The explosion, which has been named AT2022aedm, was seen emerging from a red galaxy located around 2 billion light-years from Earth by astronomers using the ATLAS network of robotic telescopes located in Hawaii, Chile, and South Africa. It was quickly recognized as something never seen before.
“We’re always on the lookout for things that are a bit weird and different from standard kinds of supernovas, of which we find hundreds or even thousands per year,” Matt Nicholl, leader of the team behind the discovery and an astrophysicist at Queen’s University Belfast, told Space.com. “AT2022aedm stood out because it was one of the brightest explosions that we’ve ever seen, and it was also one of the fastest to fade away after its peak.”
The explosion spotted by Nicholl and the team emitted as much as 100 times more energy than an average supernova. Plus, while supernovas fade over the course of months, Nicholl noted that AT2022aedm faded to 1% of its original brightness in just 14 days, after which it completely disappeared. That means, in just two weeks, AT2022aedm emitted as much energy as the sun will in its entire 10 billion-year lifetime.
One of the first steps for Nicholl and the Queen’s University Belfast scientists to take was to eliminate some of the usual culprits for cosmic cataclysms.
The explosion already didn’t present like a supernova, as it was too powerful and too fast, but the location at which it originated also helped distinguish this LFC as something entirely new.
One of the most common types of supernova is a core-collapse supernova formed when huge stars with masses over 8 times that of the sun run out of fuel for nuclear fusion. The stars’ cores become unable to battle gravity any longer and ultimately collapse. This leaves behind a black hole or a neutron star at the heart of stellar wreckage from the outer layers of the star.
“AT2022aedm can’t be a normal core-collapse supernova because the galaxy it is seen in only has old low-mass stars; it doesn’t have anything more than eight times the mass of the sun, and that’s what you need to have to get to get a supernova,” Nicholl explained. Alternatively, another common space blast, a Type-Ia supernova, happens when stellar remnants called white dwarfs strip matter from a companion star.
This stripping of matter tips the white dwarf over the mass limit needed to trigger a supernova and create a neutron star or black hole, but these events create a uniform output of radiation. For this reason, astronomers call them “standard candles” and use them to accurately measure cosmic distances.
Supermassive black holes get cleared
Events that see black holes rip up stars and then feast on the stellar remains are rare, but not unknown. Astronomers have spotted many examples of these so-called “Tidal Disruption Events” or “TDEs” as well as the light emitted during the violent proceedings.
TDEs usually occur when a star ventures too close to a huge supermassive black hole sitting at the heart of a galaxy. This black hole can have masses millions, or even billions, of times that of our sun. The gravitational influences of these monster black holes generate huge tidal forces in their star subjects that stretch and squeeze the stellar bodies, ripping them apart in a process called “spaghettification.”
Yet, Nicholl and his colleagues immediately saw that this LFC couldn’t be the result of just any TDA driven by a supermassive black hole. Again, this is due partially to where the LFC appeared to originate from. Supermassive black holes sit at the heart of galaxies, and Nicholl said AT2022aedm was seen away from the center of its home galaxy. This means a smaller black hole (not at the heart of a galaxy) could be the culprit for this LFC.