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This composite image from NASA's Spitzer Space Telescope shows the remnant
of a star that exploded, called Cassiopeia A (center) and its surrounding
"light echoes" -- dances of light through dusty clouds, created when stars
blast apart. The light echoes are colored and the surrounding clouds of
dust are gray.
In figure 1, dramatic changes are highlighted in phenomena referred to as
light echoes (colored areas) around the Cassiopeia A supernova remnant
(center). Cassiopeia A is the remnant of a once massive star that died in
a violent supernova explosion. It consists of a dead star, called a
neutron star, and a surrounding shell of material that was blasted off as
the star died.
A light echo occurs when a star explodes, acting like a cosmic flashbulb.
The light from this explosion zips through nearby dust clumps,
illuminating and heating them up slightly. This brief period of warming
causes them to glow 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. In figure 1, this
apparent motion can be seen here by the shift in colored dust clumps
Cassiopeia A is the remnant of a once massive star that died in a violent
supernova explosion. 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 11,000 light-years away in the northern
constellation Cassiopeia.
This composite consists of six processed images taken over a time span of
three years. Dust features that have not changed over time appear gray,
while those that have changed are colored blue or orange. Bluer colors
represent an earlier time and redder ones, a later time. The progression
of the light echo through the dust can be seen here by the shift in
colored dust clumps.
This light echo is the largest ever seen, stretching more than 300
light-years away from Cassiopeia A. If viewed from Earth, the entire frame
would take up the same amount of space as seven full moons. The supernova
remnant is located 11,000 light-years away in the northern constellation
Cassiopeia.
The earliest Spitzer image shown here was taken in February 2005, and the
latest one in January 2008. The image was processed to emphasize the light
echo by enhancing the areas that change, which appear in color, and
dimming regions that remain constant, seen in grayscale. Spurious color
artifacts such as diffraction spikes around stars were removed by hand.