Angular momentum of a singularity?

In summary, when an ice skater pulls their arms in while spinning, it demonstrates the conservation of angular momentum. Similarly, when a star collapses to become a neutron star or black hole, its rotational period decreases to conserve angular momentum. However, the concept of angular momentum in curved spacetime is complex and may be better understood as stored in spacetime rather than in matter. In the case of the ice skater in space, angular momentum would still apply as they bring their arms in, demonstrating the conservation of this physical property.
  • #1
Adrian Baker
378
2
We know that an ice skater pulling her arms in and spinning faster is an example of the conservation of angular momentum.

As stars collapse to become Neutron stars, the rotational period can be as low as 0.001 seconds, again to conserve angular momentum.

So what happens to this angular momentum when a very large star collapses to a black hole - ie a singularity? How can a dimensionless point have angular momentum?
Is it conserved?
 
Physics news on Phys.org
  • #2
Well you could ask the same thing of electrons. Yes angular momentum is conserved a black hole with angular momentum is called a Kerr black hole and is no longer spherically symetric. In this situation the singuularity becomes a ring:

http://www.physics.ubc.ca/~psih/kerr-metric/node5.html [Broken]
 
Last edited by a moderator:
  • #3
The definition of angular momentum in curved spacetime is very dicey, and cannot be made in general. With that warning, its probably best to consider the angular momentum "stored" in spacetime itself, not the underlying matter.
 
  • #4
To all

Just a question:

If the ice skater was spinning in outer space
with arms straight out and the skater started
to bring in the arms towards himself or herself,
would angular momentum still apply in this case?
or are there other factors to be considered?
 
  • #5
Thanks for the replys jcsd and stingray... I'm not sure I fully understand the answer, but at least I now know that it was a sensible question... :wink:

Poorichard2 - It would be just the same in space - the skater would speed up as they moved their arms in - angular momentum would still apply in this case. (in fact, without friction it would be a great example of angular momentum being consered)
 

1. What is angular momentum?

Angular momentum is a physical quantity that measures the amount of rotational motion of an object. It is a vector quantity, which means it has both magnitude and direction.

2. What is a singularity?

A singularity is a point in space where the laws of physics break down and become infinite. It is often associated with the center of a black hole.

3. How is angular momentum of a singularity calculated?

The angular momentum of a singularity is calculated using the equation L = Iω, where L is the angular momentum, I is the moment of inertia, and ω is the angular velocity.

4. Can the angular momentum of a singularity change?

No, the angular momentum of a singularity is constant and cannot change due to the laws of conservation of angular momentum.

5. What is the significance of angular momentum of a singularity?

The angular momentum of a singularity is important in understanding the behavior of black holes and their surrounding environments. It also plays a crucial role in determining the stability and dynamics of galaxies and other celestial bodies.

Similar threads

Replies
9
Views
3K
Replies
3
Views
1K
Replies
36
Views
14K
Replies
40
Views
2K
Replies
36
Views
3K
  • Mechanics
Replies
9
Views
4K
Replies
19
Views
1K
Replies
5
Views
3K
Back
Top