Over the past five years, astronomers have been discovering strange stellar explosions that are different from previous star explosions. These rare events are known as Bright Fast Blue Light Transient (LFBOT), and you may remember the first event known as "The Cow" (AT2018cow). The Hubble telescope recently observed a distinctly anomalous phenomenon that occurred in places we thought it shouldn't have been.
LFBOTS are one of the brightest visible events in the universe, but they are very rare, with an average of only one found per year since 2018. They are similar to supernova bursts or gamma-ray bursts, becoming unusually bright but disappearing within a few days, unlike supernovae, which take weeks or even months.
The best explanation for these events is thought to be the special type of supernova from an extremely massive star. These LFBOTs occur on the spiral arms of star-forming galaxies, which is where extremely massive stars spend their extremely short lifetimes. So astronomers can imagine their surprise when they tracked down an LFBOT event and found it happening in intergalactic space.
AT2023fhn, nicknamed "The Canary", has all the characteristics of the few LFBOTs that have been discovered so far, except that it is incredibly located in the space between two galaxies. It is about 50,000 light-years away from large spiral galaxies and about 15,000 light-years from small galaxies.
"The more we know about LFBOTs, the more they surprise us. ESA researcher and lead author Ashley Chrimes said in a statement. "We have now shown that LFBOT can occur at great distances from the center of the nearest galaxy, and that the position of the canary does not meet the expectations of any kind of supernovae. ”
With a height of 20,000 °C (36,000 °F), the Canary is definitely an LFBOT, as confirmed by data from the Southern Hemisphere Observatory Telescope, the Chandra X-ray Observatory and the Very Large Array Radio Telescope.
A massive star capable of producing such a powerful explosion will only survive for millions of years, just like the one that caused the flattest explosion known. It couldn't have gone far away from the galaxy before dying.
If the supernova seems unlikely, the team suggested the possibility of a different LFBOT path. Perhaps we are witnessing an intermediate-mass black hole (between 100 and 100,000 times the mass of the Sun) tearing apart a star. These black holes may exist in star clusters orbiting galaxies.
Another possibility is the merger of neutron stars. It could take billions of years for a pair of neutron stars to spiral close to each other, enough time to be kicked out of their galaxy, perhaps in the original supernova explosion that formed them.
However, "this discovery raises far more questions than answers." Chrimes admitted. "We need more work to figure out which of the many possible explanations is correct. ”
The study has been accepted for publication in the Monthly Bulletin of the Royal Astronomical Society and is available for reading on ArXiv.