Joy Division and dead stars


Have you ever wondered about the origin of the Joy Division’s cover of “Unknown Pleasures?”

Unknown Pleasures

I must admit I’m a bit ashamed of myself, because just recently I discovered (thanks to a friend), that it’s much closer to my everyday life than I expected. Actually the “drawing” is a plot of the successive pulses of the first radio pulsar (controversially) discovered in 1967 called CP 1919 (now having a fancy name PSR 1919+21), with a pulse period of 1.337 seconds and a pulse width of 0.04 second.

Peter Saville turned it into an icon, as shown in the following video:

For those who suddenly became interested in pulsars, I may add a couple of interesting facts on them:

  • Pulsars are fast rotating magnetized neutron stars (which is the compact remaining of a past glory… which normally used to be a shiny massive star (from 10 to 20 times more massive than the Sun).
  • Pulsars have two main layers: an external rigid crust and an inner superfluid of neutrons.
  • Pulsar may be approximated by a dipole, with the magnetic poles displaced from the rotation axis.
  • The rotating magnetic field originates an electric field, which accelerates charged particles, so that they are thrown away from the surfaces of the neutron star, generating different kinds of emission.
  • There are two main populations:
    • The slow rotating classic pulsars (where slow is a full circle in more than 30 ms). It’s their natural rotation after the star explodes as a Supernova. The rotation speed tends to slow down with time. Just like a human being, while young, moves faster than when older.
    • The fast rotating pulsars, also called millisecond pulsars, (less than 30ms), which rotate faster because they gain momentum by accreting matter from a companion star, so that these one on contrary may increase their rotation speed. Here is a couple relationship, so even if you thought you had a quiet life and a peaceful retirement, getting a partner may imply messing things up and getting your life to speed up again.
  • Pulsars are very reliable clocks, as they period changes very slowly, for example the period of PSR J1603-7202 increases by 0.0000005 seconds every million years… so unless you’re a Swiss citizen, I reckon that you don’t need better precision.
  • The beautiful Crab Nebula has a pulsar just in the middle, who’s actually powering the glowing of the remnants of the last Supernova observed in the Milky Way (in 1054), and makes it one of nowadays astronomy icons. Hopefully some other band will consider this image to appear in one of their covers… 😉

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