When a star like the Sun dies, it casts its outer layers into space, leaving its hot, dense core to cool over the eons. But some other types of stars expire with titanic explosions, called supernovae. A supernova can shine as brightly as an entire galaxy of billions of "normal" stars. 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.
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. As more supernovae are discovered, though, the line dividing the two categories is blurring. The best-known Type I supernovae are known as Type Ia. 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. Astronomers 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.
Stars that live a long time cannot be particularly massive, adding credence to the white-dwarf theory. And the spectra of Type Ia supernovae show little or no hydrogen, the most common element in the universe. Instead, they show a lot of carbon and oxygen, which is the composition of a white dwarf. Animals Wild Cities Wild parakeets have taken a liking to London Love them or hate them, there's no denying their growing numbers have added an explosion of color to the city's streets. India bets its energy future on solar—in ways both small and big.
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