Resembling a rippling pool illuminated by underwater lights, the Egg
Nebula offers astronomers a special look at the normally invisible
dust shells swaddling an aging star. These dust layers, extending over
one-tenth of a light-year from the star, have an onionskin structure
that forms concentric rings around the star. A thicker dust belt,
running almost vertically through the image, blocks off light from
the central star. Twin beams of light radiate from the hidden star
and illuminate the pitch-black dust, like a shining flashlight in a
smoky room.

The artificial “Easter-Egg” colors in this image are used to dissect
how the light reflects off the smoke-sized dust particles and then
heads toward Earth.

Dust in our atmosphere reflects sunlight such that only light waves
vibrating in a certain orientation get reflected toward us. This is
also true for reflections off water or roadways. Polarizing sunglasses
take advantage of this effect to block out all reflections, except those
that align to the polarizing filter material. It’s a bit like sliding a
sheet of paper under a door. The paper must be parallel to the floor to
pass under the door.

Hubble’s Advanced Camera for Surveys has polarizing filters that accept
light that vibrates at select angles. In this composite image, the light
from one of the polarizing filters has been colored red and only admits
light from about one-third of the nebula. Another polarizing filter
accepts light reflected from a different swath of the nebula. This light
is colored blue. Light from the final third of the nebula is from a
third polarizing filter and is colored green. Some of the inner regions
of the nebula appear whitish because the dust is thicker and the light
is scattered many times in random directions before reaching us.
(Likewise, polarizing sunglasses are less effective if the sky is very
dusty).

By studying polarized light from the Egg Nebula, scientists can tell a
lot about the physical properties of the material responsible for the
scattering, as well as the precise location of the central (hidden)
star. The fine dust is largely carbon, manufactured by nuclear fusion in
the heart of the star and then ejected into space as the star sheds
material. Such dust grains are essential ingredients for building dusty
disks around future generations of young stars, and possibly in the
formation of planets around those stars.

The Egg Nebula is located 3,000 light-years away in the constellation
Cygnus. This image was taken with Hubble’s Advanced Camera for Surveys
in September and October 2002.

Credit: NASA and The Hubble Heritage Team (STScI/AURA)
Acknowledgment: W. Sparks (STScI) and R. Sahai (JPL)

NOTE TO EDITORS: For additional information, please contact
Raghvendra Sahai, Jet Propulsion Laboratory, Astrophysical Research
Elements Dept., 4800 Oak Grove Drive, Pasadena, CA 91109, (phone)
818-354-0452, (fax) 818-393-9088, (e-mail) sahai@jpl.nasa.gov or

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) bond@stsci.edu or

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://hubblesite.org/news/2003/09
http://heritage.stsci.edu/2003/09

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).