From Earth a supernova looks like an extremely bright star. The word "nova" means new, so it is very ironic that many dense stars end their life as supernova. This phenomena does not occur very often.

Birth of a Dying Star

For the majority of its life a star is a very stable sphere of hot gasses. The lifetime of a star depends on its mass, very dense stars (five to thirty times the mass of the Sun) have a relatively short life.

When a star reaches the end of its life cycle the outer part of the star fall towards the nucleus and begins its decay. An imbalance between the gravity and energy generated by its core is what causes this to occur. When the star has depleted all its sources of nuclear energy and can no longer produce a force great enough to support itself against the compressive force of its own gravitation, the star collapses. Sometimes this happens so quickly that it lasts for less than a second. During the time leading up to this explosion, the star gives off a very high luminosity. After the explosion, remnants of the star are thrown into the universe with incredible speeds. Sometimes, a new star is born from the material that the supernova left behind. An even more rare event occurs when a rather large star collapses, it can cause a black hole to form but this does not happen often. Most supernovas will end their lives as white dwarfs.

How Common is a Supernova?

Supernovas are not daily occurrences and are thought only to occur only once every fifty years in our own Milky Way galaxy. Until 1987 the famous astronomer Johannes Kepler was the last person to see a supernova with the naked eye. The amazing thing is that Kepler viewed the supernova all the way back in 1604!

When supernova SN 1987a was spotted on February 24, 1987 this streak was broken. With telescopes at the European Southern Observatory (the largest observatory of the southern hemisphere), on top of the La Silla mountain in Chili, the Canadian astronomer, Ian Shelton, discovered a new star in the Cloud of Magelhaese: the Supernova SN 1987a.

SN 1987a appeared to have originated from a blue giant, which was contrary to scientists' hypothesis. In the theory of star evolution, the supernova should have come from a red giant instead. This is why the theory of the life cycle of stars was modified, now theoretically blue giants can become supernovas too.