June 11, 2009

Radio telescopes make a space ‘yardstick’

U.S. astronomers using radio telescopes to measure the distance to a distant galaxy have created a yardstick for calibrating large astronomical distances.

The radio astronomers said their yardstick also demonstrates an important method that could help determine the nature of the so-called 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, James Braatz of the National Radio Astronomy Observatory said. 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.

The astronomers said they determined a galaxy called UGC 3789 is 160 million light-years from Earth by precisely measuring both the linear and angular size of a disk of material orbiting the galaxy's central black hole.

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, Braatz said.

Dark Energy constitutes 70 percent of the matter and energy in the universe, but its nature remains unknown. Determining its nature is considered one of the most important problems in astrophysics.

Braatz presented the work earlier this month during a meeting of the American Astronomical Society.