Astronomers work at the South Pole to take advantage of excellent viewing conditions. Cold, dry Antarctica will allow SPT to more easily detect the cosmic microwave background (CMB) radiation, the afterglow of the big bang, with minimal interference from water vapor. On the electromagnetic spectrum, the CMB falls somewhere between heat radiation and radio waves.
The CMB is largely uniform, but it contains tiny ripples of varying density and temperature. These ripples reflect the seeds that, through gravitational attraction, grew into the galaxies and galaxy clusters visible to astronomers today. The SPT's first key science project will be to study small variations in the CMB to determine if dark energy began to affect the formation of galaxy clusters by fighting against gravity over the past few billion years.
Galaxy clusters are groups of galaxies, the largest celestial bodies that gravity can hold together. "Our galaxy, the Milky Way, is in one of these clusters," Meyer said. "And these clusters of galaxies actually change with time."
The CMB allows astronomers to take snapshots of the infant universe, when it was only 400,000 years old. No stars or galaxies had yet formed. If dark energy changed the way the universe expanded, it would have left its "fingerprints" in the way it forced galaxies apart over the deep history of time. Different causes would produce a different pattern in the formation of galaxy clusters.
According to one idea, dark energy could be Albert Einstein's cosmological constant: a steady force of nature operating at all times and in all places. Einstein introduced the cosmological constant into his theory of general relativity to accommodate a stationary universe, the dominant idea of the day. If Einstein's idea is correct, scientists will find that dark energy was much less influential in the universe 5 billion years ago than it is today.
"Clusters weren't around in the early universe. They took a long time to evolve," Carlstrom said.
Another version of the dark energy theory, called quintessence, suggests a force that varies in time and space. Some scientists even suggest there is no dark energy at all, and that gravity merely breaks down on vast intergalactic scales.
To pinpoint when dark energy became important, SPT will use a phenomenon called the Sunyaev-Zeldovich effect, which distorts the CMB as it passes through the hot gas of intervening galaxy clusters. As the microwaves interact with gas in the clusters, some of the microwaves get kicked into a higher frequency. SPT will measure the slight temperature difference associated with the frequency change and produce an image of the gas in the cluster.
SPT can scan large regions of the sky quickly. Scientists expect it to detect thousands, or even tens of thousands, of galaxy clusters within a few years. "To get a meaningful constraint on dark energy through measuring galaxy clusters, you need something like this South Pole Telescope," Carlstrom said. "The cluster SZ [Sunyaev-Zeldovich] signals cover small patches in the sky relative to the intrinsic variations in the cosmic microwave background. To get the necessary resolution, you need a big telescope. Now we have one."
Senior members of the SPT team include William Holzapfel, Adrian Lee and Helmuth Spieler from the University of California at Berkeley and the Lawrence Berkeley National Laborator; Joe Mohr, from the University of Illinois at Urbana-Champaign; John Ruhl from Case Western Reserve University; Antony Stark, from the Harvard-Smithsonian Astrophysical Observatory; Matt Dobbs from McGill University; and Erik Leitch of NASA's Jet Propulsion Laboratory.
The CMB is largely uniform, but it contains tiny ripples of varying density and temperature. These ripples reflect the seeds that, through gravitational attraction, grew into the galaxies and galaxy clusters visible to astronomers today. The SPT's first key science project will be to study small variations in the CMB to determine if dark energy began to affect the formation of galaxy clusters by fighting against gravity over the past few billion years.
Galaxy clusters are groups of galaxies, the largest celestial bodies that gravity can hold together. "Our galaxy, the Milky Way, is in one of these clusters," Meyer said. "And these clusters of galaxies actually change with time."
The CMB allows astronomers to take snapshots of the infant universe, when it was only 400,000 years old. No stars or galaxies had yet formed. If dark energy changed the way the universe expanded, it would have left its "fingerprints" in the way it forced galaxies apart over the deep history of time. Different causes would produce a different pattern in the formation of galaxy clusters.
According to one idea, dark energy could be Albert Einstein's cosmological constant: a steady force of nature operating at all times and in all places. Einstein introduced the cosmological constant into his theory of general relativity to accommodate a stationary universe, the dominant idea of the day. If Einstein's idea is correct, scientists will find that dark energy was much less influential in the universe 5 billion years ago than it is today.
"Clusters weren't around in the early universe. They took a long time to evolve," Carlstrom said.
Another version of the dark energy theory, called quintessence, suggests a force that varies in time and space. Some scientists even suggest there is no dark energy at all, and that gravity merely breaks down on vast intergalactic scales.
To pinpoint when dark energy became important, SPT will use a phenomenon called the Sunyaev-Zeldovich effect, which distorts the CMB as it passes through the hot gas of intervening galaxy clusters. As the microwaves interact with gas in the clusters, some of the microwaves get kicked into a higher frequency. SPT will measure the slight temperature difference associated with the frequency change and produce an image of the gas in the cluster.
SPT can scan large regions of the sky quickly. Scientists expect it to detect thousands, or even tens of thousands, of galaxy clusters within a few years. "To get a meaningful constraint on dark energy through measuring galaxy clusters, you need something like this South Pole Telescope," Carlstrom said. "The cluster SZ [Sunyaev-Zeldovich] signals cover small patches in the sky relative to the intrinsic variations in the cosmic microwave background. To get the necessary resolution, you need a big telescope. Now we have one."
Senior members of the SPT team include William Holzapfel, Adrian Lee and Helmuth Spieler from the University of California at Berkeley and the Lawrence Berkeley National Laborator; Joe Mohr, from the University of Illinois at Urbana-Champaign; John Ruhl from Case Western Reserve University; Antony Stark, from the Harvard-Smithsonian Astrophysical Observatory; Matt Dobbs from McGill University; and Erik Leitch of NASA's Jet Propulsion Laboratory.
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