Zombie worlds: 5 spooky planets orbiting dead stars

tech.hindustantimes.com:

All stars, including the Sun, have a finite lifetime.

Stars shine by the process of nuclear fusion in which lighter atoms, such as hydrogen, fuse together to create heavier ones. This process releases vast quantities of energy which counteracts the ever-present inward pull of the star's gravity. Ultimately, fusion helps stars to resist gravitational collapse.

This balance of forces is called “hydrostatic equilibrium”. However, there will come a time when the supply of fuel in the core of a star starts to run out and it eventually dies.

Stars with more than about eight times the mass of the Sun will typically burn through their fuel in less than 100 million years. Once fusion ceases, the star collapses – generating a massive instantaneous final burst of nuclear fusion which causes the star to explode as a supernova.

Supernovas release enough energy to outshine the entire galaxy in which they occur. What's left afterwards are collapsed, dead stellar cores called neutron stars or, if the progenitor star was massive enough, a black hole.

Any planets orbiting a star when it goes supernova would be obliterated. Mysteriously though, a handful of “zombie planets” have been detected orbiting neutron stars. And they are some of the weirdest worlds in the cosmos.

Neutron stars are extremely dense, containing as much mass as the Sun squashed into a sphere only a few miles across. Some neutron stars emit beams of radio waves into space – and it is around these “pulsar” stars that planets have been found.

As the pulsar spins, its radio beams sweep through space generating regular radio flashes. Pulsars were discovered in 1967 – you can listen to the sounds of the radio emission from some of them here.

The regularity of these