Black Hole Caught Sleeping on the Job, Scientists Unsure Why

NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) has caught a glimpse of a black hole napping almost a decade after it was observed snacking on gas.

The sleeping black hole is roughly 5 million times the mass of the Sun and located in the nearby Sculptor galaxy, also known as NGC 253, a so-called starburst galaxy actively giving birth to new stars.

At a mere 13 million light-years away, Sculptor is one of the closest starbursts to the Milky Way.

Bret Lehmer of John Hopkins University and NASA’s Goddard Space Flight Center is the lead author of the study regarding the black hole that, he said in a press release, appears to have become dormant in the past 10 years based on their research.

Furthermore, should it decide to end its siesta any time soon, scientists are poised to catch the process through a number of telescopes.

“Periodic observations with both Chandra and NuSTAR should tell us unambiguously if the black hole wakes up again,” Lehmer added. “If this happens in the next few years, we hope to be watching.”

Typically, black holes become dormant, according to co-author Ann Hornschemeier of Gaddard, when they run out of food.

“Black holes feed off surrounding accretion disks of material,” she said. “When they run out of fuel they go dormant.”

However, such is not the case of Sculptor’s black hole: surrounded by a smorgasbord of star-creation by-product, it remains asleep.

Seeing this, astronomers are beginning to adjust assumptions regarding the development of galaxies.

Since nearly all galaxies are suspected of harboring supermassive black holes at their centers, the most massive of these are thought to grow at the same rate that new stars form before eventually blasting radiation ultimately shuts the factory down.

In the case of the Sculptor galaxy, astronomers are not sure whether star formation is winding down or just ramping up.

“Black hole growth and star formation often go hand-in-hand in distant galaxies,” co-author Daniel Stern and NuSTAR project scientist said. “It’s
a bit surprising as to what’s going on here, but we’ve got two powerful complementary X-ray telescopes on the case.”

NASA’s Chandra X-ray Observatory first observed the black hole in 2003, allowing scientists to watch as material spiraled inward, heating up to tens of millions of degrees.

Then, in fall 2012, Chandra and NuSTAR observed the same region simultaneously. As they did so, they detected high-energy X-ray light in the region, leading scientists to determine the black hole was not accreting material or, in other words, that it had fallen asleep.

Given the new observations, however, scientists are beginning to question the assumption that the black hole was ever really awake and whether if what Chandra observed came from a different source.

The answer, many believe, lies in the same two telescopes that first prompted scientists to determine the black hole was dormant.

“The combination of coordinated Chandra and NuSTAR observations is extremely powerful for answering questions like this,” Lou Kaluzienski, NuSTAR Program Scientists said. “Now, we can get all sides of the story.”

In addition, the telescopes’ observations have revealed a smaller, flaring object that researchers have since identified as an “ultraluminous X-ray source,” or ULX.

As black holes feeding off material from a partner star, ULXs shine more brightly than typical stellar-mass black holes generated from dying stars, but are fainter and more randomly distributed than the supermassive black holes at the centers of massive galaxies.

For this reason, astronomers are still working to determine the size, origins and physics of the mysterious space bodies.

“These stellar-mass black holes are bumping along near the center of the galaxy,” Hornschemeier said. “They tend to be more numerous in areas where there is star-formation activity.”

If and when the Sculptor’s sleepy center wakes up in the next few years while all the commotion is still going on, NuSTAR and Chandra will be the first charged with monitoring the situation.

In the meantime, the team said they plan to check the system periodically.