The highest resolution mid-infrared picture ever taken of the center of our Milky Way
galaxy reveals details about dust swirling into the black hole that
dominates the region.

The image was taken by a team led by Dr. Mark Morris of the University of California, Los Angeles, at the
Keck II telescope in Hawaii,
with an infrared camera built at NASA’s Jet
Propulsion Laboratory, Pasadena, Calif. The camera, called the
Mid-Infrared Large-Well Imager, or MIRLIN, used three
different infrared wavelengths to build the color composite image available
online at http://irastro.jpl.nasa.gov/GalCen/galcen.html.

MIRLIN image of our Galaxy’s center at 9, 13, and 21
microns.

The mid-infrared part
of the electromagnetic
spectrum comprises the wavelengths at which room temperature objects glow
most brightly. Everything on Earth, including the telescope, the
astronomers, and even the atmosphere, emits a bright glow in the
mid-infrared. Seeing celestial objects though this glow is like trying to see
stars during daylight; special
techniques are needed to tease the stars from this glow to build a
recognizable picture.

Near the center of the image, but not apparent at these wavelengths, is a
black hole three million times heavier than our Sun. Its gravitational
pull, so powerful that not even light can escape from its surface,
affects the motion of dust, gas and even stars, throughout the region.

A veil of dust absorbs the visible light emitted by
most of the stars near the Galactic Center. The light warms the dust, which
then radiates in the infrared and becomes visible to the mid-infrared
camera.

The image shows this dusty material spiraling toward the black hole, most
notably the stream of gas and dust called the Northern Arm. When this
material eventually falls into the black hole, it will release energy
that affects everything in its vicinity. This event, which astronomers
are certain has happened many times in the history of the Milky Way, may
trigger the formation of a new generation of stars by causing other
nearby dust clouds to collapse, or it may actually inhibit the formation
of new stars if the released energy destroys those clouds. Either way,
the black hole continues to grow larger as new material falls into it.

Astronomers know that the stars in this image are all very luminous,
because less luminous stars appear very faint to a mid-infrared camera. A
massive star nearing the last stages of its life, the red supergiant
IRS7, is visible in this image as the smallish, bright spot just above
the center. IRS7 is simply so luminous — more than 100,000 times as
bright as our Sun — that we can see its starlight directly.

The MIRLIN image of our Galaxy’s center with the most notable
objects labeled.

The “mini-cavity” in the center is a bubble that has apparently been
evacuated of dust and gas. A star located at the center of the
mini-cavity (not visible in this image) apparently blows this bubble with
its powerful stellar wind. The “bullet” is a mysterious,
fast-moving feature pointing roughly away from the mini-cavity, just
below and to the right of the center. It may be a jet composed of gas and
dust.

Other members of the MIRLIN imaging team, along with Morris, are Dr.
Andrea Ghez, Dr. Eric Becklin and Angelle Tanner of UCLA; Drs. Michael
Ressler and Michael Werner of JPL; and Dr. Angela Cotera Hulet of the
Arizona State University, Tempe, Ariz. The camera was built at JPL by
Ressler and Werner. Some findings based on this image have been
published in the Astrophysical Journal.

Studying processes in the center of our own galaxy may teach astronomers
more about much more active, more distant galactic nuclei — objects like
quasars and Seyfert galaxies, which are the most violent places known in
the universe. More information about both the center of our Milky Way
and the centers of other galaxies may be obtained with future instruments
that have higher resolution and greater sensitivity.

For example, NASA is planning a similar infrared camera, the Mid-Infrared
Instrument, one of three instruments that will fly aboard the James Webb
Space Telescope, launching in 2010. This camera will achieve resolution
roughly equivalent to the Keck images, but because it will orbit above
the warm glow emitted by Earth’s atmosphere, it will be 1,000 times more
sensitive. Using this instrument, astronomers will be able to study the
centers of galaxies all the way to the edge of the observable universe.

JPL, in conjunction with a consortium of European countries and the
European Space Agency, is developing the Mid-Infrared Instrument. The
James Webb Space Telescope is managed by the Goddard Space Flight Center,
Greenbelt, Md.

JPL is a division of the California Institute of Technology in Pasadena.

Additional information

Images of the Galactic Center at other
wavelengths. The image at left is at visible wavelengths (from the SuperCOSMOS digitized
sky survey) – the field of view of the MIRLIN mid-infrared image is
indicated by the small box at the middle. The Galactic Center is completely
invisible due to the large amounts of dust lying along our line of sight.
In fact, there is so much dust that only 1 photon out of a trillion (1 in
1,000,000,000,000) makes it to Earth.

At near-infrared wavelengths, midway between visible and mid-infrared
light, (right, from the 2MASS sky
survey), light can penetrate the dust (similar to the infrared goggles used
by the military to see through smoke on a battlefield) and we see the vast
number of ordinary stars which lie near the Galactic Center. At these
wavelengths, stars at the distance of the Center are bright enough to be
visible (unlike at mid-infrared wavelengths), but the dust is too cold to
be detected.