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کهکشانی در اعماق فضا !
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NASA Telescopes Spy Ultra-Distant Galaxy Amidst Cosmic 'Dark Ages'



WASHINGTON
-- With the combined power of NASA's Spitzer and Hubble space
telescopes, as well as a cosmic magnification effect, astronomers have
spotted what could be the most distant galaxy ever seen. Light from the
young galaxy captured by the orbiting observatories first shone when our
13.7-billion-year-old universe was just 500 million years old.


The far-off galaxy existed within an important era when the universe
began to transit from the so-called cosmic dark ages. During this
period, the universe went from a dark, starless expanse to a
recognizable cosmos full of galaxies. The discovery of the faint, small
galaxy opens a window onto the deepest, remotest epochs of cosmic
history.

"This galaxy is the most distant object we have ever
observed with high confidence," said Wei Zheng, a principal research
scientist in the department of physics and astronomy at Johns Hopkins
University in Baltimore and lead author of a new paper appearing in
Nature. "Future work involving this galaxy, as well as others like it
that we hope to find, will allow us to study the universe's earliest
objects and how the dark ages ended."

Light from the
primordial galaxy traveled approximately 13.2 billion light-years before
reaching NASA's telescopes. In other words, the starlight snagged by
Hubble and Spitzer left the galaxy when the universe was just 3.6
percent of its present age. Technically speaking, the galaxy has a
redshift, or "z," of 9.6. The term redshift refers to how much an
object's light has shifted into longer wavelengths as a result of the
expansion of the universe. Astronomers use redshift to describe cosmic
distances.

Unlike previous detections of galaxy candidates in
this age range, which were only glimpsed in a single color, or
waveband, this newfound galaxy has been seen in five different
wavebands. As part of the Cluster Lensing And Supernova Survey with
Hubble Program, the Hubble Space Telescope registered the newly
described, far-flung galaxy in four visible and infrared wavelength
bands. Spitzer measured it in a fifth, longer-wavelength infrared band,
placing the discovery on firmer ground.

Objects at these
extreme distances are mostly beyond the detection sensitivity of today's
largest telescopes. To catch sight of these early, distant galaxies,
astronomers rely on gravitational lensing. In this phenomenon, predicted
by Albert Einstein a century ago, the gravity of foreground objects
warps and magnifies the light from background objects. A massive galaxy
cluster situated between our galaxy and the newfound galaxy magnified
the newfound galaxy's light, brightening the remote object some 15 times
and bringing it into view.

Based on the Hubble and Spitzer
observations, astronomers think the distant galaxy was less than 200
million years old when it was viewed. It also is small and compact,
containing only about 1 percent of the Milky Way's mass. According to
leading cosmological theories, the first galaxies indeed should have
started out tiny. They then progressively merged, eventually
accumulating into the sizable galaxies of the more modern universe.


These first galaxies likely played the dominant role in the epoch of
reionization, the event that signaled the demise of the universe's dark
ages. This epoch began about 400,000 years after the Big Bang when
neutral hydrogen gas formed from cooling particles. The first luminous
stars and their host galaxies emerged a few hundred million years later.
The energy released by these earliest galaxies is thought to have
caused the neutral hydrogen strewn throughout the universe to ionize, or
lose an electron, a state that the gas has remained in since that time.


"In essence, during the epoch of reionization, the lights
came on in the universe," said paper co-author Leonidas Moustakas, a
research scientist at NASA's Jet Propulsion Laboratory, a division of
the California Institute of Technology in Pasadena, Calif.


Astronomers plan to study the rise of the first stars and galaxies and
the epoch of reionization with the successor to both Hubble and Spitzer,
NASA's James Webb Telescope, which is scheduled for launch in 2018. The
newly described distant galaxy likely will be a prime target.

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  پلی میان دو خوشه کهکشانی !! amir astronomer 0 205 21-11-2012، 10:36 PM
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