By BlueShift and AFP | 2025-04-17

A massive black hole at the heart of a galaxy in the Virgo constellation is waking up, shooting out intense X-ray flares at regular intervals that have puzzled scientists, a study said.

Astronomers previously had little reason to pay any attention to galaxy SDSS1335+0728, which is 300 million light-years from Earth.

But in 2019, the galaxy suddenly started shining with a brightness that turned some telescopes its way.

Then in February 2024, Chilean astronomers started noticing regular bursts of X-rays coming from the galaxy.

This was a sign that the galaxy's sleeping black hole was waking from its slumber, according to the study published April 11 in the journal Nature Astronomy.

Most galaxies, including the Milky Way, have a supermassive black hole squatting at their heart, and if an unlucky star swings too close, it gets torn apart.

The star's shattered material becomes a stream that spins rapidly around the black hole, forming what is called an accretion disc that the black hole gradually swallows.

But black holes can go through long periods of inactivity when they do not attract matter.

And after a fairly uneventful period, astronomers have classified the bright, compact region at the heart of galaxy SDSS1335+0728 as an "active galactic nucleus" -- and gave it the nickname "Ansky."

"This rare event provides an opportunity for astronomers to observe a black hole's behavior in real time" using several X-ray telescopes, astronomer Lorena Hernandez-Garcia of Chile's Valparaiso University said in a statement.

'Pushes models to their limits'

Astronomers call Ansky's short-lived X-ray flares quasiperiodic eruptions, or QPEs.

"This is the first time we have observed such an event in a black hole that seems to be waking up," Hernandez-Garcia said.

"We don't yet understand what causes them."

The current theory links QPEs to the accretion discs that form after black holes swallow stars.

But there is no sign that Ansky has recently feasted on a star.

And its flares are quite unusual.

"The bursts of X-rays from Ansky are 10 times longer and 10 times more luminous than what we see from a typical QPE," said Joheen Chakraborty, a PhD student at the Massachusetts Institute of Technology and member of the research team.

"Each of these eruptions is releasing a hundred times more energy than we have seen elsewhere."

The intervals of 4.5 days between these blasts happen to be the longest ever observed, he added.

"This [finding] pushes our models to their limits and challenges our existing ideas about how these X-ray flashes are being generated," he said in the statement.

More observations needed

Astronomers have had to come up with some theories for what could be causing these strange bursts.

One theory holds that the accretion disc formed when gas was sucked into the black hole, which shoots out X-ray flares only when a small celestial object such as a star crosses its path.

"Simply imagine a black hole and disc around it," Norbert Schartel, chief scientist of the European Space Agency (ESA)'s XMM-Newton telescope, which has observed Ansky, told AFP.

Now imagine the star crossing the disc twice every time it orbits -- shooting out flares -- but at a particular angle that means "there is no real strong force to drag it in," he said.

X-ray astronomer Erwan Quintin told AFP that "for QPEs, we're still at the point where we have more models than data."

"We need more observations to understand what's happening."

The team's QPE observations were made possible with assistance from the ESA's XMM-Newton telescope; NASA's Neutron Star Interior Composition Explorer (NICER), an X-ray observatory on the International Space Station; NASA's Chandra X-ray Observatory, the world's most powerful X-ray telescope; and archival data from eROSITA, a powerful X-ray telescope on-board the Russian-German "Spectrum-Roentgen-Gamma" (SRG) mission.