About two billion years ago, a star died in deep space. However, this did not happen stealthily, quietly and silently, but – as is usual with very massive stars – in a hugely energetic, glittering bright explosion. The optical birth cry of a new black hole. After traveling through space for 1.9 billion years, the light from this explosion has now reached Earth and was captured by a number of telescopes on October 9. The signal, coming from the direction of the constellation Arrow, was one of the brightest and most intense gamma-ray bursts detected to date. A “beautiful flash,” as German astrophysicist Jochen Greiner of the Max Planck Institute for Extraterrestrial Physics in Garching puts it.
Within a second, gamma-ray bursts release as much energy as our sun in its entire existence, which lasted about ten billion years. The radiation from this stellar explosion has a much shorter wavelength than visible light – accordingly, an emitted photon has significantly more energy than an ordinary particle of light. In the case of the gamma-ray burst now cataloged as GRB 221009A, or GRB for short, we are talking in some cases of energies exceeding 100 million electron volts. According to a preliminary analysis, the Fermi Gamma-ray Space Telescope was able to observe the burst for a total of more than ten hours – and the event still has a faint afterglow.
While initial analyzes are still underway, astronomers are already stunned by some of the observations. This is reported by the popular scientific magazine »Physics World«. Images from Neil Gehrel’s Swift Observatory, a NASA research satellite, show prominent glowing rings around the location of GRB 221009A. These features aren’t part of the explosion, but “light echoes” produced when the event’s X-rays are scattered toward Earth by microscopic grains floating in dust clouds in our own galaxy. “This is by far the best set of rings seen around a gamma-ray burst, in part because of its X-ray brightness and proximity to the Galactic plane,” Leicester astronomer Andrew Beardmore, who works at the Swift Mission Works, is quoted as saying. . Andrea Tiengo, a physicist at Scuola Universitaria Superiore IUSS di Pavia in Italy, even thinks this could become “the best-studied gamma-ray burst in history.”
The deep-space flashes were discovered more or less accidentally during the Cold War in the 1960s, when satellites were sent to search Earth for gamma rays — evidence of an atomic bomb explosion. “The sheer brightness of gamma-ray bursts presents astronomers with a special opportunity, as their radiation illuminates nearly half of the universe in space and time,” says Jochen Greiner.
Greiner spent several years working as a senior scientist on the burst monitor of the Fermi Gamma-ray Space Telescope. In his assessment of the current gamma-ray burst and its importance for research into the phenomenon, however, he sounds a little less exuberant than his Italian colleague. “Due to the proximity of the event and the star’s apparent mass, this outburst was certainly one of the more intense flashes, but it wasn’t super spectacular either,” he says in an interview. The data from the flash itself, he says, is unfortunately unusable for evaluation and research, as the detectors were completely oversaturated due to the enormous radiation intensity. “It’s like an overexposed photo — you can’t see anything on it either.”