A new discovery source, designated GRB 221009A in honor of the time it was found, turned out to be the brightest gamma-ray burst (GRB) ever observed. In a new study published today in the Astrophysical Journal Letters, observations on new insights about cosmic explosions from radio waves to gamma rays, including crucial millimeter-wave observations with the Center for Astrophysics | Harvard & Smithsonian’s Submillimeter Array (SMA) in Hawaii, shed new light on the decades-long quest to understand the origin of these extreme cosmic explosions. For more than 300 seconds, GRB 221009A’s gamma-ray emission was visible. Such “long-duration” GRBs, according to astronomers, are the birth cry of a black hole, which is created when the star’s core collapses under the weight of a huge and fast spinning object. Strong plasma jets are sent out by the developing black hole at speeds that are almost as fast as light, piercing the collapsing star and emitting gamma rays in the process. The main question was what would occur after the initial burst of gamma-rays because GRB 221009A was the brightest burst ever observed. According to main author of the study Tanmoy Laskar, assistant professor of physics and astronomy at the University of Utah, “when the jets collide into gas surrounding the dying star, they produce a dazzling ‘afterglow’ of light throughout the entire spectrum.” The afterglow diminishes quite quickly, so we must be quick and nimble to capture the light before it vanishes and takes its secrets with it.
Edo Berger and Yvette Cendes of the Center for Astrophysics (CfA) used the SMA to acquire data quickly as part of an effort to use the greatest radio and millimeter telescopes in the world to analyze the afterglow of GRB 221009A. Edo Berger, professor of astronomy at Harvard University and the CfA, adds that because of the burst’s brightness, “we did not want to miss it! It offered a rare opportunity to examine the intricate behavior and evolution of an afterglow with unprecedented clarity.” The first GRB I ever saw was as amazing as this one, and I’ve been studying these occurrences for more than twenty years. Garrett Keating, SMA project scientist and CfA researcher, notes that the SMA’s short response time allowed for a speedy turn to the location of GRB 221009A. The afterglow of this GRB, which could be observed for more than 10 days until it faded, surprised the crew with its brightness. The astronomers were baffled after examining and merging the data from the SMA and other telescopes around the globe: the millimeter and radio wave measurements were significantly brighter than anticipated based on the visible and X-ray radiation. The millimeter and radio data simply don’t behave as expected, according to one of the most comprehensive datasets ever gathered, according to CfA research associate Yvette Cendes. “A few GRBs have previously displayed a brief excess of millimeter and radio emission, which is assumed to be the signature of a shockwave in the jet itself, but in GRB 221009A the excess emission behaves significantly differently than in these earlier examples,” the authors write.
We have probably found a brand-new method for producing more millimeter and radio waves, the author continues. The strong jet created by GRB 221009A may be more complicated than in most GRBs, according to Cendes, which is one possibility. It’s probable that one part of the jet generates visible light and X-rays, while another part generates early millimeter waves and radio waves. Berger continues, “Thanks to this afterglow’s brightness, we will be able to continue studying its radio emission for months, if not years. “We expect to unravel the enigmatic origin of the early excess emission with this considerably longer time period,” the author writes. The capacity to react quickly to GRBs and comparable occurrences with millimeter-wave telescopes is a crucial new skill for astronomers, regardless of the specifics of this GRB in particular. The most violent explosions in the cosmos could have been discovered, but we would have missed them without quick-acting radio and millimeter telescopes like the SMA, according to Berger. We must be as receptive as we can be if we want to benefit from these gifts from the cosmos because we can never predict when such events will occur.
