“For a few minutes, it was the brightest event in heaven. “On October 9, an incredible explosion occurred 1.9 billion light-years away from us, which gave food for thought to Damien Dornic, researcher at the Marseille Particle Physics Center. And not alone.
The flash, which occurred a little before snack time in France, alerted around fifteen satellites and around fifty telescopes around the world. “In these cases, in general, it is a race once morest time. Telescopes must react within hours to point to the right place. »
“The gravitational collapse of a star’s core”
A dazzling spectacle? Not for onlookers: the powerful light captured by the devices was not in the visible range, but on certain wavelengths to which the human eye is not sensitive. “We mightn’t have seen it with the naked eye,” confirms Damien Dornic.
It’s a gamma-ray burst, a sudden burst of light from another galaxy. Such an event betrays either the death of a giant star, or the merger of two neutron stars.
In the case of GRB 221009A, analyzed in a series of articles published at the end of March in the journal The Astrophysical Journal Letters, there is “no doubt”: “With the energy detected, it is certain that it is the gravitational collapse of the heart of a massive star”, explains Damien Dornic. The birth cry of a black hole.
“The Earth must be in the line of sight of the jet”
Phenomena like this are witnessed by terrestrial observatories almost every day. But of this intensity, it is unprecedented. Scientists have reviewed previous (which have been studied for 55 years) to conclude that there would be, on average, only one event of the magnitude of GRB 221009A every 10,000 years.
What makes Eric Burns, assistant professor of physics and astronomy at the University of Louisiana (United States) write, with a touch of exaggeration perhaps, that it is “the most brilliant burst of energies x-rays and gamma rays since the beginning of human civilization!
Stars are dying every day. How is it that we have witnessed a burst of such intensity? “Not all star deaths produce gamma-ray bursts,” comments Sarah Antier, astronomer at the Côte d’Azur Observatory (OCA).
Above all, we would have been very lucky. “The star, in collapsing, is crossed by jets of particles which propagate from space. For us to be able to witness it, the Earth must be in the line of sight of the jet, a bit like a lighthouse for light. The powerful jet of photons, the particles of light, from GRB 221009A may have been very narrow, but they were placed right in front of us. The relative proximity of this agony completed making it an exceptional event.
Years of observation ahead
If following its initial peak, the burst lasted only a few minutes, it continues to produce effects for several months. “It is an event that we are still following today and that we will follow for a few more years. Many questions remain unanswered, on the origin of the event, the magnetic field, the structure of the jet… What is particularly exciting is that we have a lot of data,” says Damien Dornic.
Further studies are planned in the coming months. “It’s a series with many episodes, laughs Sarah Antier. With Hubble, astronomers will be able to observe the supernova, that is to say the explosion of the outer layers of the star. But for that, the phenomenon must (the effects of the gamma-ray burst) decreases in brightness. »
