Quote:
Originally Posted by Quarkus
If we can only detect pulsars if they are beaming in our direction, how do we know that not all neutron stars are pulsars?
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All neutron stars rotate - fast - because they (must) conserve the angular momentum of the original larger star when it supernovas.
It's the rapid rotation of the (very large) magnetic field that causes the 'pulsar' radiation, like a generator. As they spin, they emit radiation from their magnetic poles. Because (like Earth) the magnetic poles do not lie on the axis of rotation - they appear to wobble, or pulse.
As far as I could find out, if we are parallel or perpendicular to the axis of
rotation we can't see the 'radio' pulse *or* if the poles are aligned just so, some pulsars re-absorb their own radiation (converting it into heat at hot spots on the surface).
[Edit: I re-read some of this stuff and I'm not so sure I've quite got this bit right - I only found one reference to the alignment of the axis of rotation, even if it does make some sense - and I'm not so sure the hot spot refers to the same radiation/particles as the radio pulse, so - caveat emptor!]Apparently there are half a dozen or so observed neutron stars that *don't* pulse in our direction.
'Radio-quiet' neutron stars are usually observed by x-ray, I think? Possibly by visible light if close enough?
Check out this link:
http://www.esa.int/esaSC/Pr_15_2004_s_en.html
They can rotate 600 times a second and have gravitational acceleration of 100 billion G's... try landing your shuttle on that puppy!