If you're reading this, then this Gamma Ray Burst is not going to hurt you.
Gamma ray bursts were first detected by satellites that had been designed to watch for nuclear weapons on Earth. They kept reporting super high energy radiation events-- bursts -- but there were no other signs of nuclear explosions. They were seeing light from outer space.
The short duration of these bursts, along with the extreme energy level of the photons, impose constraints on the type of event that could emit such light.
Light moves really fast, but it doesn't move infinitely fast, and nothing else can happen faster than light. Anything violent enough to shine mostly in gamma rays is going to be pretty much the only thing going on at the source: a big explosion. A burst two minutes long generally means that the source is two light-minutes wide. Something that would fit inside the orbit of planet Mercury. For example. It gives you an idea of limits that can be placed on the phenomena that might cause such a thing.
Two things about Earth are quite amazing: our atmosphere and Earth's magnetic field.
Earth has a solid iron and nickel inner core, surrounded by fluid iron nickel outer core. The motion of the fluid sets up a magnetic field that tends to deflect charged particles from outer space.
In particular, a great part of the Solar wind, solid matter thrown out by the Sun, is prevented from getting to the lower levels of our atmosphere.
Without the deflector shields, Earth might not be able to hold on to its atmosphere over billions of years: it would slowly be blasted away...
Currently, that's the explanation for Mars -- it used to have water and more of an atmosphere, but that's not what we see today.
Gamma rays don't go very far into our atmosphere before getting scattered or absorbed.
Radiation from the Sun is far brighter than any gamma ray burst from light years away. So far.
> Gamma rays don't go very far into our atmosphere before getting scattered or absorbed.
I think part of the "fear factor" is the idea of a much closer burst happening, dumping vastly more energy our way, which we would have no way to detect (since it travels at the speed of light), and which could instantly vaporize 1/2 of our planet's atmosphere, thanks to that absorption you mention (:
Personally, I feel like that makes it somehow less worrying, but different people are different.
Heat will increase loss of atmosphere, but vaporized isn't the right word.
The issue would not be losing even 25% of the atmosphere instead of close to 0.00% per year, but that boiling oceans, steam, and air will hit say 1000F on the size of the GRB and then over the next hours/days mix with the rest and end up with a average of 500F.
Even with that, I suspect many but not all species of life would be extinct. Anything that lives in the deep ocean might be mostly unimpacted.
I want to clarify: I chose "two minutes" as a totally arbitrary example. I think we are all clear about that -- but just "Duration X", for some value.
Important to note another class of very violent, energetic event that can emit gamma rays is an ultra-hot accretion disk around a galaxy core black hole. Something larger than our solar system... Such systems can exhibit changes in brightness, but generally we see that over much larger scale.
Something smaller than a galaxy, like a star, could change brightness much more rapidly.
If Gamma Ray Bursts have been detected by satellites, how come none of them have hit the Earth and cooked the atmosphere? I thought a GRB aimed in our general direction would be an extinction event.
Even though the beam of the gamma ray burst is incredibly focused, it still dissipates as it travels, like a searchlight beam (or even a laser). Nearly all GRBs that we detect are from really far away and so are not a threat. If one happens "nearby" and it was pointed at the earth, we'd be cooked! But they are extremely rare events.
The lucky half would be the ones who got cooked due to facing the burst. The unlucky survivors would get to take a journey with a planet on its way to being inhospitable due to just having half of its atmosphere burned away and half of the surface completely sanitized of life.
The Late Ordovician mass extinction may have resulted from a GRB 443 mya.
Its effects are observed in the fossil record of marine life (effectively: the only life on Earth at the time), and were far more pronounced at shallow depths than deeper ones, corresponding to dose-effect theories.
Note that this is a hypothesis and would likely be impossible to verify.
I'm not sure the half sheltered from the direct burst would be considered lucky. There's a cool short story about the sun going nova, and one half of the planet is immediately destroyed. For me it always seemed like going quickly would be the better option..
If the burst were very close, it would be. Most are from other galaxies, so the intensity is much lower (fewer photons) even though those few photons are still very high energy.
Not an astrophysicist, but I think the assumption is that all of the photons are emitted at once in an explosion, and of course they all travel at the same speed. So if the burst is two minutes long, the near side of the explosion was two light-minutes closer than the far side of the explosion.
Imagine observing a lightning bolt strike the ground. The bolt travels through air almost instantly and emits sound in every direction throughout its path. First you will hear the sound waves emitted from the point that it touches the ground, because that is the closest. Then you will hear the sound waves from 1 cm off the ground, 2 cm, 3 cm and so on all the way up to the lightning bolt's point of origin in the sky. By measuring the duration of the noise you can tell the length of the lightning bolt (assuming it's perpendicular to the ground).
It's basic properties of propagation of light and sound.
In practice, the duration of thunder from a given lightning bolt might be affected by echos and other phenomena, though you could probably get at least a rough estimate of bolt length by the duration of thunder.
The largest lightning bolts ever measured are hundreds of kilometers long. The longest I'm aware of was over 760 km long (477 mi), measured in February of this year:
That probably roared for a while, though attentuation of sound would likely occur within 16--32 km (10--20 mi), or a minute or two. Otherwise, it would take nearly 40 minutes for sound to propagate from one end of the strike to the other.
The length of the burst tells us the maximum size of the event. Imagine the event takes place instantly at the source, and that the source has some size. If we observe the event over two minutes, then the event size was two light-minutes.
In reality, these aren't completely instantaneous events. But any event duration at its source is going to decrease the event size. Take the extreme case: the event actually took place at its source over the course of two minutes. And we observed it over two minutes. We would have to conclude that the event had zero size.
Of course, the reality is that we have no idea how long the event took place at its source. All we know is that we observed it over two minutes. But that's enough information to conclude that the event we're seeing certainly occurred within a two light-minute sphere. If it had occurred over a larger sphere, we would have observed it over a longer period of time because of the time light takes to traverse the length of the source.
