Reconstructing the universe, piece by piece

The blue arc has been lensed, making it appear much closer than it actually is.

Each Tuesday morning, a small group of particle physicists and astrophysicists gathers on the 6th floor of Wilson Hall to discuss progress in piecing together the structure of the universe. The group, called "Fermi Clusters," uses a telescope at Apache Point Observatory, New Mexico, and images and catalogs from the Sloan Digital Sky Survey to get a better view. Recently, the group has discussed exploring how sound waves from the infant universe confirm gravity's role in its formation, and examining 11-billion-year-old stars through gravitational lensing.

"Lensing occurs when an object in space is so massive that its gravity bends distant light," said astrophysicist Huan Lin. Lensed light often appears much brighter than it would otherwise. Last November, group members announced the discovery of a dramatically lensed galaxy 11 billion light years away. Since it takes 11 billion years for that light to reach Earth, the discovery allowed researchers to observe stars in the early universe.

With his work in sound waves, Juan Estrada studies patterns in the arrangement of galaxy clusters and compares them with patterns in sound waves from the universe's first million years. These sound waves -- caused by interactions between photons and matter in the early universe -- inserted ripples into the cosmic microwave background radiation left over from the Big Bang. In 2005, Sloan found matching ripples in the distribution of matter over a large sample of galaxies. Finding the same ripples in both the early universe and in today's galaxy distribution confirmed predictions that gravity was responsible for forming the universe's current structures. The ripples also provided a way to measure the properties of dark matter and dark energy. Estrada has recently found evidence of these ripples, called "baryon acoustic oscillations," in a different sample of Sloan galaxy clusters.

The group also discusses recent work in weak lensing. "Weak lensing occurs when galaxies are just a little bit distorted, and the way you measure it is by looking at the shapes of lots of galaxies," said Lin. Postdoc Jeff Kubo is looking at weak lensing in the Coma Cluster, one of the richest known galaxy clusters covering a large enough sky area that the Sloan Survey is needed to image it all for a weak lensing study. Weak lensing can be used to "weigh" the Coma Cluster and determine what percentage is made of dark matter. "Since its gravity distorting the light, you can calculate the overall mass of the cluster by looking at the amount of distortion," said Lin. "The stuff that adds mass, but that you don't see, is dark matter."

--Siri Steiner

Scientific American,
April 27, 2007

Magnet Trouble Likely to Complicate Start of Large Hadron Collider

Repairs may preclude a test run before the particle smasher starts tackling the Higgs boson

Researchers building the world's next top particle accelerator, the Large Hadron Collider (LHC) that straddles the Franco-Swiss border, may not get a chance to work out the bugs before they fire up the machine in earnest.

The experiment is still on track to begin hunting for the long sought Higgs boson next March, says LHC project leader Lyn Evans of the European Organization for Nuclear Research (CERN). But a crucial upgrade of 16 superconducting magnets around the accelerator will likely prevent a full test run planned for this December, he says, meaning researchers will have to troubleshoot glitches on the fly. Under that scenario, "if we have any problems, we will have to stop and fix them," he says.

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