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GRB (Gamma Ray Burst).

Updated: Jul 1, 2023

Another week with no clear nights (5 weeks and counting now), so no new image again this week. So, I thought we would have a look at something that I have found very interesting recently and wanted to share with you, and that is GRB's or Gamma Ray Bursts. Now for the uninitiated, you maybe asking yourself, what is a Gamma Ray Burst? And no, they do not turn ordinary humans into the Fantastic Four, no matter what Marvel comics tell you. What do they do, then? Lets get to it..

Gamma-ray bursts are brief flashes of high-energy emission from stars, sometimes lasting a fraction of a second to a couple of hours. The short gamma-ray bursts mark the collision of two compact stellar remnants called neutron stars, and the long bursts are thought to arise when a massive, rapidly spinning star collapses to form a black hole. After the initial burst of gamma-rays, dubbed the “prompt” emission, a lengthy afterglow shines for days or weeks at radio to X-ray wavelengths. Basically that's it. This is the best description I can give you, with no technical jargon to baffle and confuse.

Artistic impression of a GRB.

On the 9th of October 2022, an incredible new gamma-ray burst named GRB 221009A was picked up by 25 satellites, most of which are not designed to detect gamma-ray bursts — like Voyager 1 and a pair of Mars orbiters. Incidentally, the name is the year first (22), followed by the month (10) and finally the day (09). GRB and A are self-explanatory, or at least I hope they are! The X-ray afterglow of this GRB is more than a magnitude brighter than other gamma-ray bursts observed by the Swift Observatory, and the analysis of its emission suggests that the jet it produced is extremely narrow. This narrow emission does not fit with the standard models for how the emission is produced — namely, a jet of energetic particles interacting with material surrounding the object — suggesting that further work is needed (as usual we are wrong) to understand the event.

An infrared image of the afterglow of GRB 221009A (red circle just below centre of image), taken 1–2 months after the onset of the burst. The burst’s host galaxy is the faint, extended source behind the burst.

NASA / ESA / CSA / STScI / A. Levan (Radboud University); Image Processing: Gladys Kober

In addition to the prompt and afterglow emission, gamma-ray bursts are often accompanied by a supernova, powered by nuclear reactions within the material expelled as the star collapses. As the emission from the burst fades, emission from the supernova brightens, eventually showing beneath the fading afterglow as a bump in the light curve days or weeks after the initial burst. However, one of the strange features of GRB 221009A is that it might not show any supernova emission. The projects team examined the light curves and spectra for signs of a supernova, but did not find a convincing signal in either. Although, the supernova could be hidden beneath the bright afterglow, depending on how much the host galaxy’s dust obscures the light from the supernova. Another possible reason is that the black hole that was formed, actually swallowed the supernova debris!

Since its discovery, GRB 221009A has been referred to as the BOAT — the Brightest Of All Time. By comparing against decades of gamma-ray burst observations, the team found that GRB 221009A had by far the highest peak flux of any gamma-ray burst measured to date, and it topped the list for two out of the remaining three measures of brightness. So, the work continues on this amazing GRB. Now, what is really far out about this GRB, and you knew I was coming to this. This burst made an actual impact on Earth's atmosphere, creating a disturbance as large as a solar flare would. To put that into some kind of context, this means that an explosion roughly 2 billion light-years away had as large an effect on our atmosphere as a solar flare more than 100 trillion times closer!!

However, the next facts are truly horrific. If this GRB was 12 light years away and the beam hit Earth, all the oceans in that hemisphere would be totally boiled away and all life would be destroyed. Studies also show that the destruction of the Earth’s ozone layer may be all that’s required to destroy all life, as this would allow the Sun’s ultra-violet rays to reach ground level, causing severe effects on life, leading to extinctions and the collapse of ecosystems. It is also estimated that a GRB needs to be no further away than roughly 3000 light years to cause these effects, and one may have already have caused a mass extinction on Earth in the past. Quite a sobering thought as you drink your beer, yes? There is no escape, so drink the lot right now...

I hope you have enjoyed this short blog on one of our Universe's most energetic and powerful explosions that I hope we never see. As usual, all comments good or bad are welcome on this blog. See you next time and keep watching the skies for flashing nukes as we have more chance of being killed by the psychopaths than a GRB...

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