J.D. Harrington
Headquarters, Washington
202-358-0321
j.d.harrington@nasa.gov
Whitney Clavin
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-4673
whitney.clavin@jpl.nasa.gov
RELEASE: 12-130
NASA'S SPITZER FINDS GALAXY WITH SPLIT PERSONALITY
WASHINGTON -- While some galaxies are rotund and others are slender
disks like our spiral Milky Way, new observations from NASA's Spitzer
Space Telescope show that the Sombrero galaxy is both. The galaxy,
which is a round, elliptical with a thin disk embedded inside, is one
of the first known to exhibit characteristics of the two different
types. The findings will lead to a better understanding of galaxy
evolution, a topic still poorly understood.
"The Sombrero is more complex than previously thought," said Dimitri
Gadotti of the European Southern Observatory in Chile and lead author
of a new paper on the findings appearing in the Monthly Notices of
the Royal Astronomical Society. "The only way to understand all we
know about this galaxy is to think of it as two galaxies, one inside
the other."
The Sombrero galaxy, also known as NGC 4594, is located 28 million
light-years away in the constellation Virgo. From our viewpoint on
Earth, we can see the thin edge of its flat disk and a central bulge
of stars, making it resemble a wide-brimmed hat. Astronomers do not
know whether the Sombrero's disk is shaped like a ring or a spiral,
but agree it belongs to the disk class.
"Spitzer is helping to unravel secrets behind an object that has been
imaged thousands of times," said Sean Carey of NASA's Spitzer Science
Center at the California Institute of Technology in Pasadena, Calif..
"It is intriguing Spitzer can read the fossil record of events that
occurred billions of years ago within this beautiful and archetypal
galaxy."
Spitzer captures a different view of the galaxy than visible-light
telescopes. In visible views, the galaxy appears to be immersed in a
glowing halo, which scientists had thought was relatively light and
small. With Spitzer's infrared vision, a different view emerges.
Spitzer sees old stars through the dust and reveals the halo has the
right size and mass to be a giant elliptical galaxy.
While it is tempting to think the giant elliptical swallowed a spiral
disk, astronomers say this is highly unlikely because that process
would have destroyed the disk structure. Instead, one scenario they
propose is that a giant elliptical galaxy was inundated with gas more
than nine billion years ago. Early in our universe, networks of gas
clouds were common, and they sometimes fed growing galaxies, causing
them to bulk up. The gas would have been pulled into the galaxy by
gravity, falling into orbit around the center and spinning out into a
flat disk. Stars would have formed from the gas in the disk.
"This poses all sorts of questions," said Rub��n S��nchez-Janssen from
the European Southern Observatory, co-author of the study. "How did
such a large disk take shape and survive inside such a massive
elliptical? How unusual is such a formation process?"
Researchers say the answers could help them piece together how other
galaxies evolve. Another galaxy, called Centaurus A, appears also to
be an elliptical galaxy with a disk inside it. But its disk does not
contain many stars. Astronomers speculate that Centaurus A could be
at an earlier stage of evolution than the Sombrero and might
eventually look similar.
The findings also answer a mystery about the number of globular
clusters in the Sombrero galaxy. Globular clusters are spherical
nuggets of old stars. Ellipticals typically have a few thousand,
while spirals contain a few hundred. The Sombrero has almost 2,000, a
number that makes sense now but had puzzled astronomers when they
thought it was only a disk galaxy.
For more information about Spitzer, visit:
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