Black hole starship engines : Whoa

[Minecrafter1]

I read the following paper that describes in some detail the theory behind such an engine : http://arxiv.org/pdf/0908.1803.pdf

The thing about it is, unlike some of the even more esoteric ideas like warp drives, this engine is really just an efficient way of converting matter to energy. There might be an easier way, but this is the way modern physics knows about. So the fundamental idea is definitely possible, even if this particular approach won't work. (the paper mentions difficulty determining some key characteristics about how a small black hole might behave)

For those who don't read the paper, here's the TLDR :

The starship engine is a black hole emitting 140 petawatts (a 30 megaton nuke going off every second) worth of gamma rays. It is being fed a steady stream of fresh matter to keep the hole the same size. The starship would weigh about 1 million tons, and the engine would just be a (very huge) parabolic gamma ray reflector, with the black hole feeding and movement hardware located where the antenna is on a satellite dish. The reason to do this is that the engine would be insanely efficient, converting mass directly into light, and would also give you a full 1 G of acceleration. You could most likely collect enough interstellar hydrogen to run your ship indefinitely. It would need about 11 grams/second of matter, or 346 tons/year. (compared to 1 million ton mass of the starship)

The drawback is you cannot turn the engine off, and it is emitting all that energy in the form of gamma rays. I'm not even certain if any amount of shielding you could fit into the ship could protect biological people and leave them a big enough space to live in. The engine must burn forever : if you stop feeding the black hole, it loses mass, and eventually will release all remaining energy in one big flash when the mass is no longer enough to support an event horizon.

I guess what I find so fascinating about this engine is it's the only engine design I have ever read about that would really provide a satisfactory starship. Your ship would not be a delicate collection of struts to save mass, and you'd be able to burn the engine all the time without worrying about running out of fuel.

This thing could be a real warship : you'd be able to chase down anyone in any vehicle that doesn't have one, and you'd have plenty of mass for the weapons and armor.

Also, the other interesting factor here is size. Whatever the minimum size is for a black hole driven ship is, anything smaller than that is trash in a world that had this technology.

One final factor that fascinates me : you'd be able to see someone coming in a vehicle using this engine system a long, long, long way away. Probably on the order of light-years. No stealth at all, and since the black hole can't be turned off, it would be completely impossible to sneak up. (since even if you turn the engine exhaust the opposite direction, you have to vent all that waste heat).

One final note : since the black hole is electrically charged in order to move it with the vehicle, atmosphere would be Kryptonite to this kind of engine. Once it is no longer charged, the black hole would fall out the bottom of the ship and probably end up in the core of the planet you were to land on. Assuming the black hole cannot eat faster than it loses mass, it would dissipate harmlessly...or it might destroy the planet. Either way, a big problem. Just a funny thought that a million ton starship powered by the mightiest engine imaginable, releasing 5000 times as much energy per second as all of humanity uses today, can't go anywhere near a bit of wind. The ship would be forced to carry shuttles, that, amusingly, would have a tough time getting back out of deep gravity wells using most engine technologies. You might have to beam power to the ships and use a heat exchanger or something.

How to build one :

You build a big sphere near the sun of gamma rays lasers focused at the same point in the middle. The power to run the lasers comes from solar panels. The sphere is not more massive than other objects humanity has already built, and it is assumed that you have self-replicating robotics which would make the job fairly straightforward. You'd need an asteroid or two to mine for the raw materials.

At the center of the sphere, all the gamma rays will overlap into a tiny point about the wavelength of one gamma ray. Light has mass, and there would be enough mass in one place to generate an event horizon. You'd leave the lasers running for several years as the black hole grows in size.

Hawking radiation would cause the black hole to emit gamma rays made from the mass inside the black hole. It would emit about 140 petajoules worth every second when the black hole is around the right size.

Once the black hole is big enough to eat small particles, you would feed it a steady diet of electrons and protons in the form of a particle beam aimed right at it. The paper mentions this may be a problem : it is uncertain just how big a particle a black hole in this size range can actually eat. It mentions a couple of work-arounds if necessary.

You would move the black hole by electrically charging it by giving it an imbalance of charge by feeding it too many electrons or protons. You would now be able to move it using electrostatics or big honking electromagnets.

[AngelLestat]

Yeah, I read this paper some time ago.. At begining I was enthusiastic about the idea (is a really good idea after all), but it has their drawbacks.

For start, gamma rays are very difficult to handle, so how you manage to focus all that power in one point (atom side).

Second problem is how you feed this beast?

You hear, when this black holes are so small they expell a lot of energy, so any kind of mater that you want to put inside the black hole will disintegrate before reach it. It will produce millons of times more force to expell than to pull.

And is a really tiny black hole, so is really hard try to put some thing in its "mounth"

Also the energy that expell is more hard to harvester than antimatter annihilations.

But well, if someone find the way to solve these issues, seems like we have a perfect machine.. I drop a banana and I get E=mc2 from that banana

Also the hawking theories needs to be right.

[InfinityArch]

How about antimatter engines? They wouldn't be able to harvest fuel in situ, but they'd be about as efficient given that antimatter annihilation is just about the most efficient way of converting matter to energy we know of, and can be shut off and, if you don't mind frying the atmosphere with gamma rays, theoretically use it in an atmosphere.

[K^2]

All you do is point a particle accelerator at it, and it's fed. This is simple enough.

The problems are in keeping black hole confined and in working with radiation. Though, simply putting a shield at the back of the rocket would already give you 1/4 of total available thrust, which really isn't bad for a photon drive.

The biggest questions, like the authors said, are in quantum gravity. Strictly speaking, BH drive does not conserve many quantum numbers. There are models that predict non-conservation under certain conditions, but whether BH actually qualifies is a question.

[AngelLestat]

All you do is point a particle accelerator at it, and it's fed. This is simple enough.

If you need to use a particle accelerator for each bit of mass that you want to convert, then you are wasting more energy that the one you get from it.

[maccollo]

Wouldn't you have to constantly put matter into the black hole to keep it from shrinking and eventually exploding?

What happens if you get a runaway effect where the black whole energy output exceeds to amount of matter you can pump into it?

[Arsonik]

Wouldn't you have to constantly put matter into the black hole to keep it from shrinking and eventually exploding?

What happens if you get a runaway effect where the black whole energy output exceeds to amount of matter you can pump into it?

Surely with such a big ship, you would have enough low ranking colonists aboard to just start shoveling people into the black hole. Interstellar population control anyone?..... Anyone? No......? Ok......

[K^2]

If you need to use a particle accelerator for each bit of mass that you want to convert, then you are wasting more energy that the one you get from it.

The beam only needs to be a few keV, and if you feed protons to it, which is easiest thing to do, you'll be getting a GeV of energy back. That's at least five orders of magnitude greater return than investment. Even if your particle accelerator is only 1% efficient, that's still 1000:1 efficiency.

[Halsfury]

Wouldn't you have to constantly put matter into the black hole to keep it from shrinking and eventually exploding?

What happens if you get a runaway effect where the black whole energy output exceeds to amount of matter you can pump into it?

Somehow I think it's a self regulating system

Think like it's a steam train, you don't get a runaway effect with how much coal you have to put into the heater, when you don't have anything to feed the black hole it shrinks, much like a fire burns lower when there is no wood to burn eventually, if you leave it long enough, the black hole will go out on it's own either in a bang or a whimper

However the way it is described would certainly motivate me to feed the black hole for one, because these physicists are essentially saying that, unlike a steam engine, which ceases to function in a benin way when you cease to feed it, the BH powered ship is like an Aztec god demanding more bloody sacrifices in exchange for not exploding in your face

[K^2]

It's unstable, though. So you can't just leave the stream of matter on and let it regulate itself. If it shrinks a little, its output increases, so it will start shrinking faster. And vice versa, if you put just a bit too much in, it will get heavier, and start growing faster. So you have to have a regulator on matter stream that adjusts it as necessary.

But yes, if you just stop feeding it all together, it will start shrinking, and eventually go out with a bang.

[AngelLestat]

The beam only needs to be a few keV, and if you feed protons to it, which is easiest thing to do, you'll be getting a GeV of energy back. That's at least five orders of magnitude greater return than investment. Even if your particle accelerator is only 1% efficient, that's still 1000:1 efficiency.

You know the amount of energy that any particle accelerator spend just to push less than 1 gram of atoms to close the speed of light?

And this su.cker is radiating petawatts of energy each second. So what difference it will makes some atoms against the mass of a montain.

I am not saying that is impossible, I just saying that looks unlikely. Where you get those numbers by the way?

Adam Crowl made a review about this paper.

Heres is a note in century dreams, if you search the word "feed" you can find a lot of skeptics. And they are all science people.

http://www.centauri-dreams.org/?p=11751

However the way it is described would certainly motivate me to feed the black hole for one, because these physicists are essentially saying that, unlike a steam engine, which ceases to function in a benin way when you cease to feed it, the BH powered ship is like an Aztec god demanding more bloody sacrifices in exchange for not exploding in your face

All depends on the size of the black hole, in the paper there is a table. From those with just 0,2 MillonsTons to 7 MillionsTons.

The life of the big one is 6000 years to some days in the small one.

The big is a lot easier to manupulate and feed, but if you want it to push an interstellar ship is not so good. Becouse you have less radiation power with more mass.

[K^2]

You know the amount of energy that any particle accelerator spend just to push less than 1 gram of atoms to close the speed of light?

Being a particle physicist, I do, actually, yes. And that's precisely why I'm talking about a keV range accelerator, and not a GeV range one.

[Jim DiGriz]

What about taking a larger black hole, spinning it up with the reverse penrose process, and then extracting energy from it to run a star drive like a large battery? Black hole could be large enough so that it wouldn't evaporate and you could turn this kind of engine off...

[nhnifong]

I'm a bit confused. Does this gamma radiation come from the accretion disk or is it all Hawking radiation? Wouldn't you be getting a bit of both, and therefore not getting your full 100% efficiency?

[K^2]

I'm a bit confused. Does this gamma radiation come from the accretion disk or is it all Hawking radiation? Wouldn't you be getting a bit of both, and therefore not getting your full 100% efficiency?

You can feed matter in a way that doesn't result in a disk. But yeah, you'd be getting radiation from in-falling matter as well. That's still 100% efficient, though.

[Tommygun]

How quickly after you stop feeding the black hole does it blow up?

[ZetaX]

Also the hawking theories needs to be right.

They might not be completely correct regarding the actual size and get problematic for very small BHs, but they are somewhat a necessity.

How about antimatter engines? They wouldn't be able to harvest fuel in situ, but they'd be about as efficient given that antimatter annihilation is just about the most efficient way of converting matter to energy we know of, and can be shut off and, if you don't mind frying the atmosphere with gamma rays, theoretically use it in an atmosphere.

You are completely ignoring how to get antimatter and how to make that sustainable and ideally without needing a refueling station every 100 light years. The antimatter one has actually no advantage over a BH as it is inherently more dangerous, harder to refuel, probably a lot less energy efficient due to losses of energy in antimatter creation, and, most of all, would probably use energy to create antimatter to create energy, i.e. no energy gain here, too.

If you need to use a particle accelerator for each bit of mass that you want to convert, then you are wasting more energy that the one you get from it.

Adding to what K^2 already said: even at a horribly inefficient accelerator you could still use its waste heat as an energy source, and the energy stored in the particles isn't lost at all.

How quickly after you stop feeding the black hole does it blow up?

See the linked paper, section III.D. At about 4·10^11 g or 0.6 attometers you get about a year and equation (11) gives you a rough estimate on more general things.

The one they propose has a lifetime of 10-100 years, so this is not that critical as long as you don't somehow loose your particle accelerator.

[K^2]

It will give you plenty of warning, too. The energy output is going to be steadily increasing as the black hole loses mass. By the time it goes, it will have lost most of its energy, but while it took a year to give up all of that, the last 1% is going to be released in the final seconds. And of that, a sizable chunk is going to be released practically at the last instance.

Edited December 20, 2013 by K^2

[Minecrafter1]

It will give you plenty of warning, too. The energy output is going to be steadily increasing as the black hole loses mass. By the time it goes, it will have lost most of its energy, but while it took a year to give up all of that, the last 1% is going to be released in the final seconds. And of that, a sizable chunk is going to be released practically at the last instance.

That sounds really, really, really bad.

Regarding antimatter : the advantage of this black hole method is it's a lot "safer" than antimatter. Sure the black hole is bad, but it's a bright object you can't lose track of. Though, I am wondering how the heck you could get an "escaped" black hole back to your ship, since even if you have secondary thrusters to move your ship to the black hole, the darn thing will push you away when you near it. As silly as it sounds, a "practical" black hole starship might use several separate engines, each with their own BH for redundancy. So it would not be a 1 million ton vehicle, it would be 5 or 10 million or more.

The engines would be on unimaginably huge rotating joints, so you could point them at angles to give you the thrust vectors needed to collect an escaped black hole, once you repair the damaged engine. A ship this big would be able to fit the factories needed to make every single part used in itself, so it could remanufacture the broken components to build new ones.

Multiple engines solves another big problem : when you arrive in orbit around a destination planet, how do you load and unload your shuttlecraft? It would be very tricky to maneuver your ship to collect shuttles since you are acclerating at 1 G all of the time. With multiple engines, you just point them in different directions to make your net thrust 0. The only problem now is approaching this ship in a shuttle on a course that won't expose you to petawatts worth of gamma rays and fry it.

Not that I think you'd use biological humans at all for this kind of thing, but even electronics have trouble with too many gamma rays. Apparently they damage the crystalline lattices used in high density solid state electronics - and solid state hardware sufficiently complex to emulate a human mind would be much, much denser than any electronics humans have built so far.

Antimatter, on the other hand, has to be isolated from normal matter, and to get similar performance to a black hole starship, you would need about 5% of the mass of your ship to be antimatter or more.

Also, the real problem with antimatter is it is apparently trash for acceleration and specific impulse, comparatively. A huge amount of the energy is lost because the gamma rays that come out have too much energy, and, apparently, various particles that will just escape will be produced. The antimatter engine proposals on atomic rocket are basically trash for performance, comparatively. They either have good ISP and bad acceleration, or they have great acceleration and bad ISP.

Look here : http://www.projectrho.com/public_html/rocket/enginelist.php . Notice how it shows a couple of high acceleration antimatter rockets, and then the "beam core", which only has an exhaust velocity of 100 million meters/second. The black hole is giving you an exhaust velocity of 300 million.

The other problem is apparently antimatter is horribly energy inefficient to produce. You'd need a much larger power plant near the sun to make the antimatter, and when you run out of it, you are in trouble. With black holes, you could use the energy produced by one to build another one, far away from any star. Just need some matter to feed it once it gets going.

K^2 : I see one big problem, then. When you try to create the black hole, the moment it forms it will count as a very small black hole and emit a gigantic amount of energy. How many lasers would you need to push against this gradient so the BH gains mass faster than it loses it?

Edited December 20, 2013 by Minecrafter1

[ZetaX]

K^2 : I see one big problem, then. When you try to create the black hole, the moment it forms it will count as a very small black hole and emit a gigantic amount of energy. How many lasers would you need to push against this gradient so the BH gains mass faster than it loses it?

I'm not K^2, but: This somewhat feels like some futuristic version of Xeno's paradox to me. One way to resolve it:

You don't create a much too small BH, but instead you make it about the size you want (and then feed some more matter into it or wait a couple of centuries). To do this, note that your problems only start after you get an event horizon or are at least close to creating one. But such a thing doesn't grow from inside out, but just "is there". It is the fact that inside some volume there is enough mass, and this can easily happen without it happening in any smaller volume because smaller BH would require higher density of energy/matter.

You can build a BH of enormous size directly without building a smaller one by just putting hydrogen into a huge sphere, but just with the density of earth's atmosphere. Do that big enough (to laze to do the calculations to get the diameter) and it will be a BH. Yet it won't be one if you use a smaller sphere of that density.

[K^2]

That would work, if we could create matter with these sort of densities. But we don't. Right now, we still know only two ways a black hole can form. Core collapse or collision of elementary particles. Former results in a black hole that's too heavy, and later in one that's too light.

There is no known mechanism that could produce a black hole of required size.

[Minecrafter1]

Maybe you create a sphere of very dense matter, and then use the lasers to compress it to black hole status? Like a sphere of iridium that you then compress down?

I don't know if the idea is even "engineerable".

Before I thought of this problem, what I liked about the black hole idea is that, as an engineer, it felt buildable. It doesn't require some handwaving : it's straightforward engineering. We have gamma ray lasers today (think free electron is what the authors of the paper had in mind), we just need to build a gigantic number of them. Today, such equipment is hand built by humans, but it is straightforward engineering to design and program robots to build the lasers. Today, the components that go into them are also very expensive because they are hand built, but it is entirely straightforward to design a machine ecosystem that can replicate itself.

Sure, the task is a big one : it might not actually happen for 50-100+ years, but since our living bodies, even bacteria, are also "self replicating machine ecosystems", it can be done.

So, some day, we have self replicating factories (using MNT they might be very small), we land one on the moon, it replicates itself, covering the lunar surface. Build some mass drivers to launch finished products into orbit, assemble those finished components into your prototype black hole engine test vehicle and black hole research facility.

Assuming the actual parameters of black holes measured empirically are such that it is practical to build an engine (something I guess we'd have to discover by building our own small black hole), we're good to go.

Course, bad sci fi trope would be that we discover small black holes can in fact eat fast enough to sustain themselves and grow, and some dumbass dumps one into the sun and extincts humanity.

[Minecrafter1]

There is no known mechanism that could produce a black hole of required size.

K^2 : what's wrong with the gamma ray lasers? The only problem i can see is that the paper may not have taken into account the energy radiating off the black hole when it first forms. You just need enough lasers to add energy in faster than it is radiating off, and it will gain mass, right? The thing is, the paper assumes a manageable number of lasers, when we really might need several planet-masses worth of them in order to do that.

Ok, thinking about it, it occurs to me that if you also had a bunch of particle beams timed just right, you could maybe feed the newly formed event horizon with a stream of electrons or something. That is, the very moment it forms, you have a bunch of equipment built to force more energy in to it to get the black hole above the mass level needed to keep it fed. It would look like a gigantic implosion when it happened. I mean, who knows, maybe there would be "shaped" atomic or antimatter explosions or some other method to force energy into it.

It certainly sounds dramatic. Wonder if it would work. You've got a much better understanding of particle physics than me, perhaps you could generate some insights into a method that might work.

Another factor is that I read that electric charge repulsion is 40 orders of magnitude stronger than gravity. Maybe there's a way you could take advantage of these forces to generate the compression needed to feed the black hole. For instance, you might feed it with an electron beam coming from one side, and a positron beam from the other, and the electrostatic forces would resist the light pressure coming off the BH as it radiates.

Edited December 20, 2013 by Minecrafter1

[Minecrafter1]

Regarding warships : suppose aliens showed up with a vehicle with this kind of engine. Even if the rest of their tech is not much more advanced, such a warship would be near impossible to hit with missiles. You've got the acceleration to run away at 1 G for years, literally. You also have the spare mass to pack plenty of weapons and you could just turn the engine side towards incoming fire.

I guess you might be able to engage such a warship using nuclear salt water or Orion engine powered vehicles. They would have enough acceleration to keep accelerating for hours or days at 1 G or more, even if their ISP is nothing like something using a black hole.

[AngelLestat]

Being a particle physicist, I do, actually, yes. And that's precisely why I'm talking about a keV range accelerator, and not a GeV range one.

Great, that is what I love of KSP community. So you can clarify so things.

I understand that you need 1kg of antimmater-matter to accelerate 1kg of payload to 0,6c with 100% of efficiency (ISP=1c).

This sBH (1 atom radius 5 years lifespam, 129 Pw) is consumming 1.4 kg of matter each second.

So you need to introduce more than 1.4 kg of matter each second with your particle accelerator in a way that consume less energy than you get from E=mc2.

What velocity your matter needs to reach to enter in this SBH?

How efficient is a particle accelerator to proppel each gram of matter into that velocity?

I'm a bit confused. Does this gamma radiation come from the accretion disk or is it all Hawking radiation? Wouldn't you be getting a bit of both, and therefore not getting your full 100% efficiency?

This radiation comes from hawking radiation. So you are getting the 100% of energy of the matter that you had inside of the black hole.

Of course, transform or harvester that kind of energy into usable energy is a pain in the ass.

The antimatter one has actually no advantage over a BH as it is inherently more dangerous, harder to refuel, probably a lot less energy efficient due to losses of energy in antimatter creation, and, most of all, would probably use energy to create antimatter to create energy.

Just one correction, energy from antimmatter annihilation is easier to use than the one from hawking radiation. At least in some antimatter annihilation you get 60% of charge pions. And there is already papers with ideas how to obtain 100% of propulsion from annihilation.

Minecrafter1

Also, the real problem with antimatter is it is apparently trash for acceleration and specific impulse, comparatively. A huge amount of the energy is lost because the gamma rays that come out have too much energy, and, apparently, various particles that will just escape will be produced

.

How I mention above hawking radition is a lot harder to manipulate. About the acceleration that you can get from antimatter at low speeds, is fix it if you use catalized fussion until you reach more speed. But this same problem also would be fund with SBH propulsion.

Look here : http://www.projectrho.com/public_html/rocket/enginelist.php . Notice how it shows a couple of high acceleration antimatter rockets, and then the "beam core", which only has an exhaust velocity of 100 million meters/second. The black hole is giving you an exhaust velocity of 300 million.

This is incomplete.

K^2 : I see one big problem, then. When you try to create the black hole, the moment it forms it will count as a very small black hole and emit a gigantic amount of energy. How many lasers would you need to push against this gradient so the BH gains mass faster than it loses it?

That is a real problem.

You can build a BH of enormous size directly without building a smaller one by just putting hydrogen into a huge sphere

This seems to contradict the Bolzano theorem