Stars with a mass of more than 6 times the mass of the Sun ends up in a supernova explosion and the stars with lesser masses (including the Sun) ends up as a White Dwarf. A white dwarf radiates the remaining heat through out the universe for billions of years.
As the outer layer of the star explodes, the core of the star collapses either as a Neutron Star. If the mass of the remnant is large, it ends up into a Black Hole.
The last supernova in the Milky Way was recorded in the year 1604 called Kepler's Supernova (SN1604) which was brighter than all stars and planets. There hasn't been a supernova recorded in our galaxy since then but many were recorded in the nearby galaxies.
This is a false-color composite of Kepler's Supernova
Supernova is classified based on absorption lines of chemical elements. But it gets too scientific and so I don't want to go into it.
On June this year, astronomers noted that a star 'Betelgeuse' (one of the brightest stars in the night sky), in the constellation of Orion has shrunk 15% since 1993 at a very high speed. It is one of the largest known stars (Red Supergaint). There is a possibility that the star has already had a supernova explosion. Since it is around 600 light years away, we could see the explosion only 600 years after it has really occured. The explosion maybe expected anytime within the next 50 years atleast. The explosion will be the largest ever recorded and it may be as large as the moon. Betelgeuse will end up into a black hole due to its huge mass. Unlike certain theories this explosion will not cause any problem to Earth.
Post requested by Sidhu