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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

#31

Post by nealabq »

deletes wrote: post #19
machrider wrote: post #16

Earlier quoted context omitted.

I think the point was that time in the center of the star is more affected by gravity than at the surface. Whereas someone on the surface (if that were possible) would experience greater time dilation relative to the center due to his high relative velocity. So for those two points (surface vs center), the two time dilation effects are working opposite each other. Edit: I may have been reading too much into it. The e…

I think you mixed up some things. There is no gravity or time dilation in the center of a massive spherical object.

If you're in a small empty room in the middle of a neutron star, you will be floating weightless, but you're still at the bottom of a gravity well. Since it's the well, not the acceleration that affects time, time will tick slower for you.

(Don't try this at home.) (And if you do, don't touch the walls.)

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

#32

Post by jurjenh »

NAFV_P wrote: post #23

You can see round the back of a neutron star: http://en.wikipedia.org/wiki/Neutron_star#Properties

Wow, that page led me to the fact that there is such a thing as centrifugal force... And all these years spent trying to correct people. Oh well, you live, you learn.

http://en.wikipedia.org/wiki/Photon_sphere

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

#33

Post by ars »

raverbashing wrote: post #26
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)

Already have this :)

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

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

#34

Post by [deleted] »

raverbashing wrote: post #26
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)

[deleted]

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

#35

Post by agonz253 »

Dropping something the mass of a tennis ball into this pulsar(assuming 2 solar masses for it) would generate approximately the same amount of energy upon impact as that of 12 atomic bombs like the one tested in New Mexico, and it would reach the surface at 60% the speed of light...relativistic effects aside

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

#36

Post by twic »

jurjenh wrote: post #32
NAFV_P wrote: post #23

You can see round the back of a neutron star: http://en.wikipedia.org/wiki/Neutron_star#Properties

Wow, that page led me to the fact that there is such a thing as centrifugal force... And all these years spent trying to correct people. Oh well, you live, you learn. http://en.wikipedia.org/wiki/Photon_sphere

Since we're already talking XKCD: http://xkcd.com/123/

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

#37

Post by deletes »

nealabq wrote: post #31
deletes wrote: post #19

Earlier quoted context omitted.

I think you mixed up some things. There is no gravity or time dilation in the center of a massive spherical object.

If you're in a small empty room in the middle of a neutron star, you will be floating weightless, but you're still at the bottom of a gravity well. Since it's the well, not the acceleration that affects time, time will tick slower for you. (Don't try this at home.) (And if you do, don't touch the walls.)

Spacetime in the center of a perfect spherical object is the same as a point in empty space, you can't tell them apart. Of course that only counts for the exact point in the center. So the time will not tick slower there as to someone far from any objects.

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

#38

Post by ubercow13 »

deletes wrote: post #37
nealabq wrote: post #31

Earlier quoted context omitted.

If you're in a small empty room in the middle of a neutron star, you will be floating weightless, but you're still at the bottom of a gravity well. Since it's the well, not the acceleration that affects time, time will tick slower for you. (Don't try this at home.) (And if you do, don't touch the walls.)

Spacetime in the center of a perfect spherical object is the same as a point in empty space, you can't tell them apart. Of course that only counts for the exact point in the center. So the time will not tick slower there as to someone far from any objects.

What? The lowest potential in a uniform sphere is at the centre not the surface (http://en.wikipedia.org/wiki/File:GravityPotential.jpg). Also graviational time dilation depends on the potential not the force (curvature) so it is irrelevant if the point at the centre is shifted in spacetime

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

#39

Post by jjoonathan »

jurjenh wrote: post #32
NAFV_P wrote: post #23

You can see round the back of a neutron star: http://en.wikipedia.org/wiki/Neutron_star#Properties

Wow, that page led me to the fact that there is such a thing as centrifugal force... And all these years spent trying to correct people. Oh well, you live, you learn. http://en.wikipedia.org/wiki/Photon_sphere

The "war on centrifugal force" is pedagogical. If you sit in an inertial frame, all forces you intend to teach are due to interactions between objects. This lets teachers introduce the interactions one at a time in a way that presents minimal opportunity for the "no, that equation doesn't work here for XYZ reasons which you won't understand until after you've taken vector calculus" problem.

If you allow rotating reference frames then you've got to talk about transformation rules in gory detail. Everyone understands centrifugal force, but what about the coriolis and euler forces? Our intuition doesn't tell us when they apply and when they don't, so we have to be systematic about it, and that means "gory details". And guess what "being systematic about it" involves? Moving to an inertial frame of reference and taking derivatives!

You can't be intuitively correct or systematic about rotating frames without thoroughly understanding inertial frames, so that's what you learn first, along with strongly worded advice to stay away from non-inertial frames (e.g. defining frame-dependent forces as "fictitious").

Anyone doing general relativity is comfortable enough with coordinate transformations that they can understand the caveats that come with frame-dependent forces and even take advantage of them to simplify calculations or definitions (the process of going from a "global" to a "local" coordinate system is highly nontrivial in GR).

That's why the Coriolis, Euler, and Centrifugal forces are called "fictitious" while gravity isn't.

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

#40

Post by lifeisstillgood »

darklajid wrote: post #14
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"

Second kid since yesterday. Fighting for humanity here.. ;-)

Twins? Congratulations - the battle is worth it :-)
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