My entire professional life, I’ve heard people saying we live in a Golden Age for astronomy. From the development of the digital camera to the repair of Hubble, down through the launch of NASA’s great observatories, and on toward the construction on the ground of so many great big telescopes and telescope arrays, we have had three decades of rapid evolution in our understanding of the sky that was brought about by advances in technology. When satellite companies aren’t bickering over bandwidth, we can celebrate everything we have learned.

But it is sometimes more interesting to celebrate the things we discovered by haven’t yet figured out. Since the 1990s, astronomers have been able to capture the transitory optical light that shines from the locations of gamma-ray bursts (GRBs). These literally shining moments have let us figure out that multiple kinds of objects create gamma-ray bursts that last for variable amounts of time. The longer ones, which can last for hundreds of seconds, seem to be associated with supernovae explosions, but exactly why some but not all supernovae have gamma-ray bursts is a curious matter.

Observationally we know these systems beam an inconstant beam of gamma rays toward us, and otherwise don’t look exceedingly different from other supernovae. One school of thought has GRBs coming from systems with a single massive star that is collapsing downward. The problem with this theory is it predicts fewer gamma-ray bursts than we see. It also doesn’t explain the changes in gamma-ray brightness during the event.

But what we can explain and figure out on paper or in simple models is often missing major details, and in the most sophisticated model today, a team led by Ore Gottlieb simulated a dying star collapsing into a black hole and discovered those missing details explain both the scarcity of GRBs and their wandering brightness. As Gottlieb explains it: These jets are the most powerful events in the universe. Previous studies have tried to understand how they work, but those studies were limited by computational power and had to include many assumptions. We were able to model the entire evolution of the jet from the very beginning—from its birth by a black hole—without assuming anything about the jet’s structure. We followed the jet from the black hole all the way to the emission site and found processes that have been overlooked in previous studies.

In their supercomputer requiring simulation, they could see that as a star collapses, material forms a disk that drives jet formation, but that disk is getting hit asymmetrically by infalling materials, and that force can tip and tilt the disk, sending the gamma-ray beam in and out of our view. This wobble also means that we can see gamma-ray bursts from more angles than if they just sat there sputtering, so a smaller number of objects are needed to explain all the GRBs we see.

I’m sure this isn’t the final word on how GRBs form, but it is one of the best theories we have at the moment. And it may be that there is more than one cause. As new ideas and new observations come in, we’ll bring them to you here on the Daily Space.

More Information

Northwestern press release

“Black Hole to Photosphere: 3D GRMHD Simulations of Collapsars Reveal Wobbling and Hybrid Composition Jets,” Ore Gottlieb et al., 2022 June 29, The Astrophysical Journal Letters