In September 2022, an automated sky survey detected what seemed to be a supernova explosion about one billion light-years away. The Zwicky Transient Facility (ZTF) spotted it and gave it the name AT2022tsd. But something was different about this supernova. Supernovae explode and shine brightly for months, while AT2022tsd exploded brightly and then faded within days. <\/p>\n
<\/p>\n That\u2019s when astronomers realized it wasn\u2019t a regular supernova at all. It was a luminous fast blue optical transient (LFBOT), a relatively new class of object that was only discovered a few years earlier and remains mysterious. <\/p>\n Then something even stranger happened. AT2022tsd, given the nickname \u2018Tasmanian Devil,\u2019 brightened again and again. This was both a surprise and a puzzle, two things that always attract the attention of astronomers. <\/p>\n After its initial detection, follow-up observations in X-rays showed that the Tasmanian Devil was the brightest LFBOT ever detected. Not only that, but it rivalled the brightest gamma-ray bursts ever detected. These facts, along with the object\u2019s repeated brightening, made it one of the strangest transients ever detected. <\/p>\n A team of researchers led by Cornell Assistant Professor of Astronomy Anna Ho gathered all the data they could to determine what was behind the Tasmanian Devil\u2019s unusual behaviour. Their results are in a new paper titled \u201cMinutes-duration optical flares with supernova luminosities.\u201d The paper was published in the journal Nature. <\/p>\n \u201cThis settles years of debate about what powers this type of explosion and reveals an unusually direct method of studying the activity of stellar corpses.\u201d<\/p>\n Anna Ho, Cornell University<\/cite><\/p><\/blockquote>\n<\/figure>\n \u201cIn recent years, certain luminous extragalactic optical transients have been observed to last only a few days,\u201d the authors write in their paper. \u201cTheir short observed duration implies a different powering mechanism from the most common luminous extragalactic transients (supernovae), whose timescale is weeks.\u201d <\/p>\n \u201cHere we report observations of minutes-duration optical flares in the aftermath of an AT2018cow-like transient, AT2022tsd.\u201d<\/p>\n The Tasmanian Devil\u2019s repeated flashes were as short as a few minutes long. They were also as powerful as the initial explosion 100 days prior. These repeated flashes only deepened the mystery around LFBOTs. 15 telescopes around the world watched the flashes, and the research team combed through the observations to try to determine what type of object was behind this remarkable behaviour. <\/p>\n In December, Ho was routinely monitoring the fading initial explosion and captured five new images of the object that each spanned a few minutes. The first image showed nothing, but the middle image showed an intense brightening that quickly vanished. Then nothing again.<\/p>\n Ho shared the images with collaborators, and they were speechless. <\/p>\n \u201cWe think these flares could be coming from one of these newly formed corpses,\u201d<\/p>\n Anna Ho, Cornell University<\/cite><\/p><\/blockquote>\n<\/figure>\n \u201cNo one really knew what to say,\u201d Ho recalled. \u201cWe had never seen anything like that before \u2013 something so fast, and the brightness as strong as the original explosion months later \u2013 in any supernova or FBOT. We\u2019d never seen that, period, in astronomy.\u201d<\/p>\n The team\u2019s analysis showed 14 separate spikes in brightness over a 120-day period. According to Ho, that\u2019s likely only a fraction of the total number.<\/p>\n \u201cAmazingly, instead of fading steadily as one would expect, the source briefly brightened again \u2013 and again, and again,\u201d she said. \u201cLFBOTs are already a kind of weird, exotic event, so this was even weirder.\u201d<\/p>\n There are some events and objects out there in the cosmos that flash repeatedly, and the researchers worked to either confirm or eliminate them. The Devil wasn\u2019t a supernova, but could it have been a tidal disruption event (TDE) where a black hole feeds on material and flares brightly? Does its light and frequency match any other type of astronomical transient? <\/p>\n The team detected a single optical and multiple x-ray flares from the Tasmanian Devil. But the optical flare didn\u2019t coincide with any of the x-ray flares. Also, there was no detectable periodicity to any of the flaring. The fact that the team couldn\u2019t find any optical flaring in the research into other LFBOTs was also confounding. <\/p>\n \u201cTo our knowledge, this phenomenon\u2014minute-timescale optical flares at supernova-like luminosities, with order-of-magnitude amplitude variations, persisting for 100+ days\u2014has no precedent in the literature,\u201d the researchers write in their paper. <\/p>\n For now, AT2022tsd is still a mystery. It could be a supergiant star collapsing as a supernova and then forming an accretion ring. It could be a black hole funnelling jets of material into space. Or it could be another LFBOT, but we could be seeing it from a strange angle. If we are, that could explain the Tasmanian Devil\u2019s X-rays. <\/p>\n \u201cThe lack of detected flares in other LFBOTs could be because of the viewing angle: AT2018cow is thought to have been observed close to the plane of the circumburst \u2018disk\u2019 rather than face-on, and a more on-axis viewing angle for AT2022tsd could also help explain the substantially more luminous X-ray emission,\u201d the authors explain in their research. <\/p>\n The researchers came to a conclusion, but it\u2019s an incomplete one. <\/p>\n The Tasmanian Devil must be a dead star, either a black hole or a neutron star. \u201cWe don\u2019t think anything else can make these kinds of flares,\u201d said Anna Y.Q. Ho, assistant professor of astronomy in the College of Arts and Sciences. \u201cThis settles years of debate about what powers this type of explosion and reveals an unusually direct method of studying the activity of stellar corpses.\u201d<\/p>\n If the Tasmanian Devil is a type of dead star, it\u2019s not behaving like the others.<\/p>\n \u201cWe might be seeing a completely different channel for cosmic cataclysms,\u201d Ho said.<\/p>\n Something unprecedented may be going on with the Devil. As a dead star, the light coming from it could signal its transition into a sort of stellar afterlife. It could be a new type of stellar corpse. <\/p>\n \u201cBecause the corpse is not just sitting there, it\u2019s active and doing things that we can detect,\u201d Ho said. \u201cWe think these flares could be coming from one of these newly formed corpses, which gives us a way to study their properties when they\u2019ve just been formed.\u201d<\/p>\n\n
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