This image, taken by the NASA/ESA Hubble Space Telescope, shows the
colorful "last hurrah" of a star like our sun. The star is ending its
life by casting off its outer layers of gas, which formed a cocoon
around the star's remaining core. Ultraviolet light from the dying star
makes the material glow. The burned-out star, called a white dwarf, is
the white dot in the center. Our sun will eventually burn out and shroud
itself with stellar debris, but not for another 5 billion years.
Our Milky Way Galaxy is littered with these stellar relics, called
planetary nebulae. The objects have nothing to do with planets.
Eighteenth- and nineteenth-century astronomers called them the name
because through small telescopes they resembled the disks of the distant
planets Uranus and Neptune. The planetary nebula in this image is
called NGC 2440. The white dwarf at the center of NGC 2440 is one of the
hottest known, with a surface temperature of more than 360,000 degrees
Fahrenheit (200,000 degrees Celsius). The nebula's chaotic structure
suggests that the star shed its mass episodically. During each outburst,
the star expelled material in a different direction. This can be seen
in the two bowtie-shaped lobes. The nebula also is rich in clouds of
dust, some of which form long, dark streaks pointing away from the star.
NGC 2440 lies about 4,000 light-years from Earth in the direction of
the constellation Puppis.
The material expelled by the star glows with different colors
depending on its composition, its density and how close it is to the hot
central star. Blue samples helium; blue-green oxygen, and red nitrogen
and hydrogen.
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