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Gantry in motion
The gantry-like Rotating Service Structure to moved around Discovery to enclose the orbiter just before sunrise, a couple of hours after the shuttle reached the pad, as seen is time lapse movie. (1min 26sec file)
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Arriving at the pad
This time lapse movie shows shuttle Discovery rolling up the ramp and arriving at launch pad 39B after the 10.5-hour trip from the VAB. (3min 32sec file)
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Discovery goes north
Discovery's rollout enters the early evening as the shuttle heads north toward launch pad 39B. (6min 15sec file)
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Past one pad
As viewed from the Vehicle Assembly Building, space shuttle Discovery rolls northward and past launch pad 39A in the background. (4min 23sec file)
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Crawlerway split
The transporter reaches the point where the crawlerway splits into two paths to the Complex 39 pads and makes the turn for pad 39B. (7min 11sec file)
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Down the crawlerway
Shuttle Discovery makes its way down the crawlerway under beautiful Florida skies. (5min 00sec file)
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Rollout of Discovery
Space shuttle Discovery begins its 4.2-mile journey from the Vehicle Assembly Building to launch pad 39B atop the Apollo-era crawler-transporter. (10min 30sec file)
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Discovery's mission
A preview of Discovery's STS-114 flight is presented in this narrated movie about the shuttle return to flight mission. (10min 15sec file)

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Station's past 2 years
The impact to the International Space Station by this two-year grounding of the space shuttle fleet in the wake of Columbia is examined in this narrated movie. (6min 46sec file)

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Discovery's astronauts
Take a behind-the-scenes look at the seven astronauts who will fly aboard the space shuttle return-to-flight mission in this movie that profiles the lives of the STS-114 crew. (10min 04sec file)

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Walking with Discovery
Walk alongside space shuttle Discovery as the motorized transporter hauls the ship a quarter-mile from the Orbiter Processing Facility to the Vehicle Assembly Building. (3min 21sec QuickTime file)
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Discovery leaves hangar
This time-lapse movie captured from an overhead camera shows space shuttle Discovery's middle-of-the-night departure from its processing hangar at Kennedy Space Center to the roll to the Vehicle Assembly Building. (4min 30sec file)
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Rolling into VAB
Discovery arrives in the Vehicle Assembly Building as viewed in this time-lapse movie. The shuttle will be mated to the redesigned external fuel tank and twin solid rocket boosters in the VAB before rolling to the launch pad for the first post-Columbia mission. (5min 00sec file)
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Concentrated dark matter at the cores of fossil galaxies
Posted: April 7, 2005

Researchers at the University of Birmingham have used the new generation of X-ray space observatories to study "fossil galaxies" - ancient galaxy groups in which all of the large galaxies have gradually merged to form one central giant galaxy.

The astronomers discovered a remarkable concentration of dark and normal matter in the cores of these isolated star systems, compared with the mass distribution in normal galaxy groups.

Many galaxies, including our Milky Way, reside in groups. Sometimes they experience close encounters with other members of the group. Computer simulations predict that such interactions cause large galaxies to spiral slowly towards the centre of the group, where they can merge to form a single giant galaxy, which progressively swallows all its neighbours.

Since many galaxy groups possess extended halos of hot gas and dark matter, it was predicted ten years ago that a class of systems dubbed "fossil groups" should exist, in which all the major galaxies have merged to form one central giant galaxy. This would be surrounded by an X-ray-bright cloud of hot gas that extends outward to many galactic radii.

"When we first discovered the large halos of hot gas in which some very compact groups of galaxies are embedded, we realised that just a few billion years of further evolution would leave a single, giant, merged galaxy sitting at the centre of a bright X-ray halo," said Trevor Ponman, the leader of the Birmingham group who made this prediction and then discovered the first fossil group in 1994.

Theories also suggested that fossil groups which fall into even larger clusters of galaxies may account for the giant elliptical galaxies which are often found in the centres of such clusters.

The Birmingham team has observed six likely "fossil groups" in the past two years, taking advantage of the sharp vision of NASA's Chandra X-Ray Space Observatory and the high sensitivity of ESA's orbiting XMM-Newton X-ray observatory. The six "fossil groups" are located up to two billion light years from Earth. The team's main objective was to explore the mechanisms by which fossil groups and giant elliptical galaxies are formed.

The key to the study was the distribution of dark matter in the fossil groups. This mysterious matter comprises over 80 per cent of the mass of the Universe, yet its nature is unknown. Dark matter has never been detected directly, but its presence is inferred through its gravitational influence on ordinary matter.

The large elliptical galaxy NGC 6482 was of special interest to the team, since it is the closest known fossil group, and could be studied in great detail. This isolated giant, which shines with the equivalent of 110 billion Suns, is located 100 million light years away in the constellation Hercules.

Using Chandra's Advanced CCD Imaging Spectrometer, Habib Khosroshahi, Trevor Ponman and Laurence Jones, used observations of the hot gas to trace the distribution of dark matter in NGC 6482. The gas is heated to a temperature of 10 million degrees Celsius, mainly due to shock heating as a result of gravitational collapse.

Speaking at the RAS National Astronomy Meeting in Birmingham, Habib Khosroshahi described the discovery of a remarkable concentration of dark matter in the core of NGC 6482.

Khosroshahi also described two more examples of high mass concentration in more massive and more distant fossil galaxies studied by both the Chandra and the XMM-Newton telescopes, although the case of NGC 6482 is unique, since it is possible to probe the centre of the system with higher accuracy.

According to Khosroshahi, the concentration of mass at the centre of these ancient galaxy groups, which is mostly in the form of dark matter, was found to be typically five times higher than in normal galaxy groups with similar mass and halo size.

This central concentration of mass supports the idea that fossil groups such as NGC 6482 are very old structures which collapsed long before the typical groups of galaxies formed.

"The explanation for such a centralised dark matter distribution could be that the system formed at very high redshift - when the Universe was very young and dense," said Khosroshahi.

"The great advantage of fossil groups compared to normal groups is that no major galaxy interaction, which can stir the hot gas, is taking place," he added. "Therefore, they provide ideal laboratories to study the properties of visible matter in the form of gas and stars as well as their container, the dark matter."

The 2005 RAS National Astronomy Meeting is hosted by the University of Birmingham, and sponsored by the Royal Astronomical and the UK Particle Physics and Astronomy Research Council (PPARC).