Composite of Supernova Remnant Cassiopeia A
This Spitzer Space Telescope composite shows the supernova remnant
Cassiopeia A (white ball) and surrounding clouds of dust (gray, orange
and blue). It consists of two processed images taken one year apart. Dust
features that have not changed over time appear gray, while those that
have changed are colored blue or orange. Blue represents an earlier time
and orange, a later time.
These observations 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.
An infrared echo is 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. This apparent motion can be seen here by the shift in
colored dust clumps.
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 earlier Spitzer image was taken on November 30, 2003, and the later,
on December 2, 2004.
