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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

#51

Post by saalweachter »

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.

You can pack a lot of energy into a rotating system. You have similar problems with ring worlds or terraforming Venus (which barely rotates at all). Transporting in the extra hydrogen and all the rest is trivial compared to spinning it up to a decent period.

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

#53

Post by saalweachter »

agonz253 wrote: post #35

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

Which is to say: the escape velocity is 60% of the speed of light! So even starting from 24% of the speed of light at the equator you need to go 10,000x faster than on Earth to escape.

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

#54

Post by [deleted] »

ubercow13 wrote: post #50
ubercow13 wrote: post #38

Earlier quoted context omitted.

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

Time will still tick slower though regardless of the first part of what you say being right

[deleted]

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

#56

Post by teamonkey »

hackaflocka wrote: post #45

Why do planets, stars and moons spin? Are there any that don't?

Classically, mathematically, the answer is conservation of angular momentum. As matter falls on to the body the body needs to rotate faster to conserve the energy of the system. A rotation happens if there is even a tiny asymmetry in the accreting matter.

In the case of our own Moon, one side is more massive than the other and over the course of millions of years became tidally locked so that the heavier side always points towards the Earth.

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

#57

Post by bautez »

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 found it quite eerie and fascinating that the "heartbeat" and "one death" categories are so alike in rhythm.

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

#58

Post by PeterisP »

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.

Being unable to tell is not an argument for time not ticking slower; the whole point of time ticking slower is that everything is consistent for your point of reference and you can't tell, but your point of reference has different time than other points.

Just as if you were inertially moving at 0.9c relative to me, the time frame would be different despite both me and you being 'the same as a point in empty space'.

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

#59

Post by ubercow13 »

ubercow13 wrote: post #50
ubercow13 wrote: post #38

Earlier quoted context omitted.

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

Time will still tick slower though regardless of the first part of what you say being right

Your link doesn't even relate to time dilation and is also about a hollow sphere, not a uniformly dense solid sphere. Moreover in a hollow sphere, time dilation still occurs because it depends on the absolute (or rather, relative to an outside distant observer) potential, not the gravitational field (which is the only thing that is necessarily zero as a result of the flat spacetime in the sphere). See for example this http://physics.stackexchange.com/questions/69821/a-hollow-bl...

It's like you didn't read your link

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

#60

Post by doorhammer »

joezydeco wrote: post #46
doorhammer wrote: post #44

Earlier quoted context omitted.

I stared at the 'my turn signal' and 'car in front of me' signal together for way too long. I went into the same trance I do sitting behind cars at a real red light.

I caught that too! That was a bit of icing on a really clever cartoon.

also, obligatory secondary xkcd reference "Turn Signal": http://xkcd.com/165/
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