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The fastest pulsar spins at 716Hz; its equator spins at 24% the speed of light

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Re: The fastest pulsar spins at 716Hz; its equator spins at 24% the speed of light

#21

Post by breischl »

Crito wrote: post #18
throwaway_yy2Di wrote: post #10

Earlier quoted context omitted.

About 10^46 J? In the classical approximation (1/2 Iω^2), assuming a uniform sphere of 2.0 solar masses and r=16 km. That's about 3% of the mass-energy (mc^2 = 3e47 J). This could be way off.

Wolfram Alpha has 10^46 J as 100x the energy given off by a supernova. I don't know if that means your numbers are off, or if this star is just mind-bendingly insane.

WA also puts the mass-energy of two solar masses at 3.574 x 10^47 J. So the initial calculation seems about right. My very-amateur-physicist guess is that the difference is because a supernova only converts a small fraction of the star's mass into energy - the remaining mass is thrown outwards to form planets and such.

[1] - http://www.wolframalpha.com/input/?i=mass-energy+of+two+sola...

Re: The fastest pulsar spins at 716Hz; its equator spins at 24% the speed of light

#22

Post by JonnieCache »

deletes wrote: post #5
fsiefken wrote: post #3

does this mean that time flows significantly faster on the outside of the pulsar then on the inside, if so does this significantly impact the pulsar dynamics?

There is not much difference. The relativistic factor is 1.030107, that is a ~3% change. EDIT: My amateur physics say that the gravitational well adds 9.7% to that. I tried the same calculation for earth and it gave a sensible result: a change of 6.95 * 10^-10. Here is an answer from physics exchange which gets the same result: http://physics.stackexchange.com/questions/10089/gravitation...

12.7% over 16km sounds like quite a lot to me. Especially since we're talking about time.

Re: The fastest pulsar spins at 716Hz; its equator spins at 24% the speed of light

#24

Post by BaryonBundle »

deletes wrote: post #5
fsiefken wrote: post #3

does this mean that time flows significantly faster on the outside of the pulsar then on the inside, if so does this significantly impact the pulsar dynamics?

There is not much difference. The relativistic factor is 1.030107, that is a ~3% change. EDIT: My amateur physics say that the gravitational well adds 9.7% to that. I tried the same calculation for earth and it gave a sensible result: a change of 6.95 * 10^-10. Here is an answer from physics exchange which gets the same result: http://physics.stackexchange.com/questions/10089/gravitation...

The quoted example admits that it ignores strong fields and non-relativistic matter, which we have already established to be dealing with. The angular momentum of an element of volume in the neutron star likely contains enough kinetic energy to affect the Einstein field equations in a significant way. General relativity can't be ignored, but the Newtonian approximations has this habit of being nearly right more often than not.

I know that for rotating black holes the Kerr solution to the Einstein equations offers the best way to test these metric-based questions but I'm not sure if that's what you'd use for a Neutron Star.

Re: The fastest pulsar spins at 716Hz; its equator spins at 24% the speed of light

#25

Post by throwaway_yy2Di »

Crito wrote: post #18
throwaway_yy2Di wrote: post #10

Earlier quoted context omitted.

About 10^46 J? In the classical approximation (1/2 Iω^2), assuming a uniform sphere of 2.0 solar masses and r=16 km. That's about 3% of the mass-energy (mc^2 = 3e47 J). This could be way off.

Wolfram Alpha has 10^46 J as 100x the energy given off by a supernova. I don't know if that means your numbers are off, or if this star is just mind-bendingly insane.

Wikipedia suggests 10^44 J for type Ia, but 10^46 J for a more energetic core collapse:

https://en.wikipedia.org/wiki/Supernova

Re: The fastest pulsar spins at 716Hz; its equator spins at 24% the speed of light

#26

Post by raverbashing »

ars wrote: post #7

Anyone feel like calculating the energy embodied in just the rotation of this star?

Makes me wonder if there will be someday an electrical generator using the rotational energy of a celestial body.

(this would need to have a reference in the main star, otherwise it would just spin with the planet)

Re: The fastest pulsar spins at 716Hz; its equator spins at 24% the speed of light

#27

Post by sanoli »

lifeisstillgood wrote: post #12
joezydeco wrote: post #2

Lemme guess, you caught this from http://xkcd.com/1331/ too?

I could not take my eyes off "One Birth" / "One Death" Fascinating - and I think humanity is "winning"

I couldn't take my eyes off of the fact that everytime wikipedia is edited someone dies.

How 'bout that for the correlation=causation folks!

Re: The fastest pulsar spins at 716Hz; its equator spins at 24% the speed of light

#28

Post by nakkiel »

sanoli wrote: post #27
lifeisstillgood wrote: post #12

Earlier quoted context omitted.

I could not take my eyes off "One Birth" / "One Death" Fascinating - and I think humanity is "winning"

I couldn't take my eyes off of the fact that everytime wikipedia is edited someone dies. How 'bout that for the correlation=causation folks!

You certainly know how to choose your battles..

Re: The fastest pulsar spins at 716Hz; its equator spins at 24% the speed of light

#30

Post by return0 »

sanoli wrote: post #27
lifeisstillgood wrote: post #12

Earlier quoted context omitted.

I could not take my eyes off "One Birth" / "One Death" Fascinating - and I think humanity is "winning"

I couldn't take my eyes off of the fact that everytime wikipedia is edited someone dies. How 'bout that for the correlation=causation folks!

Damnit you guys, stop editing!
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