Hubble discovered a strange light burst in a region of space that seemed to have no trigger point, and a few years ago astronomers formally described a new type of explosion in space - luminous fast blue-light transients (LFBOTs), or FBOTs for short. The name pretty much describes what they are - very bright flashes in the optical part of the spectrum that tend to shine brightly at blue wavelengths and then fade within a few days.
Only a few examples of LFBOTs have been found in data before 2016, but astronomers have begun to compile a list of hypotheses about their origins based on their common characteristics. The leading candidate is a rare event called a core-collapse supernova, which occurs when a giant star exhausts its fuel supply and explodes under its own gravity.
But then a new LFBOT appeared that overturned everything. This event was named AT2023fhn, nicknamed "Finch", and was discovered by the Zwicky Transient Facility (ZTF) telescope on April 10, 2023. It is bright and blue and gradually darkens over a few days. Its spectrum was analyzed by the Gemini South Telescope and estimated to be as hot as 20,000°C (36,000°F).
It wasn't until Hubble observed it that the whole thing became clear. When the iconic telescope pinpointed its location in space, it became clear that common assumptions no longer applied. Previous LFBOTs were discovered in galaxies with active star formation, but Finch appears to be wandering alone in space outside the Milky Way, at least 15,000 light-years away from the nearest galaxy. Giant stars that die in core-collapse supernovae are so short-lived that they shouldn't have enough time to drift into such isolated space.
An image of the explosion known as "Finch" captured by the Hubble Telescope. The red line indicates the cause of the explosion. The nearest galaxy is more than 15,000 light-years away, and astronomers can't explain what caused it NASA, ESA, STScI, A. Chrimes (Radboud University)
"The more we learn about LFBOTs, the more they surprise us," said Ashley Chrimes, first author of the study. "We have now shown that LFBOTs can occur very far from the center of the nearest galaxy, and Finch's location is different from what we would expect for any kind of supernova."
Astronomers are considering other possible explanations, including a star torn apart by an intermediate-mass black hole, or a collision between two neutron stars. If one of the neutron stars is a highly magnetized version, a so-called magnetar, it could be up to 100 times brighter than an ordinary supernova.
"This discovery raises many more questions than it answers," Chris said. We need to do more work to find the correct explanation among the many possible explanations. "
Follow-up observations with the James Webb Space Telescope may reveal new clues, the team said. For example, the explosion could come from a globular star cluster in the outer halo of a nearby galaxy, which would provide support for the black hole hypothesis.
The research was published in the journal Monthly Notices of the Royal Astronomical Society.