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The term came to be used to describe the supernovae of the most massive stars, the hypergiants, which have masses from 100 to over 300 times that of the Sun. Decaying 56Ni, a short-lived isotope of nickel, is believed to provide much of a hypernova's light. The core of a hypernova collapses directly into a black hole, and two extremely energetic jets of plasma are emitted from its rotational poles at nearly the speed of light. Since stars large enough to collapse directly into a black hole are quite rare, hypernovae would likewise be rare, if they indeed occur. It has been estimated that a hypernova would occur in our galaxy every 200 million years.