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Two Ways to Die

June 15, 2015

Three bright stars in this evening’s sky have a lot in common. Deneb, Antares, and Spica are among the biggest, brightest, and heaviest stars in the galaxy. And each one will end its life with a titanic explosion known as a supernova.

Deneb is in the northeast as night falls, at the tail of Cygnus, the swan. Antares is the orange heart of Scorpius, which is low in the south-southeast. And blue-white Spica is the leading light of Virgo, in the south-southwest.

All three stars are doomed because of their mass — each is more than 10 times as massive as the Sun. Because of that great heft, gravity squeezes their cores tightly, heating them to billions of degrees.

At those temperatures, nuclear reactions in the core furiously convert lighter elements into heavier ones. But when the core is converted to iron, it takes more energy to continue the process than the core can produce.

At that point, the reactions stop and the core collapses to form a neutron star — an ultra-dense object that’s a few times the mass of the Sun, but only about as big as a city. The star’s outer layers fall in toward the core, then rebound. That creates a shock wave that rips through the surrounding gas — and blows the star apart.

But that’s not the only way to make a supernova. The other involves not supergiant stars like Deneb, Antares, and Spica, but the small, hot stellar corpses known as white dwarfs. We’ll have more about that tomorrow.


Script by Damond Benningfield, Copyright 2015

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