NSF-funded 10-m South Pole Telescope in Antarctica provides new support for the most widely accepted explanation of dark energy, the source of the mysterious force that is responsible for the accelerating expansion of the universe. Credit: Daniel Luong-Van, National Science Foundation

Analysis
of data from the National Science Foundation-(NSF) funded 10-m South
Pole Telescope (SPT) in Antarctica provides new support for the most
widely accepted explanation of dark energy, the source of the mysterious
force that is responsible for the accelerating expansion of the
universe.

The
results begin to hone in on the tiny mass of the neutrinos, the most
abundant particles in the universe, which until recently were thought to
be without mass.

The
SPT data strongly support Albert Einstein’s cosmological constant—the
leading model for dark energy—even though researchers base the analysis
on only a fraction of the SPT data collected and only 100 of the over
500 galaxy clusters detected so far.

“With
the full SPT data set we will be able to place extremely tight
constraints on dark energy and possibly determine the mass of the
neutrinos,” said Bradford Benson, an NSF-funded postdoctoral scientist
at the University of Chicago’s Kavli Institute for Cosmological Physics.

 

Benson presents the SPT collaboration’s latest findings, Sunday, April 1, at the American Physical Society meeting in Atlanta.

These
most recent SPT findings are only the latest scientifically significant
results produced by NSF-funded researchers using in the telescope in
the five years since it became active, noted Vladimir Papitashvili,
Antarctic Astrophysics and Geospace Sciences program director in NSF’s
Office of Polar Programs.

“The
South Pole Telescope has proven to be a crown jewel of astrophysical
research carried out by NSF in the Antarctic,” he said. “It has produced
about two dozen peer-reviewed science publications since the telescope
received its ‘first light’ on Feb. 17, 2007. SPT is a very focused,
well-managed, and amazing project.”

The
280-ton SPT stands 75 feet tall and is the largest astronomical
telescope ever built in Antarctica. Sited at NSF’s Amundsen-Scott South
Pole station at the geographic South Pole, it takes advantage of its
location at an elevation of 9,300 feet on the polar plateau; the clear
and dry air of Antarctica; and its ability from its location at the
Earth’s axis to to conduct long-term observations.

NSF
manages the U.S. Antarctic Program through which it coordinates all
U.S. scientific research on the southernmost continent and aboard ships
in the Southern Ocean as well as providing the necessary related
logistics support.

An
international research collaboration led by the University of Chicago
manages the South Pole Telescope. The collaboration includes research
groups at Argonne National Laboratory; Cardiff University in Wales; Case
Western Reserve University; Harvard University;
Ludwig-Maximilians-Universität in Germany; the Smithsonian Astrophysical
Observatory; McGill University in Canada; the University of California,
Berkeley; the University of California, Davis; the University of
Colorado Boulder; and the University of Michigan, as well as individual
scientists at several other institutions.

SPT
specifically was designed to tackle the dark-energy mystery. The 10-m
telescope operates at millimeter wavelengths to make high-resolution
images of Cosmic Microwave Background (CMB) radiation, the light left
over from the big bang.

Scientists
use the CMB to search for distant, massive galaxy clusters that can be
used to pinpoint the properties of dark energy and also help define the
mass of the neutrino.

“The
CMB is literally an image of the universe when it was only 400,000
years old, from a time before the first planets, stars and galaxies
formed in the universe,” Benson said. “The CMB has travelled across the
entire observable universe, for almost 14 billion years, and during its
journey is imprinted with information regarding both the content and
evolution of the universe.”

The
new SPT results are based on a new method that combines measurements
taken by the telescope and by NASA and European Space Agency X-ray
satellites, and extends these measurements to larger distances than
previously achieved.

The
most widely accepted property of dark energy is that it leads to a
pervasive force acting everywhere and at all times in the universe. This
force could be the manifestation of Einstein’s cosmological constant
that assigns energy to space, even when it is free of matter and
radiation.

Einstein
considered the cosmological constant to be one of his greatest blunders
after learning that the universe is not static, but expanding.

In
the late 1990s, astronomers discovered the universe’s expansion appears
to be accelerating according to cosmic distance measurements based on
the relatively uniform luminosity of exploding stars. The finding was a
surprise because gravity should have been slowing the expansion, which
followed the big bang.

Einstein
introduced the cosmological constant into his theory of general
relativity to accommodate a stationary universe, the dominant idea of
his day. But his constant fits nicely into the context of an
accelerating universe, now supported by countless astronomical
observations.

Others
hypothesize that gravity could operate differently on the largest
scales of the universe. In either case, the astronomical measurements
point to new physics that have yet to be understood.

As
the CMB passes through galaxy clusters, the clusters effectively leave
“shadows” that allow astronomers to identify the most massive clusters
in the universe, nearly independent of their distance.

“Clusters
of galaxies are the most massive, rare objects in the universe, and
therefore they can be effective probes to study physics on the largest
scales of the universe,” said John Carlstrom, the S. Chandrasekhar
Distinguished Service Professor in Astronomy & Astrophysics, who
heads the SPT collaboration.

“The
unsurpassed sensitivity and resolution of the CMB maps produced with
the South Pole Telescope provides the most detailed view of the young
universe and allows us to find all the massive clusters in the distant
universe,” said Christian Reichardt, a postdoctoral researcher at the
University of California, Berkeley and lead author of the new SPT
cluster catalog paper.

The
number of clusters that formed over the history of the universe is
sensitive to the mass of the neutrinos and the influence of dark energy
on the growth of cosmic structures.

“Neutrinos
are amongst the most abundant particles in the universe,” Benson said.
“About one trillion neutrinos pass through us each second, though you
would hardly notice them because they rarely interact with ‘normal’
matter.”

The
existence of neutrinos was proposed in 1930. They were first detected
25 years later, but their exact mass remains unknown. If they are too
massive they would significantly affect the formation of galaxies and
galaxy clusters, Benson said.

The
SPT team has has been able to improve estimates of neutrino masses,
yielding a value that approaches predictions stemming from particle
physics measurements.

“It
is astounding how SPT measurements of the largest structures in the
universe lead to new insights on the evasive neutrinos,” said Lloyd
Knox, professor of physics at the University of California at Davis and
member of the SPT collaboration. Knox will also highlight the neutrino
results in his presentation on Neutrinos in Cosmology at a special session of the APS on Tuesday, April 3.

NSF’s
Office of Polar Programs primarily funds the SPT. The NSF-funded
Physics Frontier Center of the Kavli Institute for Cosmological Physics,
the Kavli Foundation and the Gordon and Betty Moore Foundation provide
partial support.

Source: National Science Foundation