Radio astronomers demonstrate vital tool for unraveling mystery of dark energy
9 Jun
2009, 1437 Hrs
Washington, June 9 Radio astronomers have directly measured the distance to a faraway galaxy, providing a valuable "yardstick" for calibrating large astronomical distances and demonstrating a vital method that could help determine the elusive nature of the mysterious Dark Energy that pervades the Universe.
"We measured a direct, geometric distance to the galaxy, independent of the complications and assumptions inherent in other techniques," said James Braatz, of the National Radio Astronomy Observatory (NRAO).
"The measurement highlights a valuable method that can be used to determine the local expansion rate of the Universe, which is essential in our quest to find the nature of Dark Energy," he added.
Braatz and his colleagues used the National Science Foundation's Very Long Baseline Array (VLBA) and Robert C. Byrd Green Bank Telescope (GBT), and the Effelsberg Radio Telescope of the Max Planck Institute for Radioastronomy (MPIfR) in Germany to determine that a galaxy dubbed UGC 3789 is 160 million light-years from Earth.
To do this, they precisely measured both the linear and angular size of a disk of material orbiting the galaxy's central black hole.
Water molecules in the disk act as masers to amplify, or strengthen, radio waves the way lasers amplify light waves.
The observation is a key element of a major effort to measure the expansion rate of the Universe, known as the Hubble Constant, with greatly improved precision.
That effort, cosmologists say, is the best way to narrow down possible explanations for the nature of Dark Energy.
"The new measurement is important because it demonstrates a one-step, geometric technique for measuring distances to galaxies far enough to infer the expansion rate of the Universe," said Braatz.
Dark Energy was discovered in 1998 with the observation that the expansion of the Universe is accelerating. It constitutes 70 percent of the matter and energy in the Universe, but its nature remains unknown.
Determining its nature is one of the most important problems in astrophysics.
"Measuring precise distances is one of the oldest problems in astronomy, and applying a relatively new radio-astronomy technique to this old problem is vital to solving one of the greatest challenges of 21st Century astrophysics," said team member Mark Reid of the Harvard-Smithsonian Center for Astrophysics (CfA). (ANI)
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