Rho Cassiopeia 
The heaviest stars in the universe will blast themselves to bits. But like a golfer getting ready to try a tournament-winning putt, they first get in a few practice swings. These smaller explosions blast out shells of hot gas that expand at a million miles an hour.
One example is in Cassiopeia, the queen, whose brightest stars form a letter W. It’s well up in the northeast at nightfall.
Rho Cassiopeia is one of the biggest stars in the Milky Way — a yellow hypergiant. If it took the Sun’s place in our own solar system, it would extend past the orbit of Mars.
Rho Cassiopeia is probably about 40 times heavier than the Sun. And it’s getting near the end of its life. Not long ago, it most likely was a red supergiant, so it was even bigger than it is now. But as a result of changes deep in its core, its outer layers are contracting and getting hotter. Before long, it’ll probably become a smaller and hotter blue supergiant.
These changes also trigger explosions on the star’s surface. An eruption back in 2000 blasted out the equivalent of about three percent of the mass of the Sun — a half-century after a similar explosion.
More of these eruptions are probably in the star’s future. And eventually, it’ll blow itself apart as a supernova. Its outer layers will blast into space, while its core will be crushed to form one of the strangest objects in the universe: a black hole.
We’ll talk about a star that’s already exploded tomorrow.
Script by Damond Benningfield, Copyright 2011