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MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov 

Jane Platt  (818) 354-0880
Jet Propulsion Laboratory, Pasadena, Calif.

NEWS RELEASE #2003-076      May 27, 2003

Theatre in the Rectangle
          
The great sculptor gravity ensures that larger, denser objects in the
universe -- like stars, planets and moons -- take on the familiar
spherical shape. Occasionally, though, an interplay of mysterious
cosmic forces leaves objects outside the round, those with more
geometrically curious forms. One such object, discovered in 1975, is
the Red Rectangle.

Now astronomers Dr. Raghvendra Sahai of NASA's Jet Propulsion
Laboratory, Pasadena, Calif., and Dr. Carmen Sanchez Contreras of the
California Institute of Technology, also in Pasadena, have uncovered
a physical mechanism that might support this bizarre red rectangular
structure. They report their findings in a paper titled "A Very
Young, Fast, Bipolar Outflow at the Center of the Red Rectangle" at
the 2003 summer meeting of the American Astronomical Society, being
held this week in Nashville, Tennessee.

A protoplanetary nebula forms when a red giant star ejects most of
its outer layers, and is observable when dust within the nebula
reflects light from the central star. Subsequently, as the very hot
core (six or more times hotter than the Sun) gets further exposed,
the cloud of ejected material becomes bathed with ionizing
ultraviolet light, which makes it glow. At this later stage these
objects are known as planetary nebulas.

The Red Rectangle, or HD44179, represents the crimson light from a
protoplanetary nebula that lurks about 1,000 light years from Earth.
Images taken with the sharp eyes of the Hubble Space Telescope show
that two bright diagonals intersect its roughly rectangular shape;
the diagonals appear connected by straight lines parallel
to the short side of the rectangle.

An image of the Red Rectangle and its bipolar outflows may be seen on
the Web: http://photojournal.jpl.nasa.gov/catalog/PIA04533

Coming up with a physical mechanism to produce these oddly shaped
nebulas, and the Red Rectangle in particular, has been a serious
challenge for astronomers. Many recent studies of such objects with
the Hubble have led to a new model by Sahai in which very fast
jet-like outflows carve out these diverse shapes.

The jets are thought to operate for a very short period of time --
only a few hundred or so years -- during the protoplanetary phase,
making studies of protoplanetary nebulas very important for
understanding the nature and origin of the jets. Finding direct
evidence for these jet-like outflows has been generally very
difficult, because they are compact, occasionally dormant, and
difficult to see against the bright nebular background. Fortunately,
the Hubble's imaging spectrograph provides a way to discriminate
these outflows by separating the nebular light into its constituent
colors (like a prism revealing the rainbow of colors in sunlight).

The violent interaction of these outflows with the surrounding dense
nebular gas causes hydrogen atoms in the outflow (but not the general
nebula) to emit light at a specific wavelength (called H-alpha
radiation) that is detected by the imaging spectrograph. A small
deviation, or shift, in the measured wavelength from the laboratory
value allows researchers to find out how fast, and in which direction
(i.e. towards or away from the observer), the material in the
high-speed outflow moves.

After examining archival data on the Red Rectangle, Sahai and Sanchez
Contreras have found evidence of H-alpha radiation emitted by a fast
outflow expanding with a speed of about 65 kilometers per second (40
miles per second). This is the first time this inner, bipolar outflow
has been seen in this object.

"Discovering this outflow in the famous, yet mysterious Red Rectangle
is very exciting because it provides us an unprecedented opportunity
to study the fast outflows believed to shape such objects," said
Sahai. "The outflow is very young and its innermost parts are only a
few years old, so we will be able to directly observe if, and how, it
changes with time."

One theory about the formation of such fast outflows requires the
central star to have a close companion object. Strong evidence exists
that the central star in the Red Rectangle has such a companion.

A full understanding of this outflow and how it supports the
intriguing shape of the Red Rectangle will require further
observations and detailed computer modeling.

The Space Telescope Imaging Spectrograph is managed by NASA's Goddard
Space Flight Center in Greenbelt, Maryland. The Hubble Space
Telescope is a project of international cooperation between NASA and
the European Space Agency.

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