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Radio telescope
remeasures Universe

Posted: 21 February 2011

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Using the Very Long Baseline Array (VLBA) – ten 25-metre diameter dish antennas spread from Hawaii to the Caribbean – astronomers have made important headway into studies of dark energy, extrasolar planets, and the state of our own Milky Way Galaxy.

The VLBA telescopes. Image courtesy of NRAO/AUI and Earth image courtesy of the SeaWiFS Project NASA/GSFC and ORBIMAGE.

The VLBA has the greatest resolving power of any telescope, producing images hundreds of times more detailed than the Hubble Space Telescope. In one branch of the VLBA's studies, astronomers have measured galaxy NGC 6264 at a distance of 450 million light years, a distance three times greater than ever measured directly before. Determining ever-greater distances in the Universe is crucial to determining the expansion rate of the Universe and the nature of dark energy, which thought to comprise 70 percent of the Universe. Pinpointing the distances of faraway galaxies is important, since the further away it is, the more its motion is due to the expansion of the Universe.

"Our direct, geometric measurements are independent of the assumptions and complications inherent in other techniques," says James Braatz of the National Radio Astronomy Observatory (NRAO). "Solving the dark energy problem requires advancing the precision of cosmic distance measurements, and we are working to refine our observations and extend our methods to more galaxies."

Artist's conception of Milky Way, showing locations of star-forming regions, whose distances were recently measured. Image: M. Reid, Harvard-Smithsonian CfA; R. Hurt, SSC/JPL/Caltech, NRAO/AUI/NSF.

The VLBA has also been used to identify dozens of star forming regions in the Milky Way, improving on earlier estimates by a factor of two. The new research also points to our Galaxy having four arms, and not two, as once speculated. "Because we sit inside our Galaxy, it's difficult to actually map it," says Mark Reid of the Harvard-Smithsonian Center for Astrophysics. "These precision distance measurements are our most effective tool for learning about the structure of the Milky Way." Reid's work will also determine with much greater accuracy if and when our neighbouring Andromeda galaxy will collide with the Milky Way.

Further afield, a four year project in collaboration with NRAO's Green Bank Telescope to monitor 30 stars for the tell-tale wobble of orbiting planets, is nearing completion. "This study tracks stars smaller than our Sun, seeking evidence of planets the size of Jupiter or smaller," says Geoffrey Bower of the University of California, Berkeley. "We want to learn how common it is for these low-mass stars to have planets orbiting them at relatively large distances."

The latest measurements and capabilities of the VLBA were reported the American Association for the Advancement of Science meeting in Washington.

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3D Universe
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