THE FUNDAMENTAL PHYSICIST INVESTIGATES THE UNIVERSE

FROM:  NATIONAL SCIENCE FOUNDATION 
Scientist who helped discover the expansion of the universe is accelerating
Breakthrough Prize winner continues investigating fundamental physics of the world
February 3, 2015

In the late 1980s, astrophysicist Saul Perlmutter and his colleagues set out to determine how much the expansion of the universe was slowing. At the time, the prevailing belief among scientists was that gravity would be slowing the expansion, perhaps enough to ultimately switch to a contracting universe that would cause the galaxies to draw even closer together.

Of course, the world learned in 1998 that this was not the case. As it turned out, the expansion of the universe was, in fact, not slowing at all, but speeding up.

"That means there is something else going on besides gravity," says Perlmutter, director of the Supernova Cosmology Project at Lawrence Berkeley National Laboratory, who shared the 2011 Nobel Prize in physics for the work. "We thought we understood the physics, but this was a real surprise."

The "something else" is an enduring mystery that continues to fascinate, and elude, scientists today, Perlmutter among them. Astrophysicists refer to it as "dark energy."

"We call it 'dark' because we don't know what it is," he says. "But it possibly means that as much as 70 percent of the universe could be made out of this previously unknown energy."

Moreover, researchers don't know why the universe is speeding up. "But it leaves the possibility that if whatever is speeding it up goes away, then it will start to slow down again," he says. "There is still a lot in play, and we are still trying to learn what it is."

It's an exciting prospect, since research into the ongoing puzzle of dark energy could provide "a new understanding of the fundamental physics of the world," Perlmutter says. "We have no idea what the consequences will be if we learn what dark energy is. But history has shown us that these kinds of steps forward in our fundamental understanding make us a more capable civilization.

"Moreover, learning how this world is put together, in a way, is a deep, almost poetic experience," he adds.

Perlmutter, also a professor of physics at the University of California, Berkeley, is a recent recipient of the 2015 Breakthrough Prize in Fundamental Physics, sharing the $3 million award with his Supernova Cosmology Project team, and with Brian P. Schmidt, an astrophysicist at the Australian National University Mount Stromlo Observatory and Research School, and Adam Riess, an astrophysicist at The Johns Hopkins University and the Space Telescope Science Institute, and the High-Z Supernova Search team that they led.

The three, who also shared the 2011 Nobel, received the Breakthrough Prize together with their teams for their work providing evidence that the expansion of the universe is accelerating.

For Perlmutter, the research leading to this discovery began in 1987, with a project under the auspices of the newly created Center for Particle Astrophysics, a National Science Foundation science and technology center based at Berkeley. Perlmutter, a postdoctoral fellow at the time, designed the study with Carl Pennypacker, also a researcher in the group which was then under the direction of physics professor Richard Muller, a 1978 NSF Alan T. Waterman award winner.

"When the project began in 1987, the standard picture of cosmology was that the universe was expanding, but everyone assumed it would slow down because gravity would attract everything to everything else," Perlmutter says. "We wanted to find out: How dense is the universe? How much is it slowing down?"

The scientists decided to try to measure the state of the universe by looking several billion years in the past using a new understanding in the field about a specific type of supernova, or exploding star, called Type Ia, that explodes in a similar way every time. "Since they brighten to essentially the same brightness every time, and then fade away, we can tell how far away they are by measuring how bright they appear to us," he says.

Since light always travels at 186,000 miles per second, researchers can then use the distance measurement to calculate how long ago these supernovae exploded. Also, while the light is traveling--and the universe is expanding--the light waves traveling from the exploding supernova stretch along with everything else. As these wavelengths stretch, they look redder and redder, a phenomenon in astronomy known as "redshift."

"When the supernova explodes, it sends out mostly blue light," Perlmutter explains. "That blue light means a short wave length of light. The more it stretches, the more it starts to turn red. And that tells us the amount the universe stretched between the time of the explosion, and today."

Taken together, the brightness and colors of the supernovae provide compelling evidence of an accelerating expanding universe. The degree of their brightness reveals how far back in time the star exploded, and the extent of redshift indicates how much the universe has expanded during that time. So a series of measurements each taken for a supernova exploding at a different time throughout history--7, 4 and 2 billion years ago--revealed that the stretching of the universe was increasing, and that it wasn't slowing down at all.

The difficulty initially was finding these supernovae in time, since they are rare and random, and reserving a stint at some of the largest and most advanced telescopes in the world, not to mention hoping for good weather.

Ultimately, they found a way to make discovering Type Ia supernovae more predictable.

"Instead of watching one galaxy, we figured out how to use novel wide-field cameras on the big telescopes to watch thousands of galaxies," he says. "You take a bunch of images one night, then go away, then come back two and half weeks later and take another bunch of images. Now you have two almost identical images of the galaxies, but with a time gap just long enough to allow a new supernova to appear."

"Everything had to happen like clockwork, and anytime the night was cloudy, you'd have to scramble to cover that time another night someplace else," he says.

The researchers developed a special computer program "to hunt through thousands of specks of light to find a new speck that wasn't there before," that is, looking for a new supernova. Then, using a spectrograph, they analyzed the light waves to determine whether the supernova was a Type Ia, the type they needed to study. Finally, they ran a series of observations following the supernova, obtaining images four to six more times as it brightened, then faded, which told them how bright it was at its peak.

"When we started the project, I thought we were just going out and doing a simple measurement of the brightness of exploding stars, and finding out whether the universe was going to end," he says. "It turned out that what we discovered was a huge surprise. We have been comparing it to throwing an apple up in the air, and finding that it doesn't fall back to earth, but instead blasts off into outer space, mysteriously moving faster and faster."

-- Marlene Cimons, National Science Foundation
Investigators
Saul Perlmutter
Related Institutions/Organizations
University of California-Berkeley

NASA, ESA JOIN TOGETHER TO STUDY THE DARK SIDE

Astronomers using NASA's Hubble Space Telescope took advantage of a giant cosmic magnifying glass to create one of the sharpest and most detailed maps of dark matter in the universe. Dark matter is an invisible and unknown substance that makes up the bulk of the universe's mass. Credit: NASA, ESA, and D. Coe (NASA JPL/Caltech and STScI)

FROM: NASA
NASA Joins ESA's 'Dark Universe' Mission

WASHINGTON -- NASA has joined the European Space Agency's (ESA's) Euclid mission, a space telescope designed to investigate the cosmological mysteries of dark matter and dark energy.

Euclid will launch in 2020 and spend six years mapping the locations and measuring the shapes of as many as 2 billion galaxies spread over more than one-third of the sky. It will study the evolution of our universe, and the dark matter and dark energy that influence its evolution in ways that still are poorly understood.

The telescope will launch to an orbit around the sun-Earth Lagrange point L2. The Lagrange point is a location where the gravitational pull of two large masses, the sun and Earth in this case, precisely equals the force required for a small object, such as the Euclid spacecraft, to maintain a relatively stationary position behind Earth as seen from the sun.

"NASA is very proud to contribute to ESA's mission to understand one of the greatest science mysteries of our time," said John Grunsfeld, associate administrator for NASA's Science Mission Directorate at the agency's Headquarters in Washington.

NASA and ESA recently signed an agreement outlining NASA's role in the project. NASA will contribute 16 state-of-the-art infrared detectors and four spare detectors for one of two science instruments planned for Euclid.

"ESA’s Euclid mission is designed to probe one of the most fundamental questions in modern cosmology, and we welcome NASA’s contribution to this important endeavor, the most recent in a long history of cooperation in space science between our two agencies," said Alvaro Giménez, ESA’s Director of Science and Robotic Exploration.

In addition, NASA has nominated three U.S. science teams totaling 40 new members for the Euclid Consortium. This is in addition to 14 U.S. scientists already supporting the mission. The Euclid Consortium is an international body of 1,000 members who will oversee development of the instruments, manage science operations, and analyze data.

Euclid will map the dark matter in the universe. Matter as we know it -- the atoms that make up the human body, for example -- is a fraction of the total matter in the universe. The rest, about 85 percent, is dark matter consisting of particles of an unknown type. Dark matter first was postulated in 1932, but still has not been detected directly. It is called dark matter because it does not interact with light. Dark matter interacts with ordinary matter through gravity and binds galaxies together like an invisible glue.

While dark matter pulls matter together, dark energy pushes the universe apart at ever-increasing speeds. In terms of the total mass-energy content of the universe, dark energy dominates. Even less is known about dark energy than dark matter.

Euclid will use two techniques to study the dark universe, both involving precise measurements of galaxies billions of light-years away. The observations will yield the best measurements yet of how the acceleration of the universe has changed over time, providing new clues about the evolution and fate of the cosmos.

Euclid is an ESA mission with science instruments provided by a consortia of European institutes and with important participation from NASA. NASA's Euclid Project Office is based at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif. JPL will contribute the infrared flight detectors for the Euclid science instrument. NASA's Goddard Space Flight Center in Greenbelt, Md., will test the infrared flight detectors prior to delivery. Three U.S. science teams will contribute to science planning and data analysis.

ANTARCTIC TELESCOPE SUPPORTS EXPLANATION OF DARK ENERGY FORCE

FROM NATIONAL SCIENCE FOUNDATION
Credit: Daniel Luong-Van, National Science Foundation

NSF-funded 10-meter 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.

April 2, 2012
Analysis of data from the National Science Foundation- (NSF) funded 10-meter 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 presented 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 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 the clear and dry air of Antarctica. Sited at NSF's Amundsen-Scott South Pole station at the geographic South Pole, it stands at an elevation of 9,300 feet on the polar plateau. Because of its location at the Earth's axis, it can 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-meter 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 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.