A supernova is the explosive cataclysmic end to the life of a star. A supernova can produce so much energy that it can briefly outshine a galaxy with about 1010 times the luminosity of the Sun! The energy produced in a supernova explosion is around 1046 J. This enormous release of energy may occur in only a few seconds. A star with of a mass of greater than 1.4 ☉ (☉ being the mass of the Sun) can become a supernova but the precise value depends on how it was formed).
A type 1a supernova results from the attraction of material to a white dwarf from its companion star in a binary system, increasing both its mass and core density.
If the mass of the white dwarf reaches more than about 1.4 solar masses with a correspondingly ‘super-high’ density the star then suffers a violent collapse, with a huge rise in temperature. The thermal energy produced causes the star to explode as a supernova; no individual body remains.
Type 1a supernovae are used as standard galactic candles. Since they all have approximately the same mass and absolute magnitude, a measurement of their apparent magnitude can be used to calculate their distance.
The light curve for a typical type 1a supernova is shown in Figure 1.
A type II supernova may result in the latter stages of the life of a single giant star. In the type II supernova the gravitational attraction overcomes the radiation pressure as the star ‘runs out of fuel’. The outer layers of the star fall inwards and bounce off the solid core and travel outwards towards the surface. The shock wave produced moves at up to 10 000 kms-1 and ‘blows away’ most of the outer layers of the star giving a supernova explosion. If the final mass of the core is less than about 3 solar masses a neutron star is left behind. If it is greater it collapses to give a black hole.