spacetoday.net: Chandra measures Hubble constant

Posted: Wed, Aug 9, 2006, 7:55 AM ET (1155 GMT)
Astronomers have used data from NASA's Chandra X-Ray Observatory to make an independent measure of the Hubble constant, a key metric of the expansion of the universe. The astronomers used x-ray observations of 38 galaxy clusters, coupled with separate radio observations, to measure the distances of the clusters, the most distant of which were 9.3 billion light-years away. Those distances, combined with previous measurements of the speeds at which the clusters are receding, allowed astronomers to calculate the Hubble constant. Their result, 77 kilometers per second per megaparsec (plus or minus 15 percent) is within the margin of error previous independent calculations of the constant, 72 km/sec/Mpc, using the Hubble Space Telescope. The Hubble constant is one of the key values in cosmology, telling astronomers the rate at which the universe is expanding; the result confirms earlier estimates that the universe is between 12 and 14 billion years old.