National Aeronautics and Space Administration Logo
Follow this link to skip to the main content NASA Banner
Solar System Exploration
News & Events
Galaxy Clusters and the Hubble Constant
Galaxy Clusters and the Hubble Constant
9 Aug 2006
(Source: Harvard University)

The Hubble constant, or the Hubble parameter, is a critically important number that sets the expansion rate of the Universe, and is derived by measuring the speeds that the clusters are moving away from us and dividing by the cluster distances.

A combination of X-ray and radio observations allowed astronomers to determine the Hubble constant using the so-called Sunyaev-Zeldovich effect. In this phenomenon, photons in the cosmic microwave background (CMB) interact with electrons in the hot gas that pervades the enormous galaxy clusters. The photons acquire energy from this interaction, which distorts the signal from the microwave background in the direction of the clusters. The magnitude of this distortion depends on the density and temperature of the hot electrons and the physical size of the cluster.

Astronomers used radio telescopes to measure distortions of the cosmic microwave background. Chandra measured the properties of the hot gas revealed in X-ray emission, which told astronomers the physical size of the galaxy clusters and thus allowed their distances to be determined.

The value for the Hubble constant derived from this method, which is independent of previous techniques, was found to be 76.9 in its traditional units of kilometers per second per megaparsec (a megaparsec is equal to 3.26 million light years.) Taking into account the small uncertainties, this result agrees with the values determined by other techniques, and fixes the age of the Universe between 12 and 14 billion years.

News Archive Search  Go!
Show  results per page
Awards and Recognition   Solar System Exploration Roadmap   Contact Us   Site Map   Print This Page
NASA Official: Kristen Erickson
Advisory: Dr. James Green, Director of Planetary Science
Outreach Manager: Alice Wessen
Curator/Editor: Phil Davis
Science Writers: Courtney O'Connor and Bill Dunford
Producer: Greg Baerg
Webmaster: David Martin
> NASA Science Mission Directorate
> Budgets, Strategic Plans and Accountability Reports
> Equal Employment Opportunity Data
   Posted Pursuant to the No Fear Act
> Information-Dissemination Policies and Inventories
> Freedom of Information Act
> Privacy Policy & Important Notices
> Inspector General Hotline
> Office of the Inspector General
> NASA Communications Policy
> NASA Advisory Council
> Open Government at NASA
Last Updated: 9 Aug 2006