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Three hundred years ago a star in the constellation Cassiopeia died in a cataclysmic explosion, a supernova. The shredded remnants of that explosion are called Cassiopeia A, or Cas A for short.

Cas A is the youngest supernova remnant identified in our Milky Way galaxy. The star that blew up was a big one, about 15 to 25 times more massive our Sun. Massive stars like the one that created Cas A have
short lives. They burn through their supply of fuel in tens of millions of years, 1000 times faster than our Sun. With their fuel exhausted, heavy stars begin a complex chain of events that lead to the final dramatic explosion.

The beautiful Hubble images of Cas A are allowing astronomers to study the debris with great clarity, seeing for the first time that the debris is arranged into thousands of small, cooling, knots of gas.

The image of the Cas A supernova remnant shown here is of a section taken of the upper rim of the remnant's expanding shell. Near the top of the image one can make out dozens of chains of tiny clumps. Each small clump, originally just a small fragment of the star, is tens of times larger than the diameter of our solar system!

The different colors highlight parts of the debris where particular atoms are glowing. Dark blue fragments are those richest in oxygen, red areas are rich in sulfur.

Credit: NASA and the Hubble Heritage Team (STScI/AURA)
Acknowledgment: Rob Fesen (Dartmouth University)