'Death Star' system to shoot deadly gamma beam at Earth

[Fingolfin_Noldor]

If we have hundreds of thousands of years, chances are we won't be lined up with them anymore when the system ignites, right?

There's probably an angle of dispersion to contend with.

[Kwizard]

Holy shit. As soon as I saw the thread title, a similar disaster from the novel Diaspora came to mind immediately.

Which made me wonder - how intense would a non-focused gamma ray burst , say 200 light years away, need to be for its radiation to pose an existential risk like the one discussed in the OP article?

[wjs7744]

Frankly, I'm not terribly bothered. According to the 2005 study they reference, it's at least 1,500 light years further away than the mass-extinction threshold. Given how much such a beam would spread out over that kind of distance, what kind of intensity would we be talking about here, anyway?

[fnord]

This burst wouldn't be like a laser beam; it probably expands in something more resembling a cone from the source. At the distance involved, even a very narrow cone would cover a lot of volume.

Consider a triangle with a one degree angle at the far point from us. The bottom line at 6500 light years away would be almost 13000 light years! (cos(1 degree) * 6500 ly * 2. The *2 is there to account for both sides of the base of the triangle). But, the times two isn't actually needed, since we are already in the middle. Still, 6500 light years to the side is a huge distance. We'd have to make point five past lightspeed :-p

Hang on, shouldn't that be the tangent of 1 degree (the lateral dispersion perpendicular to LOS, compared to the distance along LOS) , not the cosine? Also, isn't the burster 8k ly away instead of 6500?

2 * 8k * tan(1 degree) works out to 279.3 ly across at our distance. Not too good, actually, as that ups the burst's intensity per unit area.

Is there anything in the way that could absorb or deflect some of the blast?

[Winston Blake]

Frankly, I'm not terribly bothered. According to the 2005 study they reference, it's at least 1,500 light years further away than the mass-extinction threshold. Given how much such a beam would spread out over that kind of distance, what kind of intensity would we be talking about here, anyway?

Many GRBs have been observed to undergo a jet break in their light curve, during which the optical afterglow quickly changes from slowly fading to rapidly fading as the jet slows down.[15] Furthermore, features suggestive of significant asymmetry have been observed in at least one nearby type Ic supernova, which may have the same progenitor stars as GRBs and have been observed to accompany GRBs in some cases (see "Progenitors"). The jet opening angle (degree of beaming), however, varies greatly, from 2 degrees to more than 20 degrees. There is some evidence which suggests that the jet angles and apparent energy released are correlated in such a way that the true energy release of a (long) GRB is approximately constant—about 1044 J, or around 1/2000 of a solar mass.[16] This is comparable to the energy released in a bright type Ib/c supernova (sometimes termed a "hypernova"). Bright hypernovae do in fact appear to accompany some GRBs.[17]

Further,

WR 104's rotational axis is aligned within 16° of Earth.

Now, we may wander closer to or farther from the centreline, but let's assume it can hit us right now, i.e. Θ = 16º. We need the area of a spherical cap on the end of a cone.

Wikipedia gives the expression Area = pi * (2*r*sin(Θ/2))^2. Areal energy density will be 1e44J/Area.

Plugging that into Google gives 72 kJ/m^2. Now if it hits us with a 2º blast, we're looking at 4.6MJ/m^2. This is delivered over 2 or 3 seconds. Total energy delivered to the Earth is about 2 gigatons. (On second thought, r is so large that I may as well have used a cone.)

I don't know what the effect would be, since it wouldn't all be delivered to the surface of the Earth, and there would be chemical atmospheric effects.

[The Duchess of Zeon]

Frankly, I'm not terribly bothered. According to the 2005 study they reference, it's at least 1,500 light years further away than the mass-extinction threshold. Given how much such a beam would spread out over that kind of distance, what kind of intensity would we be talking about here, anyway?

Many GRBs have been observed to undergo a jet break in their light curve, during which the optical afterglow quickly changes from slowly fading to rapidly fading as the jet slows down.[15] Furthermore, features suggestive of significant asymmetry have been observed in at least one nearby type Ic supernova, which may have the same progenitor stars as GRBs and have been observed to accompany GRBs in some cases (see "Progenitors"). The jet opening angle (degree of beaming), however, varies greatly, from 2 degrees to more than 20 degrees. There is some evidence which suggests that the jet angles and apparent energy released are correlated in such a way that the true energy release of a (long) GRB is approximately constant—about 1044 J, or around 1/2000 of a solar mass.[16] This is comparable to the energy released in a bright type Ib/c supernova (sometimes termed a "hypernova"). Bright hypernovae do in fact appear to accompany some GRBs.[17]

Further,

WR 104's rotational axis is aligned within 16° of Earth.

Now, we may wander closer to or farther from the centreline, but let's assume it can hit us right now, i.e. Θ = 16º. We need the area of a spherical cap on the end of a cone.

Wikipedia gives the expression Area = pi * (2*r*sin(Θ/2))^2. Areal energy density will be 1e44J/Area.

Plugging that into Google gives 72 kJ/m^2. Now if it hits us with a 2º blast, we're looking at 4.6MJ/m^2. This is delivered over 2 or 3 seconds. Total energy delivered to the Earth is about 2 gigatons. (On second thought, r is so large that I may as well have used a cone.)

I don't know what the effect would be, since it wouldn't all be delivered to the surface of the Earth, and there would be chemical atmospheric effects.

Oh come on, we were going to gut-punch each other with ten times as much energy in the 80's. Is that all that Mother Nature can do?

[Havok]

Oh come on, we were going to gut-punch each other with ten times as much energy in the 80's. Is that all that Mother Nature can do?

Well to be fair to mother Nature, our full arsenal may not have effected our moon. Her light show is going to nail us from 8500ly away. You have to give her a little credit.

[Fingolfin_Noldor]

Oh come on, we were going to gut-punch each other with ten times as much energy in the 80's. Is that all that Mother Nature can do?

Well, you will certainly get your wish if the GRB is much closer, like a few hundred light years or so. A supernova will do nicely just as well.

[Winston Blake]

Oh come on, we were going to gut-punch each other with ten times as much energy in the 80's. Is that all that Mother Nature can do?

Well, I was unclear - that was for the 16º blast. The 2º one hits us with 140 gigatons. If a 2º GRB hits us from within 10 light years, it's 89 million gigatons. That is, everything within 0.7 light years gets hit with 0.7 kT/m^2.

Here's an awesome (awe-ful?) scenario, where a genuine 'nuclear winter' occurs, the skies darken with acid rain clouds, all the flora gets cancer and radioactive 'fallout' engulfs the Earth. That's the sugar-coated version. The bad version is a massive bombardment with high energy particle radiation that triggers "still more deadly atmospheric cascades of nuclear interactions lasting up to a month".

How much ozone would be destroyed? Thorsett estimated that if the burster were located near the center of our galaxy, some 30,000 light-years away, the ozone depletion would be a few percent, comparable to that produced by natural disasters like large volcanic eruptions, very intense solar flares, or even a meteor impact on the scale of the one that exploded over Tunguska, Siberia in 1908.

If the burster were closer, say less than 3,000 light-years away, the gamma-ray flux received in a few tens of seconds could wipe out the entire ozone layer for years to come. At the very least, the drastic increase in solar ultraviolet radiation reaching Earth's surface would cause severe skin cancers. For humans and other animals, slow starvation would likely result, as the harmful ultraviolet flux inhibited plant growth and damaged and altered ecosystems supporting the food chain. As in a nuclear winter, the nitric oxides darkening our skies could also cause acid rains and significant cooling of the Earth's surface. Such pollutants would take decades to settle out of the stratosphere.


But that's not all. In addition to the chemical changes in the atmosphere, the nuclear interactions induced by the high-energy gamma rays would rapidly produce huge quantities of radioactive nucleids, such as carbon-14, which has a half-life of 5,700 years. Of course, winds would distribute this fallout worldwide.


It gets worse Depending on what the mechanism for producing a gamma-ray burst actually is, a nearby burst could wreak even more havoc. Nir Shaviv and Arnon Dar of the Israel Institute of Technology have explored a particularly devastating model for generating gamma-ray bursts from co-orbiting pairs of neutron stars. All neutron star pairs eventually spiral together, losing energy through gravitational radiation as predicted by Einstein's theory of general relativity.

Shaviv and Dar postulate that as the neutron stars begin their own catastrophic merger, jets of matter would be flung from the system at nearly the speed of light. These atoms and ions would be so energetic that they would absorb visible starlight and re-emit gamma rays, which we would detect as a gamma-ray burst. Impinging on our fair planet shortly after the horrific flash of gamma rays, the energetic particles themselves would join in the destruction, triggering still more deadly atmospheric cascades of nuclear interactions lasting up to a month.


Earth If Shaviv and Dar are correct, a collapsing binary neutron star system anywhere nearby would spell doom for our fair planet.
These authors and others note that known pairs of neutron stars exist in our galaxy, including one within about 1,500 light-years. This knowledge has led to the speculation that in the past the Earth has found itself uncomfortably close to a violent neutron star merger. Some estimates hold that one occurs within about 3,000 light-years of the sun every 100 million years on average. Intriguingly, this timescale is roughly the same as the time between mass extinctions in our planet's geological record.


Learn to love the burst One shouldn't worry too much, though. For one thing, mass extinctions in the past might have been the result of purely terrestrial phenomena, such as climatic changes produced by plate tectonics and volcanic activity, or of more familiar kinds of cosmic disasters, like the asteroid impact thought to have caused the dinosaur extinction at the end of the Cretaceous Period. For another, even if the aforementioned scenarios turned out to be true, we would still have, statistically speaking, about 50 million years until the next gamma-ray burst of doom.

Which gives us time to get to know bursters better. Our understanding of them constantly changes as new findings are reported. For instance, recent afterglow studies have indicated that a burst's energy is beamed in a particular direction rather than radiating in all directions from the source, substantially reducing the burster's total energy requirement.


Hypernova This image shows M101, a nearby spiral galaxy, which bears two candidates for possible hypernovae -- hypothesized explosions of high-mass stars that release perhaps ten times the energy of conventional supernovae.
Moreover, even after three decades of study, the true nature of gamma-ray bursts remains unknown. Many astrophysicists have taken a shine to a new theory, which for the moment has eclipsed the neutron-star-merger scenario in popularity. Evidence is mounting that at least some bursters are more likely associated with star-forming regions than with binary neutron stars. Theoretical models now in vogue indicate that gamma-ray bursts result from "hypernovae" -- the collapse of the cores of extremely short-lived massive stars into black holes.

Another theory actually paints gamma-ray bursts in a positive light. University College Dublin researchers Brian McBreen and Lorraine Hanlon recently estimated the effects of a nearby gamma-ray burst on the preplanetary solar nebula, the cloud of condensing star stuff that formed our solar system some 4.5 billion years ago. They calculated that iron in the nebula would have been the major absorber of the high-energy X-rays and gamma rays from such a burst, causing the nebula's dust to become molten in seconds and then cooling slowly to form millimeter-sized chondrules, round granules of cosmic origin. Chondrules, they note, combined to form meteorites and possibly the rocky terrestrial planets, including Earth.

So, you see, despite the gloom-and-doom scenario I painted above, perhaps we should call them bursts of life.

[Paolo]

Pre-pint for Tuthill's WR-104 article.

[Kuroneko]

If the jet opening angle is θ, then corresponding solid angle is Ω = 8π sin²(θ/4), not with θ/2 as above, also gaining an extra factor of two because there are two jets. Hence, for θ = 2°, we have Ω = 1.9E-3 sr. The average incident energy for a one-foe GRB at R = 8000ly would be at 1e44J/[ΩR²] = 9.1MJ/m² inside the cones, and the expected total energy incident on Earth assuming it is within one of the cones would be 280GT. Of course, being in the path of such a focused jet is extremely unlikely, even more so given the rotational axis of WR 104.

[Zablorg]

Fuck, that article describes the most kick-ass apocolypse ever. Bring it on, baby!

I would be very interested to find out the concequences of this incident on the other planets in our solar system. Having a different atmosphere and gravity and whatnot would doubtless change the result.

[Zac Naloen]

The Incredible Hulk is going to have quite a bit of competition in the future.

Near the end it talks about this happening 433 million years ago, killing most of the life on earth and cooling the earth. How does this gamma blast cool the earth exactly?

It wipes away the Ozone layer.

A main component in the Greenhouse effect iirc.

Where on earth did you get that idea?

I meant Ozone, not the Ozone layer.

Either way, wiping out the Ozone layer would mean less spare Ozone to act as a greenhouse gas in the troposhere.

[Junghalli]

correct me if I'm wrong, but if the earth is hit by a GRB there will be no "duration of the crisis", the earth will just be totally oblitterated. Sure we could live in artificial structures forever, but I believe the surface of the earth will be totally lost.

Most of the estimates being thrown around are a few megawatts per meter for a few seconds. Certainly enough to be devestating, but not enough that an underground bunker couldn't survive or the oceans would boil. The surface could be reseeded once the atmospheric effects had passed.

[wjs7744]

Well, I was unclear - that was for the 16º blast. The 2º one hits us with 140 gigatons. If a 2º GRB hits us from within 10 light years, it's 89 million gigatons. That is, everything within 0.7 light years gets hit with 0.7 kT/m^2.

Of course, we must remember that as we decrease the angle, the chance of us getting hit will decrease exponentially.

[Molyneux]

The one phrase that popped into my head on reading that description was this: "Light the sky on fire."

[Turin]

It wipes away the Ozone layer.

A main component in the Greenhouse effect iirc.

Where on earth did you get that idea?

I meant Ozone, not the Ozone layer.

Either way, wiping out the Ozone layer would mean less spare Ozone to act as a greenhouse gas in the troposhere.

While tropospheric ozone is apparently a much larger source of radiative forcing than I thought off-hand, the degree of stratospheric contribution to tropospheric ozone is a matter of some debate. Here's a link to a NOAA article on the subject.

But it occurs to me this is probably an irrelevant nitpick in this case -- if we were talking about a spike in the sun's activity or something I might have a point, because the tropospheric ozone doesn't absorb as much of the incoming radiation as the stratospheric ozone. But with a gigantic burst of radiation like we're talking about here, there's plenty of radiation to go around; the tropospheric ozone will absorb a lot of the incoming energy as well. So nevermind.

[Winston Blake]

If the jet opening angle is θ, then corresponding solid angle is Ω = 8π sin²(θ/4), not with θ/2 as above, also gaining an extra factor of two because there are two jets.

θ is the half-angle in that diagram. You're right about neglecting the other jet.

Hence, for θ = 2°, we have Ω = 1.9E-3 sr. The average incident energy for a one-foe GRB at R = 8000ly would be at 1e44J/[ΩR²] = 9.1MJ/m² inside the cones, and the expected total energy incident on Earth assuming it is within one of the cones would be 280GT.

Putting a half-angle of 1º into my google link and halving to account for the other jet reproduces this result.

[Kuroneko]

θ is the half-angle in that diagram. You're right about neglecting the other jet.

Correct, but θ is not the opening angle in that diagram. I suppose that in order to prevent confusion, I should have used a different symbol for the opening angle, rather than redefining θ to be so, but my statement is correct. Alright; from now on, let α be the opening angle. Then, to follow your diagram, θ = α/2, and so we get a total solid angle of Ω = 8π sin²(θ/2) = 8π sin²(α/4) for the two jets.

Putting a half-angle of 1º into my google link and halving to account for the other jet reproduces this result.

Since sin²x = [x + O(x³)]², so for small opening angles, doubling the angle gives a result that's four times less than it should be, but neglecting the other jet doubles it. That's why your figure is half what it should've been.

Not that it really matters all that much--the values used here are rather arbitrary in the first place. It's not good for anything but a very rough order of magnitude.

[Winston Blake]

Kuroneko

Sorry, I misinterpreted your post as shooting down my calculations, rather than you simply doing your own example.

[Kuroneko]

Kuroneko
Sorry, I misinterpreted your post as shooting down my calculations, rather than you simply doing your own example.

Well, it pretty much was... or so I thought at first. There seems to be some confusion over the term "opening angle". The way I've seen it used prior to today was the vertex angle of a cross-section of a plane containing the axis of the cone, as in here. By that definition, your calculations would be somewhat incorrect, since where you calculated entered θ = 16° or 2° into google's calculator, the actual opening angles would be 32° and 4°, respectively.

However, quickly looking the term on google to make sure I haven't lost my sanity, it seems there's a contrary definition here. According to that source, your interpretation of measuring the opening angle from the axis itself is correct. Yet others call your θ the semi-opening angle instead, suggesting the previous cross-section definition.

Very strange. The discrepancy makes me wonder whether "2-20° opening angle" in statement regards to GRBs refers to angles measured from the axis or through the axial cross-section. [Edit: The usage I've seen prior to now has always been the latter. Re-reading your post, it seems that by "x° blast", you mean "x°" for specifically θ. So I think I've probably misinterpreted you, although there's just that factor of two for the other jet. Consider this retracted.]

[Paolo]

Just mining through the references in the Tuthilll paper, θ_j appears to always measure from 0 to π/2, implying a measurement from the axis.