how can you tell if a star is dead?

Question: how can you tell if a star is dead?
- Keywords:
  galaxy,
  star,
  universe
Asked by to Sarah on 13 Jun 2014. This question was also asked by , .
- Sarah Casewell answered on 13 Jun 2014:
  
  Dead stars are in general very compact. Because they are formed as a star dies, they tend to be very small and very dense.
  White dwarfs have all the mass of the sun squeezed into the volume of the Earth.
  Neutron stars have more mass again, but are only 10 km across!
  Normal stars are much, much bigger, and brighter than this.

Question: how can you tell if a star is dead?