APOD: A Pulsar s Hand (2010 May 01)

[Chris Peterson]

7revolutions per second on a 20klm diameter object gives a surface speed of 220klm/sec or almost 800,000klms /hour. Like I said, you have to have mythical material to keep it from flying apart.

And like I said, describe the physics you are using to arrive at this conclusion.

By my calculation, the centrifugal force on a particle at the surface of the neutron star is 1.9e7 N/kg. The force of gravity is 1.3e10 N/kg. So for this object, spinning at a mere 7 rotations per second, gravity is 684 times stronger than the force that tries to pull it apart. No mythical material required- this neutron star could be made of cotton candy and it would hold together.

It is not established beyond reasonable doubt, it is only a current theory, based on known facts at present. A theory is not scientific fact

You are right, a theory is not a fact. But the theory here is extremely well supported by multiple lines of evidence. It is so well supported that it is treated as a fact: nobody is looking for alternatives. There are many theories that reach this level of certainty.

[Chris Peterson]

yes my sentence was wrong. what i meant was that the 7times/sec pulses may not be necessarily because of the rotation around the axis of rotation; they may be the result of another motion like Precession.
could it be?

In principle, I suppose a very newly created pulsar might precess, and if its emission were polar, that could create periodicity. But I think the nature of the forces involved would snub precession very quickly. In any case, I don't think any actual pulsars have been associated with precession.

[alter-ego]

yes my sentence was wrong. what i meant was that the 7times/sec pulses may not be necessarily because of the rotation around the axis of rotation; they may be the result of another motion like Precession.
could it be?

In principle, I suppose a very newly created pulsar might precess, and if its emission were polar, that could create periodicity. But I think the nature of the forces involved would snub precession very quickly. In any case, I don't think any actual pulsars have been associated with precession.

Amir,
Here is a 2006 conference paper discussing neutron star model(s) and using precession to probe a neutron star's interior. Not hard to read and some interesting stuff. Specifically, there is some data supporting (long period) precession, but is rare.

As far as we can tell from surveys of radio pulsars, precession in isolated neutron stars is a
rare phenomenon. Precession, once excited, would eventually damp through internal friction.
The rareness of precession could mean that it is rarely excited in isolated neutron stars.

http://iopscience.iop.org/1742-6596/31/ ... 31_013.pdf.

Just thought this might help

[moontrail3]

Does anyone else see the figure in the bottom half with flowing robes moving to the right with arms outstretched?

I do. This was my first impression and still is when I look to the image.

[Amir]

Just thought this might help

thanks alter-ego. i'm gonna take a look.

[Keldor]

Looks like the hand of God to me.

Which is actually not too far from the truth - after all, supernovas are responsible for creating the elements needed to form rocky planets like Earth, and this is a supernova remnant.

[neufer]

• Hamlet: Or like a whale.
  
  Polonius: Very like a whale.

<<The heart of an adult blue whale is about the size of VW Beetle. The carotid artery is about 12" to 18" in diameter, compared to 1/4" for humans. The heart (pulse) rate at rest is 5 to 10 beats per minute.>>