Astronomers receive $16.6 million to continue scrutiny of dark energy

John Carlstrom

Albert Einstein considered his famous cosmological constant to be the biggest mistake of his career, but these days, astronomers think he may have been right all along. A team of astronomers led by John Carlstrom, the S. Chandrasekhar Professor in Astronomy & Astrophysics and the College, plan to build a new telescope at the South Pole with $16.6 million from the National Science Foundation that will settle the issue once and for all.

The telescope will help scientists to reveal new details regarding a mysterious phenomenon called dark energy, which makes the expansion of the universe accelerate. Einstein’s “cosmological constant,” which is one possible explanation for the dark energy, will come under the telescope’s scrutiny.

Unlike the gravitational force of ordinary matter, the “gravity” of dark energy is repulsive. It overwhelms ordinary gravity and pushes the universe apart. Dark energy is invisible, but astronomers will be able to see its influence on clusters of galaxies that formed within the last few billion years.

South Pole Telescope

“With the South Pole Telescope we can look at when galaxy clusters formed and how they formed. That is critically dependent on the nature of the dark energy, this elusive component of the universe,” said Carlstrom. “We’ve only known about dark energy for a few years, but no one really knows what it is.”

Carlstrom’s partners in the project are Stephan Meyer, Professor in Astronomy & Astrophysics and the College; Clem Pryke, Assistant Professor in Astronomy & Astrophysics; Erik Leitch, Research Scientist in Astronomy & Astrophysics; and scientists at the University of Illinois, Urbana-Champaign; University of California, Berkeley; Case Western Reserve University; and the Harvard-Smithsonian Center for Astrophysics.

Also contributing to the project are Wayne Hu, Assistant Professor in Astronomy & Astrophysics, and Andrey Kravtsov, Assistant Professor in Astronomy & Astrophysics. The University’s Center for Cosmological Physics provided seed funding for the project.

“One of our main goals is to figure out what the dark energy is,” said center Director Bruce Winstein, the Samuel K. Allison Distinguished Service Professor in Physics. “Is it a cosmological constant or is it dynamical? The South Pole Telescope holds the promise to give us a lot of new, valuable information on this.”

Understanding dark energy is one of the key scientific questions called out in the Astronomical Decadal Survey. In the survey, astronomers identified a South Pole telescope as one of their highest-priority projects for the next 10 years.

The telescope will measure eight meters (26.4 feet) in diameter and will operate at submillimeter wavelengths, between microwaves and the infrared on the electromagnetic spectrum. The Berkeley scientists will lead the effort to construct the telescope’s array of 1,000 bolometers (heat detectors). “This will be the largest bolometric array yet built,” Carlstrom said.

The bolometers will be sensitive enough to measure temperature differences in the sky with an accuracy of 10 millionths of a degree. The background temperature of the universe is so cold–hundreds of degrees below zero–that even ice is hot by comparison.

The telescope will be located at the National Science Foundation’s South Pole Station to take advantage of Antarctica’s clear, dry skies.

The new telescope is scheduled to become operational in four years. Its first key science project will be to search one-tenth of the sky for the Sunyaev-Zel’dovich effect in galaxy clusters.

The S-Z effect is created when the cosmic microwave background radiation, the afterglow of the big bang, passes through the gas contained within galaxy clusters. As the microwaves interact with the gas in the clusters, some of the microwaves change in frequency. The South Pole Telescope will measure the slight temperature difference associated with the frequency change and produce an image of the gas in the cluster.

By the end of the telescope’s first year of operation, scientists expect to be able to confirm or disprove the validity of Einstein’s cosmological constant. If Einstein’s idea is correct, the telescope team will find that dark energy was a less influential force in the universe 5 billion years ago than it is today.

The National Science Foundation, the McDonnell Foundation, the Packard Foundation and the Center for Cosmological Physics fund the SZA.