Signal From Star Being Destroyed at Supermassive Black Hole's Event Horizon Captured

The pulse from a star being torn apart by a supermassive black hole has been captured by scientists, allowing them to better understand the physical properties of these extreme regions of space.

Stellar black holes—like the one studied—form when the center of a huge star collapses in on itself, causing a supernova. The resulting black hole has such a strong gravitational pull not even light can escape—meaning scientists cannot observe them. This makes understanding their physical properties is extremely challenging.

Read more: 'Great collision' could wake up the supermassive black hole at the Milky Way's center

However, the boundary of a black hole—the event horizon, which is the point of no return—offers some opportunity for study.

For the first time, scientists have observed a star being torn apart at the event horizon of a supermassive black hole—and have used the data to estimate how fast the black hole is spinning. The findings, published in Science, focus on a supermassive black hole located almost 290 million light years away.

Researchers from the U.S. and the Netherlands were looking at a 'tidal disruption event' or TDE (the name for a star being destroyed by a black hole) that was detected in 2014. When a star is torn apart, it releases electromagnetic energy, such as X-rays. This pulse allows scientists to try to define certain properties of the black hole in question, such as its mass and spin.

Through extensive analysis, the team discovered a stable, periodic signal coming from the doomed star—it appeared to brighten and fade once every 131 seconds. These X-rays were coming from an area extremely close to the black hole's event horizon, leading the team to suggest the signal is orbiting the black hole.

Because of the stability of the signal and its proximity to the event horizon, researchers were able to calculate the spin of the black hole—roughly 50 percent of the speed of light, which would be around 93,000 miles per second.

"That's not super fast—there are other black holes with spins estimated to be near 99 percent the speed of light," Dheeraj Pasham, first author of the study, said in a statement. "But this is the first time we're able to use tidal disruption flares to constrain the spins of supermassive black holes."

event horizon black hole
Artist impression of a star being destroyed at the event horizon of a black hole. NASA/CXC/M. Weiss

Pasham added that the supermassive black hole from their paper is exciting "because we think it's a poster child for tidal disruption flares." The event, he said, appears to match theoretical predictions. The team now hopes to find more stable signals from TDEs to estimate the properties of other black holes. "Estimating spins of several black holes from the beginning of time to now would be valuable in terms of estimating whether there is a relationship between the spin and the age of black holes," Pasham said.

The European Space Agency's Norbert Schartel, another author on the paper, added: "We're only just beginning to understand the complex physics at play here. By finding instances where the mass from a shredded star glows especially brightly we can build a census of the black holes in the universe and probe how matter behaves in some of the most extreme areas and conditions in the cosmos."