When the Earth will be overtaken by a gamma-ray burst and why all living things will die

2024 Author: Seth Attwood | [email protected]. Last modified: 2023-12-16 15:55

As Plait writes in Death From Above, a gamma ray burst is the most striking event since the Big Bang. None of such outbursts repeats another, but they all arise due to catastrophes of a galactic scale: when very large stars die, ceasing to "burn" and collapse under the influence of their own gravity or, presumably, due to the collision of two neutron stars (objects the size of city, but with a mass, like one or two Suns).

In such cases, the energy is ejected not evenly in all directions, but in directed beams. This event is so grandiose that sometimes it can be seen with the naked eye for billions (!) Of light years. What will happen if such a beam hits the Earth?

Let's assume that the GRB happened very close: 100 light years away. Even at such a close distance, the diameter of the gamma-ray burst beam would be gigantic, 80 trillion km. This means that the entire Earth, the entire solar system would be swallowed up by it, like a sand flea captured by a tsunami.

Fortunately, GRBs are relatively short-lived, so the beam will hit us in less than a second to several minutes. The average burst lasts about ten seconds.

This is not long compared to the rotation of the Earth, so the beam would hit only one hemisphere. The second hemisphere would be relatively safe … at least for some time. The most dire consequences would be in places directly below the gamma-ray burst (where the flare would be visible directly overhead, at the zenith), and minimal where the flare would be visible on the horizon. But all the same, as we shall see, no place on Earth would be completely safe.

The unbridled energy that would be dumped on Earth is overwhelming. This is more than the worst nightmares of the Cold War: it is like detonating a one megaton nuclear bomb from the side of a gamma-ray burst over every 2.5 km2 of the planet. This is (probably) not enough to make the oceans boil or to rip the atmosphere off Earth, but the destruction would be beyond comprehension.

Keep in mind, all this is from an object located at a distance of 900 trillion km.

Anyone looking at the sky at the time of the flash could go blind, although the peak of brightness in the visible range would probably only be reached after a few seconds - enough to flinch and turn away. Not that it helped much.

Those who at that moment would have been caught on the street would have had big problems. Even if they had not been burned by the heat - and they would have been - they would have instantly received a fatal burn from a huge stream of ultraviolet radiation. The ozone layer would be literally destroyed instantly, and UV radiation from both the gamma-ray burst and the Sun would freely reach the Earth's surface, making it, as well as the oceans, to a depth of several meters, barren.

And this is only from UV radiation and heat. It seems cruel to even mention the much, much worse effects of exposure to gamma and X-rays.

Instead, let's digress a little. Gamma-ray bursts are incredibly rare. While they most likely occur several times a day somewhere in the universe, the universe itself is very large. Currently, the probability that one of them will occur at a distance of 100 light years from us is zero. Perfect, absolute zero. There are absolutely no stars near us that could, in principle, generate a gamma-ray burst. The closest supernova candidate is farther away, and GRBs are much rarer than supernovae.

Feel better? Okay. Now let's try a more realistic approach. What is the closest candidate for gamma-ray burst sources?

In the sky of the southern hemisphere there is an unremarkable star to the naked eye. It is called Eta Carinae, or simply Eta, a dim star in a crowd of brighter stars. However, her dim light is deceiving, hiding her fury behind it. It is actually about 7,500 light-years distant - in fact, the most distant star that can be seen with the naked eye.

The star itself (in fact, Eta may be a binary system, two stars orbiting each other. The material surrounding the star gives so much brightness and interference that astronomers are still not one hundred percent sure) is a monster: its mass can be 100 times the mass of the Sun or more, and it emits 5 million times more energy than the Sun - in one second it emits as much light as the Sun will emit in two months. From time to time, Eta has spasms, and she spews out huge amounts of matter. In 1843, she had such a violent seizure that she became the second brightest star in the sky, even at such a great distance. It threw out gigantic amounts of matter in excess of ten times the mass of the Sun at speeds in excess of 1.5 million km / h. Today we see the consequences of that explosion in the form of two huge clouds of diverging matter, similar to the shot of a space gun. That event was almost as powerful as the supernova.

Eta has all the hallmarks of an impending GRB. It will surely explode like a supernova, but it is not known whether it will be a hypernova-type gamma-ray burst or not. It should also be noted that if it explodes and emits a gamma-ray burst, the orientation of this system is such that the beam will not hit the Earth. We can determine this from the geometry of the gas clouds ejected during the seizure of 1843: the portions of the swelling gas are tilted relative to us at an angle of about 45 °, and any gamma-ray bursts would be directed along that axis. Let me explain more specifically: in the short or even medium term, the gamma-ray burst from Eta or elsewhere does not threaten us.

But it's still interesting to ponder "what if". What if Eta had targeted us and turned into a hypernova? What would happen then?

Again, nothing good. Despite the fact that it would not even come close in brightness to the Sun, it would be as bright as the Moon, or even ten times brighter. You couldn't look at it without squinting, but that brightness would only last a few seconds or minutes, so there probably wouldn't be any long-term damage to the life cycles of flora or fauna.

The ultraviolet beam would be intense but brief. People outdoors would experience moderate sunburn, but there is likely to be no statistically significant increase in skin cancer incidence in the future.

But with gamma and X-rays, the situation is completely different. The Earth's atmosphere would absorb these types of radiation, and the consequences would be much worse than in the case of a nearby supernova.

The most direct consequence would be a powerful electromagnetic pulse, much more powerful than the one generated in Hawaii during the nuclear tests of the Starfish Prime device. In this case, EMP (electromagnetic pulse - approx. TASS) would instantly destroy any unshielded electronic device in that hemisphere of the Earth, which was directed towards the burst. Computers, telephones, airplanes, cars, any object with electronics would stop working. This also applies to power systems: huge currents would be injected into the power lines, causing them to overload. People would be without electricity and without any means of long-distance communication (the equipment of all satellites would have burned out from gamma radiation anyway). This would not be just an inconvenience, because it means hospitals, fire departments and other emergency services would also be without electricity.

But, as we will see in a moment, we may not need emergency services …

The consequences for the Earth's atmosphere would be severe. Scientists are studying this situation closely. Using the same models described in Chapter 3 and assuming that the GRB originated at Eta's distance, they determined what the consequences would be. And these consequences are not at all encouraging.

The ozone layer would be hit hard. The gamma rays from the burst would completely destroy the ozone molecules. The ozone layer worldwide would be reduced by an average of 35%, and in some selected regions it would be reduced by more than 50%. This is incredibly harmful in itself - mind you, our current ozone problems are caused by a relatively small decline, only 3% or so.

The consequences of this are very long-term and can last for years - even after five years, the ozone layer can remain 10% thinner. During this time, UV radiation from the Sun would be more intense on the Earth's surface. The microorganisms that form the backbone of the food chain are very sensitive to it. Many would die, leading to the eventual extinction of other species higher up the food chain.

To top it all off, the reddish-brown nitrogen dioxide generated by the gamma-ray burst from Eta Carina (see Chapters 2 and 3) would significantly reduce the amount of sunlight reaching Earth.

The exact consequences of this are difficult to determine, but it seems likely that a decrease in the amount of sunlight on the entire Earth by even a few percent (nitrogen dioxide would spread throughout the atmosphere) would lead to a significant cooling of the Earth and could, presumably, become an initiating factor for the ice age.

In addition, there would be enough nitric acid in the chemical mixture that acid rain would represent, and this would also theoretically have devastating consequences for the environment.

Next, there is a problem with subatomic particles (cosmic rays) from the burst. What damage would have been from them is not known specifically. But, as we discussed in Chapters 2 and 3, high-energy particles can have a wide variety of consequences on Earth. A gamma-ray burst 7,500 light-years away would send a huge number of subatomic particles into our atmosphere, and they would fly at a speed slightly less than the speed of light. Just a few hours after the outburst appeared, they would have already burst into our atmosphere, pouring out a shower of muons. We constantly observe muons arriving from space, but in small quantities. However, a nearby GRB would generate a mass of muons. One group of astronomers calculated that up to 46 billion muons per cm2 would fall on the Earth's surface across the entire burst hemisphere. Something you get from this, then just remember that a nearby burst of gamma radiation is bad - author's note). It seems that this is a lot - well, yes, it is. These particles would cascade out of the sky and be absorbed by whatever gets in their way. Considering how well body tissues can absorb muons, the astronomers who performed the calculation found that an unprotected person would receive a dose of radiation tens of times higher than the lethal dose. Hiding will not help much: muons can penetrate into water to a depth of almost 2 km and up to 800 m into rocks! Therefore, almost all life on Earth would be affected.

So ozone depletion would not be such a big deal. By the time it became a problem, most of the animals and plants on Earth would have been dead long ago.

This is the nightmare scenario described at the beginning of this chapter. However, before you start to panic, remember: the possible gamma-ray burst of Eta Carina will most certainly not be directed in our direction. But before we round off, I will say that there is another possible progenitor of the gamma-ray burst, which we need to remember. It's called WR 104 and coincidentally is about the same distance from us as Eta. WR 104 is a binary system, one of the stars of which is a bloated massive beast approaching the end of its life. It might explode, emitting a gamma ray burst, and it might be aimed more or less at us, but both of these assumptions are inaccurate. In all likelihood, this monster does not threaten us either, but it is worth mentioning.