Astrophysics: A new kind of cosmic explosion?
One of the brightest explosions ever observed has scientists puzzled. The explosion shone brighter than a supernova, but took place in a galaxy in which it should not occur.
AT2022aedm was a huge event: the flash in a galaxy two billion light years away shone hundreds of billions of times brighter than our sun. But the observing scientists led by Matt Nicholl from Queens University in Belfast do not yet know what triggered the huge cosmic explosion, as they write in the "Astrophysical Journal Letters". This is because the duration and location of the explosion do not actually match a supernova, which is a prime candidate for such luminous phenomena.
"We've been searching for the most powerful cosmic explosions for over a decade, and this is one of the brightest we've ever seen," says Nicholl: "Normally, a very bright supernova fades to about half its peak within a month. In the same period of time, AT2022aedm faded to less than one per cent of its peak brightness. It has practically disappeared!"
The team first noticed the explosion with the help of the ATLAS network of automated telescopes in Hawaii, Chile and South Africa. They scan the entire visible sky every night to look for objects that move or change in brightness. A few days after the first appearance of AT2022aedm, the working group received further data via the New Technology Telescope in Chile. And this - together with other observations around the Earth - suggested that, contrary to all expectations, a supernova was not the trigger.
A comparison of historical data revealed only two other cosmic events with similar properties in 2009 and 2020, and the extensive dataset obtained for AT2022aedm shows that it must be a new type of cosmic event. "We have named this new class of luminous sources 'Luminous Fast Coolers' or LFCs. This is partly to do with how bright they are and how quickly they fade and cool down. At the same time, some of the researchers are big fans of Liverpool FC. It's a nice coincidence that our LFCs seem to prefer red galaxies!" (Editor's note: Liverpool FC is also called the "Reds" because of the colour of their home shirts.)
The most likely cause of the event is thought by Nicholl and co. to be that a small black hole collided with a star. In the case of an extremely massive black hole, the signal would have been different again. The search for LFCs is therefore to be intensified in order to prove or disprove this hypothesis. The scientists want to focus on dense clusters of stars, where such collisions are more likely.
Spectrum of Science
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Cover image: ASA, ESA, CSA, M. Matsura (Cardiff University), R. Arendt (NASA's Goddard Spaceflight Center & University of Maryland, Baltimore County), C. Fransson (Stockholm University), and J. Larsson (KTH Royal Institute of Technology). Image Processing: A. Pagan
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