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First tile gap filler
This extended movie shows Steve Robinson riding the station's robot arm, moving within reach of Discovery's underside and successfully pulling out the first protruding tile gap filler. (6min 45sec file)
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Second tile gap filler
This extended movie shows Steve Robinson successfully pulling out the second protruding tile gap filler. (9min 23sec file)
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Storage platform
The External Stowage Platform-2 designed to hold spares and replacement equipment for the space station is attached to the Quest airlock module's outer hull during the spacewalk. (6min 29sec file)
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Station experiments
Japanese astronaut Soichi Noguchi climbed 60 feet above Discovery's payload bay to the space station's P6 solar array truss to attach the Materials International Space Station Experiment-5 package. (4min 08sec file)
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Opening the suitcase
Noguchi deploys the MISSE-5 package, revealing a host of material samples to the space environment for extended exposure. (3min 43sec file)
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Atop the station
Noguchi's helmet-mounted camera provides a stunning view atop the P6 truss showing Discovery to his right and the Russian segment of the space station on his left. (2min 31sec file)
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Inside Mission Control
This behind the scenes footage was recorded inside Houston's space station flight control room during the third Discovery spacewalk. (8min 45sec file)
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Next mission to Mars
NASA's next voyage to the Red Planet is introduced by project managers and scientists in this news conference from 1 p.m. EDT on Thursday, July 21. The Mars Reconnaissance Orbiter will launch in August on a mission to provide the sharpest images ever taken of Earth's neighboring planet. (34min 10sec file)

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Spitzer telescope finds hidden, hungry black holes
NASA NEWS RELEASE
Posted: August 3, 2005

Most of the biggest black holes in the universe have been eating cosmic meals behind closed doors - until now.

With its sharp infrared eyes, NASA's Spitzer Space Telescope (SST) peered through walls of galactic dust to uncover what may be the long-sought missing population of hungry black holes known as quasars.


This false-color image from NASA's Spitzer Space Telescope shows a distant galaxy (yellow) that houses a quasar, a super-massive black hole circled by a ring, or torus, of gas and dust. Spitzer's infrared eyes cut through the dust to find this hidden object, which appears to be a member of the long-sought population of missing quasars. The green and blue splotches are galaxies that do not hold quasars. Credit: NASA/JPL-Caltech/A. Martinez-Sansigre (Oxford University)
 
"From past studies using X-rays, we expected there were a lot of hidden quasars, but we couldn't find them," said Alejo Martinez-Sansigre of the University of Oxford, England. He is lead author of a paper about the research in this week's Nature. "We had to wait for Spitzer to find an entire population of these dust-obscured objects," he said.

Quasars are super-massive black holes that are circled by a giant ring of gas and dust. They live at the heart of distant galaxies and can annually consume up to the equivalent mass of one thousand stars. As their black holes suck in material from their dusty rings, the material lights up brilliantly, making quasars the brightest objects in the universe. This bright light comes in many forms, including X-rays, visible and infrared light.

Astronomers have puzzled for years over the question of how many of these cosmic behemoths are out there. One standard method for estimating the number is to measure the cosmic X-ray background. Quasars outshine everything else in the universe in X-rays. By counting the background buzz of X-rays, it is possible to predict the approximate total number of quasars.

But this estimate has not matched previous X-ray and visible-light observations of actual quasars, which number far fewer than expected. Astronomers thought this might be because most quasars are blocked from our view by gas and dust.

They proposed that some quasars are positioned in such a way their dusty rings hide their light, while others are buried in dust-drenched galaxies. Spitzer appears to have found both types of missing quasars by looking in infrared light. Unlike X-rays and visible light, infrared light can travel through gas and dust.

Researchers found 21 examples of these quasars in a small patch of sky. All the objects were confirmed as quasars by the National Radio Astronomy Observatory's Very Large Array radio telescope in New Mexico and by the Particle Physics and Astronomy Research Council's William Herschel Telescope in Spain.

"If you extrapolate our 21 quasars out to the rest of the sky, you get a whole lot of quasars," said Dr. Mark Lacy of the Spitzer Science Center, California Institute of Technology (Caltech), Pasadena, Calif., a co-author of the Nature paper. "This means that, as suspected, most super-massive black hole growth is hidden by dust."

The discovery will allow astronomers to put together a more complete picture of how and where quasars form in our universe. Of the 21 quasars uncovered by Spitzer, 10 are believed to be inside fairly mature, giant elliptical galaxies. The rest are thought to be encased in thick, dusty galaxies that are still forming stars.

A team of researchers based at the University of Arizona, Tucson, found similar quasars using Spitzer. Their research is described here.

Other authors of the Nature paper include Drs. Steve Rawlings and Matt Jarvis of the University of Oxford; Drs. Dario Fadda and Francine Marleau, Spitzer Science Center; Dr. Chris Simpson, University of Durham, England; and Dr. Chris Willott, National Research Council Canada, Victoria.

JPL, a division of Caltech, manages the SST mission for NASA's Science Mission Directorate. Science operations are conducted at the Spitzer Science Center at Caltech.