The birth of a black hole has created the brightest space explosion ever

A record The most powerful sky-lighting space explosion we’ve ever seen was caused by a structured jet carrying massive amounts of exploded stellar innards aimed directly at Earth, scientists have determined.

The gamma-ray burst GRB 221009A, detected in October last yearwas so brilliant that our instruments struggled to measure it. But as clues emerged, scientists scrambled to point their telescopes in its direction, and with the wealth of data gathered, an international team of scientists finally figured out how the supernova generated such a powerful boom.

GRB 221009A, dubbed BOAT (for Brightest of All Time), was the result of the death of a massive star at a relatively close distance of 2.4 billion light-years, which collapsed into a black hole after ejecting its envelope external. The gamma-ray burst produced by this collapse contained a narrow, textured jet surrounded by a larger outflow of gas.

This is unexpected; our current models predict that the explosion would produce only a jet. The findings have implications for our understanding of black hole formation and how the brightest explosions in the Universe occur.

GRB 221009A (within the purple circle) shining bright among the stars. (NASA)

“GRB 221009A represents a huge leap forward in our understanding of gamma-ray bursts and demonstrates that the most extreme bursts do not obey the standard physics assumed for garden-variety gamma-ray bursts,” says astronomer Brendan O’Connor of the George Washington University, lead author of the new paper.

“GRB 221009A may be the Rosetta Stone equivalent of long GRBs, forcing us to revise our standard theories about how relativistic outflows form in massive collapsing stars.”

Gamma-ray bursts are the most powerful explosions seen throughout the cosmos, and they occur in a variety of ways. Long-duration gamma-ray bursts, such as GRB 221009A, are caused by the death of massive, rapidly rotating stars.

When they reach the end of their lives, the cores of these stars, no longer supported by the external pressure of the merger, collapse under gravity to form an ultradense object, such as a black hole. At the same time, the star’s outer material is ejected outward in a huge explosion, the supernova.

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It wasn’t immediately obvious what we were looking at with GRB 221009A, although its long duration suggested a supernova. But the sheer power of the explosion of up to 18 teraelectron volts, a staggering record, was truly staggering, and the puzzle only deepened as scientists continued to dig.

We know that gamma-ray bursts are accompanied by jetstwin columns of material emerging from opposite sides of a collapsing object, carrying material a relativistic speeds; that is, a significant percentage of the speed of light. We also know that these jets appear brightest when pointed directly at us; think staring directly into the beam of a flashlight, instead of at an angle.

Scientists had already concluded that GRB 221009A’s jet was aimed at Earth, but the glow from the explosion was still bright months later. This is uncharacteristic of a narrow emission jet, suggesting that something else was going on.

That something else, the team’s analysis suggests, was a large amount of ejected external stellar material that was pulled along by the jet as it passed through it.

Artist’s impression of a gamma-ray burst. (ESO/A.Roquette)

“GRB jets must pass through the collapsing star in which they form”, explains astrophysicist Hendrik Van Eerten of the University of Bath in the UK.

“What we think made the difference in this case was the amount of mixing that occurred between the stellar material and the jet, such that gas heated by the impact kept appearing in our line of sight up to the point where any characteristic features of the jet would have been lost in the overall afterglow emission”.

The findings could help explain previous bursts of exceptionally bright gamma-rays that didn’t show the typical jet signature. These outbursts could also consist of a narrow jet aimed in our direction, piercing and dragging the guts of the exploded stars with it.

“The exceptionally long GRB 221009A is the brightest GRB on record and its afterglow is breaking all records at all wavelengths,” says O’Connor.

“Because this flash is so bright and so close, we think this is a once-in-a-thousand-year opportunity to address some of the most fundamental questions surrounding these outbursts, from the formation of black holes to testing dark matter models.”

The research was published in The progress of science.

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