The starry sky continues to gradually deliver the secrets of its poetry. This Friday, astronomers announced the discovery of the “biggest” cosmic explosion ever recorded. It is a ball of energy one hundred times the size of our solar system that suddenly ignited three years ago. Scientists have a new explanation to explain the cause of the phenomenon, but they insist on the imperative of continuing research to clarify the matter.
The event, cataloged AT2021lwx, is not the brightest on record. That distinction goes to gamma-ray burst (a colossal burst of energy in a star’s collapse) GRB221009A, detected in October 2022 and thought to be “the brightest of all time.” But the explosion described in Britain’s Royal Astronomical Society’s Monthly Notices can be described as the “biggest” because it released infinitely more energy than the gamma-ray burst in three years, according to the lead author of the report. study, Philip Wiseman, an astrophysicist at Britain’s University of Southampton.
An “accidental discovery” difficult to understand
AT2021lwx is the result of an “accidental discovery”, he says. The explosion had certainly been detected in 2020, automatically, by the American observatory Zwicky Transient Facility in California. But this detection “remained unused in the database” of the observatory, according to Philip Wiseman. Before scientists noticed it the following year.
A direct observation of the phenomenon changed the game. Analysis of the light has established that it took eight billion years to reach the telescope. Astronomers are still wondering about the cause of the phenomenon. It could be a supernova, the explosion of a massive star at the end of its life, but the luminosity here is ten times greater than expected. Another possibility is a tidal rupture event, in which a star is torn apart by the attractive forces of a black hole it has come too close to.
“As if out of nowhere”
But again, AT2021lwx is three times too bright to validate such a scenario. The brightness measured has no known equivalent except with that of quasars, these galaxies harboring in their heart a supermassive black hole which gorges itself with matter by emitting a phenomenal quantity of light. But the light from the quasars is scintillating, whereas in this case, it suddenly increased three years ago.
“We have never observed such a thing (…). It seemed to come out of nowhere,” notes the scientist. His team has an idea, set out in the study. His theory is that a gigantic cloud of gas, the size of 5,000 suns, is being devoured by a supermassive black hole.
A “real enigma”
Since the principle of science is that “there are never certainties”, the team is working on new simulations – using the data – to test the “indisputable plausibility” of their theory. The problem is that supermassive black holes are supposed to be at the center of galaxies. And that of the event AT2021lwx should have a size equivalent to our Milky Way.
However, no one has yet detected a galaxy in the vicinity of the observed event. “It’s a real puzzle,” says Philip Wiseman. It remains to search the skies, and in the databases of celestial observations, similar events likely to help lift the veil on the explosion.