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Inner Workings: A massive star dies without a bang, revealing the sensitive nature of supernovae

In 2008, a huge red star in another galaxy reached the end of its life. A star as heavy as this one, born with 25 times the mass of the Sun, was supposed to go out in a fiery flash of light known as a supernova, millions or billions of times brighter than our Sun. But this one refused to play the role of drama queen. Instead, it brightened just a little, then vanished, possibly leaving behind a black hole.



The spiral galaxy NGC 6946 spawned the first, and so far the only, failed supernova ever seen: a red supergiant star that vanished from the heavens without exploding. Image credit: Science Source/Robert Gendler.



No one had ever seen one of these huge red stars wink out of existence with so little fuss before. It was a sign that the lives and deaths of these stars are more complex than our simplest theories had claimed. “As amazing and important and fun and exciting as this is, it’s not a surprise,” says Stan Woosley at the University of California, Santa Cruz. In fact, the discovery may help explain why the massive stars in computer models often fail to blow up.

Conventional theory says that nearly all stars born more than eight times as massive as the Sun explode as supernovae. When young, a massive star is bright and blue. Nuclear reactions in its core generate an immense amount of energy. This keeps the star hot so that gas pressure pushes outward and partially counteracts the inward pull of the star’s gravity; so does the pressure of the many photons streaming out of the star’s core. As long as it generates energy, the star can hold itself up.

In the end, though, gravity always wins. Later in life, as a massive star begins …