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Phoenix update

Scientists report on the progress of the Phoenix lander exploring the northern plains of Mars during this July 31 update.

 Briefing | Panorama

Expedition 18 crew

The American, Russian and Japanese crewmembers to serve aboard the space station during various stages of the Expedition 18 mission, plus spaceflight participant Richard Garriott hold this pre-flight news conference.

 Play

STS-94: Rapid re-flight

Three months after their 1997 flight was cut short by a fuel cell problem, the same seven astronauts returned to space aboard shuttle Columbia to fulfill the Spacelab science mission. The STS-94 crew tells the story in this post-flight presentation.

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STS-124: In review

The STS-124 crew narrates highlights from its mission that delivered Japan's Kibo lab module to the station.

 Full presentation
 Mission film

Jason 2 launch

A ULA Delta 2 rocket launched the Jason 2 oceanography satellite from Vandenberg Air Force Base on June 20.

 Full Coverage

Jason 2 preview

The joint American and European satellite project called Jason 2 will monitor global seal levels.

 Mission | Science

STS-124 space shuttle mission coverage

Extensive video collection covering shuttle Discovery's mission to deliver the Japanese Kibo science lab to the station is available in the archives.

 Full Coverage

Phoenix lands on Mars

The Phoenix spacecraft arrived at Mars on May 25, safely landing on the northern plains to examine the soil and water ice.

 Full Coverage

STS-82: In review

The second servicing of the Hubble Space Telescope was accomplished in Feb. 1997 when the shuttle astronauts replaced a pair of instruments and other internal equipment on the observatory.

 Play

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Hubble finds large sample of very distant galaxies
HUBBLE EUROPEAN SPACE AGENCY INFORMATION CENTRE
Posted: August 4, 2008

New Hubble Space Telescope observations of six spectacular galaxy clusters acting as gravitational lenses have given significant insights into the early stages of the Universe. Scientists have found the largest sample of very distant galaxies seen to date: ten promising candidates thought to lie at a distance of 13 billion light-years (~redshift 7.5).


The picture shows Abell 2218, a rich galaxy cluster composed of thousands of individual galaxies. Credit: NASA, ESA, and Johan Richard (Caltech, USA); Acknowledgement: Davide de Martin & James Long (ESA/Hubble)
 
By using the gravitational magnification from six massive lensing galaxy clusters, the NASA/ESA Hubble Space Telescope has provided scientists with the largest sample of very distant galaxies seen to date. Some of the newly found magnified objects are dimmer than the faintest ones seen in the legendary Hubble Ultra Deep Field, which is usually considered the deepest image of the Universe.

By combining both visible and near-infrared observations from Hubble's Advanced Camera for Surveys (ACS) and Near Infrared Camera and Multi- Object Spectrometer (NICMOS), scientists searched for galaxies that are only visible in near-infrared light. They uncovered 10 candidates believed to lie about 13 billion light-years away (a redshift of approximately 7.5), which means that the light gathered was emitted by the stars when the Universe was still very young ‹ a mere 700 million years old.

"These candidates could well explain one of the big puzzles plaguing astronomy today. We know that the Universe was reionised within the first 5-600 million years after the Big Bang, but we don't know if the ionising energy came from a smaller number of big galaxies or a more plentiful population of tiny ones", said Johan Richard, from the California Institute of Technology.

The relatively high number of redshift 7.5 galaxies claimed in this survey suggests that most of the ionising energy was produced by dim and abundant galaxies rather than large, scarce ones.

"The challenge for astronomers is that galaxies beyond a distance of 13 billion light-years (past a redshift of 7) are exceedingly faint and are only visible in the near-infrared ‹ just at the limit of what Hubble can observe" explained Jean-Paul Kneib from the Laboratoire d'astrophysique de Marseille.

This new result was only made possible with some cosmic assistance in the form of gravitational lensing that magnified the light from the distant galaxies enough for Hubble to detect them. A firm confirmation of their distance was beyond even the capabilities of the 10-meter Keck telescope and must await powerful future ground-based telescopes.


This image illustrates a gravitational lensing effect. Imagine the Earth (represented as a blue sphere on the left), a massive body (represented as a yellow sphere near the centre) and a spiral galaxy are aligned. The massive body distorts the spacetime (represented as the yellow grid) and observers on Earth, instead of seeing the spiral galaxy as it is, see the galaxy distorted, as arcs of light. It is like having a "lens" in front of the galaxy. Credit: NASA, ESA, and Johan Richard (Caltech, USA); Acknowledgement: Davide de Martin & James Long (ESA/Hubble)
 
First confirmed in 1979, gravitational lenses were predicted by Albert Einstein's theory of General Relativity, a theory that allows astronomers to calculate the path of starlight as it moves through curved space-time. According to the theory, the bending of light is brought about by the presence of matter in the Universe, which causes the fabric of space-time to warp and curve.

Gravitational lensing is the result of this warping of spacetime and is mainly detected around very massive galaxy clusters. Due to the gravitational effect of both the cluster's observable matter and hidden dark matter, the light is bent around the cluster. This bending of light allows the clusters in certain places to act as natural gravitational telescopes that give the light of faint and faraway objects a boost.

Where Earth-bound telescopes fail to detect such faint and distant objects due to the blurring introduced by the Earth's atmosphere, a combination of Hubble's location in space and the magnification of the gravitation lenses provides astronomers with a birds-eye view of these elusive objects.

This technique has already been used numerous times by Hubble and has helped astronomers to find and study many of the most distant known galaxies.