New Measurements: The Universe Weighs Less

The universe just got a little bit slimmer. 

Revised calculations indicate the universe contains less normal and dark matter than previously thought, resulting in a "weight loss" of 10 to 20 percent. 

Dark matter is a mysterious substance that is invisible to current technologies and which scientists think outnumbers normal "baryonic" matter by about 5-to-1.  

The new weight estimate, detailed in the Oct. 20 issue of Astrophysical Journal, comes from new observations of the galaxy cluster Abell 3112. In 2002, astronomers announced they had traced X-rays in the cluster to clouds of dust and gas between the galaxies. But new observations by NASA's Chandra X-ray Observatory failed to detect the light signature, or "spectral emission lines," that should be given off by atoms in the clouds. 

The team now thinks the X-rays are the result of collisions between lightweight electrons and photons in space. This changes the mass estimate of the cluster.

"This means the mass of these X-ray emitting clouds is much less than we initially thought it was," said study team member Max Bonamente, an astrophysicist at the University of Alabama in Huntsville. 

Dark matter was initially invoked to provide the extra gravity needed to explain how galaxies can spin so fast without breaking apart. If there is less normal matter in Abell 3112, then less dark matter is needed to hold the cluster together, Bonamente said. 

If the results also apply to other galaxy clusters, then "the universe as a whole ends up being a little bit lighter," he told

It's as if billions of lights thought to come from billions of aircraft carriers were found to instead emanate from billions of extremely bright fireflies. 

Confirmation of the team's finding will have to await the launch of future space missions, Bonamente said, which can scan the skies for emission lines of normal matter more probingly. 

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Staff Writer

Ker Than is a science writer and children's book author who joined as a Staff Writer from 2005 to 2007. Ker covered astronomy and human spaceflight while at, including space shuttle launches, and has authored three science books for kids about earthquakes, stars and black holes. Ker's work has also appeared in National Geographic, Nature News, New Scientist and Sky & Telescope, among others. He earned a bachelor's degree in biology from UC Irvine and a master's degree in science journalism from New York University. Ker is currently the Director of Science Communications at Stanford University.