In November, Ho and Perley discovered another new LFBot, this time designated AT2024wpp, but has yet to gain a nickname. “We were thinking ‘the Wasp’,” says Ho. This explosion was particularly interesting because it was the brightest LFBot observed since the Cow, and it was also discovered very early on in its brightening phase, meaning astronomers could train lots of telescopes on it – including the Hubble space telescope – in order to learn more about it. “It’s the best one since the Cow itself,” says Perley.
Early observations hint that the Wasp was not caused by a failed supernova. In that theorised scenario, a star would collapse in on itself while in the process of exploding. Inside the star’s shell, a black hole or a dense neutron star would then form, and blast out jets of radiation through the shell, creating what’s called a central engine. This would explain the brief cow flare that was visible on Earth.
But the Wasp seemed to lack any sign of material flowing away from the explosion that scientists would expect from such an event, says Perley. However, he notes that current findings are preliminary. “We’re still analysing the data,” he says.
It looked like the remnants of a star that was being eaten by an intermediate mass black hole
In September 2024, Zheng Cao at the Netherlands Institute for Space Research and colleagues re-examined the first detected LFBot, and also found evidence that challenged the failed supernova theory.
By studying X-ray observations of the event, they found what appeared to be a disk of material surrounding the explosion. After making a computer model of the disk, they found that it looked like the remnants of a star that was being eaten by an intermediate mass black hole, one about 100 to 100,000 times the mass of our Sun. Larger black holes could have a mass millions or even billions of times greater than our Sun. (Find out just how big black holes can get in this article about the largest black holes in the Universe.)
As the star was eaten, it would occasionally cause the black hole to suddenly brighten as larger chunks of the star were consumed, producing the Cow flares spotted by astronomers on Earth.
“I believe our study supports the intermediate mass black holes nature of AT2018cow and similar LFBots,” says Cao.
Another idea is that LFBots are actually a class of giant stars called Wolf-Rayet stars that are being torn apart by much smaller black holes only 10 to 100 times the mass of our Sun. Brian Metzger, a theoretical astrophysicist at Columbia University in New York, is among those who support this idea. He says these could form in a similar way to pairs of black holes – which have been detected by the gravitational waves they produce – except on this occasion only one of the stars becomes a black hole.
NasaThe intermediate mass black holes theory is perhaps the most alluring and favoured idea at the moment, though. If correct, it would mean that LFBots are a unique opportunity for us to study mysterious mid-sized black holes. While astronomers are reasonably confident that intermediate mass black holes exist in the Universe, no-one has yet found definitive proof for them.