Astronomers think the GRB 221009A gamma-ray burst represents the birth of a new black hole formed at the heart of a collapsing star. Credit: NASA/Swift/Cruz deWilde
On the morning of October 9, multiple space detectors picked up a powerful gamma-ray burst (GRB) passing through our solar system, causing astronomers around the world to scramble to train their telescopes on that part of the sky to collect vital data about the event and the aftermath of it. Called GRB 221009A, astronomers say the gamma-ray burst is the most powerful yet recorded and could likely be the “birth cry” of a new black hole. The event was promptly published in the Astronomer’s Telegram and the sightings are still ongoing.
“In our research group, we have referred to this burst as the ‘BOOT’ or Brightest Of All Time, because if you look at the thousands of bursts that gamma-ray telescopes have detected since the 1990s, it stands apart,” said Jillian Rastinejad, a graduate student. at Northwestern University Rastinejad led one of two independent teams that used the Gemini South telescope in Chile to study the aftermath of the event.
“This burst is much closer than typical GRBs, which is exciting because it allows us to detect a lot of details that would otherwise be too faint to see,” said Roberta Pillera, a graduate student at the Polytechnic University of Bari, Italy. and member of the Fermi Large Area Telescope (LAT) collaboration. “But it’s also one of the most energetic and luminous eruptions ever seen, regardless of distance, making it doubly exciting.”
Gamma-ray bursts are extremely high-energy explosions in distant galaxies that last only a few milliseconds to several hours. The first gamma-ray bursts were observed in the late 1960s, thanks to the US launch of the Vela satellites. They were intended to detect telltale gamma-ray signatures from nuclear weapons tests in the wake of the 1963 Nuclear Test Ban Treaty with the Soviet Union. The US feared that the Soviets were conducting secret nuclear tests, in violation of the treaty. In July 1967, two of those satellites picked up a flash of gamma rays that was clearly not the hallmark of a nuclear weapons test.
NASA/Swift/A. Beardmore (University of Leicester)
That data was saved, but later Vela satellites with improved instruments registered a number of gamma-ray bursts. A team at Los Alamos National Laboratory analyzed when each burst was detected by different satellites to estimate the aerial position of 16 such bursts. And they determined that the eruptions were not from Earth or our solar system, publishing their conclusions in a 1973 article in the Astrophysical Journal.
There are two classes of gamma-ray bursts. Most (70 percent) are long bursts of more than two seconds, often with a bright glow. These are usually associated with galaxies with rapid star formation. Astronomers think long bursts are linked to the death of massive stars collapsing to form a neutron star or a black hole (or, alternatively, a newly formed magnetar). The baby black hole would produce beams of highly energetic particles traveling nearly at the speed of light, powerful enough to penetrate the remnants of the precursor star and emit X-rays and gamma rays.
Those gamma-ray bursts that last less than two seconds (about 30 percent) are considered short bursts, usually emitted from regions of very little star formation. Astronomers think these gamma-ray bursts are the result of mergers between two neutron stars, or a neutron star merging with a black hole, which includes a “kilonova.”
That hypothesis was confirmed in 2017, when the LIGO collaboration picked up the gravitational wave signal from two neutron stars merging, accompanied by the powerful gamma-ray bursts that accompany a kilonova. Earlier this year, astrophysicists spotted mysterious X-rays that they believed could be the first-ever detection of a kilonova afterglow from that same merger. (Alternatively, it could be the first observation of matter falling into the black hole that formed after the merger.)
