# Thread: Do black holes move?

1. I'm just wondering this. If the center of a black hole is essentially a whirling disc, spinning at more or less the speed of light, then for the black hole itself to be moving through space, one of a few things has to happen:

1) - Some of the matter would have to go faster than light

2) - The spin would have to be perpendicular to the direction the black hole is moving, and spinning slightly slower than C. (So the total speed of the matter is still just C)

3) - If the spin isn't perpendicular to the direction of motion, matter would have to be speeding up and slowing down, or something like that.

I'm just saying, the internal angular momentum counts against the C limit. I almost want to draw pictures to try and explain what I mean, but I think I'm making sense. If it's spinning at C, then to move through space as well would require going faster than C.

2.

3. Originally Posted by kojax
1) - Some of the matter would have to go faster than light
.
Relative to what?

4. G'day from the land of ozzzzzzzz

http://arxiv.org/abs/astro-ph/0701083

Fallback and Black Hole Production in Massive Stars

Authors: Weiqun Zhang, S. E. Woosley, A. Heger
(Submitted on 4 Jan 2007 (v1), last revised 12 Nov 2007 (this version, v2))

Abstract: The compact remnants of core collapse supernovae - neutron stars and black holes - have properties that reflect both the structure of their stellar progenitors and the physics of the explosion. In particular, the masses of these remnants are sensitive to the density structure of the presupernova star and to the explosion energy. To a considerable extent, the final mass is determined by the fallback'', during the explosion, of matter that initially moves outwards, yet ultimately fails to escape. We consider here the simulated explosion of a large number of massive stars (10 to 100 \Msun) of Population I (solar metallicity) and III (zero metallicity), and find systematic differences in the remnant mass distributions. As pointed out by Chevalier(1989), supernovae in more compact progenitor stars have stronger reverse shocks and experience more fallback. For Population III stars above about 25 \Msun and explosion energies less than $1.5 \times 10^{51}$ erg, black holes are a common outcome, with masses that increase monotonically with increasing main sequence mass up to a maximum hole mass of about 35 \Msun. If such stars produce primary nitrogen, however, their black holes are systematically smaller. For modern supernovae with nearly solar metallicity, black hole production is much less frequent and the typical masses, which depend sensitively on explosion energy, are smaller. We explore the neutron star initial mass function for both populations and, for reasonable assumptions about the initial mass cut of the explosion, find good agreement with the average of observed masses of neutron stars in binaries. We also find evidence for a bimodal distribution of neutron star masses with a spike around 1.2 \Msun (gravitational mass) and a broader distribution peaked around 1.4 \Msun.

Black holes are star bodies with compacted matter. The issue is the type of matter that makes it up.

What ever the matter is, it forms a unit called a nucleon, that acts as one unit and the particles work as one matrix or a possible composite of subatomic particles, maybe quarks or preon matter. Just a theory.

5. Originally Posted by Ophiolite
Originally Posted by kojax
1) - Some of the matter would have to go faster than light
.
Relative to what?
Center of the disc. :?

6. Originally Posted by Ophiolite
Originally Posted by kojax
1) - Some of the matter would have to go faster than light
.
Relative to what?
I guess this would be relative to an external observer (and her coordinate system) witnessing the motion of the black hole as a whole, i.e. its drifting or orbiting somewhere in space.

But apparently the catch is that no external observer can see the swirling of any parts of the matter inside the black hole. Right?

7. What I'm saying is that the total speed of matter on the outer edge of any spinning object consists in both its speed around the core and its speed traveling through space.

If the spin is perpendicular to the direction of motion, then the total speed is a vector defined by the hypotenuse of a right triangle, where one of the shorter legs is its speed going around the core and the other shorter leg is the speed the core itself is moving at as it drifts through space.

That final vector has to be less than C.

I wonder what effect the repulsive force between the atoms (if it even has atoms any more) has on its spin. I mean, the force can't move anything outward any more, so do you think it starts pushing sideways?

8. Yes they do. Some spin around their axes. And that generates velocity.

9. Originally Posted by kojax
What I'm saying is that the total speed of matter on the outer edge of any spinning object consists in both its speed around the core and its speed traveling through space.

If the spin is perpendicular to the direction of motion, then the total speed is a vector defined by the hypotenuse of a right triangle, where one of the shorter legs is its speed going around the core and the other shorter leg is the speed the core itself is moving at as it drifts through space.
That final vector has to be less than C.
Are you saying that matter just on the outside of the event horizon travel at close to C? 'Cause that is not the case if it is measured relative to the axis of rotation. It does approach C relative to other things, but in a similar way that the black hole itself (or any other body) moves relative to that other viewpoint. To the observer at that distance the rotating side going away from it would still not reach C, but would still be closer to C than the side coming toward the observer. But as I said, the same would go for any rotating body (a planet with a moon for instance). The black hole would also add a bit of time dilation due to the strong gravity field.

I wonder what effect the repulsive force between the atoms (if it even has atoms any more) has on its spin. I mean, the force can't move anything outward any more, so do you think it starts pushing sideways?
If you are talking about matter just inside the event horizon, then the "outward" direction for the particle would have it follow the curved space-time that would curve inward to an outside conceptualizer (did I just invent that word?). From the perspective of the particle though, it would just move in a straight line I think, similar to how a big bang universe precludes us from being able to contemplate an "outside" relative to which space can be curved in on itself. Anyway, that is how I think it works….

10. So, at the event horizon, the time dilation accommodates an object's orbit, so it doesn't have to go faster than C in order to stay where it is?

As for the other part, I guess I'm thinking of inside the singularity. I wonder of the repulsive force causes the mass to spin instead of trying to push against the attractive force. IE. maybe it pushes sideways instead of trying to push out.

If the singularity itself has spin, I wonder how fast it spins.

11. I think Kalster has made the points (better than I could) that were vaguely in my mind when I asked the question 'relative to what'. My understanding of relativity is based upon the principle that when presented with information pertinent to relativity, or to which relativity is pertinent, simply ask that question. The slickness,, promtpness and directness of the response are good indicators of the depth of understanding of the respondee. (And you don't even have to understand what their response means. 8) )

12. Maybe I do misunderstand it. I always assumed that C was relative to some absolute frame of reference. I mean, I know the Michealson Morley experiment showed that an object moving at C perceives distance to be shorter in the direction of motion (Or maybe the perception is longer, to avoid seeing an approaching object as closing a distance faster than a total speed of C)

However: I'm going to go with a speed of C relative to some object near the black hole, but not inside of its event horizon.

So, if star X is a star orbiting the inner portion of a galaxy, and bh Y is the center of the black hole at the center of that galaxy, and particle Z is a particle located on the outer edge of the spinning singularity in the black hole ....

Z's speed around the center (Y) is one vector, Y's speed relative to X is another vector, and the hypotenuse of a right triangle using those two vectors as the shorter legs would represent Z's total velocity relative to X.

If X is moving at sub-relativistic speeds, and Y is moving away from X, then something has to prevent Z's speed relative to X from being greater than C.

(Now, I know when I start talking like that that I'm on the outer edge of my ability to reason, so I could just totally be off the deep end.)

13. G'day from the land of ozzzz

The speed of light is constant.

Relative speed of light is not constant.

14. Originally Posted by kojax
If X is moving at sub-relativistic speeds, and Y is moving away from X, then something has to prevent Z's speed relative to X from being greater than C.
That "something" is the addition of velocities theorem:

Where u is the velocity of one object with respect to you
v is the velocity of a second object relative to the first object as measured by either object.
W is the velocity of the second object relative to you.

Example: object X is moving away at .75c and fires an object away from itself at .75c relative to itself in the same direction, you will measure the second object's velocity as .96c.

15. Originally Posted by Harry Costas
Relative speed of light is not constant.
Relative to the observer, in a vacuum, yes it is constant.

And, except for amphetamine, every speed is relative.

16. G'day from the land of ozzzz

Leszek I agree with you.

You said

Relative to the observer, in a vacuum, yes it is constant.

And, except for amphetamine, every speed is relative.
But! Why is the speed of light constant if we see it at zero

17. Originally Posted by Harry Costas
But! Why is the speed of light constant if we see it at zero

18. G'day from the land of ozzzzzzz

Lets put it another way.

If light is travelling in one direction and there is a force acting in the opposite direction, making light speed to the observer zero. The theoretical extreme at the event horizon.
Why do we consider the speed of light constant?

19. Originally Posted by Harry Costas
If light is travelling in one direction and there is a force acting in the opposite direction, making light speed to the observer zero. The theoretical extreme at the event horizon.
A force acting on what? With what effect in terms of acceleration and possibly speed? Speed of what, relative to what, measured by whom?

Originally Posted by Harry Costas
Why do we consider the speed of light constant?
Don't blame me for that, it was Einstein's idea.

20. Originally Posted by Harry Costas
G'day from the land of ozzzzzzz

Lets put it another way.

If light is travelling in one direction and there is a force acting in the opposite direction, making light speed to the observer zero. The theoretical extreme at the event horizon.
Why do we consider the speed of light constant?
Gravity curves space-time and then light simply follows the contours. The speed at which it follows those contours remain C.

21. G'day from the land of ozzzz

OK...........done

22. Originally Posted by Ophiolite
I think Kalster has made the points (better than I could) that were vaguely in my mind when I asked the question 'relative to what'. My understanding of relativity is based upon the principle that when presented with information pertinent to relativity, or to which relativity is pertinent, simply ask that question. The slickness,, promtpness and directness of the response are good indicators of the depth of understanding of the respondee. (And you don't even have to understand what their response means. 8) )
OK. After a lengthy discussion with Janus about relativity, I think I have an intelligent answer to your question finally, so we continue this inquiry further.

Let's use the perspective of a particle of matter on the outside of the spinning singularity, traveling at C relative to the core. From its perspective, if the core is in motion as well, and the motion is parallel to the axis the singularity is spinning on, and there exists a star nearby located in the opposite direction from the direction the bh is moving, then either:

A) The particle would have to be moving faster than C relative to that star. (Or maybe it perceives the star moving faster than C relative to it)

or

B) The particle would have to move slower than C relative to the core during part of its path around the core.

While the particle never communicates with the star in any way whatsoever, the star does communicate with the particle, or well.... kind of.

23. G'day Kojax

I'm trying to understand your post.

Can you expalin it further.

24. I guess I'm just nit-picking.

My thinking is that the core of a black hole could accelerate particles to such speeds that the black hole itself would be incapable of motion because the internal particles that make it up are already moving at the C limit.

The question becomes, "C relative to what?", and I'm just trying to make sense of that part of it. I guess an internal particle of the black hole might already be moving at C relative to ..... oh... .say.... a nearby star outside the event horizon, so the only way the black hole itself could move in that direction would be for the particle to slow down relative to the black hole..... this is the part where I become confused myself, so there's no reason for anyone else to worry if they don't understand me. (I don't understand myself)

I'm trying to imagine these internal particle moving around, but having to move slower than C relative to the center of the BH during part of their movement so as to avoid going faster than C relative to other objects in the galaxy, like stars... and I guess that's my answer: The particle can somehow move at C relative to the BH, and C relative to a star outside the BH at the same time????

So, I guess my real question is:

Does relativity allow for that? Can an object move at C relative to two other objects at the same time, even if the two objects have additional motion relative to each other?

25. G'day Kojax

You said

My thinking is that the core of a black hole could accelerate particles to such speeds that the black hole itself would be incapable of motion because the internal particles that make it up are already moving at the C limit.
The centre of any compact matter is a soup of suatomic particles. These particles have charge and have properties that are related to plasma. In so doing the question is what creates jets from these black holes to be ejected close to the spedd of light.

In order to find this out may need to reed up on black holes and possible processes that can produce these jets.

One processes is via Z-pinch of the magnetic fields within and out of the black hole. Its like the chicken and the egg, they go together like peanut butter and bread.

In reality nobody knows whats in a black hole. Observations based on gravity and properties of ejected matter may give us hints on the make upof the matter within. Also experiments with Z-pinch of plasma.

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

http://arxiv.org/abs/astro-ph/0311137
Precession in the inner jet of 3C 345

Design of Jet-Driven, Radiative-Blast-Wave Experiments for Omega EP

Electron magnetohydrodynamics

Investigation of flute and lower hybrid drift instabilities in application to laboratory astrophysics and Z-pinch experiments

Sheared Flow as a Stabilizing Mechanism in Astrophysical Jets

Abstract
It has been hypothesized that the sustained narrowness observed in the asymptotic cylindrical region of bipolar outflows from Young Stellar Objects (YSO) suggests that an intrinsic collimating mechanism is present in these jets. The jz × B&#952 force observed in z-pinch plasmas is a possible explanation for these observations. However, z-pinch plasmas are subject to current driven instabilities (CDI). The interest in using z-pinches for controlled nuclear fusion has lead to an extensive theory on the stability of magnetically confined plasmas. Analytical, numerical, and experimental evidence from this field suggest that sheared flow in magnetized plasmas can reduce the growth rates of the sausage and kink instabilities. Here we propose the hypothesis that sheared helical flow can exert a similar stabilizing influence on CDI in YSO jets.

26. I don't know. My thinking on the jets is that maybe they're composed of matter that approaches the black hole, but never actually enters its event horizon. The force of gravity just outside of the event horizon would probably still be very strong, even if it's not so strong that nothing can escape.

27. G'day Kojax

Maybe you should read some papers on the subject

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