Astrophysics research improves understanding of how gamma-ray bursts produce light

Gamma-ray bursts (GRBs) are intense bursts of gamma radiation that typically produce more energy in a few seconds than the Sun produces in its 10 billion-year lifetime. These transient phenomena are one of the most challenging puzzles in astrophysics, dating back to their accidental discovery in 1967 by a nuclear surveillance satellite.

Dr. Jon Hakkila, a researcher at the University of Alabama in Huntsville (UAH), part of the University of Alabama System, is the lead author of a paper The Astrophysical Journal By focusing on the motion of the jets from which these forces originate, it is possible to shed light on the behavior of these mysterious cosmic powerhouses. The paper was co-authored by UAH alumni Timothy Giblin, Ph.D., Robert Preece, Ph.D., and Geoffrey Pendleton, Ph.D., of deciBel Research, Inc.

“Despite more than fifty years of research, the mechanism by which gamma-ray bursts produce light remains unknown and is one of the great mysteries of modern astrophysics,” explains Hakira. “Understanding gamma-ray bursts can help us understand the mechanisms used by nature. Some of the fastest and most powerful light-emitting mechanisms are so bright that they can be seen throughout the universe, and – because light travels at a finite speed – they allow us to travel back to the earliest days of stars. .

One reason for this mystery is that theoretical models cannot provide a consistent explanation of the gamma-ray burst characteristics of their light curve behavior. In astronomy, a light curve is a graph of a celestial object’s light intensity as a function of time. Studying light curves can yield important information about the physical processes that produce them and help define theories about light curves. No two gamma-ray bursts’ light curves are exactly the same, and the emission can last from a few milliseconds to tens of minutes as a series of high-energy pulses.

“The pulse is the basic unit of gamma burst emission,” Hakira said. “They indicate the time when the GRB brightens and then disappears. During the emission of a GRB pulse, it undergoes changes in brightness, which can sometimes occur on very short time scales. The strange thing about these changes is that they are reversible, like Single words like “spinner” or “kayak” (palindromes) are reversible.

“It’s hard to understand how this happens because time only moves in one direction. The mechanism that generates light in a GRB pulse somehow creates a pattern of brightness and then the same pattern in reverse order. It’s weird, it makes GRB Horse storms become unique.

Gamma burst emissions are generally thought to occur within relativistic jets (powerful streams of radiation and particles emitted from newly formed black holes).

“In these models, the core of a dying massive star collapses to form a black hole, and the material that falls into the black hole is torn apart and redirected outward along two opposing beams, or jets,” Hakila noted. “Pointing to us The directional jets of material are ejected outward at nearly the speed of light. Because of the relatively short lifetime of the GRB, it has been thought that the jets are always pointed at us throughout the event. But the time-reversed pulse nature makes it difficult to explain whether they come from a plane. Stationary jet.

To help demystify these features, this article suggests adding motion to the jet.

“The idea of ​​laterally moving jets provides a simple solution to explain the time-reversed gamma burst pulse structure,” the researchers said. “As the jet crosses the line of sight, an observer will see one side of the jet first. The light produced, then the center of the jet, and finally the other side of the jet will brighten and then dim as the light changes.

The rapid expansion of the gamma-ray burst jet, combined with the motion of the jet’s “nozzle” relative to the observer, helps to elucidate the structure of the gamma-ray burst jet.

“The jet has to spray the material similar to how a fire hose sprays water,” Hakila said. “The jet behaves more like a fluid than a solid, and an observer who can see the entire jet would think it is curved rather than straight. The motion of the nozzle causes light from different parts of the jet to reach us at different speeds .