Six hundred and fifty light-years away in the constellation Aquarius, a
dead star about the size of Earth, is refusing to fade away peacefully.
In death, it is spewing out massive amounts of hot gas and intense
ultraviolet radiation, creating a spectacular object called a "planetary
nebula."
In this false-color image, NASA's Hubble and Spitzer Space Telescopes have
teamed up to capture the complex structure of the object, called the Helix
nebula, in unprecedented detail. The composite picture is made up of
visible data from Hubble and infrared data from Spitzer.
The dead star, called a white dwarf, can be seen at the center of the
image as a white dot. All of the colorful gaseous material seen in the
image was once part of the central star, but was lost in the death throes
of the star on its way to becoming a white dwarf. The intense ultraviolet
radiation being released by the white dwarf is heating and destabilizing
the molecules in its surrounding environment, starting from the inside
out.
Like an electric stovetop slowly heating up from the center first, the
hottest and most unstable gas molecules can be seen at the center of the
nebula as wisps of blue. The transition to more stable and cooler
molecules is clearly depicted as the color of the gas changes from very
hot (blue) to hot (yellow) and warm (red).
A striking feature of the Helix, first revealed by ground-based images,
is its collection of thousands of filamentary structures, or strands of
gas. In this image the filaments can be seen under the transparent blue
gas as red lines radiating out from the center. Astronomers believe that
the molecules in these filaments are able to stay cooler and more stable
because dense clumps of materials are shielding them from ultraviolet
radiation.
This image is a composite showing ionized H-alpha (green) and O III (blue)
gases from the Hubble Space Telescope, and molecular hydrogen (red) from
Spitzer observations at 4.5 and 8.0 microns.
