Thursday, November 11, 2010

Physics News: The New Technique for Learning The Dark Energy of Universe


ScienceDaily (July 23, 2010)Pioneering observations by National Science Foundation's giant Robert C. Byrd Green Bank Telescope (GBT) has given astronomers a new tool for mapping the structure of the macrocosm. This new tool promises to provide valuable clues about the nature of "dark energy" believed to be mysterious is almost three-quarters of the mass and energy of the universe.

Dark Energy is a label that scientists have to explain what is causing the universe to grow at accelerating rates. While the acceleration was discovered in 1998, the cause is still unknown. Physicists have developed competing theories to explain the acceleration, and believe that the best way to test these theories is to measure precisely the large-scale cosmic structure.
Sound waves in matter-energy soup very early universe is thought to have left traces were detected in large-scale distribution of galaxies in the universe. The researchers developed a way to measure these trace by observing radio emissions from hydrogen gas. Their technique is called intensity mapping. When applied to an area larger than the universe, it can reveal how such a large-scale structure has changed over the last several billions of years and provide insight that the theory of dark energy is the most accurate.
"Our project to map the hydrogen gas to a larger cosmic distances than ever before, and showed that the technique we developed can be used in large volumes from the map of the Universe in three dimensions and to test competing theories about dark energy, "said Tzu-Ching Chang, from Academia Sinica in Taiwan and University of Toronto.
To get their results, the researchers used the GBT to study the sky that had been surveyed in detail in the visible by telescope Keck II in Hawaii. The survey uses optical spectroscopy to map the locations of thousands of galaxies in three dimensions. With the GBT, not looking in the hydrogen gas, an individual galaxy far - a daunting challenge beyond current technical capabilities instruments - a team that uses their intensity mapping technique to collect radio waves emitted by hydrogen gas in bulk volume of space, including many galaxies.
"Since the beginning of the 20th century, astronomers have traced the expansion of the universe by observing galaxies. Our new technique allows us to ignore the step and the detection of galactic radio emission collected from thousands of galaxies within a given time, and any other material that glow faintly between them, "said Jeffrey Peterson, from Carnegie Mellon University.
The astronomers also developed new techniques issued from both man-made radio waves and radio emissions caused by astronomical sources closer, leaving only a very faint radio waves coming from hydrogen gas that is very far away. The result is a map of part of "cosmic web" which correlates neatly with the structure indicated by previous optical studies. The team was first proposed their intensity mapping technique in 2008, and GBT observations of them as an idea first experiment.
"These observations of hydrogen gas detected more than all previously detected hydrogen in the universe, and at a distance of ten times further than previously seen radio waves emitted by hydrogen," said Ue-Li Pen of the University of Toronto.
"This is a demonstration of the important technical very promising for future studies on the evolution of large-scale structure in the universe," said Chief Scientist National Radio Astronomy Observatory Chris Carilli, which is not part of the research team.
In addition to Chang, Peterson, and Pen, the research team included Kevin Bandura from Carnegie Mellon University. The scientists reported their work in the edition of scientific journals Nature in 22 July.
National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement with Associated Universities, Inc.

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