The Crab Nebula formed from a supernova. http://upload.wikimedia.org/wikipedia/commons/0/00/Crab_Nebula.jpg
Supernovae are the explosions of stars at the of their life span and are the reason black holes, neutron stars and nebulae, like the crab nebula pictured above form. They can be separated into type I and type II supernovae depending on a number of factors.
Type I supernova:
Type I supernovae occur when a star in a binary system becomes a white dwarf star at the end of its life cycle whilst the other star in the binary system is beginning the process of forming a red giant. When the formation of the red giant occurs it spills gas onto its white dwarf companion in the binary system. If the white dwarf is able to obtain enough mass during the process of the red giant spilling gas onto it and it is able to reach the Chandrasekhar limit of 1.44 solar masses ( 1 solar mass being the mass of the sun), then the white dwarf will collapse into a type I supernova.
Alternatively a type I supernova can occur when both stars are white dwarf or one is a neutron star so long as one of the dwarf stars is able a to accrete mass then when it reaches 1.44 solar masses it will become a supernova. However this process of forming a type I supernova takes much longer which is why Perlmutter described it is a “slow, relentless approach to a cataclysmic conclusion”.
If you are still having trouble picturing what happens during a type I supernova imagine a balloon being filled with air until no more air can be forced into the balloon and it pops, or if you want a more visual representation search Monty Python Mr Creosote on youtube.
Type II supernova:
Type II supernova occur when massive stars swiftly and uncontrollably collapse. These stars must be at least 8 times the mass of the sun. Due to their huge mass stars of type II supernova size are able to perform nuclear fusion on elements heavier than hydrogen and helium like our sun, but when they start fusing iron and nickel there is no net energy output so the core of the star becomes inert, because of this that the star is not able to produce any heavier elements and the iron and nickel core continues to grow right up to the Chandrasekhar limit. When the core reaches the limit the electron degeneracy is not enough to maintain the stellar equilibrium and the star’s gravity causes it to catastrophically implode. The outer layers of the star are accelerated at 23% of the speed of light towards the core whilst the core reaches temperatures of 100 billion kelvin. During this process reverse beta decay occurs forming neutrons and neutrinos and releasing 10 to the power of 46 joules in about 10 seconds. After this the inward collapse is stopped by the Neutron degeneracy and the implosion is rebounded outwards causing all surrounding stellar matter to reach escape velocity and form a supernova explosion.
After a type II supernova one of four things will happen:
1. The explosion will have been so powerful that the stellar mass was scattered so far it could not reform.
2. The some of the mass remains to form a Neutron star
3. If the remnants of the star exceeds 3-4 solar masses then nothing can prevent complete gravitational collapse and a black hole is formed. For more on black holes please visit https://rgsphysics.wordpress.com/2013/09/26/black-holes/
4. Nebula can be formed e.g. the crab nebula in the image at the top.
Perhaps the next star to collapse in a super or even hypernova will be Betelgeuse which is visible in our night sky during the winter.