Figure 1: Supernova Remnant Cassiopeia A One Year Apart
These Spitzer Space Telescope images, taken one year apart, show the
supernova remnant Cassiopeia A (yellow ball) and surrounding clouds of
dust (reddish orange). The pictures illustrate that a blast of light from
Cassiopeia A is waltzing outward through the dusty skies. This dance,
called an "infrared echo," began when the remnant erupted about 50 years
ago.
Cassiopeia A is the remnant of a once massive star that died in a violent
supernova explosion 325 years ago. It consists of a dead star, called a
neutron star, and a surrounding shell of material that was blasted off as
the star died. This remnant is located 10,000 light-years away in the
northern constellation Cassiopeia.
Infrared echoes are created when a star explodes or erupts, flashing
light into surrounding clumps of dust. As the light zips through the dust
clumps, it heats them up, causing them to glow successively in infrared,
like a chain of Christmas bulbs lighting up one by one. The result is an
optical illusion, in which the dust appears to be flying outward at the
speed of light. Echoes are distinct from supernova shockwaves, which are
made up material that is swept up and hurled outward by exploding stars.
This infrared echo is the largest ever seen, stretching more than 50
light-years away from Cassiopeia A. If viewed from Earth, the entire
movie frame would take up the same amount of space as two full moons.
Hints of an older infrared echo from Cassiopeia A's supernova explosion
hundreds of years ago can also be seen.
The top Spitzer image was taken on November 30, 2003, and the bottom, on
December 2, 2004.
