A cow, a camel and a Finch exploded in space. What is going on?

What do a cow, a koala, a camel, a Tasmanian devil and now a finch all have in common?

It’s not the plot of a new movie in the “Madagascar” series. They are nicknames given to a weird class of space explosions scientists can’t explain.

“We’ve been naming these things after animals just for fun,” said Daniel Perley, an astronomer at Liverpool John Moores University in England.

The latest, the Finch, was first spotted April 10 using the Palomar Observatory in California. After a few weeks, Perley and his colleagues confirmed that the event matched its companions. A new animal had been found outside of a galaxy for the first time, making it the most intriguing detection yet.

So, what are these things? They are more technically called luminous fast blue optical transients, or LFBOTs. These space explosions are much brighter than supernovas (which occur when stars explode), hence the “luminous” designation. They brighten quickly — hence “fast” — and are extremely hot, reaching 70,000 degrees Fahrenheit, and thus emitting “blue” light.

“Typically supernovae brighten and fade over weeks to months,” said Deanne Coppejans, an astronomer at Warwick University in England. “These LFBOTs brighten in just three to four days and fade on much faster time scales.”

The first to be found, in 2018, was the Cow, its name deriving from the sequence of letters and numbers it was automatically assigned — AT2018cow. Among the half dozen since discovered are ZTF18abvkwla (the Koala) and AT2022tsd (the Tasmanian devil).

AT2023fhn (the Finch) is the latest, given its name in a paper led by Ashley Chrimes, an astrophysicist from Radboud University in the Netherlands — although Perley and colleagues had been referring to it as “the Fawn” and may continue to do so. “We’re a little bit annoyed that they decided it was up to them to name the object,” he said.

Chrimes’ paper, submitted to The Monthly Notices of the Royal Astronomical Society for peer review, highlights the most unusual feature of the Finch, namely that it was found outside any galaxy, seemingly exploding in intergalactic space near two potential host galaxies about 3 billion light-years from our own.

“It’s about three to four times outside the radius of the galaxies,” Chrimes said. “At that distance you don’t expect to have many, or any, stars.”

That could help astronomers clarify what an LFBOT is. At the moment, there are a few leading ideas. The most promising one is that it is a giant star, about 20 times the mass of our sun, that has undergone a failed supernova as a black hole forms at its core. If the star is massive enough, it might collapse into the black hole, rather than exploding back out as a supernova. That produces powerful jets that shoot outward and are detected as LFBOTs.

“That’s the model I’ve tended to favor over the past few years,” Perley said, “but I wouldn’t say I’m willing to definitively say that’s the one.”

The Finch could pose problems for that model. “It’s so far outside of the two nearby galaxies,” Chrimes said. “A massive star shouldn’t have been able to get there,” unless there is an unseen cluster of stars in its vicinity.

Another possibility is that LFBOTs are tidal disruption events, where a black hole is eating material from a companion star, shining brightly in the process. “But that also has a bit of a problem, because you don’t expect to have massive black holes outside galaxies,” Chrimes said.