Summary
A supernova is a stellar explosion or the explosion of a star that briefly outshines an entire galaxy, radiating as much energy as the Sun or any ordinary star is expected to emit over its entire life span, before fading from view over several weeks or months. The extremely luminous burst of radiation expels much or all of a star's material at a velocity of up to 30,000 km/s (10% of the speed of light), driving a shock wave into the surrounding interstellar medium. This shock wave sweeps up an expanding shell of gas and dust called a supernova remnant.
What Causes a Supernova?
A supernova happens where there is a change in the core, or center, of a star. A change can occur in two different ways, with both resulting in a supernova.
The first type of supernova happens in binary star systems. Binary stars are two stars that orbit the same point. One of the stars, a carbon-oxygen white dwarf (a star near the end of its life that has used most or all of its nuclear fuel and collapsed into a size similar to Earth), steals matter from its companion star. Eventually, the white dwarf accumulates too much matter. Having too much matter causes the star to explode, resulting in a supernova.
The second type of supernova occurs at the end of a single star’s lifetime. As the star runs out of nuclear fuel, some of its mass flows into its core. Eventually, the core is so heavy that it cannot withstand its own gravitational force. The core collapses, which results in the giant explosion of a supernova. The sun is a single star, but it does not have enough mass to become a supernova.
Observation of Supernovas
Scientists use different types of telescopes to look for and study supernovas. Some telescopes are used to observe the visible light from the explosion. Others record data from the X-rays (a type of electromagnetic radiation with a very short wavelength and very high-energy. They have shorter wavelengths than ultraviolet light but longer wavelengths than gamma rays) and gamma rays (the highest-energy, shortest-wavelength electromagnetic radiations) that are also produced.
Power of a Supernova
The normal Type Ia supernovae usually releases energy equating between 1 and 2 Foe under just a few seconds.
Others
Observable Universe
Note: For a much better explanation about Supernovas please look at this.