# A black hole traveling at .99999999999 c

## Recommended Posts

Hi,

Setting aside how it gets up to this speed, what other problems do we have?

Rusty

##### Share on other sites

Blackholes have mass... Usually lots of it... So much, in fact, that they are often explicitly labeled "supermassive."

##### Share on other sites

Blackholes have mass... Usually lots of it... So much, in fact, that they are often explicitly labeled "supermassive."

And as you approach the speed of light, mass approaches infinity.

Okay. BTW, the power accelerating the singularity comes from the singularity so, as it's mass increases we have more power, yes... or no??

So what kind of problems will we have?

##### Share on other sites

Mass is mass, i can see no special problems with a black hole traveling at relativistic speeds

##### Share on other sites

Okay, I'll admit I'm relatively new to relativity (kapow! pun) but I had an idea when I read this, and so I'm hoping one of the other Physicists here could help out.

Let's think of it differently. Let's say the black hole isn't what's moving (hence, remove the problem of mass moving close to the speed of light, or how it achived that speed) but rather that the observer is. Therefore, to *us* the observers, it moves at that speed. Does that make sense?

My point is that I don't see a problem with thinking of a moving black hole as long as we take into account that movement is relative. We, planet Earth, are probably moving at close to the speed of light for some other random observer on the universe whose frame of reference is moving (relative to us) at close to the speed of light. We don't think we're moving, but the distant observer sees us as if we are. That's the point of relativity.

So there shouldn't be many problems with a black hole moving close to the speed of light. In "no problem" I mean it *could* be treated realistically. There's no reason not to think that at some place in the universe such black hole moves at close to the speed of light in some reference frame. That's the point of relativity.

When I was in E&M course a year ago (the course leading to Relativity) we drew up "time" graphs, where you can compare plausible frames of reference per events. We even had an exam question where to one observer event A happened before event B, and to another event B happened before event A, while to a third both event A and B happened at the same time. It all depended on which frame of reference you picked, and as long as the speed of the frame of reference isn't above the speed of light, it's "fair game".

That said, there's a lot of other things happening with a black hole that should be considered in terms of what we would see in our moving frame of reference for that black hole. I am not sure it's as simple a calculation as to just include its massive mass, seeing as its mass affects time next to and its gravity affects light coming to/back from it.

In terms of how to describe it, I'm not sure. Maybe one of the Physics experts could shed some light on it, it sounds extremely interesting as a thought exercise anyways..

##### Share on other sites

There is no such thing as an object moving at .99999999999 c. You can, however, have an object moving at .99999999999 c with respect to some other object. Motion is relative. So numerous black holes are moving at that speed as measured by some particle in an accelerator, or by a high-energy cosmic ray proton. There are zero problems.

##### Share on other sites

There is no such thing as an object moving at .99999999999 c. You can, however, have an object moving at .99999999999 c with respect to some other object. Motion is relative. So numerous black holes are moving at that speed as measured by some particle in an accelerator, or by a high-energy cosmic ray proton. There are zero problems.

Did it kill you to just say I was right?

##### Share on other sites

Okay, I'll admit I'm relatively new to relativity (kapow! pun) but I had an idea when I read this, and so I'm hoping one of the other Physicists here could help out.

Damned if I do, damned if I don't. Sheesh!

Yes, you were right, but … one might not get the point that there is no absolute frame from your post, since you speak of the object moving and then the observer moving. That's what I was trying to clarify.

##### Share on other sites

Hi!

I love you guys, lol!

Okay... how about streaking by our solar system... relative to our solar system? Any problems now?

Rusty

##### Share on other sites

I'm not sure, but if it emits gravitational waves, that might slow it down. A fair warning: I don't really know what gravitational waves are.

##### Share on other sites

Damned if I do, damned if I don't. Sheesh!

Yes, you were right, but … one might not get the point that there is no absolute frame from your post, since you speak of the object moving and then the observer moving. That's what I was trying to clarify.

Yeah, that's what I meant, but I definitely see your point. It's still good to know that I was right.

But say, now that we're talking about black holes moving at almost the speed of light compared to an observer -- what would we observe. That's an interesting concept.. the black hole absorbs light, but it's moving, so will we see a streak of blackness? Actually, we might because it will be expanded along the axis of movement, won't it?

Will regular math work on this type of problem (If I want to check how much mass the black hole will have compared to rest-mass, etc, while moving) or are there any concepts that need to be added in (like Hawkings Radiations, for instance)..?

That might help us see what would happen if a black hole comes close to the solar system at close to the speed of light compared to the solar system.

Will we even feel any of its big effects? Sounds like it will be next to us for such a short time that the effect will be miniscule... or am I missing anything?

##### Share on other sites

It will depend on how big the black hole is. If it is moving at 99999999999c with respect to Earth, I wouldn't want to be in the way. Such an object would have an enormous kinetic energy, and if it crashed into our planet, even a small one would turn the crust into slag. A bigger one would just blow it apart (and probably ruin the entire solar system with it...), and a supermassive black hole would just gobble our planet up.

I don't think we would have time to perceive it if such a black hole was headed our way. The only thing we would see is planets being flung right out of their orbits, if it was large enough. And if it was so small as to be of negligible importance, we would probably never detect it.

Also, look at Relativistic Kill Vehicle: http://en.wikipedia.org/wiki/Relativistic_kill_vehicle

Edited by Reaper
##### Share on other sites

Actually, we might because it will be expanded along the axis of movement, won't it?

there is a reason it is called length CONTRACTION

##### Share on other sites

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.

##### Share on other sites

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.

If it was very small, then yes. But I think the OP was referring to any sized black hole, not just very small (i.e. subatomic sized) ones.

##### Share on other sites

even if it was a solar mass blackhole it would only leave a small(compared with the rest of the planet) hole through the planet.

##### Share on other sites

there is a reason it is called length CONTRACTION

Oops.

You're right, it should be 'contract'.. sorry. Still, though, would it? 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? And seeing as most of the relativistic effects are demonstrated by the light coming back and forth between the two frames of reference, would there be other effects worth mentioning that we would see if something like this happens?

Actually, seeing as this is all about relativistic frames, I wonder if we have an example of something similar that we know of already. Did we spot a black hole that is - relative to us - moving at fast velocities? Maybe not .99999c, but close enough to make a comparison based on actual observation?

Just wondering.

##### Share on other sites

even if it was a solar mass blackhole it would only leave a small(compared with the rest of the planet) hole through the planet.

Why?

A black hole is just like any other object, except really, really dense. Conservation of momentum still applies; if it crashes into some object, at least some of its kinetic energy will be transferred into the planet. It's the same as shooting an asteroid or a neutron star into a planet at relativistic speeds (except that a black hole is much more massive, and thus has a great deal more kinetic energy at those speeds).

If black hole that sized collided with our planet at that speed, the Earth would probably be vaporized.

Merged post follows:

Consecutive posts merged
Oops.

Actually, seeing as this is all about relativistic frames, I wonder if we have an example of something similar that we know of already. Did we spot a black hole that is - relative to us - moving at fast velocities? Maybe not .99999c, but close enough to make a comparison based on actual observation?

Just wondering.

I know of some claims of artificial black holes, but I have not heard of any ones that move at relativistic speeds w.r.t Earth.

Edited by Reaper
Consecutive posts merged.
##### Share on other sites

Why?

A black hole is just like any other object, except really, really dense. Conservation of momentum still applies; if it crashes into some object, at least some of its kinetic energy will be transferred into the planet. It's the same as shooting an asteroid or a neutron star into a planet at relativistic speeds (except that a black hole is much more massive, and thus has a great deal more kinetic energy at those speeds).

If black hole that sized collided with our planet at that speed, the Earth would probably be vaporized.

the thing is though, thing other than black holes tend to collide, the blackhole will absorb everything directly infront of it and some stuff to the side but it will still exit with pretty much the same velocity as it exited as the force never gets distributed through out the bulk of earth.

Mooey, the even horizon would become length contracted i think, as for whats inside it, well we don't really know.

##### Share on other sites

the thing is though, thing other than black holes tend to collide, the blackhole will absorb everything directly infront of it and some stuff to the side but it will still exit with pretty much the same velocity as it exited as the force never gets distributed through out the bulk of earth.

That doesn't matter though. You are assuming that at black hole is some "hole" in space that just sucks everything up. 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. Just because it can "suck" in light doesn't mean that it can't collide like any other solid object. Any other action would be a violation of the laws of physics, and as far as I know, even black holes are bound by them.

As well, black holes only have the gravitational pull that their mass allows for. A black hole with the mass of the sun, for example, will still only have the gravitational pull of that of the sun. It's just that you have to get a lot closer to it in order to cross the event horizon. Even smaller objects will have an even less gravitational influence...

------------------------------------------------------------

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.

Edited by Reaper
##### Share on other sites

no, thats not how black holes work. anything that passes the event horizon gets sucked in. matter does not bounce off it.

the only way it interacts with the earth is via the attractive force of gravity.

##### Share on other sites

Oh yeah it does. Especially if we are considering one that is not that big and moving at extreme velocities. Or much bigger objects (Although with bigger/more massive objects, what would happen is that the matter would warp around the black hole, thereby tearing it apart...)

##### Share on other sites

can you show me any reliable sources that state blackholes are solid objects?

##### Share on other sites

Well, lets see. According to Berekely University: http://cosmology.berkeley.edu/Education/BHfaq.html

Loosely speaking' date=' a black hole is a [b']region of space that has so much mass[/b] concentrated in it that there is no way for a nearby object to escape its gravitational pull...

How is what he is describing not a solid object? More generally, a black hole is the result of a giant star collapsing in on itself. The mass gets compacted into such a small space that the resulting escape velocity near it's surface is greater then that of the speed of light. Thus forming a "black hole" in a metaphorical sense. A much more accurate term is actually a "dark star", but the word black hole sounded so much cooler, so that's what we use.

It is not a hole in any sense of the word. It is a solid object, like anything else, except really, really dense. It has a mass, and a speed, thus it has momentum and kinetic energy. Unless you can somehow show that conservation of momentum does not apply, I don't see how the Earth would survive such a collision course (assuming that the gravitational force doesn't rip it apart before it reaches this planet...)

=================================================

Here is another fun fact about the term "black hole":

Incidentally' date=' the name 'black hole' was invented by John Archibald Wheeler, and seems to have stuck [i']because it was much catchier than previous names[/i]. Before Wheeler came along, these objects were often referred to as 'frozen stars.' I'll explain why below.

=========================================

Here is another good article on the nature of black holes: http://astronomy.swin.edu.au/~gmackie/DarkStar/alpha.html

It turns out that people have been speculating about such objects as early as the 1700's! Back then it wasn't clear if light was a particle or a wave, but they already knew it had a finite speed. Therefore, it was hypothesized that there were "dark stars" out there that could only be detected via gravity because it's escape velocity would be that of the speed of light.

However, all of Newtonian mechanics would still apply (e.g. it would have mass, speed, momentum, angular momentum, etc.). For relativistic speeds (or extreme gravitational fields), we would use special and general relativity. We can therefore apply basic physics concepts like conservation of momentum to try and guess at what would happen if a massive relativistic black hole were on a collision course with Earth...

*NOTE: If I made any mistakes in my reasoning, then please either Swansont or Martin or Severian correct me.

Edited by Reaper
Consecutive posts merged.
##### Share on other sites

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.

## Create an account

Register a new account