For those curious, the lethal range is thought to be 5,000--8,000 light years, at least for supernovae GRBs, if directed toward our solar system. (GRBs are directional rather than omnidirectional.)
I wonder about a merger of a pair of supermassive black holes, say a billion solar masses each. Would it sterilize the whole galaxy?
A galaxy is a pretty dangerous place to be. Probably we should get clear at first opportunity.
A pretty big pair is scheduled to merge sometime in the next three years. Probably we will get enough warning to be watching carefully when it happens.
Don't most of the computation as to the total energy of the event assume the event radiates equally in all directions?
Isn't the amount of energy drastically smaller if it's a focused beam?
Why do we assume spherical and not, for example, a directed attempt to communicate, the back end of a starship drive pointed at us, or just a natural phenomenon the is unidirectional.
It would have been useful to put it on a scale to compare it against other measured GRB. It is hard to get a sense from the article on how much more powerful it was.
GRB 221009A is detected by LHAASO-WCDA at energy above 500 GeV, centered at
RA = 288.3, Dec = 19.7 within 2000 seconds after T0, with the significance above
100 s.d., and is observed as well by LHAASO-KM2A with the significance about 10 s.d.,
where the energy of the highest photon reaches 18 TeV.
So 2.4 billion light years away, yet several times the article says things like "This event, because of its relative proximity to Earth, is also a unique opportunity" and "Because this burst is so bright and also nearby, we think this is a once-in-a-century opportunity."
LHC has a center of mass energy of 14 TeV, pretty close to the mentioned 18 TeV. That's however for protons, not photons. You really can only accelerate charged particles, as we use magnetic and electric fields for that. You need roughly a factor of ten higher energy of the charged particle to produce a certain energy gamma ray.
Proton collisions are messy, and not the best way to get photons at certain energies. There is a new up to 1 TeV electron collider planned in Japan [1].
Note however that these 18 TeV are only the highest energy Photon from a GRB. LHAASO observed gamma rays up to 1.4 PeV from other sources (mostly galactic super nova remnants) [2].
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.
The Fermi GRB is one of the instruments listed in the article as detecting the initial burst and would had generated a redirection request for a whole family of different telescopes, including Fermi itself.
Actually, this is a better page with both the swift and fermi images.
Longevity: The explanation on NASA's APOD page states:
" In low Earth orbit Fermi’s Large Area Telescope recorded gamma-ray photons from the burst for more than 10 hours as high-energy radiation from GRB 221009A swept over planet Earth last Sunday, October 9. "
while the second is more specific: "the afterglow of GRB 221009A faded over the course of about 10 hours."
Related interest: The Earth's atmosphere itself produces gamma flashes up to 20MeV:
I like how no matter how awesome we think we are we’re one grb away from extinction of all life. Reminds of of the smashing pumpkins lyric “despite all my rage, I’m still just a rat in a cage”.
Because an extinction level gamma ray burst directed at Earth is an extremely unlikely event compared to many other possibilities, such as humanity trashing our own ecosystem, which is pretty close to a certainty at this point.
Also, outer space is really incredibly hostile to life. The likelihood of dying in space, on the Moon, on Mars, is vastly higher than the likelihood of the aforementioned GRB.
Let me put it this way: the Earth, in the aftermath of getting hit by the dinosaur-killing asteroid 66 million years ago, was still infinitely more habitable to life than Mars is today. The grass is not greener on the other side.
It would be so much easier to build underground or underwater shelters on Earth than it would be to build permanent shelters on other planets.
The Earth is the only habitable place in the solar system. Everywhere else requires humans to bring along their own life support systems, fresh water, and means to produce food. Human occupation of any body in the solar system or artificial bodies like a space station will always be limited by the amount of high tech infrastructure that can be built there. Even on Mars there's no guarantee there's enough in situ resources for humans to be self-sufficient.
So the only was an extinction event on Earth would be survived by off-world colonies is if they were 100% self sufficient. Even a broken toilet could kill everyone in a space vehicle, human lungs don't appreciate aerosolized shit in them.
Building a permanent off-world base is a huge undertaking. Building an actual colony is an order of magnitude more difficult. And building a completely self sufficient colony is several orders of magnitude more difficult than that.
In any sort of near term setting an extinction level event on Earth is going to lead to the extinction of all off-world colonies/bases. They stand even chances of completely dying out even with unlimited support from an intact Earth.
A solar flare could wipe out a space station or Mars base. A GRB capable of wiping out life on Earth will wipe out life pretty much everywhere in the solar system.
Life on earth, er outside the oceans would end with sterilization down to 1M. Likely 99.99% or more of humans dead within a year.
Mars however is very cold, highly radioactive, practically no atmosphere, and vulnerable to meteor strikes. So to fix all those problems inhabitants would likely be under 1 meter to minimize air leakage, radiation, heat leakage, etc. So it might well be that 99% of people survive a 1M deep sterilization ... only if self sufficient, which does seem a stretch, at least for the next century.
One example is infrared which we sense as warmth. I am somewhat fuzzy here, but I imagine that these photons bump into the atoms of our skin such that they tend to shake more vigourously than before. This is heat.
I can imagine that gamma rays of a gamma ray burst are plentiful and hard enough to influence the tardigrade matter to an extent to even kill tardigrades.
This said I see a way how tardigrades could survive a gamma ray burst. They are inside an asteroid or even inside a Mars-like planet. Even if the gamma rays ablate a significant chunk of the crust, enough will remain to protect the tardigrades.
So some tardigrades might be lucky to survive a gamma ray burst nearby.
So in order to survive the colonies would need to be entirely self sustaining, and would only save humanity from an event that wiped out earth but left the colonies unharmed.
Given the huge efforts that would be needed to create such colonies I think the work on spotting potentially dangerous asteroids and working out how to affect their orbits is probably a much better option.
A post apocalyptic earth after every nation on earth detonated all their nukes on each others population centers or a post dinosaur killer event would both leave the earth substantially more survivable than Mars at present. The world faces unlikely total destruction from space. More likely species extinction, and inevitable economic failure.
In the foreseeable future of the coming decades even inevitable economic failure is likely to doom any colony we establish whereas such colonies are not going to be enough to save the species from any species extinction scenario.
In the near term space exploration is about developing our potential not preserving it from destruction. Indeed this argument is both more palatable and potentially effective than doom and gloom.
From a philosophical point of view, what difference does it make if life on earth ends?
I am all for colonizing the galaxy, but just because I think it would be cool. It doesn't really matter whether or not it actually happens, does it? Why I personally think it is not widely a high priority is because establishing off-world colonies is just one of a really long list of things we could spend our time and money on, and most people themselves would not directly benefit.
I would prioritize it to some extent (maybe not highest priority) but I certainly understand why it is not a general priority.
> From a philosophical point of view, what difference does it make if life on earth ends?
Technically speaking, the end of life on Earth would be philosophically devastating, as all knowledge and subjective existence would vanish. Granted it may make no difference to you, but it would be catastrophic for philosophy.
Some very insightful and thought-provoking comments are under the above downvoted parent comment. I wonder what the Hacker News algorithm does with threads that have a downvoted parent but with highly upvoted replies? Does it push the thread down or keep it high? In either case, I've often thought that this was small flaw with threaded discussions (though I don't know a solution): There should be a way to maintain visibility or priority for great comments that are buried in downvoted threads.
There would be such a solution if users were able to adjust the weight of downvotes or if the vote mechanism was changed to include a mandatory category or reason, i.e. '-1 spam' or '-1 disagree' or '-1 flamebait'. This, in combination with a way to adjust the weight of those categories - i.e. I would give 'disagree' votes a weight of 0 since I don't care whether someone else agrees as I like to make up my own mind about things - would make it possible for those who like to downvote from the hip to continue doing so without ruining the discourse for others.
Such a system would quickly be gamed by the downvoters who would start marking things they disagree with as 'spam' so another layer would need to be added in which certain types of downvotes - spam, flamebait and other such categories - are checked and undone if needed. Downvoters who abuse their voting privilege too often would loose it for a day, then a week, then a month, etc.
In other words, something like the Slashdot moderation/meta-moderation system of old.
My read on downvotes is that they exist for managing signal/noise, basically for avoiding comments that are better off not read or engaged with. If a reader has to get through a noisy comment to get to a good comment that only exists because of the noise, is it worth it for the platform to try to lead them to it? And that's a pretty rare case anyway. So yeah, pretty hard to even specify a solution.
The general problem with up-votes, down-votes and no-votes is that the discourse mechanism behind them is so complex that the quality of the comment is only vaguely related to the number of votes. Sometimes I get lots of up-votes for a casual remark on a general topic, but none at all for a detailed reply on a specific question. When someone makes a false factual claim and is corrected by someone else, the last comment is often up-voted, but rarely is the original claim down-voted because people think the matter is settled.
Appart from obvious nonsense, the typical cases for down-votes are not descriptive (what is true or false), but normative comments (what should or should not be the case). Normative comments, such as what user `blueprint` has written, have the tendency that people up-vote or down-vote according to their own, often quite ad-hoc opinion, using the system like a poll. I think that this is not good. Instead, one should either just ignore it or try to initiate a debate. For the vast majority of opinions that contradict one's own, there are plenty of representatives out there who are at least as clever as oneself. Being curious about why they have such a view does not have to mean that one relativises everything. There is almost always something to learn.
I also think that we should strive to apply the principle of charity[1] in our responses, mending small flaws or bad rhetoric in a person's statements and instead challenge the essence of her or his thoughts. Although user `blueprint` does not elaborate on his topic, the topic itself is quite interesting. He just worded it a bit clumsily. Its essence may be reformulated as: "Given that an extremly devastating, but also extremly unlikely cosmic event could wipe out humanity in an instant, should we not prioritize to spread out across the galaxy, so that a single event could not affect all of us?" Has this statement the same chance to be down-voted? If this is not the case, doesn't it mean that a down-voter should have applied the principle of charity instead?
[1] Wikipedia's definition: "In philosophy and rhetoric, the principle of charity or charitable interpretation requires interpreting a speaker's statements in the most rational way possible and, in the case of any argument, considering its best, strongest possible interpretation." -- https://en.wikipedia.org/wiki/Principle_of_charity
