scientists suspect that most galaxies have black holes at their centre, so this discovery will help them understand how the galaxies grow over time. In the largest galaxies, black holes are believed to grow at the same rate as the stars form, until they shut down star formation altogether.

Astronomers aren’t sure if star formation in the Sculptor Galaxy is slowing down or speeding up, but there are two powerful telescopes on the case. When black holes pull in material, it heats up to tens of millions of degrees and glows in X-ray light, so NASA’s Chandra X-ray Observatory and NuStar will keep monitoring the X-ray light around the black hole.

Another possibility is that the black hole has actually been sleeping for much longer–Chandra detected the X-rays in 2003, but they could have come from another source. Future observations from both telescopes may solve this mystery–and tell us if the black hole wakes up.

“Periodic observations with both Chandra and NuSTAR should tell us unambiguously if the black hole wakes up again,” says lead author Bret Lehmer of the Johns Hopkins University, Baltimore, and NASA’s Goddard Space Flight Center. “If this happens in the next few years, we hope to be watching.”

Source [JPL, NASA]

Did you know?
Our galaxy, the Milky Way, is also believed to have a black hole at its centre that is about four million times the mass of our sun.