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Hubble's Deep View of the Universe Unveils Earliest Galaxies



 
 
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Old March 9th 04, 06:44 PM
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Default Hubble's Deep View of the Universe Unveils Earliest Galaxies

Donald Savage
Headquarters, Washington March 9, 2004
(Phone: 202/358-1547)

Ray Villard
Space Telescope Science Institute, Baltimore
(Phone: 410/338-4514)

Lars Lindberg Christensen
HST ESA Information Centre
(Phone: 011/49-89-320-06-306)

RELEASE: 04-086

HUBBLE'S DEEP VIEW OF THE UNIVERSE UNVEILS EARLIEST GALAXIES

Astronomers today unveiled the deepest portrait of the
visible universe ever taken. A one million second long exposure
taken by NASA's Hubble Space Telescope (HST) may reveal the
first galaxies to emerge from the so-called "dark ages" shortly
after the big bang.

The new image, called the Hubble Ultra Deep Field (HUDF),
should offer new insights into what types of objects reheated
the cold, dark universe about one billion years after the big
bang, when stars first started to shine, about 13 billion years
ago. The image reveals some galaxies at distances until now too
faint to be seen even in Hubble's previous faraway looks,
called the Hubble Deep Fields (HDFs), taken in 1995 and 1998.

"Hubble takes us to within a stone's throw of the big bang
itself," said Massimo Stiavelli of the Space Telescope Science
Institute (STScI) in Baltimore, and the HUDF project lead. A
key question for HUDF astronomers is whether the universe
appears the same at this very early time as it does when the
cosmos was between one and two billion years old.

The HUDF field contains an estimated 10,000 galaxies. In
ground-based images, the patch of sky in which the galaxies
reside is largely empty, just one-tenth the diameter of the
full moon. Located in the constellation Fornax, the region is
below the constellation Orion.

This new view is actually two separate images taken by Hubble's
Advanced Camera for Surveys (ACS) and the Near Infrared Camera
and Multi-object Spectrometer (NICMOS). The combination of ACS
and NICMOS images will be used to search for galaxies that
existed between 800 and 400 million years after the big bang.

The ACS field is studded with a wide range of galaxies of
various sizes, shapes, and colors. In vibrant contrast to the
image's rich harvest of classic spiral and elliptical galaxies,
there is a zoo of oddball galaxies littering the field. Some
look like toothpicks, others like links on a bracelet. A few
galaxies appear to be interacting. These oddball galaxies, that
existed 800 million years after the big bang, chronicle a
period when the universe was chaotic, when order and structure
were just beginning to emerge.

The NICMOS reveals the farthest galaxies ever seen, perhaps
just some 400 million years after the birth of the cosmos.
That's because the expanding universe has stretched their light
into the near-infrared portion of the spectrum, where NICMOS
observes.

"The images will also help us prepare for the next step from
NICMOS on Hubble to the forthcoming James Webb Space Telescope.
The NICMOS images reach back to the distance and time that Webb
is destined to explore at much greater sensitivity," explained
Rodger Thompson of the University of Arizona and the NICMOS
principal investigator.

The entire HUDF was observed with the advanced camera's "grism"
spectrograph, an instrument used to measure distances to these
distant objects. "The grism spectra have already yielded the
identification of about a thousand objects. Included among them
are some of the intensely faint and red points of light in the
ACS image, prime candidates for distant galaxies," said
Sangeeta Malhotra of the STScI and Principal Investigator for
the Ultra Deep Field's ACS grism follow-up study. "Based on
those identifications, some of these objects are among the
farthest and youngest galaxies ever seen. The grism spectra
also distinguish among other types of very red objects, such as
old and dusty red galaxies, quasars and cool dwarf stars," he
said.

The ACS picture required a series of exposures taken over the
course of 400 HST orbits around Earth from Sept. 24, 2003, to
Jan. 16, 2004. The size of a phone booth, ACS captured ancient
photons of light that began traversing the universe even before
Earth existed. Photons of light from the very faintest objects
arrived at a trickle of one photon per minute, as opposed to
millions of photons per minute from nearer galaxies.

The STScI is operated by the Association of Universities for
Research in Astronomy, Inc. under contract with NASA's Goddard
Space Flight Center, Greenbelt, Md. The HST is a project of
international cooperation between NASA and the European Space
Agency.

For information about NASA and agency projects on the Internet,
visit:

http://www.nasa.gov/formedia

For HST images and information on the Internet, visit:

http://hubblesite.org/news/2004/07


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