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First discovered incidentally by US military satellites in the late 1960s, cosmic explosions known as gamma-ray bursts (GRBs) have come to be considered the brightest explosions in the
First discovered incidentally by US military satellites in the late 1960s, cosmic explosions known as gamma-ray bursts (GRBs) have come to be considered the brightest explosions in the universe. As a rule, they are the result of the catastrophic birth of a black hole in a distant galaxy. One way this happens is when a single massive star collapses.
Astronomers like myself working in this field are well aware of the enormous energy scale associated with gamma-ray bursts. We know that they can emit as much gamma rays as the Sun during their lifetime. But there is an occasional event that still gives us pause. In October 2022, gamma-ray detectors on the orbiting Fermi satellites and the Neil Gehrels Swift Observatory recorded an explosion known as GRB 221009A (discovery date).
This quickly turned into a record. It was nicknamed “The Brightest Ever” or “The Boat” as an apt abbreviation among astronomers who studied and observed the event. Not only was the boat bright at first, it refused to fade like other flashes. We still don’t fully understand why the explosion was so extraordinarily bright, but our new study has been published. Science Advancesresponds to her stubborn insistence.
The explosion occurred 2.4 billion light-years away – relatively close to a gamma-ray burst. But even considering relative distance, the energy of the event and subsequent radiation were off the charts. It is completely abnormal for a distant cosmic event to release about one gigawatt of energy into Earth’s upper atmosphere.
Like boats, GRBs launch a stream of gas traveling at very close to the speed of light into space. Exactly how the jet was triggered remains a mystery, but it likely involves magnetic fields near the black hole’s formation site. It is the early emission of this jet that we see as a flash. The jet then slows down and produces additional radiation, a fading flash of light, ranging from radio waves (in exceptional cases) to gamma rays.
We do not directly observe the jets. Instead, we see GRBs as spots in the sky, like distant stars. However, we have good reason to believe that GRBs do not explode equally in all directions. For GRB 221009A, this would be absolutely illogical as it would require multiplying the amount of energy detected on Earth by all other aspects, which is much more energy than any single star.
Another indication that gamma-ray bursts originate from jets aiming approximately at us is the special theory of relativity. The theory of relativity teaches us that the speed of light is constant no matter how fast the source moves towards us. However, this still allows the light to be disoriented. Because of this funhouse specular effect, the light radiating in all directions from the surface of the fast jet will be strongly focused along the direction of motion.
However, the edges of the jet pointing in our direction will be bent very slightly, meaning its light will be focused in a different direction. But then, as the jet slows down, the edges often become visible and the post-sunset glare begins to fade faster. But here too GRB 221009A broke the rules. Its edges were not visible at all, and it joined a select group of very bright flashes that refused to go out normally. Instead of starting to fade slowly and then disappearing rapidly, it starts to fade slowly over time.
In our work, we show how the appearance of jet edges can be consistently obscured by Chuvne observations. The gist is this: yes, a narrow jet was launched, but it had trouble escaping the collapsing star, resulting in the jet’s strong mixing with stellar gas along its edges.
To test whether this is indeed the case, we took the result of a computer simulation showing this mix and applied it to a model that could be directly compared to the Boat data. And it showed that what would normally be a rapid transition to a heavily attenuated signal is now a long-term issue.
Radiation from the dying star’s heated gas continued to appear in our field of view, which explains why the star remained so bright. This continued until any distinctive jet signature was lost in the overall emission.
Thus, GRB 221009A not only confirms the simulation’s expectations, but also hints at similar bright events observed in the past that people have to constantly revise their energy estimates upwards while waiting for the tip of the jet to appear.
We estimate the chance of seeing such a bright flash is about once in a thousand years, so we’re lucky to be able to spot it. But questions remain. For example, what role do magnetic fields play? Theorists and numerical modelers will explore these questions for years to come, examining Boat data as we await the next big event. Source
Source: Port Altele
As an experienced journalist and author, Mary has been reporting on the latest news and trends for over 5 years. With a passion for uncovering the stories behind the headlines, Mary has earned a reputation as a trusted voice in the world of journalism. Her writing style is insightful, engaging and thought-provoking, as she takes a deep dive into the most pressing issues of our time.
