I am currently studying Cosmology in School, and was told that after a supernova there can still be some of the core remaining which becomes a superdense neutron star. I was also told that these spin with a frequency of 30.2Hz. Is there any particular reason for that frequency? Do all neutron stars spin at this rate, and why?

The spin rate varies by star. You can get some general information from Wikipedia on their spins, and why they spin as fast as they do.

 

http://en.wikipedia.org/wiki/Neutron_star#Rotation

30.2 Hz is the frequency of rotation of the neutron star in the Crab nebula, the remnants of a fairly well-known supernova (viewed in 1054 AD), i.e. that was one specific example, rather than being a generally true claim.

 

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

And observing this remnant at other wavelengths would be fantastic... Radiotelescopes tell exactly where it is, but in visible light, nothing, nada, niente, g'è minga - disappointing.

And observing this remnant at other wavelengths would be fantastic... Radiotelescopes tell exactly where it is, but in visible light, nothing, nada, niente, g'è minga - disappointing.

 

Surely the Crab Pulsar is the one of the best known x-ray sources in the sky such that it is was once used as a test-bed for new telescopes

 

http://physicsworld.com/cws/article/news/2011/jan/13/astronomers-say-goodbye-to-the-millicrab

 

According to wiki the Crab Pulsar is one of 6 that CAN be observed optically

 

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

 

And you can see the Nebula - which shines around the pulsar with a good camera or binoculars on a good night

The others answered the question on spin rate frequency, but didn't cover the question "what determines the spin rate"

 

Take any star with spin, now decrease the stars radius. The spin rate will increase. Conservation of angular momentum. Think of a spinning figure skater that tucks in her arms.

Oops, my bad. Thanks, +.

Mordren

If the stars radius reduces then to maintain the angular momentum the spin rate must increase. Do you mean matter momentum or the magnetic momentum of that material?

What, pray tell, is magnetic momentum?