A dying star, IC 4406, dubbed the “Retina Nebula” is revealed in this month’s Hubble Heritage image.

Like many other so-called planetary nebulae, IC 4406 exhibits
a high degree of symmetry; the left and right halves of the
Hubble image are nearly mirror images of the other. If we
could fly around IC4406 in a starship, we would see that the
gas and dust form a vast donut of material streaming outward
from the dying star. From Earth, we are viewing the donut from
the side. This side view allows us to see the intricate tendrils
of dust that have been compared to the eye’s retina. In other
planetary nebulae, like the Ring Nebula (NGC 6720), we view the
donut from the top.

The donut of material confines the intense radiation coming
from the remnant of the dying star. Gas on the inside of the
donut is ionized by light from the central star and glows.
Light from oxygen atoms is rendered blue in this image;
hydrogen is shown as green, and nitrogen as red. The range
of color in the final image shows the differences in
concentration of these three gases in the nebula.

Unseen in the Hubble image is a larger zone of neutral gas
that is not emitting visible light, but which can be seen by
radio telescopes.

One of the most interesting features of IC 4406 is the
irregular lattice of dark lanes that criss-cross the center
of the nebula. These lanes are about 160 astronomical units
wide (1 astronomical unit is the distance between the Earth
and Sun). They are located right at the boundary between the
hot glowing gas that produces the visual light imaged here
and the neutral gas seen with radio telescopes. We see the
lanes in silhouette because they have a density of dust and
gas that is a thousand times higher than the rest of the
nebula. The dust lanes are like a rather open mesh veil
that has been wrapped around the bright donut.

The fate of these dense knots of material is unknown. Will
they survive the nebula’s expansion and become dark denizens
of the space between the stars or simply dissipate?

This image is a composite of data taken by Hubble’s Wide Field
Planetary Camera 2 in June 2001 by Bob O’Dell (Vanderbilt
University) and collaborators and in January 2002 by The
Hubble Heritage Team (STScI). Filters used to create this
color image show oxygen, hydrogen, and nitrogen gas glowing
in this object.

Image Credit: NASA and the Hubble Heritage Team (STScI/AURA)
Acknowledgment: C.R. O’Dell (Vanderbilt University)

NOTE TO EDITORS: For additional information, please contact
Dr. C.R. (Bob) O’Dell, Vanderbilt University, Physics and Astronomy

Box 1807 Station B, Nashville, TN 37235, (phone) 615-343-1779,
(fax) 615-343-7263, (e-mail) cr.odell@vanderbilt.edu 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) noll@stsci.edu.

Electronic images and additional information are available at:

http://heritage.stsci.edu and
http://oposite.stsci.edu/pubinfo/pr/2002/14 and via links in