9.2.12 Supernovae & Gamma Ray Bursts (GRBs)

• A supernova is defined as

An object which exhibits a rapid and enormous increase in absolute magnitude 

• Supernovae are found to occur when:
  • Either, a supergiant star collapses and then explodes - a Type II supernova
  • Or, a white dwarf accrues matter and explodes - a Type 1a supernova

A supernova

A supernova explosion

• A gamma-ray burst (GRB) is defined as:

A short, extremely high energy burst of gamma radiation emitted by a collapsing supergiant star

Gamma ray burst

Gamma ray burst from a collapsing star

• These bright gamma sources can produce, in a very short period of time, as much energy as the total energy output of the Sun over its 10 billion-year lifespan
  • They typically emit energies in the region of 10⁴⁴ to 10⁴⁷ J

• This energy is usually highly focused, or collimated, as narrow beams which are ejected from the poles of the exploding star
  
  • Because of this, some astronomers have concerns that the evolution of a supergiant star in the local part of our galaxy could pose a danger to life on Earth

• However, so far, gamma-ray bursts have only ever been detected at great distances, and never in the Milky Way