Press Release

An Old Star Gives up the Ghost

By SpaceRef Editor
November 7, 2002
Filed under , ,

NASA’s Hubble Space Telescope has recently obtained images of
the planetary nebula NGC 6369. This object is known to amateur
astronomers as the “Little Ghost Nebula,” because it appears
as a small, ghostly cloud surrounding the faint, dying central
star. NGC 6369 lies in the direction of the constellation
Ophiuchus, at a distance estimated to be between about 2,000
and 5,000 light-years from Earth.

When a star with a mass similar to that of our own Sun nears the
end of its lifetime, it expands in size to become a red giant.
The red-giant stage ends when the star expels its outer layers
into space, producing a faintly glowing nebula. Astronomers call
such an object a planetary nebula, because its round shape
resembles that of a planet when viewed with a small telescope.

The Hubble photograph of NGC 6369, captured with the Wide Field
Planetary Camera 2 (WFPC2) in February 2002, reveals remarkable
details of the ejection process that are not visible from
ground-based telescopes because of the blurring produced by the
Earth’s atmosphere.

The remnant stellar core in the center is now sending out a
flood of ultraviolet (UV) light into the surrounding gas. The
prominent blue-green ring, nearly a light-year in diameter, marks
the location where the energetic UV light has stripped electrons
off of atoms in the gas. This process is called ionization. In
the redder gas at larger distances from the star, where the UV
light is less intense, the ionization process is less advanced.
Even farther outside the main body of the nebula, one can see
fainter wisps of gas that were lost from the star at the
beginning of the ejection process.

The color image has been produced by combining WFPC2 pictures
taken through filters that isolate light emitted by three
different chemical elements with different degrees of
ionization. The doughnut-shaped blue-green ring represents light
from ionized oxygen atoms that have lost two electrons (blue)
and from hydrogen atoms that have lost their single electrons
(green). Red marks emission from nitrogen atoms that have lost
only one electron.

Our own Sun may eject a similar nebula, but not for another
5 billion years. The gas will expand away from the star at about
15 miles per second, dissipating into interstellar space after
some 10,000 years. After that, the remnant stellar ember in the
center will gradually cool off for billions of years as a tiny
white dwarf star, and eventually wink out.

Credits: NASA and The Hubble Heritage Team (STScI/AURA)

NOTE TO EDITORS: For additional information, please contact
Dr. Howard Bond, Hubble Heritage Team, Space Telescope Science
Institute, 3700 San Martin Drive, Baltimore, MD 21218, (phone)
410-338-4718, (fax) 410-338-4579, (e-mail) or

Dr. Keith Noll, Hubble Heritage Team, Space Telescope Science
Institute, 3700 San Martin Drive, Baltimore, MD 21218, (phone)
410-338-1828, (fax) 410-338-4579, (e-mail)

Electronic images and additional information are available at:

The Space Telescope Science Institute (STScI) is operated by the
Association of Universities for Research in Astronomy, Inc. (AURA),
for NASA, under contract with the Goddard Space Flight Center,
Greenbelt, MD. The Hubble Space Telescope is a project of
international cooperation between NASA and the European Space
Agency (ESA).

SpaceRef staff editor.