For the past five years, astronomers have been monitoring peculiar star explosions which do not behave like any other known stellar bursts. The rare phenomenon, called luminous fast blue optical transients (LFBOT), was recently detected on a spot where it was not expected to be found.
What Are LFBOTS?
LFBOT is an explosion event similar to supernovae and gamma-ray bursts where high optical luminosity can be observed. They are characterized by luminous X-ray and radio emission, featureless blue spectra at early times, and rapid evolution.
They are among the brightest visible events in the universe, but they are extremely rare, with only one detected per year. The first prototypical example of LFBOT was discovered in 2018 and was named AT2018cow.
So far, LFBOTs have been exclusively found at small projected offsets from star-forming host galaxies. The origins of this rare class of events are still poorly understood, although a number of potential explanations have been proposed.
Experts have identified a particular set of LFBOT characteristics that have been detected so far. These phenomena intensely shine in blue light and evolve rapidly, fading away in a few days after reaching peak brightness.
Solving the Mystery of the Finch
In a recent study, a team of researchers discovered the latest LFBOT which appeared in a location where it is not expected to be found. Scientists were puzzled to find it far between two galaxies.
Known as AT2023fh, the strange LFBOT nicknamed "the Finch" was first spotted on April 10 by the Zwicky Transient Facility, a ground-based camera which scans the northern sky every two days. Since then, it has been observed using multiple telescopes across the electromagnetic spectrum from radio waves to X-rays.
Once the Finch was spotted, researchers initiated a pre-planned program of astronomical observations that had been on standby, so they could easily turn their attention to any potential LFBOT that may arise. Spectroscopic measurements were conducted by the Gemini South telescope in Chile in collaboration with NASA's Chandra X-ray Observatory and the National Science Foundation's Very Large Array radio telescope which calculated its luminosity by determining its distance from the Earth.
Since astronomical transients are relatively fleeting, researchers need to rely on other observatories such as the Hubble Space Telescope to conduct follow-up observations. It was the Hubble which accurately pinpoints the exact location of the Finch - about 50,000 light-years from a nearby spiral galaxy and 15,000 light-years from a small galaxy.
LFBOTs are assumed to be a rare type of supernova called core-collapse supernovae. The massive progenitor stars do not have time to travel very far from their birthing site before exploding. Because of this, all previous LFBOTs have been found in the spiral arms of galaxies where star birth happens. However, the Finch is not found in any galaxy.
Experts consider the possibility that the Finch is the result of a collision of two neutron stars. These stars could be traveling far outside their host galaxy, which have been spiraling toward each other for billions of years, and ended in a clash that resulted in a powerful explosion known as kilonova.
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