NASA Hubble Space Telescope Sees Dying Star Sculpt Rings of Gas and Dust
Astronomers may not have observed the fabled “Stairway to Heaven,”
but they have photographed something almost as intriguing:
ladder-like structures surrounding a dying star.
A new image, taken with NASA’s Hubble Space Telescope, reveals
startling new details of one of the most unusual nebulae known in
our Milky Way. Cataloged as HD 44179, this nebula is more commonly
called the “Red Rectangle” because of its unique shape and color
as seen with ground-based telescopes.
Hubble has revealed a wealth of new features in the Red Rectangle
that cannot be seen with ground-based telescopes looking through
the Earth’s turbulent atmosphere. Details of the Hubble study were
published in the April 2004 issue of The Astronomical Journal.
Hubble’s sharp pictures show that the Red Rectangle is not really
rectangular, but has an overall X-shaped structure, which the
astronomers involved in the study interpret as arising from
outflows of gas and dust from the star in the center. The outflows
are ejected from the star in two opposing directions, producing a
shape like two ice-cream cones touching at their tips. Also
remarkable are straight features that appear like rungs on a
ladder, making the Red Rectangle look similar to a spider web, a
shape unlike that of any other known nebula in the sky. These
rungs may have arisen in episodes of mass ejection from the star
occurring every few hundred years. They could represent a series
of nested, expanding structures similar in shape to wine glasses,
seen exactly edge-on so that their rims appear as straight lines
from our vantage point.
The star in the center of the Red Rectangle is one that began its
life as a star similar to our Sun. It is now nearing the end of
its lifetime, and is in the process of ejecting its outer layers
to produce the visible nebula. The shedding of the outer layers
began about 14,000 years ago. In a few thousand years, the star
will have become smaller and hotter, and will begin to release a
flood of ultraviolet light into the surrounding nebula; at that
time, gas in the nebula will begin to fluoresce, producing what
astronomers call a planetary nebula.
At the present time, however, the star is still so cool that
atoms in the surrounding gas do not glow, and the surrounding
dust particles can only be seen because they are reflecting the
starlight from the central star. In addition, there are molecules
mixed in with the dust, which emit light in the red portion of
the spectrum. Astronomers are not yet certain which types of
molecules are producing the red color that is so striking in the
Red Rectangle, but suspect that they are hydrocarbons that form
in the cool outflow from the central star.
Another remarkable feature of the Red Rectangle, visible only
with the superb resolution of the Hubble telescope, is the dark
band passing across the central star. This dark band is the shadow
of a dense disk of dust that surrounds the star. In fact, the star
itself cannot be seen directly, due to the thickness of the dust
disk. All we can see is light that streams out perpendicularly
to the disk, and then scatters off of dust particles toward our
direction. Astronomers found that the star in the center is
actually a close pair of stars that orbit each other with a
period of about 10 1/2 months. Interactions between these stars
have probably caused the ejection of the thick dust disk that
obscures our view of the binary. The disk has funneled subsequent
outflows in the directions perpendicular to the disk, forming the
bizarre bi-conical structure we see as the Red Rectangle. The
reasons for the periodic ejections of more gas and dust, which are
producing the “rungs” revealed in the Hubble image, remain unknown.
The Red Rectangle was first discovered during a rocket flight in
the early 1970s, in which astronomers were searching for strong
sources of infrared radiation. This infrared source lies about
2,300 light-years from Earth in the direction of the constellation
Monoceros. Stars surrounded by clouds of dust are often strong
infrared sources because the dust is heated by the starlight and
radiates long-wavelength light. Studies of HD 44179 with ground-based
telescopes revealed a rectangular shape in the dust surrounding the
star in the center, leading to the name Red Rectangle which was
coined in 1973 by astronomers Martin Cohen and Mike Merrill.
This image was made from observations taken on March 17-18, 1999
with Hubble’s Wide Field Planetary Camera 2.
Credits: NASA; ESA; Hans Van Winckel (Catholic University of
Leuven, Belgium); and Martin Cohen (University of California,
Berkeley)
NOTE TO EDITORS: For more information, please contact
Donna Weaver, Space Telescope Science Institute, Baltimore, Md.,
(phone) 410-338-4493, (e-mail) dweaver@stsci.edu or
Lars Lindberg Christensen, Hubble European Space Agency
Information Centre, Garching, Germany, (phone) 011-49-89-320-
06-306, (cellular) 011-49-173-3872-621, (e-mail) lars@eso.org
or
Hans Van Winckel, Catholic University of Leuven, Heverlee,
Belgium, (phone) 011-32-1-632-70-39, (e-mail)
hans@ster.kuleuven.ac.be or
Martin Cohen, University of California, Berkeley, (phone) 510-
642-2833, (e-mail) mcohen@astro.berkeley.edu or
Howard E. Bond, Space Telescope Science Institute, Baltimore, Md.,
(phone) 410-338-4718; (e-mail) bond@stsci.edu or
Ted Gull, NASA Goddard Space Flight Center, Greenbelt, Md.,
(phone) 301-286-6184, (e-mail) gull@sea.gsfc.nasa.gov.
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).
