When a star dies it explodes in a supernova. This happens when heavier elements like iron is fused in the core of the star. Then the star collapses under its own gravity. This leaves a black hole behind. Now in order to conserve momentum the star must spin. So does a black hole spin? If so at what speed does a black hole spin?
Asked
Active
Viewed 180 times
0
-
3Possible duplicate of Do black holes have a moment of inertia? or What is black hole spin? – AccidentalFourierTransform Feb 10 '17 at 11:48
-
It does spin: https://en.wikipedia.org/wiki/Rotating_black_hole – Feb 10 '17 at 11:53
-
You answered your own question. Conservation of momentum must be maintained. – MaDrung Feb 10 '17 at 11:54
-
Note also that a supernova does not always leave being a black hole, it can (possibly more often) leave behind a neutron star. – Kyle Kanos Feb 10 '17 at 12:13
1 Answers
0
I think I have the answer. Suppose Mass of the star is 10 kg and its velocity is 100 m/s initially. So initial momentum is 1000 kg m/s. Now some mass has exploded into a supernova and what remains is a dense ball of matter which is caused due to the collapse of the gravity of the star.
Now mass is say 5 kg after the supernova (Which is mass of the black hole) so velocity must be 200 m/s. So final momentum is again 1000 kg m/s. This way we can apply conservation of momentum and derive the velocity. Is this correct?
avito009
- 565
-
One black hole, at the heart of galaxy NGC 1365 is turning at 84% the speed of light. – avito009 Feb 10 '17 at 14:21
-
1
-
@avito009 You are missing liniar momentum with angular momentum. To conserve angular momentum rotational speed needs to increase because as radius shrinks. – Pere Sep 13 '17 at 17:39