On the morning of October 9, astronomers’ inboxes pinged with a relatively modest alert: NASA’s Swift Observatory had just detected a fresh burst of energy, assumed to be coming from somewhere within our own galaxy. But six hours later—when scientists realized an instrument on the Fermi Space Telescope had also flagged the event—another more pressing email arrived. “We believe that this source is now likely a gamma-ray burst,” it read. “This would suggest a highly energetic outburst, and therefore we strongly encourage follow-up.” In other words, this was a career-making chance to catch a rare celestial event in real time.
Astronomers around the world sprang into action. They were eager to point their telescopes at this powerful, jetted explosion of the most energetic photons in our universe. “And by jetted, I mean like a firehose of emission,” says Wen-fai Fong, an astrophysicist at Northwestern University. Blasts like this are thought to be caused by the supernovae of giant stars, destructive collapses that give birth to black holes. The burst, dubbed GRB 221009A, went off about 2 billion light years away in the Sagitta constellation—one of the closest and most energetic ever observed—and it’s likely that one of the jets was fortuitously pointed directly at Earth. Together, these factors made for a flash at least 10 times brighter than all the others spotted in the three decades since such bursts were discovered, leading some astronomers to dub it the “BOAT”—brightest of all time.
“I kept thinking, is this real? Because if it is, it’s an extremely rare, once-in-a-lifetime type of event,” Fong says. She and others are in the thick of collecting data that they hope will confirm that the rays actually came from a supernova, and help them isolate which stellar properties led to such an energetic explosion and how much of the collapsing material got spat out by the infant black hole. (Theoretical musings have already started appearing on the arXiv preprint server.)
While detecting supernovae is now fairly common, it’s rarer to catch one in conjunction with a gamma-ray burst—they’re usually too faint to show up because they are so far away, and only a fraction of supernovae actually generate these explosions. But since this burst was so intense, scientists expect to see the supernova very clearly. “It’s really reinvigorated the community,” Fong says. “Everyone who has a telescope, even if they don’t normally study gamma-ray bursts, is trying to point their detectors at this to get the most complete dataset that we can.”
Gamma rays from the blast were recorded for several hundred seconds. Next came a slew of lower energy photons, including x-rays, optical and infrared light, and radio waves. It’s this afterglow that astronomers at ground-based telescopes are hungry to capture, because observing how the influx of photons changes over time will help them characterize the types of stars producing such bursts, the mechanisms driving these explosions, and the resulting environments they produce. These insights could shed light on what influence gamma-ray bursts have on future generations of stars, and determine whether stellar deaths make life possible for us on Earth by producing the heavy elements that can heat a planet’s interior and help sustain its magnetic field.
Because the emission spans nearly all wavelengths of light, many different instruments can observe it, which has turned the gamma-ray burst postmortem into a global scientific event. Orbiting satellites like NASA’s NuSTAR are measuring its high energy x-rays, while sites like the Australia Telescope Compact Array are collecting the burst’s radio emission. “If we don’t get data one night, we can pretty much guarantee that someone will,” says Jillian Rastinejad, a Northwestern graduate student working with Fong. Together, they’re spearheading observations of visible light from the burst using the Gemini South telescope in Chile, data that will be supplemented by measurements from the Lowell Discovery Telescope in Arizona, South Korea’s Bohyunsun Optical Astronomy Observatory, and India’s Devasthal Fast Optical Telescope. Even the James Webb Space Telescope got in on the action, as scientists reported the afterglow observed in infrared last Friday.
