3.9.2.12
Supernovae & Gamma Ray Bursts
Astrophysics | AQA A-Level Physics
Key Definition
Supernova: an object which exhibits a rapid and enormous increase in absolute magnitude.
Types of supernovae
- Supernovae are found to occur in two main ways:
- Type II supernova: a supergiant star collapses and then explodes. This occurs when the iron core of a massive star can no longer sustain fusion, and gravity causes the core to collapse catastrophically.
- Type 1a supernova: a white dwarf accretes matter and explodes. This occurs in a binary star system when a white dwarf attracts material from its companion star. When its mass reaches the Chandrasekhar limitThe maximum mass of a stable white dwarf star, approximately 1.4 solar masses. Beyond this limit, electron degeneracy pressure cannot support the star against gravitational collapse. (about 1.4 solar masses), it undergoes a thermonuclear explosion.
Gamma ray bursts (GRBs)
Key Definition
Gamma-ray burst (GRB): a short, extremely high energy burst of gamma radiation emitted by a collapsing supergiant 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 $10^{44}$ to $10^{47}$ 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.
Common Mistake
Do not confuse Type II and Type 1a supernovae. A Type II supernova involves the collapse of a massive star's iron core. A Type 1a supernova involves a white dwarf in a binary system exceeding the Chandrasekhar limit. The key part is that Type 1a supernovae are used as standard candles because they always explode at the same mass, producing a consistent peak absolute magnitude.