Tour: NASA Telescopes Work Out Black Hole's Snack Schedule

Astronomers have correctly forecast when a giant black hole finished its last meal — and predicted when its next snack will occur.

By using new data from NASA’s Chandra X-ray Observatory and Neil Gehrels Swift Observatory as well as ESA’s XMM-Newton, a team of researchers have made important headway in understanding how — and when — this supermassive black hole consumes material.

This result is based on studies of a supermassive black hole — with about 50 million times more mass than the sun — in the center of a galaxy located about 860 million light-years from Earth.

In 2018, the optical ground-based survey ASAS-SN noticed this system had become much brighter. After observing it with NASA’s NICER and Chandra, and XMM-Newton, researchers determined that the surge in brightness came from a “tidal disruption event,” or TDE, which signals that a star was completely torn apart and partially ingested after flying too close to a black hole. They called it AT2018fyk.

When material from the destroyed star approached close to the black hole, it got hotter and produced X-ray and ultraviolet, or UV, light. These signals then faded, agreeing with the idea that nothing was left of the star for the black hole to digest.

However, about two years later, the X-ray and UV light from the galaxy got much brighter again. This meant, according to astronomers, that the star likely survived the initial gravitational grab by the black hole and then entered a highly elliptical orbit with the black hole. During its second close approach to the black hole, more material was pulled off and produced more X-ray and UV light.

Initially the researchers thought this was a garden-variety case of a black hole totally ripping a star apart. But instead, the star appears to be living to die another day.

Based on what they had learned about the star and its orbit, a team of astronomers predicted that the black hole’s second meal would end in August 2023 and applied for Chandra observing time to check. Chandra observations on August 14, 2023, indeed showed the telltale sign of the black hole feeding coming to an end with a sudden drop in X-rays. The researchers also obtained a better estimate of how long it takes the star to complete an orbit, and predicted future mealtimes for the black hole.

They think this process will repeats each time the star returns to its point of closest approach, which is approximately every 3.5 years, until the star is completely gone.