Credit: X-ray: NASA/UIUC/Y.Chu et al., Optical: NASA/HST
Sparkle in the Cat's Eye
As stars like the sun age they use up their nuclear fuel. As the fuel runs
low, the innermost regions of the star will contract due to the weight of
the overlying stellar material. As the central regions contract, the outer
regions expand and the star becomes much bigger and brighter, a so-called
"red giant". Since the star is essentially going two ways at once, there
may come a point at which the outer parts of the star become disconnected
from the inner parts; the outer parts can become so disconnected that they
leave the star entirely and form an extensive cloud of gas around the star.
This gas cloud is called a "planetary nebula" (because in small telescopes
some of these nebula appear as resolved disks, as do the real planets in
our solar system). Though planetary nebula have been seen for hundreds of
years, the mechanism by which the stellar atmosphere detaches itself and
expands into space is not yet understood. Now theChandra X-ray Telescope has added
another piece to the puzzle. The image on the left is an X-ray
image of the "Cat's Eye" planetary nebula obtained by the Chandra ACIS
camera, at the same spatial scale as the optical image. Chandra reveals
the central star as a bright point source of high temperature X-rays. This
is the first time astronomers have seen such X-ray emission from the
central star of a planetary nebula. Chandra shows that the "bubbles"
around the central star contain extremely hot, million-degree gas which
also glows bright in X-rays. The image above right is a Hubble Space telescope image of the "Cat's
Eye". The swirls of colorful gas emphasize the complex nature of the
ejection of the stellar envelope. The Chandra image is superposed on the
Hubble image to show where the X-ray emitting gas is located among the
bright optical swirls of gas.
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Page Author: Dr. Michael F.
Corcoran
Last modified June 14, 2001
