# A black hole traveling at .99999999999 c

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yes the mass is compacted within the event horizon(the extent of distribution within is obviously unknown, may be zero) but this does not mean that stuff will bounce off of the event horizon.

he also doesn't state that it is solid, he just states that it is dense. he also says nearby objects cannot escape its pull. specifically, once an object crosses the event horizon it isn't coming back out.

so lets look at the blackhole impacting earth scenario.

black hole hits surface, the matter contacting the event horizon gets pulled beyond it. according to the rest of the earth, this matter has ceased to exist(except for the gravitational attraction). the black hole continues in a similar manner till it gets to the other side.

the black hole will also pull in matter from the sides of the tunnel it creates(it does have a strong gravitational field after all). again once this matter crosses the event horizon it can no longer bounce back and repel the rest of the incoming material.

now, if we look at the case of something without an event horizon, the object strikes the surface and moves the matter AWAY from it and out of its way to the side causing cratering and massive momentum transfer. blackholes are incapable of imparting momentum by this mechanism.

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yes the mass is compacted within the event horizon(the extent of distribution within is obviously unknown, may be zero) but this does not mean that stuff will bounce off of the event horizon.

he also doesn't state that it is solid, he just states that it is dense. he also says nearby objects cannot escape its pull. specifically, once an object crosses the event horizon it isn't coming back out.

I don't really think you are understanding what I'm saying. First, your nitpicking terms (it could be semi-fluid or super dense plasma, same difference. Though the word "frozen star" implies solid object....). Besides which, since black holes have no hair, we might as well just treat it as a solid object anyway. So what, exactly, a black hole is made of is irrelevant.

And second, transfer of kinetic energy doesn't mean that things will "bounce off" the event horizon. It just means that when things collide, some of that energy will be transferred.

A black hole is the same as any other object. Gravitationally, it's pull will be the same as that of an object with the same mass...

so lets look at the blackhole impacting earth scenario...

The scenario that I laid out would probably be the one that would happen. Just get over it. The black hole could either be the mass of a star or an asteroid; if a black hole the mass of the asteroid were to collide with the Earth, it would have exactly the same effect as if an asteroid (even one moving at relativistic speeds...) were to collide. I don't even want to think about what would happen if a black hole with 5 solar masses were to go on a collision course with our planet, although some of the scenarios I laid out earlier would likely occur (e.g. planets getting flung from orbits, Earth vaporized, sun exploding, etc.)

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Gravity is gravity. What would happen if a black hole passed by is gravitationally the same as if a non-black-hole of equal mass passed by.

Thank you.

Edited by Reaper
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it sounds to me like you are saying that the blackhole should behave much the same as an object without an event horizon like a neutron star.

also, the only evidence you have presented for a 'solid' black hole is the antiquated term 'frozen star' which has been discredited for decades.

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I mean, a black hole is supposedly a huge mass in a very very small area.. aren't we usually treating it as a "dot" ? how could something like that contract, if at all?

Well, there supposedly is a singularity at the center that would have infinite density and zero volume. But that doesn't matter, because it will be within the event horizon. See http://en.wikipedia.org/wiki/Schwarzschild_radius. Since black holes are not physical objects like rocks but rather a product of bent space, I don't know whether length contraction would apply, or would apply by the same rules. We'd have to ask someone familiar with general relativity.

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it sounds to me like you are saying that the blackhole should behave much the same as an object without an event horizon like a neutron star.

Exactly. As counter-intuitive as that might seem, there is no reason that it can't behave (at least on a large scale) like any other object without an event horizon. Like Swansont said, gravity is gravity; it's influence depends only on it's mass.

also, the only evidence you have presented for a 'solid' black hole is the antiquated term 'frozen star' which has been discredited for decades.

Did you even read through any of the articles that I presented to you? That statement is wrong on so many levels. The truth is, we don't really know what goes on black hole (although I can tell you what it is not, a wormhole). General relativity suggests that there should be a singularity at the center, but such objects only represent a failure of General Relativity, not the actual situation.

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That doesn't matter though. You are assuming that at black hole is some "hole" in space that just sucks everything up.

Pretty much, although of course it doesn't "suck" any more than a regular object of that mass.

A black hole is a solid object, like anything else. And like all objects in the universe, it has a speed, a mass, and momentum. Thus, it can carry and transfer energy to other objects, whether they are black holes or not.

Oh, it can indeed interact with other objects. Gravitationally, such as the slingshot effect. However, an impact with a "solid" object is an electromagnetic interaction. This is the cause of the "pushing" that results, as atoms get pushed out of the way. A black hole will not be pushing things.

It would be kind of like shooting a bunch of neutrinos at something.

Of course, I'm just assuming that's its gravitational effects won't tear the Earth apart first before it even reaches it, which is what such an object would do to a planet under normal circumstances.

Yeah, I did mention the tidal forces would be nasty.

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The scenario that I laid out would probably be the one that would happen. Just get over it. The black hole could either be the mass of a star or an asteroid; if a black hole the mass of the asteroid were to collide with the Earth, it would have exactly the same effect as if an asteroid (even one moving at relativistic speeds...) were to collide.

Nope, if a black hole the mass of an asteroid were to collide with Earth, it would leave a small hole about an atom wide through the earth. Odds are we wouldn't notice.

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so will we see a streak of blackness? Actually, we might because it will be expanded along the axis of movement, won't it?

<snip>

You're right, it should be 'contract'.. sorry.

It was always my understanding that an event horizon could probably not be seen by the naked eye. No light comes directly from it so if there was nothing behind it (kind of impossible) you'd just see black, otherwise the light from what's behind it wraps around it. That's pretty boring for a sci-fi book so there, it's viewed through a view screen w/computer enhancement showing a black sphere with the light around it bending inward and, on the black sphere some purple haze for Hawking Radiation (yes I grew up in the 60s and in Hollywood).

But, I never thought of contraction! I would say that what you 'see' (the lens effect on surrounding light or, via a view screen the black sphere) is what contracts. How much contraction would there be????

Re the singularity, it is thought to have no volume, yes? But still, a charged singularity is thought to spin so fast that it morphs into a one dimensional donut as I recall. So I think it would contract though no one would see it (well, in the story someone will but besides the point).

Re: hitting a planet.

I also never considered what would happen if a black hole traveling at .99 c to an unfortunate planet hit that planet but if I had, I would have thought that what would happen would be determined by some simple math. You have the size of the bh*, its gravitation force, its area of falloff, the speed at which it travels, the speed at which the bh is traveling, the gravitational force and time needed to suck down a planet whose size and so forth we can... make up. I don't have the knowledge to do this but I'd LOVE to do the computer simulation in 3D software (I have and use 3D software but plugging in the formulas is not something I've ever done).

* In the book, the bh is the gentle giant type thought to be found in the center of galaxies. The event horizon at rest is thought to be the size of a solar system (why screw around? besides anything else would be to turbulent for... ah... well, what's inside).

Any of that sound right or reasonable?

Rusty

Edited by rrw4rusty
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Pretty much, although of course it doesn't "suck" any more than a regular object of that mass.

Oh, it can indeed interact with other objects. Gravitationally, such as the slingshot effect. However, an impact with a "solid" object is an electromagnetic interaction. This is the cause of the "pushing" that results, as atoms get pushed out of the way. A black hole will not be pushing things.

It would be kind of like shooting a bunch of neutrinos at something.

Yeah, I did mention the tidal forces would be nasty.

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Nope, if a black hole the mass of an asteroid were to collide with Earth, it would leave a small hole about an atom wide through the earth. Odds are we wouldn't notice.

Houston, you have a problem

A black hole with the mass of an asteroid would radiate huge amounts of radiation. The radiation would sterilize the earth, the smaller a black hole is the faster it evaporates a tiny black hole would radiate energy mostly in the form of gamma rays.

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Houston, you have a problem

A black hole with the mass of an asteroid would radiate huge amounts of radiation. The radiation would sterilize the earth, the smaller a black hole is the faster it evaporates a tiny black hole would radiate energy mostly in the form of gamma rays.

Nice Photoshop work!

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A black hole with the mass of an asteroid would radiate huge amounts of radiation. The radiation would sterilize the earth, the smaller a black hole is the faster it evaporates a tiny black hole would radiate energy mostly in the form of gamma rays.

Yes, it would emit tremendous amount of radiation. A black hole the mass of a 50 m radius asteroid would weigh about 10,000,000 kg and be about 10-19 meters (about 1/10,000th the size of a proton), and would emit about 1018 watts, which is more than all the energy the earth receives from the sun.

OK, so that is the sort of thing we'd notice. Traveling at near c, it would pass through earth in 42 milliseconds, during which time it would emit 4 × 1016 joules or about 10 megatons. Which is not counting what it would emit during its approach. And that it would be nastily blueshifted.

Incidentally, I have a thread where I suggested the use of black holes as a power source. Having thought about it some more, I think it would be an excellent item for science fiction, and I would call it a Hawking reactor.

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Not my photo shop work but it is cool. Like most power sources where you have to convert on type of energy into another wouldn't creating a black hole take much more energy than you could get out of it?

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A black hole would be a terrible choice for a relativistic kill vehicle; it would for the most part fly straight through the target rather than release its energy on impact. The tidal forces of the black hole would be rather damaging, but overall it would be much smaller and unable to release the vast majority of its energy.

I agree that the hole would not transfer kinetic energy to the planet the way a normal object would do, but I think the effects would be very devastating because of how mass outside the horizon but near enough to get flung around would act. Considering a test particle 100 km from the point of entry the particle accelerates (where the hole is stellar sized, 2E30 kg):

$a = \frac{GM}{r^2} = \frac{1.33 \times 10^{20}}{10^{10}} = 1.33 \times 10^{10} \ m/s^2$

[with a post-Newtonian correction it is (1-2GM/rc^2)^(-1/2)*GMm/r^2 = 1.36 * 10^10]

Since the hole is moving near the speed of light the test particle would not feel that acceleration for long. Just for a rough estimate it takes something moving at the speed of light about 0.00033 s to travel 100 km making it safe to say the test particle is accelerated in the order of 10^10 m/s^2 for about 0.00001 s. Multiplying those, it gets a speed of about 1 million m/s.

As the black hole passes through the earth it would make a clean hole which isn't very devastating. But, all the mass around the axis-shaped hole would be flung toward the center of the axis with devastating speeds. if a good portion of earth's mass were to collide with itself at hundreds of thousands of meters / second then the resulting energy would surely be enough to vaporize the planet.

Unless something is wrong with my reasoning (which is entirely possible, I'm not a trained physicist), I believe the planet would be vaporized.

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Not my photo shop work but it is cool. Like most power sources where you have to convert on type of energy into another wouldn't creating a black hole take much more energy than you could get out of it?

In my book (almost done!) a small one is created as a primer then larger and larger ones are 'captured'.

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In my book (almost done!) a small one is created as a primer then larger and larger ones are 'captured'.

How small? How do you deal with the intense gamma ray output?

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Exactly. As counter-intuitive as that might seem, there is no reason that it can't behave (at least on a large scale) like any other object without an event horizon. Like Swansont said, gravity is gravity; it's influence depends only on it's mass.

A collision is not a gravitational reaction, it's an electromagnetic one. Things do not bounce off black holes. That does not violate conservation of momentum.

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A collision is not a gravitational reaction, it's an electromagnetic one. Things do not bounce off black holes. That does not violate conservation of momentum.

Yes and no. Gravitational near-misses look an awful lot like charged particle scattering, which are treated as collisions. Just not "physics-101" collisions.

What would happen in the case of a black hole is that the earth would begin to move toward the black hole, the black hole (assuming it is "small") would pass through, and the earth would be dragged along with it, slowing it back down. You'd have to work out the details, as this is an inelastic collision, because of the mass transfer and other effects. But there's no "bounce" like for hard sphere scattering, where the target moves off at a speed greater than the incident particle.

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Right. My point is just that hitting the earth with a 0.9999c relativistic velocity 100kg iron cannonball and hitting it with a black hole of the same mass and velocity will have very different effects. The cannonball would collide with the Earth and transfer all of that energy into heat, shockwaves, etc. The black hole would only transfer a small amount its energy to the Earth, via gravitational drag, and nobody would notice. (This is of course ignoring radiation the black hole emits as it decays.) Kind of like firing a stream of neutrinos through your head, vs. punching you in the face.

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How small?

"Small" is all I was going to specify in the book. It would need to be about Cygnus X1 size.

How do you deal with the intense gamma ray output?

I was just going to use Norton's RAD Scrubber22 with the intense gamma ray plug-in... unless you know of a better way.

Rusty

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Right. My point is just that hitting the earth with a 0.9999c relativistic velocity 100kg iron cannonball and hitting it with a black hole of the same mass and velocity will have very different effects. The cannonball would collide with the Earth and transfer all of that energy into heat, shockwaves, etc. The black hole would only transfer a small amount its energy to the Earth, via gravitational drag, and nobody would notice. (This is of course ignoring radiation the black hole emits as it decays.) Kind of like firing a stream of neutrinos through your head, vs. punching you in the face.

What if the earth was struck by a relativistic neutron star? Would it just trash the Earth (similar the pic i posted) or would it vaporise the earth? I once read a story about aliens destroying the earth. (some sort of interstellar war of whack a mole) but they used basket ball sized chucks of neutronium, one was anti-matter and one was was matter neutronium, they dropped them into the Earth and they orbited inside the earth until they finally came together at the center of the earth and "wump there it is" or was! The point is the neutronium didn't do much damage when it hit the earth, it acted like the earth wasn't even there. So if a black hole would just go straight through would a neutron star a few miles in diameter do the same thing?

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What if the earth was struck by a relativistic neutron star? ...

That, as awesome as it sounds, would be super massive overkill. It would be on the order of using ICBM equipped with multiple nuclear warheads to rid your dog of fleas.

Just a small chunk of neutronium moving even at somewhat conventional speeds would be more then enough kinetic energy to devastate the planet.

The weapon described would be something I would use to destroy Dyson Sphere type objects, that is, technology of type II civilization(one that is harnessing nearly all the energy of a star by building a sphere around it to capture the majority of the radiation to convert it into usable energy of some form).

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