What do a cow, a koala, a camel, a Tasmanian devil and now a goldfinch have in common?
It’s not the plot of a new movie in the “Madagascar” series. They’re nicknames given to a strange class of space explosions that scientists can’t explain.
“We named these things after animals just for fun,” said Daniel Birley, an astronomer at Liverpool John Moores University in England.
Last, finchIt was first spotted on April 10 using the Palomar Observatory in California. A few weeks later, Dr. Burley and his colleagues confirmed that the event fit his companions. A new animal has been found outside a galaxy for the first time, making it the most intriguing discovery yet.
So, what are these things? They are called more technically luminous fast blue optical transients, or LFBOTs. These space explosions are much brighter than supernovae (which occur when stars explode), hence the “luminous” name. They light up quickly – hence “fast” – and are extremely hot, reaching 70,000 degrees Fahrenheit, thus emitting a “blue” light.
“Usually supernovae rise and fade over a period of weeks to months,” said Dean Copegans, an astronomer at the University of Warwick in England. “These LFBOTs light up in just three to four days and fade on much faster time scales.”
It was the first to be found cow in 2018, its name is derived from the sequence of letters and number that was automatically assigned – AT2018cow. Among the half-dozen discovered since then are ZTF18abvkwla (the koala) and AT2022tsd (the Tasmanian devil).
AT2023fhn (Finch) is the latest, named in a paper led by Ashley Kremes, an astrophysicist from Radboud University in the Netherlands — although Dr. Bierle and colleagues have been referring to it as “Fawn” and may continue to do so. “We’re a little upset that they decided it was up to them to name the thing,” he said.
Dr. Kremes’ paper, submitted to the Monthly Notices of the Royal Astronomical Society for peer review, highlights Finch’s most unusual feature, which is that it has been found outside of any galaxy, and appears to explode in intergalactic space near two potential host galaxies about three billion light-years away from our own.
“It’s within three to four times the radius of the galaxies,” Dr. Kremes said. “At that distance, you wouldn’t expect to have many or any stars.”
This could help astronomers explain what LFBOTs are. For now, there are some groundbreaking ideas. The most promising of these is that it is a giant star, about 20 times the mass of our sun, that has undergone Failed supernova A black hole is also forming in its core. If the star is massive enough, it may collapse into the black hole, rather than exploding again as a supernova. This results in powerful jets that shoot outward and are detected as LFBOTs.
“This is the model that I have tended to favor over the past few years, but I wouldn’t say I would be prepared to say definitively that is the model,” said Dr. Burley.
Finch can pose problems for this model. “It is very far from the two neighboring galaxies,” said Dr. Kremes. “No massive star should be able to get there,” unless there is an invisible cluster of stars in its vicinity.
Another possibility is that LFBOTs are tidal disturbance events, in which a black hole eats material from a companion star, shining brightly in the process. “But this also has a small problem, because you don’t expect massive black holes to exist outside galaxies,” said Dr. Kremes.
LFBOTs can also be caused by the merger of two neutron stars, the remaining cores of dead massive stars. This process could take billions of years – which might “give them time to migrate away from their galaxies” as Finch did, Dr. Kremes said.
Anna Y-Q Ho, an astronomer at Cornell University He also studied closely The Finch (or Fawn), isn’t ready to jump to any conclusions. “It’s hard to make a statement from just one being,” she said. “You can’t really rule anything out.”
Astronomers find about one or two LFBOTs each year. But upcoming telescopes like Israeli telescopes ULTRASAT space telescope missionscheduled for release in 2026, that number could increase dramatically.
“You can find 10 or even 100 a year,” Dr. Hu said. “It will really dominate the discovery rate.”
Finding more extragalactic LFBOTs could provide hints as to their origin. And as the discoveries continue to trickle in, the astronomers intend to continue with their naming system—which, aside from being a bit fun, is useful for better curating results. “People are much better at remembering and categorizing the characteristics of events when there is a more recognizable name,” said Dr. Hu.
“There are not many of them yet,” she said. “So we never run out of animals.”
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