Extract from ABC News
Some 500 million light-years from Earth, a star similar to our Sun is having a terrible, horrible, no good, very bad time.
Key points:
- NASA's Swift observatory has spotted a black hole snacking on a Sun-like star
- The star's unusual orbit sees it stripped of gas every time it gets close to the black hole
- It provides a new system to model interactions between black holes and stars
Its orbit takes it perilously close to a supermassive black hole with an insatiable hunger.
Every time it zooms around the black hole, its gaseous body gets nibbled away by the extreme gravitational force, producing a flash of X-rays.
The discovery, published in Nature Astronomy, was made on June 22, 2022, using NASA's space-based Swift Observatory.
It was named "Swift J0230", but we're dubbing it the "Snack Hole".
Using the telescope, researchers picked up a flash of X-ray light over a period of several months from the direction of the supermassive black hole.
This, they suggest, is likely due to "a repeating, partial tidal disruption event". So, what does that mean?
Snack attack
When a star strays too close to a black hole, extreme gravitational forces start cause it to stretch and bulge.
Typically, this is a death blow for the star and is known as a tidal disruption event. The star gets ripped apart and its gases spill out into the cosmos and stream around the black hole.
As those gases collide with material already circling the black hole, they produce flashes of X-rays.
"We try to find these events because they allow us to, essentially, probe black holes," said Katie Auchettl, an astrophysicist at the University of Melbourne who was not involved in the study.
But a repeating, partial tidal disruption event is a little different.
If the star is in just the right orbit around the black hole, it might be able to escape the death pull and zip back off into space … only to find itself, on the next orbit, being eaten again.
On each pass, the star loses some material, producing flashes of light.
These events have been spotted before with huge black holes and giant stars. They've also occurred with the remnants of stars, known as white dwarfs.
For instance, in 2019, researchers thought they spotted a repeating tidal disruption event between a white dwarf and a black hole about 400,000 times the mass of our Sun. In that instance, the flashes of X-ray light were seen every 9 hours.
The same thing is happening with the new Snack Hole, but on a longer time frame. It doesn't take just one big bite of a star — it pecks away at it, gradually stripping it of its gas.
In total, nine outbursts of X-ray light associated with the feast were recorded around every 25 days. Each outburst lasted between 10 and 15 days.
It's an intriguing find because it provides a new system to study interactions between black holes and stars, Dr Auchettl said.
"It provides a new mechanism of understanding black holes in our nearby galaxies."
Stellar find
Astronomers were able to catch the black hole snack-attack in the act thanks to a recent advance, the Living Swift-XRT Point Source (LSXPS) catalogue.
X-ray data obtained by Swift is often out of date. The time it takes to process and compile the telescope's data means astronomers might miss signals that repeat on timescales less than a year.
If they do notice them, they can't track them in real time.
Essentially, LXSPS grabs recent Swift images of the sky and then quickly compares them with previous snapshots. If something has changed between images, it pings astronomers who can schedule follow-up observations immediately.
Just two months after LXSPS switched on, the Snack Hole was spotted. Without the advance, Dr Auchettl said, we may have even missed this Snack Hole altogether.
"It bodes well for the detector's ability to identify other transient events and for Swift's future exploring new spaces of science," noted S. Bradley Cenko, Swift's principal investigator at NASA's Goddard Space Flight Center in a statement.
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