The most popular theory for turning a white-dwarf star into a supernova is through an act of stellar cannibalism. White dwarfs of nearly the Chandrasekhar mass are essentially identical, so they undergo nearly identical explosions. The maximum mass for a white dwarf is 1.4 times that of the Sun, a value known as the Chandrasekhar limit. Instead, they show a lot of carbon and oxygen, which is the composition of a white dwarf.
And the spectra of Type Ia supernovae show little or no hydrogen, the most common element in the universe. Stars that live a long time cannot be particularly massive, adding credence to the white-dwarf theory. A Type Ia probably occurs when a white-dwarf star - the "corpse" of a medium-mass star like the Sun - is completely blown to bits.Īstronomers suspect white dwarfs as the culprits because Type Ia supernovae typically occur in regions of space that contain mostly older stars, suggesting that a Type Ia is the explosion of a long-lived star.
The best-known Type I supernovae are known as Type Ia. As more supernovae are discovered, though, the line dividing the two categories is blurring. Supernovae come in two broad categories, known as Type I and Type II, which are defined by the spectrum of the matter that's ejected into space, and by the way the stars brighten and fade. Some of these explosions completely destroy the star, while others leave behind either a super-dense neutron star or a black hole - an object with such powerful gravity that not even light can escape from it. A supernova can shine as brightly as an entire galaxy of billions of "normal" stars. But some other types of stars expire with titanic explosions, called supernovae. When a star like the Sun dies, it casts its outer layers into space, leaving its hot, dense core to cool over the eons.
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