Supernova in Galaxy Messier 100

Monday, February 27th, 2006 at 05:27 PM by Dave

A supernova was recently discovered in the galaxy, Messier 100. This galaxy is about 60 million light-years away from the Earth. It has a beautiful spiral shape with a bright core, two large arms, and a pair of fainter spiral arms. On February 4, 2006, a Type Ia (”one A”) supernova was found in this galaxy. There are several types of supernova but this one is of great interest for astronomers.

(Click on image for full-size version.) A pair of photos showing Supernova 2006X in M100 (Credit: ESO)

Supernova type Ia explosions are formed when a white dwarf star gathers additional mass from a companion star within a binary system. White dwarfs are small, extremely compact objects that are the remnants of medium mass stars (like the Sun) that are slowly giving off their heat energy. They are very hot giving them a white color. Subrahamanyan Chandrasekhar studied these stars and determined that the interiors of white dwarf stars cannot support the mass of the star against gravity if the white dwarf’s mass exceeds 1.4 times the mass of the Sun.^[1] If their mass exceeds 1.4 solar masses, the star will collapse in a supernova explosion fusing all the elements in this star. This supernova briefly shines with a light equal to over 10 billion times the amount of light that the sun gives off. This allows the explosion to be seen from great distances.

The main element found in a white dwarf is carbon. This is the leftover element from a medium mass star. A medium mass star fuses hydrogen to helium, then helium to carbon. When carbon is formed in the core the fusion process stops. The mass of these stars are not great enough to cause the carbon to fuse. During carbon fusion, the core does heat up, effectively heating up the outer layers of the star causing them to expand outward. Since gravity weakens with distance, these outer layers often escape from the star, forming a planetary nebula. The left over core of the star is a White Dwarf. This is the ultimate fate of our Sun. Our Sun will not form a supernova because our star is not massive enough and we are not in a binary star system (thank goodness!). However, White Dwarfs that do form in binary star systems can start accreting mass from their companion until their mass exceeds 1.4 solar masses. At this point, you get a Type Ia Supernova.
Astronomers have studied Type Ia Supernovae and have found that the amount of light, and the resulting light curve, is very consistent between different Type Ia Supernovae. Because the star’s mass cannot exceed 1.4 solar masses there is a limit of the amount of light that can be given off when this star explodes. Thus, these supernovae can be used as a measuring stick for distant galaxies to find their distance from the Earth. These supernovae have helped astronomers find the distance to the farthest galaxies in our universe.

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