June 5, 2002
Photo No: H2002-13b2 (middle view)
NICMOS Finds a Golden Ring at the Heart of a Galaxy
The revived Near Infrared Camera and Multi-Object Spectrometer (NICMOS)
aboard NASA's Hubble Space Telescope has pierced the dusty disk of the
"edge-on" galaxy NGC 4013 and peered all the way to the galactic core.
To the surprise of astronomers, NICMOS found a brilliant band-like
structure, that may be a ring of newly formed stars [yellow band in
middle photo] seen edge-on.
In the visible-light view of the galaxy [top photo], the star-forming
ring cannot be seen because it is embedded in dust. The most prominent
feature in the visible-light image -- taken by the Wide Field and
Planetary Camera 2 (WFPC2) -- is the thin, dark band of gas and dust,
which is about 500 light-years thick.
NICMOS enables the Hubble telescope to see in near-infrared wavelengths
of light, so that it can penetrate the dust that obscures the inner
hub of the galaxy. The ring-like structure spied by NICMOS encircles
the core and is about 720 light-years wide, which is the typical size
of most star-forming rings found in disk galaxies.
The small ring is churning out stars at a torrid pace. The Milky Way
Galaxy, for example, is more than 10,000 times larger than the ring.
If the Milky Way produced stars at the same rate, it would be making
1,000 times more stars a year.
The human eye cannot see infrared light, so colors have been assigned
to correspond with near-infrared wavelengths. The blue light
represents shorter near-infrared wavelengths and the red light
corresponds to longer wavelengths.
The ring-like structure is seen more clearly in the photo at bottom.
This picture, taken with a filter sensitive to hydrogen, shows the
glow of stars and gas. Astronomers used this information to calculate
the rate of star formation in the ring-like structure.
The extremely bright star near the center of each picture is a nearby
foreground star belonging to our own Milky Way.
Rings of developing stars are common in barred spiral galaxies, which
have "bars" of stars and gas slicing across their disks. The bars
funnel gas to the galactic cores. But gravitational disturbances near
the cores cause gas to accumulate into a lane or a ring. The gas then
condenses to form stars. Because NGC 4013 is seen edge-on, astronomers
don't know whether a bar of gas or some other mechanism formed the
NGC 4013, which looks similar to our Milky Way Galaxy, resides in the
constellation Ursa Major, 55 million light-years from Earth.
The middle picture is a color composite image that was made by
combining photographs taken with the J-band, H-band, and
Paschen-alpha filters. The bottom picture was taken with the
Paschen-alpha filter. The images were taken on May 12.
Credits for NICMOS images: NASA, the NICMOS Group (STScI, ESA),
and the NICMOS Science Team (University of Arizona)
Credits for WFPC2 image: NASA, the Hubble Heritage Team (STScI/AURA)