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It might look like a spoked wheel or even a "Chakram" weapon wielded
by warriors like "Xena," from the fictional TV show, but this ringed
galaxy is actually a vast place of stellar life. A newly released image
from NASA's Spitzer Space Telescope shows the galaxy NGC 1291. Though
the galaxy is quite old, roughly 12 billion years, it is marked by an
unusual ring where newborn stars are igniting.
"The rest of the galaxy is done maturing," said Kartik Sheth of the
National Radio Astronomy Observatory of Charlottesville, Virginia. "But
the outer ring is just now starting to light up with stars."
NGC 1291 is located about 33 million light-years away in the
constellation Eridanus. It is what's known as a barred galaxy, because
its central region is dominated by a long bar of stars (in the new
image, the bar is within the blue circle and looks like the letter "S").
The bar formed early in the history of the galaxy. It churns material
around, forcing stars and gas from their original circular orbits into
large, non-circular, radial orbits. This creates resonances -- areas
where gas is compressed and triggered to form new stars. Our own Milky
Way galaxy has a bar, though not as prominent as the one in NGC 1291.
Sheth and his colleagues are busy trying to better understand how
bars of stars like these shape the destinies of galaxies. In a program
called Spitzer Survey of Stellar Structure in Galaxies, or S4G, Sheth
and his team of scientists are analyzing the structures of more than
3,000 galaxies in our local neighborhood. The farthest galaxy of the
bunch lies about 120 million light-years away -- practically a stone's
throw in comparison to the vastness of space.
The astronomers are documenting structural features, including bars.
They want to know how many of the local galaxies have bars, as well as
the environmental conditions in a galaxy that might influence the
formation and structure of bars.
"Now, with Spitzer we can measure the precise shape and distribution
of matter within the bar structures," said Sheth. "The bars are a
natural product of cosmic evolution, and they are part of the galaxies'
endoskeleton. Examining this endoskeleton for the fossilized clues to
their past gives us a unique view of their evolution."
In the Spitzer image, shorter-wavelength infrared light has been
assigned the color blue, and longer-wavelength light, red. The stars
that appear blue in the central, bulge region of the galaxy are older;
most of the gas, or star-making fuel, there was previously used up by
earlier generations of stars. When galaxies are young and gas-rich,
stellar bars drive gas toward the center, feeding star formation.
Over time, as the fuel runs out, the central regions become quiescent
and star-formation activity shifts to the outskirts of a galaxy. There,
spiral density waves and resonances induced by the central bar help
convert gas to stars. The outer ring, seen here in red, is one such
resonance area, where gas has been trapped and ignited into star-forming
NASA's Jet Propulsion Laboratory, Pasadena, California, manages the
Spitzer Space Telescope mission for NASA's Science Mission Directorate,
Washington. Science operations are conducted at the Spitzer Science
Center at the California Institute of Technology in Pasadena. Spacecraft
operations are based at Lockheed Martin Space Systems Company,
Littleton, Colorado. Data are archived at the Infrared Science Archive
housed at the Infrared Processing and Analysis Center at Caltech.
Caltech manages JPL for NASA.