Click on the image for movie of
Order Amidst Chaos of Star's Explosion
This artist's animation shows the explosion of a massive star, the remains
of which are named Cassiopeia A. NASA's Spitzer Space Telescope found
evidence that the star exploded with some degree of order, preserving
chunks of its onion-like layers as it blasted apart.
Cassiopeia A is what is known as a supernova remnant. The original star,
about 15 to 20 times more massive than our sun, died in a cataclysmic
"supernova" explosion viewable from Earth about 340 years ago. The remnant
is located 10,000 light-years away in the constellation Cassiopeia.
The movie begins by showing the star before it died, when its layers of
elements (shown in different colors) were stacked neatly, with the
heaviest at the core and the lightest at the top. The star is then shown
blasting to smithereens. Spitzer found evidence that the star's original
layers were preserved, flinging outward in all directions, but not at the
same speeds. In other words, some chunks of the star sped outward faster
than others, as illustrated by the animation.
The movie ends with an actual picture of Cassiopeia A taken by Spitzer.
The colored layers containing different elements are seen next to each
other because they traveled at different speeds.
The infrared observatory was able to see the tossed-out layers because
they light up upon ramming into a "reverse" shock wave created in the
aftermath of the explosion. When a massive star explodes, it creates two
types of shock waves. The forward shock wave darts out quickest, and, in
the case of Cassiopeia A, is now traveling at supersonic speeds up to
7,500 kilometers per second (4,600 miles/second). The reverse shock wave
is produced when the forward shock wave slams into a shell of surrounding
material expelled before the star died. It tags along behind the forward
shock wave at slightly slower speeds.
Chunks of the star that were thrown out fastest hit the shock wave sooner
and have had more time to heat up to scorching temperatures previously
detected by X-ray and visible-light telescopes. Chunks of the star that
lagged behind hit the shock wave later, so they are cooler and radiate
infrared light that was not seen until Spitzer came along. These lagging
chunks are seen in false colors in the Spitzer picture of Cassiopeia A.
They are made up of gas and dust containing neon, oxygen and aluminum --
elements from the middle layers of the original star.
