Hold the pickles; hold the lettuce. Space is serving up giant
hamburgers. NASA’s Hubble Space Telescope has snapped a photograph of a
strange object that bears an uncanny resemblance to a hamburger. The
object, nicknamed Gomez’s Hamburger, is a sun-like star nearing the end
of its life. It already has expelled large amounts of gas and dust and
is on its way to becoming a colorful, glowing planetary nebula.

The ingredients for the giant celestial hamburger are dust and light.
The hamburger buns are light reflecting off dust and the patty is the
dark band of dust in the middle. The Hubble Heritage image, taken
Feb. 22, 2002, with the Wide Field Planetary Camera 2, shows the
structure of Gomez’s Hamburger with high resolution, particularly the
striking dark band of dust that cuts across the middle. The dark band
is actually the shadow of a thick disk around the central star, which
is seen edge-on from Earth. The star itself, with a surface temperature
of approximately 18,000 degrees Fahrenheit (10,000 degrees Celsius), is
hidden within this disk. However, light from the star does emerge in
the directions perpendicular to the disk and illuminates dust above and
below it.

The reason why the star is surrounded by a thick, dusty disk remains
somewhat uncertain. It is possible that the central object is actually
a pair of stars. If so, then the star that ejected the nebula may be
rapidly rotating, expelling material mostly from its equatorial regions.

Stars with masses similar to our Sun’s end their lives as planetary
nebulae. The star evolves to become a bloated red giant, with a girth
about 100 times greater than its original diameter. Then it ejects its
outer layers into space, exposing the star’s hot core. Ultraviolet
radiation from the central core streams out into the surrounding
ejected gas, causing it to glow. The glowing gas is called a planetary
nebula. The Hubble Space Telescope has provided numerous spectacular
images of planetary nebulae over the past several years, including the
Ring Nebula and several others that have been released in the Hubble
Heritage series.

Less well known are “proto-planetary nebulae,” objects like Gomez’s
Hamburger that are in a state of evolution immediately before the true
planetary-nebula stage. Just after the red giant expels its outer
layers, the remnant star in the center is still relatively cool.
Consequently, it emits ordinary visible light, but very little
ultraviolet radiation. Therefore the surrounding gas does not glow.
However, the ejected material also contains vast numbers of
microscopic dust particles, which can reflect the starlight and make
the material visible. This same effect of light scattering produces
halos around streetlights on a foggy night.

The lifetime of a proto-planetary nebula is very brief. In less than a
thousand years, astronomers expect that the central star will become hot
enough to make the dust particles evaporate, thus exposing the star to
view. At that time the surrounding gas will glow. Gomez’s Hamburger will
have become a beautiful, glowing planetary nebula.

Gomez’s Hamburger was discovered on sky photographs obtained by Arturo
Gomez, an astronomer at the Cerro Tololo Inter-American Observatory in
Chile. The photos suggested that there was a dark band across the
object, but its exact structure was difficult to determine because of
the atmospheric turbulence that hampers all images taken from the
ground. Gomez’s Hamburger is located roughly 6,500 light-years away in
the constellation Sagittarius.

Image Credit: NASA and the Hubble Heritage Team (STScI/AURA)
Acknowledgment: A. Gomez (Cerro Tololo Inter-American Observatory)

NOTE TO EDITORS: For additional information, please contact
Dr. Howard E. Bond, Space Telescope Science Institute, Baltimore, MD
21218, (phone) 410-338-4718, (e-mail) bond@stsci.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/2002/19 and via links in




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).