Do All Black Holes Exhibit Rotation?

In summary, there are two representations of black holes commonly seen in popular media. These include a feeding black hole with an accretion disk, which is a product of the rotation and angular momentum of the matter being attracted to the black hole, and a black hole passing in front of a star field, causing gravitational lensing. Realistic black holes will always rotate due to the angular momentum inherited from the stars that give birth to them. Lensing is not dependent on rotation. The infalling material from a non-rotating black hole would cause it to start rotating, and it is unlikely that a black hole would have a rotation rate of exactly zero. The event horizon of a highly rotating black hole
  • #1
Lino
309
4
There are two representations of black holes that I see in the popular media. Could you help me find the answer to a (or two) question about this please?

1. Feeding black hole with an accretion disk - I assume that the accretion disk is a product / consequence of rotation (in addition to the feeding) ... but we all know what they say about assumptions ... ?

2. A black hole passing in front of a star field, causing gravitational lensing. I don't know if these are rotating, or where to start looking for discussions on the topic. Any ideas?


Basically, do black holes always rotate? Any pointers / suggestions would be greatly appreciated.


Regards,


Noel.
 
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  • #2
Lino said:
Basically, do black holes always rotate? Any pointers / suggestions would be greatly appreciated.

Realistic black holes will always rotate. This is because the stars which give birth to them always rotate, and that angular momentum becomes the rotation of the black hole during the collapse.

Note: Lensing doesn't really have anything to do with rotation. It's an effect observed even in a nonspinning black hole.
 
  • #3
The accretion disk is not a product of the balck hole rotating, but of the angular momentum of the matter being attracted to the black hole.

Suppose you a non-rotating black hole with a star close enough to the black hole so that some of the gases from the star's outer layers is being pulled towards the black hole. The star would have to be revolving around the black hole so that itself is not pulled in, all at once. Therefor the star has an angular velocity, or a forward speed around the black hole. As the gases get closer and closer to the black hole, they still keep this forward motion, and thus spiral around the black hole forming the accretion disk.
 
  • #4
Nabeshin said:
Realistic black holes will always rotate. ... It's an effect observed even in a nonspinning black hole.

Thanks Nabeshin. Can I just ask, is "realistic" a classification - I can't find any references to it when I search for it.
 
  • #5
"Realistic" as in what one would expect to see. Think of it probabilistically: What is the probability that a black hole has a rotation rate of that is exactly zero? I would venture that it is exactly zero.
 
  • #6
Thanks 256bits.

256bits said:
The accretion disk is not a product of the balck hole rotating, but of the angular momentum of the matter being attracted to the black hole.

Of course! Sorry, I should have seen that.

256bits said:
... a non-rotating black hole with a star close enough to the black hole so that some of the gases from the star's outer layers is being pulled towards the black hole.

Am I right in thinking that this infalling material would cause the (non-spinning) black-hole to start to rotate? Also, on a different note, would the infalling material start accelerating to the speed of light once it crosses the event horizion?

Thanks again 256bits.

Regards,

Noel.
 
  • #7
D H said:
"Realistic" as in what one would expect to see. Think of it probabilistically: What is the probability that a black hole has a rotation rate of that is exactly zero? I would venture that it is exactly zero.

OK, I think I understand. Thanks D H.
 
  • #8
Yes

They must. As results of stellar system they were once the sun of..They have A/momentum.
The speed of rotation is interesting.. the event horizon bulges as in an oblate sphere at very high rotation.

DH the probability is .. zero. Though that statistics and my field is stochastics related to humanity
 

1. Do all blackholes rotate?

No, not all blackholes rotate. Some blackholes are non-rotating, also known as Schwarzschild blackholes. These blackholes have a singularity at the center and do not have any angular momentum.

2. How can we tell if a blackhole is rotating?

We can tell if a blackhole is rotating by observing the surrounding matter around it. If there is matter orbiting the blackhole in a disk-like structure, then it is likely that the blackhole is rotating. Additionally, we can measure the gravitational effects of the blackhole on nearby objects to determine its rotation.

3. Can a non-rotating blackhole become a rotating blackhole?

Yes, a non-rotating blackhole can become a rotating blackhole. This can happen if the blackhole accretes matter from its surroundings, which can add angular momentum to the blackhole and cause it to rotate.

4. What is the maximum rotation rate for a blackhole?

The maximum rotation rate for a blackhole is known as the Kerr limit. This is when the blackhole is rotating at the speed of light at its event horizon. However, it is theoretically impossible for a blackhole to reach this maximum rotation rate.

5. Can a blackhole stop rotating?

No, a blackhole cannot stop rotating. Once it has acquired angular momentum, it will continue to rotate unless it loses it through a process such as accretion or gravitational waves. This means that a rotating blackhole will always rotate, even as it evaporates and eventually disappears.

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