How Close Can Spaceships Safely Approach Black Holes?

[essenmein]

Trying to understand radiation near black holes, specifically sgr-a, and more generally "radiation in space" and its general threat to the survival of spaceship occupants. Please let me know if this would be more appropriate in a different section here, eg astrophysics.

In my little story the human protagonists discover some alien tech that gives them FTL capability, so one of the first things they decide is to do circumnavigate sgr-a. However rather than the usual fears about black holes (ie the gravity well), they can't even get close without being heavily irradiated, exceeding the ships shielding very quickly, I used 10's of light years as being "too close to survive", as well as time dependent radiation, ie at 100ly everything was fine, but 50ly closer (and 50 years difference in when that radiation was emitted) they find their ship overwhelmed in a wash of radiation cause by "something", say a star being gobbled up by the black hole etc.

As a guide I look at for example the xray burst from SGR 1806-20, a neutron star that exploded and sent X-rays flooding through the galaxy on December 27, 2004. Now its obvious the star didn't explode on December 27 of 2004, that's when we saw it, the star is about 50kly away from earth, so it happened about 50k years ago.

"The peculiar oscillations the researchers found began three minutes after a titanic explosion on a neutron star that, for only a tenth of a second, released more energy than the sun emits in 150,000 years. The oscillations then gradually receded after about 10 minutes. "

So if you have an xray flash that contains such an obscene amount of energy, if you were to run into the wave of such a pulse as it rippled through our galaxy, I imagine that can't be good news for the crew. Which sets up a situation of dangerous distance/time related coincidences where you might accidentally run into such a thing.

Thoughts? given the radiation reduces with cube of distance, how "close" to say that pulse from SGR1806-20 could you be without insta death in a reasonably shielded ship, now I know this is a large "unknown" here, the shielding is good, but not impossibly good? How about when would that turn mass into plasma?

Its conceivable that the galaxy is full of these wave fronts that we haven't seen yet, or washed past us before we had the tech to detect them, so how dangerous really is this if you have ftl capability?

I imagine this threat would be quite different for "warp" type drives that travel linearly through space, they could drive through one with bad side effects vs a jump type drive where you are removed from our "space" during your "journey".

 

[anorlunda]

For SF purposes, I think it is much easier, and maybe more plausible to say that we develop immunity to radiation. Perhaps nanobots that repair DNA damage one molecule at a time. Similar bots could repair electronics by shoving atoms around.

 

[essenmein]

For SF purposes, I think it is much easier, and maybe more plausible to say that we develop immunity to radiation. Perhaps nanobots that repair DNA damage one molecule at a time. Similar bots could repair electronics by shoving atoms around.

This is already the case, the whole "system interface" between humans and computers is augmented reality via nano machines that connect into various section of your brain, they are also capable of some repairs. We essentially become functionally immortal after we continue advancing the tech. But there is a limit, like being vaporized by high radiation flux would be one.

However this is more about vessel vulnerability. It is meant to be hard ish sf, ie I've made a couple of technologies available, but other than that space is space. I can't believe anything would be still solid say one light year away from that neutron star explosion.

 

[anorlunda]

I can't believe anything would be still solid say one light year away from that neutron star explosion.

Are you thinking of ablation? If so, then radiation is not the best word in the title.

 

[essenmein]

Are you thinking of ablation? If so, then radiation is not the best word in the title.

I would have though ablation would be the result of high photon flux?

(its actually the weakness of the nuke pumped xray guns in the story, ablation causes vapor cloud which absorbs part of the pulse rather than the "target")

So just warping some numbers around that neutron star explosion. According to that link would take 150k years for our sun to produce that energy. So that is ~4.7e12 x the radiation output we see today from our star, by radiation I mean it in electromagnetic sense, ie energy transfer via photons.

Pretty sure some very bad things would happen if we got 4e12 x the solar radiation even if only for 0.1s!

Basically from a plot perspective, I'm looking for plausible "space dangers" and enormous energy level radiation pulses from stars/black holes etc would be undetectable till they hit you (speed of light), seem like the only realistic thing that actually exists. Sort of semi kinda like rogue waves.

 

[stefan r]

Basically from a plot perspective, I'm looking for plausible "space dangers" and enormous energy level radiation pulses from stars/black holes etc would be undetectable till they hit you (speed of light), seem like the only realistic thing that actually exists. Sort of semi kinda like rogue waves.

As a particle approaches light speed its energy approaches infinite. Any particle should penetrate through any amount of armor. Any impact with an electron, neutron, or proton would produce a shower of many other high energy particles. A thicker shield will just cause a larger shower. You are moving faster than light so the only option is to disregard that.

Also frequencies of light shift as you move toward them. Approaching light speed regular sunlight that is directly ahead would become gamma radiation. Closer to light speed radio waves would increase to x-ray and then gamma radiation. Very high energy gamma radiation will generate particles in your radiation shield. You need to disregard that too.

So just warping some numbers around that neutron star explosion. According to that link would take 150k years for our sun to produce that energy. So that is ~4.7e12 x the radiation output we see today from our star, by radiation I mean it in electromagnetic sense, ie energy transfer via photons.

Pretty sure some very bad things would happen if we got 4e12 x the solar radiation even if only for 0.1s!

At 1 au solar radiation is 1368 W, so 5.5 petawatt in your example. In 0.1s you get 550 terrajoules. Slightly more than 100 kilotons TnT per square meter.
Intensity decreases with the square of distance. (cube of distance is only explosions inside of something). 0ne light year is 63,241 au so around 1.4 megawatt per meter squared. At 10 light year it is 14 kilowatt or 1.4 kilo joules in 0.1s.

1.4 kilo Joule is enough energy to convert 4.1 grams of ice into water or boil 1 g/m² of ammonia. If you are using ice water as your radiation shield you should use more than 4 grams per square meter IMO. 100 kg/m² is only fist size thickness.

A thin plate of lead/gold/uranium would adsorb the energy in a much thinner layer. That could melt or even boil. You could anticipate that and put the gold/lead pipes inside of water ice. The radiation heating could boil the ammonia on the inside of the pipes but the pipes would stay where they are inside of the water ice. A graphene or even plastic film could prevent evaporation from the outside surface of the ship. The structural component of the hull would be inside of the shield. Bronze, Steal, and aluminum layers would adsorb the secondary x-rays coming off of the lead. An inner layer of plastic foam keeps the ship warm and adsorbs any secondary/tertiary florescence from the steal and aluminum. You need something similar to block normal cosmic radiation.

The primary problem with gamma rays is the possibility of the ray coming straight through the shield.

I would have though ablation would be the result of high photon flux?

(its actually the weakness of the nuke pumped xray guns in the story, ablation causes vapor cloud which absorbs part of the pulse rather than the "target")

Can be any energy source. For example the heat shield on the Apollo reentry vehicles. If you are talking about glaciers, ablation is usually caused by evaporation, wind, rain, and runoff. A glacier could absorb a lot of x-rays. The water, steam, and plasma leaving a glacier's surface would adsorb x-rays too.

 

[essenmein]

As a particle approaches light speed its energy approaches infinite. Any particle should penetrate through any amount of armor. Any impact with an electron, neutron, or proton would produce a shower of many other high energy particles. A thicker shield will just cause a larger shower. You are moving faster than light so the only option is to disregard that.

Also frequencies of light shift as you move toward them. Approaching light speed regular sunlight that is directly ahead would become gamma radiation. Closer to light speed radio waves would increase to x-ray and then gamma radiation. Very high energy gamma radiation will generate particles in your radiation shield. You need to disregard that too.

Re particle near luminal velocity, is this in relation to the expanding radiation waves propagating through the galaxy as a result of large events or in relation to a vessel traveling at super luminal linear velocity encountering a slower bit of stuff? The radiation waves would be expanding at exactly the speed of light.

In the story the vessels do not actually exceed light speed, its either via einstein rosen bridge, or the alcubierre drive. Although the linear collision issue with the alcubierre drive is a problem, but more for larger bodies?

So the alcubierre type drive would have to go through these waves, possibly with reasonably probability of an encounter, whereas the jump drive doesn't, but that doesn't mean you couldn't by exceedingly small probability jump into the way of such a wave since you cannot detect its imminent arrival.

The vessel armor is built of composite layers of passive protection, similar to wipple shields, but many many meters thick, this armor is sacrificial and replaced as it wears out.

At 1 au solar radiation is 1368 W, so 5.5 petawatt in your example. In 0.1s you get 550 terrajoules. Slightly more than 100 kilotons TnT per square meter.
Intensity decreases with the square of distance. (cube of distance is only explosions inside of something). 0ne light year is 63,241 au so around 1.4 megawatt per meter squared. At 10 light year it is 14 kilowatt or 1.4 kilo joules in 0.1s.

Hah, it should have occurred to me to simply calculate the rest from where I started, thanks!

Either way gives me some good perspective of the power/energy levels.

Even at Pluto distance (~1W/m2 solar rad) its still 73tons of TNT per m2 (100/1366).

Thanks for the input!

 

[hmmm27]

so one of the first things they decide is to do circumnavigate sgr-a

So, no sequel planned, eh?

"Hey guys, I just got a sailboat !"
"Neat, let's see how it works in the lava pit"

 

[essenmein]

So, no sequel planned, eh?

Well, that ship doesn't survive... but not because of the black hole.

 

[GTOM]

Against charged particles at least, there could be an electromagnetic field to divert them.
Otherwise they shouldn't go anywhere near to so dangerous objects IMHO.

 

[essenmein]

Against charged particles at least, there could be an electromagnetic field to divert them.
Otherwise they shouldn't go anywhere near to so dangerous objects IMHO.

Yeah magnetic field would divert charged particles.

Re going anywhere near those dangerous objects, that's the question in the thread, how far away is safe? At the moment I only have one data point, Earth is ~26kly away from sgr-a and seems safe.