Astronomers have uncovered the feeding schedule of a supermassive black hole, revealing that it consumes material about every three and a half years.
This discovery provides critical insights into the behaviour of these mysterious cosmic forces, deepening scientists’ understanding of the powerful formations that shape the universe.
A team of astronomers used three space telescopes to make these observations, including Nasa’s Chandra X-ray Observatory, with findings published in The Astrophysical Journal Letters on Wednesday.
The subject of this study was a supermassive black hole located at the centre of a galaxy about 860 million light-years from Earth.
With a mass of about 50 million times that of the Sun, this black hole was observed engaging in an interaction with a star that ventured too close to its immense gravitational pull.
Astronomers first noticed the black hole's activity when the galaxy it resides in experienced a significant increase in brightness in 2018.
They identified this as a tidal disruption event, which occurs when a star is torn apart by the intense gravitational forces of a black hole.
As the star was pulled apart, its material heated up, producing X-ray and ultraviolet light that was observed by the telescopes.
This emission eventually faded, suggesting that the black hole had consumed the matter.
However, astronomers were surprised when, about two years later, the X-ray and UV light from the galaxy flared up again.
This unexpected resurgence suggested that the star had been only partially consumed during its first encounter, with more material being stripped away as it neared the black hole again.
“Initially, we thought this was a garden-variety case of a black hole totally ripping a star apart,” said Thomas Wevers from the Space Telescope Science Institute in Baltimore.
“But instead, the star appears to be living to die another day.”
Going into orbit
The astronomers learnt that after the first encounter, the star moved into a highly elongated orbit around the black hole.
When it eventually approached the black hole again, the galaxy lit up with X-ray and UV light as more of the star’s material was consumed.
This discovery allowed the scientists to calculate the star's orbital period, helping them to learn that the black hole consumes material approximately every three and a half years.
The most recent event, which concluded in August last year, was timed by researchers using Chandra observations to confirm the exact moment when the black hole had finished devouring the star.
“The telltale sign of this stellar snack ending was a sudden drop in the X-rays, and that's exactly what we saw in our Chandra observations,” said Dheeraj Pasham of the Massachusetts Institute of Technology.
“In August last year, the black hole was essentially wiping its mouth and pushing back from the table.”
The team predicts that the black hole's next encounter with the star will begin between May and August 2025, although it is expected to be smaller, as the star has mostly already been ripped to shreds.
The fate of the star probably began when it was part of a binary system, orbiting closely with a companion star. As the pair approached the black hole, the intense gravitational forces tore them apart, sending one star hurtling into space while the other was captured in a death spiral around the black hole.
