A strange cosmic explosion was followed by repeated energetic flares, observed for several months. This phenomenon has never been observed before
The flares were brief, lasting just a few minutes, and a hundred days later they were as strong as during the original explosion. They appeared after a rare type of stellar cataclysm, known as a fast luminous blue optical transient (LFBOT) event. The explosion has been officially named AT2022tsd and is known as ‘the Tasmanian Devil’.
Since its discovery in 2018, there has been much speculation about the cause of these extreme explosions. These are much brighter than the supernova explosion that typically kills massive stars, but they take days rather than weeks to fade.
To study these unprecedented flares, 15 telescopes located in different parts of the world have been used.
The authors of a new study believe that the flare activity confirms that the origin must be in a stellar corpse: a black hole or a neutron star.
This team has been led by Cornell University and involves researchers from the Institute of Space Studies of Catalonia (IEEC) at the Institute of Space Sciences (ICE) of the Higher Council for Scientific Research (CSIC) in Spain.
Lluís Galbany, Claudia Gutiérrez and Tomás E. Müller-Bravo, IEEC researchers at ICE, contributed to the research as part of ePESSTO+ (extended Public ESO Spectroscopic Survey of Transient Objects). This collaboration began in 2019 and seeks to explore new populations of transient events.
Anna YQ Ho, associate professor of astronomy in the College of Arts and Sciences, is the first author of the study. She helped characterize the ‘Tasmanian devil’ and the resulting pulses of light observed approximately one billion light-years from Earth. «We do not believe that anything else could cause this type of flare. “This ends years of debate about what drives this type of explosion and reveals an unusually direct method for studying the activity of stellar corpses,” she says.
She wrote the software that alerted to the event in September 2022, while analyzing half a million changes, or transient events, detected daily through all-sky mapping carried out by the Zwicky Transient Facility telescope, based in California, USA. During routine monitoring of the fading explosion in December 2022, the team discovered that one of the images analyzed recorded light, followed by a bright spike in the central frame that quickly disappeared.
“No one really knew what to say,” Ho recalls. “We’ve never had anything like this before—something as fast and as bright as the original explosion months later—in any supernova or FBOT. “We have never seen this in astronomy, period.”
«Finding and characterizing LFBOTs is a challenge due to their nature: they are objects that evolve very quickly. We lose important information about their explosion mechanisms and physics if we wait a few days to coordinate observations. Therefore, we must activate observations when a good candidate is found,” explains Claudia Gutiérrez. «Despite all our efforts, we have detected about a dozen LFBOTs, of which only six provide any clues about this new class of events. Of them, only one, the ‘Tasmanian devil’, shows these unprecedented flares,” she adds.
To further investigate this glow, the team involved colleagues who contributed observations from more than ten telescopes, including one equipped with a high-speed camera. The team reviewed previous data and worked to rule out other possible light sources. Their analysis ultimately confirmed at least 14 irregular light pulses over a 120-day period, which is likely only a fraction of the total number, according to Ho.
Artistic recreation of an LFBOT type explosion. (Illustration: Amazings/NCYT)
Exploring stellar evolution
Exactly what processes were at work continue to be studied, perhaps a black hole channeling jets of stellar matter outward at near the speed of light. The team hopes the research will advance their long-term goals to record how the properties of stars can predict the way they will die and the type of corpse they will produce. LFBOTs can be an opportunity to observe a star as it transitions to its post-death stage.
“Given that the current sample of LFBOTs remains small, current and future high-rate studies, such as LS4, GOTO and BlackGem, will be essential to increase their number and help elucidate the progenitor scenario of these types of transient events,” he notes. Tomás E. Müller-Bravo.
«It is a good time to study the universe of transient events. Just five years ago it would have been impossible to detect such an event. Our ICE-CSIC supernova research group is making an extra effort to be part of these international collaborations and to be the first to detect, follow and study extraordinary events like AT2022tsd,” concludes Lluís Galbany.
The study is titled “Minutes-duration Optical Flares with Supernova Luminosities.” And it has been published in the academic journal Nature. (Source: IEEC / ICE / CSIC)