The Hubble Space Telescope
has taken a snapshot of a picturesque planetary nebula tucked away in a distant
cluster of stars within the Milky Way Galaxy
The image, a swirl of wispy
green, red and blue hues, spotlights the unique nebula NGC 2818 nestled within
a star cluster some 10,000 light-years from Earth in the southern constellation
Pyxis, or The Compass.
NGC 2818 is one of very few
planetary nebulae in our galaxy located within an open cluster, in this
case cluster NGC 2818A. Open clusters, in general, are loosely bound and they
disperse over hundreds of millions of years. Stars that form planetary nebulae
typically live for billions of years. Hence, it is rare that an open cluster
survives long enough for one of its members to form a planetary nebula. This
open cluster is particularly ancient, estimated to be nearly one billion years
old.
The spectacular structure
of NGC 2818 (also known as PLN 261+8.1) contains the outer layers of a sun-like
star that were sent off into interstellar space during the star's final stages
of life. These glowing gaseous shrouds were shed by the star after it ran out
of fuel to sustain the nuclear reactions in its core.
Planetary
nebulae can have extremely varied structures. NGC 2818 has a complex shape
that is difficult to interpret. However, because of its location within the
cluster, astronomers have access to information about the nebula, such as its
age and distance that might not otherwise be known.
Planetary nebulae fade away
gradually over tens of thousands of years. The hot, remnant stellar core of NGC
2818 will eventually cool off for billions of years as a white dwarf. Our own
sun will undergo a similar process, but not for another 5 billion years or so.
This Hubble image was taken
in November 2008 with the Wide
Field Planetary Camera 2. The colors in the image represent a range of
emissions coming from the clouds of the nebula: red represents nitrogen, green
represents hydrogen, and blue represents oxygen.
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