What does a million-ton black hole eat?

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What does a million-ton black hole eat?

Postby snowyowl » Sun Jun 01, 2014 3:25 pm UTC

Let's say you like the sound of having an exawatt of power at your disposal. So you collapse a million tons of rock into a black hole (somehow), and build a space station around it. Based on the figures on this page, it produces 1.6 exawatts of Hawking radiation, or 18kg/s. (If this is too energetic, start with a larger black hole.) Left unattended, it will burn through its entire mass in a year, incidentally producing a gamma-ray burst in its last seconds. To keep its output at comfortable power-a-civilisation levels instead of annihilate-a-star-system levels, it needs to be fed with 18kg of mass every second.

It seems to me that fitting 18kg/s into an object 15 nanometers across (a good size for a protein molecule) will be quite difficult. Can you just toss any old waste into it, or are there some materials that are better than others? What is the ideal fuel source? Will it absorb visible light, considering that light has a wavelength in the 500 nm range? Or is there nothing that can feasibly be fed into it at fast enough speeds, and you should start seeing how quickly you can get out of GRB range?
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Re: What does a million-ton black hole eat?

Postby SlyReaper » Sun Jun 01, 2014 4:05 pm UTC

If you have the technology to collapse a pile of rocks into a singularity, you probably have the technology to force more material into the singularity against the radiation pressure. Ideal material would be the densest material you can manipulate this way. I'd suggest more black holes.
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Re: What does a million-ton black hole eat?

Postby stoppedcaring » Mon Jun 02, 2014 2:49 pm UTC

Yeah, find a nice-sized globular cluster and set up some sort of unobtanium superstructure to daisy-chain black hole creation, pulling matter out of it and compressing it and tossing it into your power source. Messier 80 is 5e5 solar masses, which should keep your black hole at constant mass for ten million billion times the present age of the universe.

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Re: What does a million-ton black hole eat?

Postby speising » Mon Jun 02, 2014 6:09 pm UTC

talk about the dangers of nuclear power!
if you should ever, for whatever reason, fail to feed the beast regularly, it'll destroy everything in the system.

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Re: What does a million-ton black hole eat?

Postby snowyowl » Mon Jun 02, 2014 7:58 pm UTC

Hmm, noted.

So if you wanted to use this as a power source without a daisy-chain of constant black hole production (and let's face it, I don't see how you're producing million-ton black holes without collapsing a star in the process), you'd better start with something a bit cooler. A billion-ton hole, perhaps, which only needs to be fed at 18mg/s, but still puts out a terawatt or so. That seems a bit anticlimactic, though. A terawatt isn't very much by star-collapsing standards.
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Re: What does a million-ton black hole eat?

Postby stoppedcaring » Mon Jun 02, 2014 8:04 pm UTC

If you have the capacity to collapse a black hole, why don't you put a dyson sphere around it and reflect the Hawking radiation back in except when you need it? Then you basically end up with an antimatter-free mass-to-light converter.

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Re: What does a million-ton black hole eat?

Postby speising » Mon Jun 02, 2014 9:47 pm UTC

how do you keep the bh centered in the sphere?

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Re: What does a million-ton black hole eat?

Postby gmalivuk » Mon Jun 02, 2014 9:57 pm UTC

Open windows in the sphere from time to time so radiation pressure on the opposite side pushes it in that direction.

The bigger issue is that your material is still going to reach thermal equilibrium at some point and leak energy, and even if it didn't you'd still be losing mass every time you used some of the energy, so the problem of what to "feed" it isn't fixed.

snowyowl wrote: Will it absorb visible light
Even if it could, if you've already got a source of light that powerful, what do you need the black hole for?
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Re: What does a million-ton black hole eat?

Postby iChef » Fri Jun 20, 2014 2:11 am UTC

Whatever it wants.

But seriously, how accurate do you need to be with the 18kg/s. What are the tolerances to keep this thing from going haywire. If you forget to perfectly calibrate your scale one day lots of little pieces of you and your co-workers WILL go to space today.
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Re: What does a million-ton black hole eat?

Postby gmalivuk » Fri Jun 20, 2014 2:28 am UTC

At that size, it'll still take awhile before it becomes unmanageable at approximately 18kg/day, give or take a bit. As long as you're keeping fairly close track of the black hole's mass or energy output, your input can vary by a few percent each day without causing any real harm.
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Re: What does a million-ton black hole eat?

Postby iChef » Fri Jun 20, 2014 4:37 am UTC

Ah ok, but is it 18kg a day or 18kg a second it needs to be fed. I can see 18 kg a day being easy to track. At 18kg a second a small error can add up quickly. Hopefully with the kind of tech level it takes to make something like this that kind of measurement would be no problem, but nothing is fool proof.
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Re: What does a million-ton black hole eat?

Postby gmalivuk » Fri Jun 20, 2014 11:36 am UTC

Ah, right, per second. I'd forgotten how absurd we were talking.
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Re: What does a million-ton black hole eat?

Postby PM 2Ring » Sat Jun 21, 2014 8:42 am UTC

Yeah, feeding 18kg a second into an event horizon that small requires the "food" to have a ridiculously huge density, even if we assume it's traveling close to c. So maybe we should go with the larger cooler BH suggested in snowyowl's later post.

But I just noticed that the figures for Hawking radiation at the OP link http://www.xenology.info/Xeno/17.3.5.htm don't agree with those calculated by the Hawking Radiation Calculator. I can't see the formulas Robert A. Freitas Jr. used to calculate his figures in that table. OTOH, I haven't checked all the formulas stated on the xaonon page, either, but the ones I have checked look right.

Hmmm.

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Re: What does a million-ton black hole eat?

Postby stoppedcaring » Mon Jun 23, 2014 2:53 pm UTC

Black holes are still entirely subject to conservation of momentum, right?

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Re: What does a million-ton black hole eat?

Postby SDK » Mon Jun 23, 2014 3:57 pm UTC

PM 2Ring wrote:Yeah, feeding 18kg a second into an event horizon that small...

Wow, that really is small. Even the larger billion ton black hole would have an event horizon smaller than a nanometer. Good luck with that.
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Re: What does a million-ton black hole eat?

Postby stoppedcaring » Mon Jun 23, 2014 7:48 pm UTC

KazukoKodo wrote:
PM 2Ring wrote:Yeah, feeding 18kg a second into an event horizon that small...

Wow, that really is small. Even the larger billion ton black hole would have an event horizon smaller than a nanometer. Good luck with that.

A million-tonne black hole has an event horizon surface area of only 3e-35 m2. Which is problematic. Forcing 18 kg per second into that small an area means you're going to need an ungodly density; that's a mass flux density of 6e35 kg/s*m2. If you fling your mass in at 50% the speed of light, it's still going to need to have a density of 4e27 kg/m3, ten orders of magnitude more dense than neutron starstuff.

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Re: What does a million-ton black hole eat?

Postby PM 2Ring » Tue Jun 24, 2014 2:02 pm UTC

stoppedcaring wrote:Black holes are still entirely subject to conservation of momentum, right?


Sure. And so for an isolated non-rotating black hole the Hawking radiation is spherically symmetric. Obviously, we don't want to disrupt that symmetry with our feeding and energy harvesting processes.


KazukoKodo wrote:Wow, that really is small. Even the larger billion ton black hole would have an event horizon smaller than a nanometer. Good luck with that.


Yes. But at least the gigaton BH is larger than a proton, making it somewhat easier to feed. I guess electrons (and neutrinos) are small enough to be eaten by a megaton BH, and it could even eat nucleons by spaghettify them (but I expect that process would create jets as the BH attempts to separate the quarks). That's assuming you can get the particles close enough to the BH, which is going to be rather difficult with all that ultra-hard gamma Hawking radiation blasting out of it...


stoppedcaring wrote:A million-tonne black hole has an event horizon surface area of only 3e-35 m2. Which is problematic. Forcing 18 kg per second into that small an area means you're going to need an ungodly density; that's a mass flux density of 6e35 kg/s*m2. If you fling your mass in at 50% the speed of light, it's still going to need to have a density of 4e27 kg/m3, ten orders of magnitude more dense than neutron starstuff.


We'd have to fling the mass in at highly relativistic speed, both to achieve sufficient density and to get past the Hawking radiation. The effective mass of the food isn't just its rest mass: the faster the food's going the more KE it can feed to the BH; I suppose that this is one of those rare situations where it is useful to think in terms of relativistic mass. We also get a (radial) density boost courtesy of Lorentz-FitzGerald contraction (I think :) ).


I'm going to assume that the table in the OP link is wrong, and use the calculator on the xaonon page. Here's what it says for a gigaton BH:

Radius = 1.484852 fm
Area = 0.2770613 barns
Surface gravity = 3.026414e+31 m/s²
Temperature = 1.227203e+11 K
Luminosity = 3.563442e+8 W
Lifetime = 2.664132e+12 years

Converting that luminosity into mass per unit time (using the Google calculator) gives
3.563442e+8 W / c² = 3.964864 µg/s = 0.3425642 g / day

which is a lot smaller than the figure given in the xenology table.

Wikipedia says that neutron star density ranges from around 1E9 kg/m³ in the crust, and ranging to above 6E17 kg/m³ deeper inside; normal atomic nuclear density is around 3E17 kg/m³.

If we assume the food has a density of 3E17 kg / m³, we get a very modest speed of
(((3.964864E-6 g/s) / (3E17 kg/m^3)) / (0.2770613 barns))
= 477 m/s.

...

Alternatively, let's assume the food has the density of water: 1000 kg/m^3. Then the speed required (doing a non-relativistic calculation) is
((((3.964864E-6 g/s) / (1E3 kg / m^3)) / (0.2770613 barns)))
= 1.43104216E17 m/s = 477344282c

Now let's treat that 477344282 as a Lorentz factor and find the corresponding speed (using python's mpmath module to do the arithmetic).

sqrt(1-(1/477344282)^2)
~= 0.9999999999999999978 = 1 - 2.2e-18

So we can feed the gigaton BH with water if we blast it in at 0.9999999999999999978c. :)

EDIT

Note that the last calculation doesn't take into account Lorentz-FitzGerald contraction. I think we can do that by taking the square root, i.e.,
v/c = sqrt(1 - 1/477344282)
giving a speed of 0.99999999895c = (1 - 1.05e-9)c

(but it's getting late...)

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Re: What does a million-ton black hole eat?

Postby Livemike » Thu Apr 07, 2016 1:14 pm UTC

Ok, a few things, the size of the black hole is in _attometers_ not nanometers and it's 1.5 not 15. That's 1.5 * 10^-18 meters so basically 1/500th the size of a proton. So hiting it is going to be hard. Sure the gravity will pull it in, but you're still talking about a ridiculously precise hyperbolic trajectory.

The total momentum of the radiation in one second is going to be 18 kgs * speed of light = 5.4 *10^9. Momentum is force * time so total force applied by radiation pressure is, if I haven't made a major blunder, which I probably did, 5.4 * 10^9 Newtons. So if the containment area is a 1 km sphere the pressure it has to take is about 5.4 * 10^9 Newtons/ 12566370 m^2 or about 430 pascals. The gravity is about 6.6726 *10-8 m/s. So there is about 6,440,043,556 times as much force pushing out over a meter than there is pushing in on a kilogram. So nothing's going in unless you it isn't affected by radiation pressure. Which I think means only light.

stoppedcaring is right, you need to reflect almost all the radiation back in if you want to keep it fed. What else you throw in I have no idea, since I don't think matter will go.

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Re: What does a million-ton black hole eat?

Postby Neil_Boekend » Thu Apr 07, 2016 2:45 pm UTC

speising wrote:how do you keep the bh centered in the sphere?

You give it an electric charge and center it with electric fields (© Larry Niven).

Livemike wrote:Ok, a few things, the size of the black hole is in _attometers_ not nanometers and it's 1.5 not 15. That's 1.5 * 10^-18 meters so basically 1/500th the size of a proton. So hiting it is going to be hard. Sure the gravity will pull it in, but you're still talking about a ridiculously precise hyperbolic trajectory.

The total momentum of the radiation in one second is going to be 18 kgs * speed of light = 5.4 *10^9. Momentum is force * time so total force applied by radiation pressure is, if I haven't made a major blunder, which I probably did, 5.4 * 10^9 Newtons. So if the containment area is a 1 km sphere the pressure it has to take is about 5.4 * 10^9 Newtons/ 12566370 m^2 or about 430 pascals. The gravity is about 6.6726 *10-8 m/s. So there is about 6,440,043,556 times as much force pushing out over a meter than there is pushing in on a kilogram. So nothing's going in unless you it isn't affected by radiation pressure. Which I think means only light.

stoppedcaring is right, you need to reflect almost all the radiation back in if you want to keep it fed. What else you throw in I have no idea, since I don't think matter will go.

Radiation pressure works on surface. Gravity works on mass. If you make stuff dense enough you'll make the surface area small and the mass high. Black holes would do nicely (although they are difficult to handle) , or anything at sufficient high speed to overcome that exact radiation pressure (and to have sufficient relativistic mass).
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Re: What does a million-ton black hole eat?

Postby gmalivuk » Thu Apr 07, 2016 5:49 pm UTC

Neil_Boekend wrote:Radiation pressure works on surface. Gravity works on mass. If you make stuff dense enough you'll make the surface area small and the mass high. Black holes would do nicely (although they are difficult to handle) , or anything at sufficient high speed to overcome that exact radiation pressure (and to have sufficient relativistic mass).
Okay, but the stuff has to have 6 billion kg behind every square meter on the inside of the containment, and if any of that mass is significantly farther away than 1km, gravity will affect it less and you'll need even more of it.

Also, remember that the radiation pressure goes up as you get closer, so even if something can get past 1km, how's it supposed to get past 1m, where the radiation pressure is a million times stronger?

To actually get anything into a black hole this small, it needs to be a massive particle moving with more kinetic energy than its rest mass, or it needs to be photons. In either case, you need some power source outside the black hole that can produce as much or more energy than the mass equivalent of what you're feeding it, which renders the black hole itself useless.
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Re: What does a million-ton black hole eat?

Postby Hypnosifl » Fri Apr 08, 2016 10:15 pm UTC

gmalivuk wrote:To actually get anything into a black hole this small, it needs to be a massive particle moving with more kinetic energy than its rest mass, or it needs to be photons. In either case, you need some power source outside the black hole that can produce as much or more energy than the mass equivalent of what you're feeding it, which renders the black hole itself useless.

I wonder how particles that are electrically neutral but do interact via the weak force, like neutrinos or WIMPs or mirror matter, would behave around that that level of radiation pressure--they are mostly "blind" to the electromagnetic force which is why they generally pass right through the Earth like it wasn't there, although they can interact with photons indirectly through the intermediary of a particle (perhaps including a virtual one?) that interacts via both the weak and electromagnetic force (as noted here they can have an interaction mediated by an electron for example).

I also wonder about trying to feed it with other, smaller black holes, which could spiral into the main black hole by mutual gravitational attraction even if they weren't initially aimed precisely right to hit each other. They would be able to absorb incoming photons and presumably this would cause some recoil, but they also have a very tiny surface area along with a huge mass, so if you did a Newtonian approximation it might not work out that their momentum would be changed too much.

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Re: What does a million-ton black hole eat?

Postby Xanthir » Sat Apr 09, 2016 2:03 am UTC

Gravitating bodies don't "spiral into each other", they orbit. Orbits only decay (into "spirals") when they're losing energy, which doesn't happen on useful timescales here. (Unless the ammo BHs are charged, but that gives the same problems as any other charged material.)
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Re: What does a million-ton black hole eat?

Postby Hypnosifl » Sat Apr 09, 2016 5:53 am UTC

Xanthir wrote:Gravitating bodies don't "spiral into each other", they orbit. Orbits only decay (into "spirals") when they're losing energy, which doesn't happen on useful timescales here. (Unless the ammo BHs are charged, but that gives the same problems as any other charged material.)

I was thinking specifically of the mechanism of orbital decay that caused the black hole collision detected by LIGO, gravitational wave emission--I didn't know how the timescales would compare given their much smaller size, which is why I prefaced the comment with "I also wonder", but it seemed at least possible it could be faster (for example if the same total number of orbits would be required, then simply because any given orbit will be much faster than for an astrophysical black hole the process would be faster). Doing a little googling, I found this paper where equation 44 gives the time for massive bodies to spiral into each other due to gravitational wave emission, if you assume the two bodies are of equal mass then the numerator is proportional to the initial distance to the fourth power while the denominator is proportional to the mass of each one to the third power. That would seem to imply if you scaled down a pair of black holes proportionally by some factor (reducing their initial separation by the same factor by which you reduce their masses, and hence their Schwarzchild radii) then the time for them to spiral into each other should be lessened by that same factor.

edit: formula 44 in the linked paper seems to be given in units where the initial distance between the two bodies has been converted to a time by dividing distance by the speed of light, 299792458 meters/second, and the masses of the two objects have also been converted to time by multiplying by (G/c^3) which works out to 2.47702 * 10^-36 seconds/kilogram. So, if you take the formula below:

(5*(R/299792458)^4)/(256*((2.47702*10^(-36))*M)*((2.47702*10^(-36))*N)*(((2.47702*10^(-36))*M)+((2.47702*10^(-36))*N)))

...and copy and paste it into the online calculator here, then hit "execute", you can fill in the value for the radius R in meters and the masses of the two bodies M and N in kilograms to get the time for them to spiral into each other in seconds. So with both M and N set to a million metric tons or 10^9 kg, if they were initially orbiting at 10^(-10) meters = 0.1 nanometers, they would spiral into each other in 7955 seconds, or 2.2 hours.

If the second black hole is only one one-hundredth of the mass, i.e. 10^7 kg, then placed at this distance they will spiral into each other in 1575206 seconds, still only 18.23 days. This might be enough time that you'd have to be concerned with the amount the smaller black hole's mass would decrease due to Hawking radiation, but if you started with a slightly larger mass so it would end up at 10^7 kg after 18.23 days, then it should take less than 18.23 days to spiral in.

So if you have the power to more create black holes the same size as your original or a few orders of magnitude smaller, and place them near the original to within a tenth of a nanometer (a fairly high degree of precision, but a lot less precise then placing them within 1 Schwarzchild radius of each other, which for a 10^9 kg black hole works out to 1.485 * 10^(-18)), then assuming the radiation pressure each exerts on each other doesn't significantly affect the inspiral time, this would be one way to give your original black hole regular "feedings".

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Re: What does a million-ton black hole eat?

Postby gmalivuk » Sun Apr 10, 2016 2:39 pm UTC

Hypnosifl wrote:If the second black hole is only one one-hundredth of the mass, i.e. 10^7 kg, then placed at this distance they will spiral into each other in 1575206 seconds, still only 18.23 days. This might be enough time that you'd have to be concerned with the amount the smaller black hole's mass would decrease due to Hawking radiation
That's an understatement. A 10^7kg black hole has a lifetime of 8407 seconds.

but if you started with a slightly larger mass so it would end up at 10^7 kg after 18.23 days
"Slightly larger", in this case, means 5.73 times larger.

and place them near the original to within a tenth of a nanometer
That doesn't account for the fact that you also need to force it into a circular orbit at that distance. Sure, both black holes are radiating more than enough power to do that, but only if you can point it in the right direction to slow it down just at the right point.
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Re: What does a million-ton black hole eat?

Postby Hypnosifl » Sun Apr 10, 2016 8:07 pm UTC

gmalivuk wrote:"Slightly larger", in this case, means 5.73 times larger.

Thanks for doing the math on that.
gmalivuk wrote:That doesn't account for the fact that you also need to force it into a circular orbit at that distance. Sure, both black holes are radiating more than enough power to do that, but only if you can point it in the right direction to slow it down just at the right point.

At large multiples of a Schwarzschild radius the orbit would apparently be fairly well approximated by the predicted orbit in Newtonian gravity (see the Paczynski-Witta potential, which approaches the Newtonian potential as the radius becomes large relative to the Schwarzschild radius), which means if you err on the side of making the speed smaller than that needed for circular orbit, you should get an elliptical orbit whose semi-major axis is smaller than the radius of a circular orbit, and whose semi-minor axis is even smaller (as in the diagram here showing the orbits of cannonballs fired with less than the velocity needed for circular orbit, found on slide 23 of this lecture). Although I don't know this for a fact, my intuition would be that the closer approaches to the central black hole would result in more energy being lost to gravitational waves than the corresponding circular orbit, so the time to spiral in would be shorter than for a circular orbit with the same initial radius. If that's correct, then you just need an initial speed that's less than or equal to that required for circular orbit--and that gives a pretty wide margin for error, since in Newtonian gravity a circular orbit at radius r from a mass M would have tangential velocity v = sqrt(GM/r), which in the case of M=10^9 kg and r=10^(-10) m works out to 25834 meters/second.

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Re: What does a million-ton black hole eat?

Postby gmalivuk » Sun Apr 10, 2016 8:45 pm UTC

None of that answers the question of how you slow it down in the first place.
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Re: What does a million-ton black hole eat?

Postby Hypnosifl » Sun Apr 10, 2016 10:11 pm UTC

gmalivuk wrote:None of that answers the question of how you slow it down in the first place.

Why "slow it down"? Are you assuming that whatever machine is used to create a million-ton black hole would tend to create one that has a very high velocity relative to the machine? If so, why?

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Re: What does a million-ton black hole eat?

Postby gmalivuk » Sun Apr 10, 2016 10:45 pm UTC

Hypnosifl wrote:
gmalivuk wrote:None of that answers the question of how you slow it down in the first place.

Why "slow it down"? Are you assuming that whatever machine is used to create a million-ton black hole would tend to create one that has a very high velocity relative to the machine? If so, why?
No, I'm simply assuming that whatever machine is creating black holes isn't dispensing them directly into a circular orbit 0.1nm from another black hole.

Gravity itself causes the high velocity.

Edit:

If a small mass starts from rest at infinity and falls toward a large mass, then its velocity at every point in its fall will be the escape velocity from that distance away from the large mass. Escape velocity has twice as much kinetic energy as a circular orbit at the same distance. For a 10^9kg point mass, a few meters is basically an infinite distance away, as far as orbital velocities and energies are concerned.

If you manage to drop your new black hole precisely enough that it will get as close as 0.1nm from the other black hole, it will be moving 41% faster by the time it gets there as what you want for a circular orbit.

My question is, how do you get rid of this extra 41% of velocity?
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Re: What does a million-ton black hole eat?

Postby Hypnosifl » Mon Apr 11, 2016 12:18 am UTC

gmalivuk wrote:
Hypnosifl wrote:
gmalivuk wrote:None of that answers the question of how you slow it down in the first place.

Why "slow it down"? Are you assuming that whatever machine is used to create a million-ton black hole would tend to create one that has a very high velocity relative to the machine? If so, why?
No, I'm simply assuming that whatever machine is creating black holes isn't dispensing them directly into a circular orbit 0.1nm from another black hole.

Gravity itself causes the high velocity.

Since we don't have even a sketch of how this technology might work it's hard to say, but I suppose I was imagining that the second black hole would be created by the machine within 0.1 nm of the first, as opposed to creating it far away and then letting them fall towards each other. This is bordering on "technology indistinguishable from magic", but suppose for example these mini black holes were created by causing two massive and oppositely-charged particles to move at ultra-relativistic speed in opposite directions towards the spot you want to create the black hole, with mutual attraction helping make sure they'd collide even if your aim wasn't precise, and with such a high gamma factor that their total energy in the center-of-mass frame would be equivalent to a million tons of mass. In that case the precision with which you could determine the location of a newly-created black hole would just be limited to how precisely you could aim the original two particles. I dunno, is there any more plausible method that could be used to create a black hole with such a small mass, one which would require that if you created multiple black mini holes they would start out far apart?

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Re: What does a million-ton black hole eat?

Postby gmalivuk » Mon Apr 11, 2016 12:25 am UTC

No, there aren't plausible ways to create black holes that size on demand, but there are fictional methods that at least don't nullify the entire premise of why you'd be using the black hole in the first place. If you can move things fast enough to have tons worth of kinetic energy, then you've got tons worth of energy already and wouldn't need the black hole's matter-to-energy conversion at all.

Also, if the particles aren't black holes until after they get to within a nanometer of the existing black hole, you haven't actually solved the problem of not being able to get matter that close to a radiating micro black hole. You know, the very problem "feed it with black holes" was supposed to be the solution for?
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Re: What does a million-ton black hole eat?

Postby Hypnosifl » Mon Apr 11, 2016 2:33 am UTC

gmalivuk wrote:No, there aren't plausible ways to create black holes that size on demand, but there are fictional methods that at least don't nullify the entire premise of why you'd be using the black hole in the first place. If you can move things fast enough to have tons worth of kinetic energy, then you've got tons worth of energy already and wouldn't need the black hole's matter-to-energy conversion at all.

One can imagine situations where you would, though--for example, the equipment needed to accelerate massive particles to those ultra-relativistic speeds might be larger than would fit on a convenient-sized ship, so the ship could use the black hole for energy storage between stopovers at systems where the black hole could be re-fed.
gmalivuk wrote:Also, if the particles aren't black holes until after they get to within a nanometer of the existing black hole, you haven't actually solved the problem of not being able to get matter that close to a radiating micro black hole. You know, the very problem "feed it with black holes" was supposed to be the solution for?

It's not that clear what the main problem is given that we're talking about an unspecified semi-magical technology like this, but I had thought of the problem not as the Hawking radiation but as the tiny size of the black hole event horizon (Schwarzschild radius about 1.5 * 10^-18 meters, which as someone mentioned is smaller than the size of a proton), requiring enormous precision to aim anything to fall into--if you can create another black hole nearby the level of spatial precision needed goes down by a factor of a hundred million or so, more like the size of an atom. As far as the Hawking radiation goes, as I said before, if you use electrically neutral particles the interaction with the radiation may not have much effect on them. And if you use ultra-relativistic particles as I suggested in my last post, they will have enormous momentum and will only be close to the other black hole for an extremely brief period of time before colliding with one another, so I suspect the radiation wouldn't deflect them too badly.

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Re: What does a million-ton black hole eat?

Postby gmalivuk » Mon Apr 11, 2016 3:15 am UTC

Hypnosifl wrote:As far as the Hawking radiation goes, as I said before, if you use electrically neutral particles the interaction with the radiation may not have much effect on them.
Okay, but you just suggested smashing charged particles together to create the nearby feeder black hole.
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Re: What does a million-ton black hole eat?

Postby Hypnosifl » Mon Apr 11, 2016 3:20 am UTC

gmalivuk wrote:
Hypnosifl wrote:As far as the Hawking radiation goes, as I said before, if you use electrically neutral particles the interaction with the radiation may not have much effect on them.
Okay, but you just suggested smashing charged particles together to create the nearby feeder black hole.

I only mentioned neutral particles to explain why I thought the tiny size of the black hole was a bigger problem than Hawking radiation. And in the next sentence after the one you quoted, I explained why I suspected the Hawking radiation also wouldn't cause significant deflection for the type of ultra-relativistic charged particles in my example (due to their huge momentum and the very brief time they spend near the black hole before colliding).


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