http://www.msnbc.msn.com/id/17189843/
A star found spinning more than a thousand times every second is thought to be the fastest rotating star known.

The neutron star is a burned out corpse that's collapsed into an incredible density rivaled only by black holes. It packs the mass of the sun into a sphere the size of a city. It has been reduced to nothing but tightly huddled neutrons. A thimbleful would weigh a hundred million tons back here on Earth.

The neutron star rotates rapidly because, like a skater pulling her arms in, all its momentum is now highly concentrated.

The tiny but mighty star siphons material from a larger companion. Every now and then, a coating of the material ignites a thermonuclear explosion on the neutron star, and X-rays are released. Using the European Space Agency's Integral satellite, astronomers watched these emissions to measure the spin rate of the star, catalogued as XTE J1739-285.

It is zipping around on its axis 1,122 times every second. That smashes the previous record of 760 spins per second for a neutron star.

"It was quite a surprise to us," said ESA scientist Erik Kuulkers.

More observations are needed to confirm the new speed record, however.

"Our detection is just above the level where we think there is something real," Kuulkers said. "We definitely need more observations. If we see the signal again, then everyone will believe it."

There's a limit to how fast stars can spin. Too fast and they'd break apart. But since astronomers don't know the exact make-up of neutron stars, the speed limit is not known.

"If we can find more stars that spin in this range, it will certainly allow us to exclude some models of their interior structure," Kuulkers said.

Last year astronomers clocked a black hole spinning 950 times per second. The sun, by comparison, spins on its axis once every 25 days as measured at its equator.

I wonder how fast the rotation rate is using the star's "local clock" since neutron stars should cause measureable time dilation.

Our clocks, being fast compared to the neutron star's clock, clock it at 1122 rotations per second but if the gamma factor is 0.6, for instance, then the rate is: 1870 rotations per second.

Assuming 10 km diameter the speed of rotation would be 35,000 km/sec, ~ 0.1 c.

__________________
What brings us together is stronger than what pulls us apart

I'm just guessing (I'm too lazy to calculate it) but I think you give the time dilation due to the tangential velocity (SR) at the surface ... but there must also be GR time dilation from the gravity.

If the blackhole, mentioned in the O.P., is spinning at 950 rotations per second (our time) and if time is stopped, compared to our time, then the local rotational measurement should be infinite rotations per second for the blackhole.

Imagine the effects of frame dragging near this thing!

__________________

Re tangential speed, it´s worth noticing that a neutron star is constantly changing rotation speed [decelerating, and, some times, accelerating].

Also, we should keep in mind that the emission comes from the magnetic poles and not from a point on the equatorial 'surface' [as if it were a lighthouse, as people frequently think].

__________________
What brings us together is stronger than what pulls us apart

There'd be a centrifugal force at the surface of 25 billion X g.

If your calculation is correct then the star has to have enough mass to produce 25 billion g's of inward force to offset the 25 billion g's of outward centrifugal force.

I wonder what the mass of that star is?

And since Argos is correct about the emission being only from the poles then since the star spins on more than one axis then the combined vectorial centrifugal force must be even greater than 25 billion g's - must be pretty massive to produce so much gravity.

- - - - - - - - - - - - - - - - - - - -

This also makes me wonder on how many axes can an object rotate around? I'm thinking only three axes.

One thing you're missing is that the emission is from the magnetic poles, which do not have to align with the rotational poles! For an example, we need look no farther than our own planet.

__________________
Any day you wake up on "the right side of the dirt" is a good day.

T. Anderson

It seems about right. As this RCF calculator for centrifuge rotors can demonstrate, you get about 250,000 X g for a 90 mm (r) object spinning at 60000 rpm. The star's ~5km in radius and spinning at 67000 rpm, so the effective force should be several orders of magnitude larger.

Good point, I forgot about the possibility that the magnetic pole need not be at the same location as the rotational pole.

Is the magnetism caused by a counter-rotating charge (or counter-rotating charged substance)?

If so then it makes me wonder ...

Read more


Title: Rotation at 1122 Hz and the neutron star structure
Authors: M. Bejger, P. Haensel, J.L. Zdunik

Recent observations of XTE J1739-285 suggest that it contains a neutron star rotating at 1122 Hz. Such rotation imposes bounds on the structure of neutron star in XTE J1739-285. These bounds may be used to constrain poorly known equation of state of dense matter. One-parameter families of stationary configurations rotating rigidly at 1122 Hz are constructed, using a precise 2-D code solving Einstein equations. Hydrostatic equilibrium solutions are tested for stability with respect to axi-symmetric perturbations. A set of ten diverse EOSs of neutron stars is considered. Hypothetical strange stars are also studied. For each EOS, the family of possible neutron star models is limited by the mass shedding limit, corresponding to maximum allowed equatorial radius, R_max, and by the instability with respect to the axi-symmetric perturbations, reached at the minimum allowed equatorial radius, R_min. We get R_min \simeq 10-13km, and R_max \simeq 16-18km, with allowed mass 1.4-2.3 M_\odot. Allowed stars with hyperonic or exotic-phase core are supramassive and have a very narrow mass range. Quark star with accreted crust might be allowed, provided such a model is able to reproduce X-ray bursts from XTE J1739-285.

Read more (34kb, PDF)


Sub-millisecond Pulsar & Constraints

__________________
`Irony` actually does mean `metal like`...

A picture is worth a thousand words. See how both axes are misaligned. If the rotational axis were pointing to Earth, the pulsar wouldn´t be noticed.

__________________
What brings us together is stronger than what pulls us apart

Just out of curiosity, how close to the equator can the magnetic poles be? Maybe the star is only rotating at 571 times per second and we get a flash from both poles.

__________________
Any day you wake up on "the right side of the dirt" is a good day.

T. Anderson

How do they measure star spin rates, anyway? I would guess (and please correct this if wrong, or confirm if correct) that you need a scope with sufficient resolution to see both sides of the star, and you measure redshift off each side. That gives you the component of spin that is along the plane in which you're viewing the star. If you were to then take redshifts from all around the edge of the star, you could build a profile about where the axis was pointing, too, and correct for that.

If that's at all right, how is this done when you don't have the ability to sample over the edges? Do they track the path that the x-ray emission takes as it traces over the surface, and determine the direction of the axis from that? Do telescopes have sufficient resolution for that? Or am I way off base on this?

Whew... (and thanks).

__________________
"It's turtles all the way down."

For normal stars you use a spectrometer and measure the red/blue shift at the fringes.
For neutron stars though you just listen to the beeps and time them.

We would have to be precisely aligned along both poles so that we get the same flux from each one otherwise the signal would have alternating high and low peaks. Given that the poles themselves don't have to be aligned 180deg apart it would seem unlikely.

I´ve wondered that myself...

__________________
What brings us together is stronger than what pulls us apart

Well, in order for the surface gravity to be 25 billion g's, an object 4.8 kilometers in radius (the claimed size of the pulsar) would have to be roughly 2 x 10^24 kg, or roughly 1/3 the mass of the earth. This isn't at all unreasonable, unless I screwed up the calculations (not unheard of...). Obviously, the mass would have to be higher than this to keep it together, as this would only exactly cancel, but this still shows that it does not require excessively massive stars to be able to hold together under this force.

ahem... the centrifugal acceleration would not be 25 billion gs, in fact it is closer to 25 million:
a=rw^2=4800m*(1120*2*pi)^2=2.37E8 m/s^2=24 million gs.

the mass required to counteract that centrifugal acceleration would be given by the equation a=GM/r^2 or M=ar^2/G=2.37E8*4800^2/6.67E-11=8.21E28kg, or 4% of the mass of the sun. Since they said it had about the same mass as the sun, that is perfectly reasonable.

1120*2*pi = 7033
7033^2 = 49,463,089
49,463,089*4800 = 237,422,827,200
237,422,827,200/9.8 = 24,226,819,102
-With a B

Okay guys, I want this to be a clean fight, hands on the keyboards and no thinking below the belt...

__________________
In your rush to call everyone "entrenched" or closed-minded or "limited" you fail to note that the "limit" here has a very natural boundary: that point at which the evidence stops. - JayUtah

Science fiction was never meant to be an educational tool. - Editor Amazing Tales

No fight. It just looks like his calculator slipped a few zeroes. It happens.

Yeah, you're right, I plugged it in again and got the same answer that you did. My bad . I apparently can't count digits