World News | Brightest cosmic explosion ever seen: How we can solve the mystery of its puzzling persistence

London, June 8 (Dialogue) First accidentally detected by US military satellites in the late 1960s, cosmic explosions known as gamma-ray bursts (GRBs) have been understood to be the brightest explosions in the universe.

Often, they are the result of the catastrophic birth of black holes in distant galaxies. One way this can happen is through the collapse of a massive star.

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Astronomers like myself who work in this field are well aware of the enormous energy scales involved with GRBs. We know they can emit as much energy in gamma rays as the Sun does in its entire lifetime. But every once in a while, observed events still give us pause.

In October 2022, gamma-ray detectors on the orbiting satellite Fermi and the Neil Gehrels Swift Observatory detected a burst known as GRB 221009A (detection date).

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This quickly proved to be a record-breaker. It has been dubbed the brightest ever, or “ship,” as a convenient shorthand for astronomers studying and observing the event. Not only does the ship start off bright, but it doesn’t fade away like other bursts.

We still don’t fully know why the bursts are so unusually bright, but our new research, published in the journal Science Advances, provides an answer to its stubborn persistence.

The burst originated at a distance of 2.4 billion light-years—relatively close for a GRB. But even accounting for relative distances, the energy of the event and the radiation from its aftermath are off the charts. For a cosmicly distant event, it is absolutely abnormal to deposit about 1 gigawatt of energy into the Earth’s upper atmosphere.

Observing narrow cosmic jets of gas

GRBs such as Boat launch a stream of gas into space at very close to the speed of light. Exactly how the jet is launched remains a mystery – but most likely, it involves the magnetic field near the black hole’s formation.

What we saw was an early launch of the jet. Later, the jet slows down and produces additional radiation, a fading afterglow of light — from radio waves to (in special cases) gamma rays.

We do not directly observe the jet stream. Instead, like distant stars, we perceive gamma-ray bursts as points in the sky. Nonetheless, there are good reasons to believe that GRB will not explode equally in all directions. For GRB 221009A, this is certainly unreasonable, since it involves multiplying the energy detected on Earth by all other directions — adding up to far more energy than is available to any star.

Another indication that GRBs come from jets pointing roughly at us is due to special relativity. The theory of relativity tells us that the speed of light is constant no matter how fast the light source is moving toward us. But this still allows the direction of the light to become distorted. Light emitted in all directions from the surface of a fast-moving jet ends up being strongly focused along its direction of motion due to this interesting mirror effect.

That is, the edges of jets flying in our direction will be slightly curved, which means their light will be directed away from our direction. Only later, when the jet slows down, do edges usually come into view and the afterglow starts to fade more quickly.

But here, GRB 221009A breaks the rules again. Its edges never show, and it joins a select group of very bright bursts that refuse to fade properly. Instead of starting out slowly and then fading quickly, it fades steadily over time.

In our work, we demonstrate how to blur the appearance of jet edges in a way that matches observations of ships. The key idea is as follows: Yes, a narrow jet is fired, but it has a hard time escaping the collapsing star, causing massive mixing of the sides of the jet with the star’s gas.

From simulation to observation

To test whether this is indeed the case, we took the results of computer simulations showing this mixing and implemented it in a model that could actually be compared directly to the ship data. It shows that what would normally turn quickly into a strongly weakening signal has now become a protracted affair.

Radiation from the dying star’s hot gas is constantly in view, which explains why it remains so bright. This continues to happen until any typical jet character is lost in the overall emissions.

In this way, GRB 221009A not only confirmed what the simulations expected, but also provided clues to similarly bright events seen in the past, where one had to keep revising energy estimates upwards while waiting for the jet edge to emerge.

We calculate that the chance of seeing such a bright outburst is about once in a thousand years, so we’re lucky to spot one. But the problem remains. For example, what does a magnetic field do?

Theorists and numerical modelers will explore these questions for years, scouring ship data, while we continue to look for the next big thing to come. (dialogue)

(This is an unedited and auto-generated story from a Syndicated News feed, the content body may not have been modified or edited by LatestLY staff)