The Hubble Telescope captured a mysterious intergalactic explosion that astronomers can’t explain

Bright, fast blue optical transients (LFBOTs) are among the brightest visible light events known in the universe – lighting up suddenly like a camera flash. Only a few have been discovered since the first discovery in 2018. Currently, LFBOTS are detected about once a year. Following its initial discovery, the latest LFBOT was observed with multiple telescopes across the electromagnetic spectrum, from X-rays to radio waves. Only Hubble’s extremely precise resolution can determine its exact location. Designated AT2023fhn and nicknamed “The Sparrow,” this fleeting event demonstrates all the hallmarks of LFBOT. It glows strongly under blue light and grows rapidly, reaching peak brightness and fading within days, unlike supernovae which take weeks or months to fade. But unlike any other LFBOT observed before, Hubble discovered that Finch is located in a distinctly isolated position between two neighboring galaxies – about 50,000 light-years from a nearby spiral galaxy and about 15,000 light-years from a nearby spiral galaxy. celestial bodies. it was previously thought to exist in host galaxies.

“The Hubble observations were really the crucial thing. They made us realize that this was unusual compared to the other ones like that, because without the Hubble data we would not have known,” said Ashley Chrimes, lead author of the Hubble paper reporting the discovery in an upcoming issue of the Monthly Notices of the Royal Astronomical Society (MNRAS). He is also a European Space Agency Research Fellow, formerly of Radboud University, Nijmegen in the Netherlands. While these awesome explosions have been assumed to be a rare type of supernova (called core-collapse supernovae), the gargantuan stars that turn into supernovae are short-lived by stellar standards. Therefore, the massive progenitor stars to supernovae don’t have time to travel very far from their birthing place – a cluster of newborn stars. All previous LFBOTs have been found in the spiral arms of galaxies where star birth is ongoing. “The more we learn about LFBOTs, the more they surprise us,” said Chrimes. “We’ve now shown that LFBOTs can occur a long way from the center of the nearest galaxy, and the location of the Finch is not what we expect for any kind of supernova.”

The Zwicky Transient Facility – an extremely wide-angle ground-based camera that scans the entire northern sky every two days – first alerted astronomers to the Finch on 10 April 2023. Once it was spotted, the researchers triggered a pre-planned program of observations that had been on standby, ready to quickly turn their attention to any potential LFBOT candidates that arose. Spectroscopic measurements made with the Gemini South telescope in Chile found that the Finch is a scorching 20,000 degrees Celsius. Gemini also helped determine its distance from Earth so its luminosity could be calculated. Together with data from other observatories including the Chandra X-ray Observatory and the Very Large Array radio telescope, these findings confirmed the explosion was indeed an LFBOT. The LFBOTs could be the result of stars being torn apart by an intermediate-mass black hole (between 100 to 1,000 solar masses). The NASA/ESA/CSA James Webb Space Telescope’s high resolution and infrared sensitivity might eventually be used to find that the Finch exploded inside a globular star cluster in the outer halo of one of the two neighboring galaxies. A globular star cluster is the most likely place an intermediate-mass black hole could be found.

To explain Finch’s unusual position, researchers are considering the alternative possibility that it was the result of the collision of two neutron stars, moving away from their host galaxy, which had already approached each other for centuries and billions of years. Such collisions create kilonovas – explosions 1,000 times more powerful than a standard nova. However, a highly speculative theory is that if one of the neutron stars was strongly magnetized – a magnetar – it could greatly amplify the power of the explosion, up to 100 times the luminosity of the supernova. normal semen. “This discovery raises more questions than it answers,” Chrimes said. “Further research is needed to determine which of the many possible explanations is correct.” Because astronomical transits can appear anywhere at any time and are relatively fleeting in astronomical terms, researchers rely on large-scale surveys that can continuously monitor monitor large areas of the sky to detect them and alert other observatories like Hubble to follow. observe. The researchers believe that a larger sample is needed to converge to better understand this phenomenon. Future sky survey telescopes may be able to detect more, depending on the underlying astrophysics.