Examples of Planetary Nebulae
A
planetary nebula
has nothing to do with planets. The name survives from times when
planetary nebulae
were sometimes confused with planets when observed through small telescopes.
In reality, they are clouds of gas and dust emitted by red giant stars late in their lives.
BD+303639
The adjacent near-infrared (the portion of the IR spectrum near the visible spectrum)
image shows a planetary nebula called BD+303639 that is
glowing in the light of hydrogen. It lies
about 10,000 light years away in the direction of the
constellation Cygnus.
Although the planetary nebula appears to be a ring, it is
really a hollow, expanding, three-dimensional shell of gas--a bubble--that gives the illusion
of a ring (see the right panel).
Millions of years ago the central
star in this image was probably similar to our Sun, but it evolved into
a red
giant and shed its outer layers. The
planetary
nebula seen here then resulted when the ejected material was heated by strong UV radiation from
the hot
central star until it began to glow. Planetary nebulae such as this are relatively short-lived
when compared with the lifetimes of stars.
In only a few tens of thousands of years, this planetary nebula
will be
dispersed into the interstellar medium and the central star will probably cool to become a white
dwarf.
The Cat's Eye
The image on the left shows a Hubble Space Telescope image of one of the most beautiful and
also
unusual planetary nebula, NGC 6543, which is 3000 light years away in the contellation Draco.
It is often called the Cat's Eye Nebula, and it appears to be about 1000 years old.
The complex structure of the Cat's Eye
is not well understood. One
hypothesis is that the central star is actually a binary star system
(though it is not resolved in this
image)
and the interaction of the two stars in the binary coupled with strong stellar wind emission has
produced the intricate structure.
