Hubble views enigmatic Red Rectangle
EUROPEAN SPACE AGENCY INFORMATION CENTRE
Posted: May 11, 2004
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This image, taken
with the NASA/ESA Hubble Space Telescope, reveals startling new details of one
of the most unusual nebulae known in our Galaxy. Catalogued as HD 44179, this
nebula is more commonly called the "Red Rectangle" because of its unique shape
and colour as seen with ground-based telescopes.
Hubble has revealed a wealth of new features in the Red Rectangle that cannot be seen
by 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.
[Click image to enlarge.]
Image credit: NASA/ESA, Hans Van Winckel (Catholic University of Leuven, Belgium)
and Martin Cohen (University of California, USA).
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This image, taken with the NASA/ESA Hubble Space Telescope, reveals
startling new details of one of the most unusual nebulae known in our
Galaxy. Catalogued as HD 44179, this nebula is more commonly called
the "Red Rectangle" because of its unique shape and colour as seen
with ground-based telescopes.
Hubble has revealed a wealth of new features in the Red Rectangle
that cannot be seen by 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.
Hans Van Winckel, Catholic University of Leuven, Belgium, the
principal investigator for the Hubble observations, says: "The
structure of the Red Rectangle revealed by Hubble is surprisingly
complex. The features that impress me most look like the rungs of a
ladder, although they are actually projections of gas cones, like a
series of nested wine glasses filled to their brim with gas and seen
from the side."
Hubble's sharp pictures show that the Red Rectangle is not really
rectangular, but has an X-shaped structure, that astronomers
interpret as arising from outflows of gas and dust from the star in
the centre. The cone-like outflows are ejected from the star in two
opposing directions. In addition there are straight linking features
that look like the rungs on a ladder, making the Red Rectangle look
similar to a spider's 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 that occur every few hundred years and could
represent a series of 'smoke rings', seen almost exactly edge-on from
our vantage point.
The star at the centre of the Red Rectangle 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, and in a few thousand years, the star will have become smaller
and hotter, releasing a flood of ultraviolet light into the
surrounding nebula. When this occurs the gas in the nebula will begin
to fluoresce, producing a "planetary nebula".
At the present time, however, the star is still so cool that atoms in
the nebula do not glow and the surrounding dust particles are only
visible as they reflect light from the central star. Exactly which
molecules in the dust cloud are responsible for the striking red
colour of the Rectangle is not yet clear, but it is likely that they
are some kind of hydrocarbon formed in the cool outflows 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 is the shadow of a dense disc
of dust that surrounds the star and obscures it from direct view. The
light we see streams out along the axis of the disc, and is scattered
towards us by dust particles. Astronomers have found that the central
star is actually a close pair of stars orbiting each other with a
period of about 10.5 months. Interactions between these stars have
probably caused the ejection of the thick dust disc that obscures our
view of the binary. The disc then funnels subsequent dust and gas
outflows out along its axis, forming the bizarre bi-conical structure
we see as the rung of the Red Rectangle. The reasons for these fresh
periodic ejections of more gas and dust 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 then re-radiates
long-wavelength red light. Studies of HD 44179 with ground-based telescopes revealed
a rectangular shape in the dust surrounding the star at the centre, leading to
the name "Red Rectangle", coined in 1973 by astronomers Martin Cohen and Mike
Merrill.
This image was made from observations taken on 17 March 1999 with
Hubble's Wide Field Planetary Camera 2.
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