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DarkSide-50 experiment on BBC
February 6, 2013
BBC World Service
BBC World Service gives a tour "inside" the DarkSide-50 detector. The experiment, ready to be assembled at National Laboratory of Gran Sasso, is searching for Dark Matter interactions in a low background two-phase Time Projection Chamber featuring 50 kg of Underground Argon as the sensitive target. To further suppress the background the liquid argon detector will be fully immersed in a liquid scintillator and surrounded by a large water Cherenkov detector working as active vetoes. The commissioning of the detector is expected to start in about two weeks.Learn more >>
Alpha Magnetic Spectrometer to release first results
February 18, 2013
BBC News Science & Environment
The scientist leading one of the most expensive experiments ever put into space says the project is ready to come forward with its first results.
The Alpha Magnetic Spectrometer (AMS) was put on the International Space Station to survey the skies for high-energy particles, or cosmic rays.
Nobel Laureate Sam Ting said the scholarly paper to be published in a few weeks would concern dark matter.
This is the unseen material whose gravity holds galaxies together.
Researchers do not know what form this mysterious cosmic component takes, but one theory points to it being some very weakly interacting massive particle (or Wimp for short).
Although telescopes cannot detect the Wimp, there are high hopes that AMS can confirm its existence and describe some of its properties from indirect measures.
The imminent publication in an as yet undetermined journal will detail the progress of that investigation.
The Massachusetts Institute of Technology professor said the project he first proposed back in the mid-1990s had now reached an important milestone.
"We've waited 18 years to write this paper, and we're now making the final check," he told reporters.
"I would imagine in two or three weeks, we should be able to make an announcement.
"We have six analysis groups to analyse the same results. Physicists as you know - everybody has their own interpretations, and we're now making sure everyone agrees with each other. And this is pretty much done now."
Sam Ting was speaking here in Boston at the annual meeting of the American Association for the Advancement of Science (AAAS).
$2bn machine to 'probe the unknown'
His $2bn machine was taken up to the ISS in 2011 - on the final mission of Shuttle Endeavour.
The seven-tonne experiment holds a giant, specially designed magnet that bends the paths of particles that fall on it.
The way they bend reveals their charge, a fundamental property that, together with information about their mass, velocity and energy, garnered from a slew of detectors, tells scientists precisely what they are dealing with.
Prof Ting said that in its first 18 months of operation, AMS had witnessed 25 billion particle events.
Of these, nearly eight billion were fast-moving electrons and their anti-matter counterparts, positrons.
Colliding and annihilating Wimps ought to produce showers of these electrons and positrons. And it is by measuring the ratio of the latter to the former, and the behaviour of any excess across the energy spectrum, which may provide a way into the dark matter problem.
"The smoking gun signature in the positron to electron ratio is a rise and then a dramatic fall. That is the key signature for the dark matter annihilation in our galaxy's halo," observed Prof Michael Turner from the Kavli Institute for Cosmological Physics, University of Chicago. Prof Turner is not part of the AMS Collaboration.
"Also in this energy regime, is there anisotropy? Do the positrons come from a fixed direction or all directions?" Prof Ting pondered to the BBC.
"Dark matter is supposed to be everywhere. So if we see the positrons coming from a particular direction, it means astrophysics like a pulsar (a type of neutron star) is responsible for the signal, not dark matter."
The AMS paper will report the positron-electron ratio in the mass range of 0.5 to 350 Gigaelectronvolts. This covers territory at the top end where some other experiments have already reported tantalising hints of dark matter.
Prof Turner said science was closing in on its quarry.
He predicted the next few years would be remembered as the "decade of the Wimp", and looked forward to dark matter's properties being exposed via a number of investigation strands that included Wimp production at the Large Hadron Collider (LHC).
"Theory says that this particle might weigh somewhere between 30, 40 and 300 times what the proton does, so somewhere between 30 and maybe 1,000 GeV.
"The LHC can produce particles of that mass, Sam Ting's AMS detector can see particles of that mass annihilating, and then the detectors deep underground are also sensitive to particles of this mass.
"If we get very lucky, if Santa answers our wish-list, we could get a triple signature of the dark matter particle, by seeing the annihilations, by directly detecting it, by producing it at the LHC - all three of these methods are sensitive across the same mass range."Learn more >>
'Nuisance' data lead to surprising star-birth discovery
March 13, 2013
The University of Chicago News Office
When a batch of bright cosmic objects first appeared in maps in 2008 made with data from the South Pole Telescope, astronomers at the University of Chicago's Kavli Institute for Cosmological Physics regarded it only as an unavoidable nuisance.
The light sources interfered with efforts to measure more precisely the cosmic microwave background-the afterglow of the big bang. But the astronomers soon realized that they had made a rare find in South Pole Telescope's large survey of the sky. The spectra of some of the bright objects, which is the rainbow of light they emit, were inconsistent with what astronomers expected from the well-known population of radio galaxies.
Instead they looked like dust-enshrouded, star-forming galaxies. Such galaxies should be easily identified in infrared sky surveys, but there were no known counterparts for what the South Pole Telescope had found. They had to be extremely distant to avoid infrared detection, and therefore extremely luminous. Intrigued, the astronomers performed detailed follow-up imaging of the sources with the new Atacama Large Millimeter Array (ALMA) in Chile's Atacama Desert. These observations show the dust-filled galaxies were bursting with stars much earlier in cosmic history than previously thought.
Joaquin Vieira, now a postdoctoral scholar at the California Institute of Technology, leads a team that will report the discovery in the March 13 issue of the journal Nature and in two other papers that will appear in the Astrophysical Journal.
"We have been eagerly waiting for ALMA to be ready so we could conduct these observations," said Vieira, MS'05, PhD'09, who based his doctoral research at UChicago on the discovery of the extragalactic sources. "The sources we discovered with the South Pole Telescope were so far in the southern sky that no telescopes in the Northern Hemisphere could observe them. We are very privileged to be among the first astronomers to use ALMA."
Vieira has supported the South Pole Telescope from the beginning, helping to build the telescope and its camera, said John Carlstrom, S. Chandrasekhar Distinguished Service Professor in Astronomy & Astrophysics at UChicago. "He's been involved from the ground up, or the ice up, if you will," said Carlstrom, who leads the SPT collaboration and is a co-author of the Nature paper.
Prodigious star production
The starburst galaxies produce stars at a prodigious rate, creating the equivalent of a thousand new suns annually. Vieira and his colleagues have found starbursts that were churning out stars when the universe was just a billion years old. Previously astronomers were unsure whether galaxies could form new stars so quickly at this very early point in the history of the universe.
Shining with the energy of a trillion suns or more, these newly discovered galaxies are observed as they were nearly 12 billion years ago, showing us a representative baby picture of the most massive galaxies in Earth's cosmic neighborhood today. "The more distant the galaxy, the further back in time one is looking, so by measuring their distances, we can piece together a timeline of how vigorously the universe was making new stars at different stages of its 13.7-billion-year history," Vieira said.
The astronomers found dozens of these galaxies with the South Pole Telescope, a 10-meter dish in Antarctica that surveys the sky in millimeter-wavelength light (situated between radio and the infrared on the electromagnetic spectrum). The team then took a more detailed look using ALMA in Chile. "These aren't normal galaxies," Vieira said. "They're forming stars at an extraordinary rate when the universe was very young - we were very surprised to find galaxies like this so early in the history of the universe."
The new observations represent some of ALMA's most significant scientific results yet, Vieira said. "We couldn't have done this without the combination of the South Pole Telescope and ALMA," he added. "ALMA is so sensitive, it is going to change our view of the universe in many different ways."
The astronomers used only 16 of 66 dishes that will eventually come online for ALMA, which is the most powerful telescope observing in millimeter and sub-millimeter wavelengths. ALMA began observing last year.
ALMA data analysis
Analysis of the ALMA data showed that more than 30 percent of the new galaxies existed just a billion years after the big bang. Only nine such galaxies were known previously. The number of such galaxies now has nearly doubled, providing valuable data that will help other researchers constrain and refine computer models of star and galaxy formation in the early universe.
Vieira's team directly determines the distance of these dusty starburst galaxies from emission from their gas and dust itself. Astronomers previously had to rely on a cumbersome combination of indirect optical and radio observations using multiple telescopes to study the galaxies. But ALMA's unprecedented sensitivity and ability to measure spectra enabled the astronomers to make their observations and analyze them directly in one step. As a result, the new distances are more reliable and represent the best sample yet of this population of early galaxies.
The unique properties of these objects also enabled the measurements. First, the observed galaxies happened to be gravitationally lensed - a phenomenon predicted by Einstein in which another galaxy in the foreground bends the light from the background galaxy like a magnifying glass. This lensing effect makes the background galaxies appear brighter, cutting the amount of telescope time needed to observe them by 100 times.
Second, the astronomers took advantage of a fortuitous feature of these galaxies' spectra. Normally, more distant galaxies appear dimmer. But it turns out that the expanding universe shifts the emitted spectra in such a way that the light we receive at millimeter wavelengths is not diminished for sources that are more distant from us. Consequently, the galaxies appear just as bright in these wavelengths no matter their distance.
The new results represent approximately a quarter of the total number of sources that Vieira and his colleagues discovered with the South Pole Telescope. They anticipate finding more of the dusty starburst galaxies and expect some to be from even earlier times in the universe as they continue analyzing their data.
UChicago scientists contributing to the March 13 Nature paper are faculty members John Carlstrom, Mike Gladders and Steve Meyer; senior researchers Bradford Benson, Clarence Chang, Tom Crawford and Kathryn Schaffer; associate fellows Will High, Stephen Hoover, Ryan Keisler and Tom Plagge; associate Steve Padin; research associate Keren Sharon; and graduate students Lindsey Bleem, Monica Mocanu, Tyler Natoli and Kyle Story.
The South Pole Telescope is funded primarily by the National Science Foundation's Office of Polar Programs. Partial support also is provided by the NSF-funded Physics Frontier Center of UChicago's Kavli Institute for Cosmological Physics, the Kavli Foundation, and the Gordon and Betty Moore Foundation.Learn more >>
Spotlight Roundtable: Witnessing Starbursts in Young Galaxies
March 13, 2013
The Kavli Foundation
Three leading scientists discuss how the world's most powerful radio telescope revealed that the most vigorous bursts of star birth in the cosmos took place much earlier than previously thought.
IN THE EARLY UNIVERSE, new stars were bursting to life at rates far higher than we see today. The Milky Way today may fire up one new star every year; but billions of years ago, a subset of galaxies in the relatively young universe were producing new stars at a rate of 1,000 per year.
Now, a multi-national team of astronomers has found that these distant, dusty galaxies were churning out stars much earlier than once believed - as early as one billion years after the Big Bang, nearly 13 billion years ago. Their study was published online on March 13 by the journal Nature. (Press releases: California Institute of Technology, ESO, KICP/University of Chicago, University of Arizona)
Measuring just how far away these galaxies are, and examining the rapid star formation going on inside them, was no trivial feat. Armed with a catalog of galaxies discovered by the South Pole Telescope (SPT), the astronomers used some fortuitous natural phenomena and the great resolving power of the Atacama Large Millimeter/submillimeter Array, or ALMA - an array of radio antennas situated on a high plateau in the Atacama Desert of Northern Chile - to learn about some of the most distant star-forming galaxies.
Three members of the team spoke recently with The Kavli Foundation in a roundtable discussion about their discovery and what they plan next. The participants:
* John E. Carlstrom - Subrahmanyan Chandrasekhar Distinguished Service Professor in the Departments of Astronomy and Astrophysics as well as Physics at the University of Chicago, and Deputy Director of the UChicago's Kavli Institute for Cosmological Physics (KICP). Prof. Carlstrom is an observational cosmologist who studies the Cosmic Microwave Background (CMB). He is also leader of the 10-meter South Pole Telescope project, which recently completed a survey of 2,500 square degrees of the sky, and is now conducting a survey of the polarization of the CMB.
* Dan P. Marrone - Assistant Professor in the Department of Astronomy at the University of Arizona. Prof. Marrone is interested in galaxy clusters, galaxy formation in the early universe, and the physics of the supermassive black hole in our galaxy, Sagittarius A*.
* Joaquin D. Vieira - Postdoctoral Scholar at the California Institute of Technology and a member of Caltech's Observational Cosmology Group. Dr. Vieira is interested in studying galaxy evolution at very high redshifts, the first stars and galaxies, and the evolution of large-scale structures in the universe. He is the leader of the group studying the galaxies discovered by the South Pole Telescope.
The following is an edited transcript with remarks added by the participants.
THE KAVLI FOUNDATION: About a third of the galaxies that you observed in your study existed at extremely early times, when the universe was only about one billion years old. You must all have mental picture of what the early universe could have been like. How did your findings change your views about what was actually going on then?
JOAQUIN VIEIRA: My expectations before this study were more focused on what I thought we'd be able to detect, rather than what I thought the universe was like back then. We knew we'd be excited to find anything at a redshift greater than four.
To understand what that redshift measurement means, it's important to understand, by the time it reaches us, the wavelength of light from very distant galaxies is stretched by the expansion of the universe. The result is that the light spectrum of these galaxies - that is, the rainbow of colors that make up the overall light emitted by each galaxy - has been shifted toward the redder end of the electromagnetic spectrum, from the part that's visible to our eyes toward longer wavelengths of light that make up the infrared part.
By measuring how much the light from these galaxies has been shifted toward the infrared, we can calculate how far away they are and how far back in time they existed. That's where the word "redshift" comes from, and higher numbers in the redshift scale correspond to farther distances from Earth, and farther back in time.
Now, a redshift of 4 corresponds to a time more than 12 billion years ago, when the universe was about 1.6 billion years old. That light has been traveling for 12 billion light years and when we observe those galaxies, we aren't seeing them as they are, but as they were. Observing very distant galaxies is a way for us to observe the Universe in its infancy - to look back in time.
TKF: But ALMA has changed all that.
VIEIRA: It's changed everything. After making our observations with ALMA, we doubled the number of these dusty starburst galaxies above a redshift of four. When we first started planning the redshift survey with ALMA, we had already tried with four other observatories to measure redshifts for the SPT sources - and it was very difficult and very frustrating. We basically had no success at all. We were thinking that if we got just a handful of redshifts with ALMA, we would be really lucky. But in the end we got redshifts for 90-percent of the sources in our survey catalog - out to higher redshifts then we really thought was possible.
JOHN CARLSTROM: We did expect to see bright galaxies in the South Pole Telescope survey, but not the dusty star-forming galaxies that we found. Instead, we thought we'd detect the very bright centers of galaxies where jets of radiation are emitted from black holes. These phenomena, often referred to as radio sources, are pretty well known.
Before our observations with ALMA, Joaquin had catalogued galaxies detected by the South Pole Telescope. When he analyzed the spectra of these objects, he discovered that some of the sources appeared to be dominated by emission from dust. They were not in line with what you would expect from the well known population of radio sources. This was the first clue we were onto something interesting. Then Joaquin discovered there were no counterparts to these galaxies catalogued by infrared surveys of the sky. That was baffling. It meant that they had escaped detection in the infrared surveys. No one had predicted that we would see such a luminous population of dusty galaxies so far back.
DAN MARRONE: I agree with Joaquin and John that our ability to get redshifts for these galaxies was a surprise - and that's a testament to the power of ALMA. Previously, we had tried making observations at the same wavelengths with the southernmost observatory available, the Submillimeter Array in Hawaii, and we pointed the radio dishes basically at the horizon to watch these galaxies just barely come up over the dirt. We were able to see them, but we had no real hope of getting redshifts for them. We still couldn't really figure out how far away they were. We needed something like ALMA to pull that off.
TKF: John, I wanted to come back to something that you said earlier. You said it was a surprise for you to find these dusty star-forming galaxies at such early times. When we talk about "dusty, star-forming galaxies" do we mean galaxies that show elements other than hydrogen and helium? Like iron, carbon, silicon, etc.?
CARLSTROM: By "dusty" I do mean that. When stars form, they quickly enrich the gas surrounding them with heavier elements. And those elements then form dust particles, and the dust particles absorb the starlight and then re-radiate that as a thermal emission at much longer wavelengths. We refer to that thermal radiation at longer wavelengths as "dusty emission" because it's coming from the dust. But it is actually energy that is generated by the stars that form.
TKF: These early dusty galaxies were churning out stars, as your study says, at a rate of 1,000 stars per year - compared to about one star per year for the Milky Way and other galaxies in modern times. Why do we think that star formation was so much more vigorous in the early universe?
MARRONE: In the early universe, in general, a much larger fraction of the mass of galaxies was in gas. That alone pushes up the star formation rate.
The universe also was much smaller back then, so galaxies were much closer together. As a result, we expect that they were much more likely to have interacted with one another. And collisions between two galaxies will trigger bursts of star formation. Today, because of the expansion of the universe, galaxies are further apart on average and these interactions are much less common.
TKF: In your study, you note that these early galaxies you observed are shining with the energy of a trillion suns but have masses that are much less than that. This suggests that stars burned brighter back then. Was this finding a surprise, and what does it tell us about the character of stars at these early times?
VIEIRA: When stars form, they come in a wide range of masses, from much less than the Sun to tens of times more massive than the Sun. The most massive stars are incredibly bright, but they live very short lives before they become supernovae. The energy output we measure from these galaxies shows us that the most massive stars created in the starburst have not yet used up their fuel and exploded, though they will do so relatively soon.
TKF: The team took advantage of two natural phenomena to observe these galaxies in detail: one was that their light was magnified by the gravity of closer objects - a phenomenon known as gravitational lensing. But there was a second phenomenon that's a bit harder to understand, and it has to do with the fact that dusty galaxies are not dimmer the farther away they are. Why is this the case?
MARRONE: At wavelengths near 1 millimeter, the spectrum of dust is very interesting. It gets brighter very quickly as you look at shorter and shorter wavelengths. For example, the SPT observes these galaxies at 2 millimeters (and 1.4 and 3). If you look at a dusty galaxy at 2 millimeters and 1 millimeter wavelengths, it will be about 10 times brighter at 1 millimeter than at it is at 2 millimeters wavelength. That's for looking at the same galaxy (at the same redshift). Now imagine you look at two different galaxies at two different redshifts, but at the same wavelength. The light from the higher redshift (more distant) galaxy will have been stretched more, so you measure the light at, say, 2 millimeters wavelength, but the original wavelength will have been not 1 millimeter, but maybe 0.5 millimeters. It was 100 times brighter when it was emitted. Of course, because it's further away it looks fainter, just like a light bulb would look fainter across the street instead of in your house. But starting out so much brighter almost perfectly cancels that effect.
This is incredibly valuable for us. You have all these dusty galaxies existing throughout the history of the universe, and no matter how far away they are they're not really getting much dimmer when we look at these wavelengths. So, unlike at optical wavelengths, where distant galaxies get dimmer and dimmer and the deep sky ends up looking black, light from these dusty galaxies creates a mostly diffuse and flat infrared sky. And we call that the Cosmic Infrared Background.
TKF: And that's where ALMA comes in. It's used to measure the spectra of these dusty galaxies and determine how far away they actually are.
MARRONE: That's right. Because these dusty galaxies do not get any dimmer as they get farther away, we actually don't know where they are. But ALMA's sensitivity in measuring the spectra of each of these objects allows us to measure how much those spectra are shifted toward the redder end of the spectrum - and obtain precise redshifts.
TKF: Tell me about ALMA. How would you describe it?
CARLSTROM: ALMA is like a very high-powered telescope. Imagine you're looking through a large telescope; you need a finder scope on the side to see where you're pointing. That's because the field of view of the big telescope is so tiny. ALMA, like the big telescope, gives you this incredibly detailed image of whatever you're looking at, plus this beautiful spectroscopic capability. But it only looks a very tiny field of view.
TKF: So ALMA allows you to look much closer at galaxies already identified by the South Pole Telescope, which is being used to survey a large fraction of the sky, correct?
CARLSTROM: Yes. ALMA is most powerful when it's teamed up with other observatories that conduct surveys of huge swaths of the sky to identify interesting targets worthy of more detailed examination. It enables a detailed examination of extremely distant objects because it operates as an interferometer. That means its effective resolving power isn't equal to that of one antenna, but to an antenna that is the diameter of the entire array. So ALMA's 12-meter antennas, collectively, get orders of magnitude higher angular resolution than what you would get from the single 10-meter South Pole Telescope. As a result, ALMA gives us very, very detailed images.
TKF: So ALMA's role here was critical.
CARLSTOM: ALMA is designed to detect the exact same wavelengths of light in which the dusty galaxies were discovered by the South Pole Telescope. As a result, there was no doubt ALMA was seeing the same galaxies. Also, ALMA gives us very high spectral resolution, so we were able to analyze the light from these galaxies with great precision to identify carbon monoxide and other molecules. That told us about what's in those galaxies, but more importantly for our study, that level of detail allowed us to measure the shifting of that spectra toward the red part of the spectrum - the redshift. And measuring changes in this part of the spectrum is the way we could tell how far away these objects are.
TKF: The ALMA observatory isn't completed. Right now it has an array of about 16 antennas, but within a year or so it will have 66. How will this help you in the future?
MARRONE: With little more than a dozen antennas at ALMA, we were able to make very detailed images of these galaxies - and that was after just 2 minutes of observations per galaxy. When we were trying this with The Submillimeter Array in Hawaii - which has only eight antennas, each only half the size as the ones at ALMA - we were observing each galaxy for a couple of hours. Even then, we were not getting anything like the detail that ALMA gave us, though this is a little unfair to the SMA, since it had to look so low on the horizon to see our sources. When ALMA is completed, the observations we obtained for this first study are just going to be trivial. You almost feel bad using ALMA to look at them - the exposures are so fast. You want to give ALMA more of a challenge.
CARLSTROM: I would add that a key science goal for the James Webb Space Telescope is to study the very first galaxies that emerged in the universe. This telescope is regarded as the successor to the Hubble Space Telescope, and it's anticipated for launch in 2018. The studies we're doing with ALMA now are allowing us to get to a jumpstart on that whole quest.
TKF: In a way, what you have is the ultimate zoom camera, letting you see details about the early universe once unimaginable. Now that you've seen what ALMA can do, what are your next steps?
MARRONE: I'd really like to push ALMA to its full potential and examine individual star-forming regions within these galaxies. One of our galaxies, at a redshift of 5.7, is forming stars at a rate per unit area that's as high as anything we've ever observed in the entire universe. ALMA is going to make it possible for us to pick that apart, to resolve the individual star-forming regions that are giving us those incredible starbursts.
VIEIRA: Now that we have the redshifts for these galaxies, we can dig deeper into the spectra of these galaxies to find out what they're made of; we can do chemistry with them. We have a sample of about 100 galaxies, and so what we want to do is get redshifts for all of them. Then we can map out the redshift distribution of these sources in an unbiased way. We'll be looking at individual spectral lines in detail, and examining the chemical makeup of these galaxies - even from region to region within them. Future studies also will help us answer other important questions, such as how they formed. Did they form through mergers, or through the slow accretion of gas? How many stellar generations reside in these galaxies?
These questions are all really exciting, and answering them is eventually going to change our view of the universe. Right now we've only taken the first step.
- Winter, 2013Learn more >>
Michael S. Turner, The Nora and Edward Ryerson Lecture: Quarks and the Cosmos
May 2, 2013
The University of Chicago News Office
Pioneering University of Chicago cosmologist Michael S. Turner focuses his remarks on "the Chicago School of Cosmology," from Edwin Hubble and George Ellery Hale to the present. Hubble, SB 1910, PhD 1917, discovered that the universe consists of billions of galaxies and that it has been expanding since it began in a big bang. Hale was the first chairman of the University's Department of Astronomy and Astrophysics. He also founded Yerkes Observatory, which under his leadership developed the big reflecting telescopes that are the workhorses of optical astronomy today, making discoveries from the expanding universe to planets orbiting other stars. Turning to more recent times, Turner discusses efforts that started in the 1980s at UChicago to establish the new field of particle astrophysics and cosmology. At that time, the Chicago School, consisting primarily of the late David Schramm, Edward "Rocky" Kolb, the Arthur Holly Compton Distinguished Service Professor in Astronomy and Astrophysics, and Turner, was alone in pushing this idea. "Today this idea that there are deep connections between the very big and the very small is universally accepted, has propelled the field to its current prominence, and underpins our understanding of the universe," Turner said. "As we say at Chicago, ideas matter!" The Ryerson Lecture grew out of a 1972 bequest to the University by Nora and Edward L. Ryerson, a former chairman of the board of trustees. The lecture honors excellence in academic pursuits. A faculty committee selects the Ryerson Lecturer based on research contributions of lasting significance.Learn more >>
New dark matter detector begins search for invisible particles
May 7, 2013
The University of Chicago News Office
Scientists heard their first pops last week in an experiment that searches for signs of dark matter in the form of tiny bubbles.
They will need to analyze them further in order to discern whether dark matter caused any of the COUPP-60 experiment's first bubbles at the SNOLAB underground science laboratory in Ontario, Canada. Dark matter accounts for nearly 90 percent of all matter in the universe, yet it is invisible to telescopes.
"Our goal is to make the most sensitive detector to see signals of particles that we don't understand," said Hugh Lippincott, a postdoctoral scientist with Fermi National Accelerator Laboratory. Lippincott has spent much of the past several months leading the installation of the one-of-a-kind detector at SNOLAB, 1.5 miles underground.
COUPP, or the Chicagoland Observatory for Underground Particle Physics, is a dark-matter experiment funded by the Department of Energy's Office of Science. Fermilab managed the assembly and installation of the experiment's detector. Leading the experiment is Juan Collar of the Kavli Institute for Cosmological Physics at the University of Chicago.
"Operation of COUPP-60 at SNOLAB is the culmination of a decade of work at the University of Chicago and Fermilab," said Collar, an associate professor in physics. "This device has the potential to become the most sensitive dark matter detector in the world, for both modes of interaction expected from Weakly Interacting Massive Particles."
The COUPP-60 detector is a jar filled with 60 kilograms of purified water and CF3I - an ingredient found in fire extinguishers. The liquid in the detector is kept at a temperature and pressure slightly above the boiling point, but it requires an extra bit of energy to actually form a bubble. When a passing particle enters the detector and disturbs an atom in the clear liquid, it provides that energy.
Dark matter particles, which scientists think rarely interact with other matter, should form individual bubbles in the COUPP-60 tank.
"The events are so rare, we're looking for a couple of events per year," Lippincott said.
Other, more common and interactive particles such as neutrons are more likely to leave a trail of multiple bubbles as they pass through.
Over the next few months, scientists will analyze the bubbles that form in their detector to test how well COUPP-60 is working and to determine whether they see signs of dark matter. One of the advantages of the detector is that it can be filled with a different liquid, if scientists decide they would like to alter their techniques.
"We are already working on a 500-kilogram chamber, to be installed in the same site starting in 2015," Collar said.
The COUPP-60 detector is the latest addition to a suite of dark-matter experiments running at SNOLAB. Scientists run dark matter experiments underground to shield them from a distracting background of other particles that constantly shower Earth from space. Dark matter particles can move through the mile and a half of rock under which the laboratory is buried, whereas most other particles cannot.
Scientists further shield the COUPP-60 detector from neutrons and other particles by submersing it in 7,000 gallons of water.
Scientists first proposed the existence of dark matter in the 1930s, when they discovered that visible matter could not account for the rotational velocities of galaxies. Other evidence, such as gravitational lensing that distorts the view of faraway stars and the inability to explain how other galaxies hold together if not for the mass of dark matter, have improved scientists' case. Astrophysicists think dark matter accounts for about a quarter of the matter and energy in the universe. But no one has conclusively observed dark matter particles.
The COUPP experiment includes scientists, technicians and students from UChicago, Indiana University South Bend, Northwestern University, University of Valencia, Virginia Tech, Fermilab, Pacific Northwest National Laboratory and SNOLAB.
- This article was adapted from a Fermilab announcement:
http://www.fnal.gov/pub/presspass/press_releases/2013/Dark-Matter-Detector-2013.htmlLearn more >>
Clarence Chang to receive DOE's Early Career Research Program Funding
May 8, 2013
DOE's Office of Science
WASHINGTON, DC - DOE's Office of Science today announced that 61 scientists from across the nation will receive up to $15.3 million in funding for research as part of DOE's Early Career Research Program. The effort, now in its fourth year, is designed to bolster the nation's scientific workforce by providing support to exceptional researchers during the crucial early career years, when many scientists do their most formative work.
"By providing support to the most creative and productive researchers in their early career years, this program is helping to build and sustain America's science workforce," said Patricia M. Dehmer, Acting Director of DOE's Office of Science. "We congratulate this year's winners on having competed successfully for these very selective awards, and we look forward to following their accomplishments over the next five years."Learn more >>
Polarization detected in Big Bang's echo
July 25, 2013
B-mode signal provides a way for astronomers to calculate neutrino masses.
Astronomers have detected a long-predicted polarization signal in the ripples of the Big Bang. The signal, known as B-mode polarization, is caused by the gravitational tug of matter on microwave photons left over from the Big Bang.
Its detection, posted this week to the arXiv preprint server and made by a microwave telescope at the South Pole, raises hopes that the signal can be used to map out the matter content of the Universe and determine the masses of the three types of neutrinos - in effect, using astronomy to achieve a key goal of particle physics. The detection also suggests that it might be possible to detect another type of B-mode, which would be evidence that the Universe, in the moment after the Big Bang, underwent a wrenching expansion known as inflation.
"The reason no one's been able to see this before is that it is a very small signal - about 1 part in 10 million," says Duncan Hanson, an astrophysicist at McGill University in Montreal, Canada, who led the work, which used ultrasensitive microwave receivers on the 10-metre South Pole Telescope (SPT). In comparison, the first measurements of ripples in the cosmic microwave background, released in 1992 by researchers using the NASA Cosmic Background Explorer satellite, was sensitive to differences of 4 parts in 100,000.
Other instruments are also seeking to detect B-modes, including the POLARBEAR experiment and the Atacama Cosmology Telescope (ACT), both in Chajnantor, Chile.
"They beat us, and hats off to them," says Lyman Page, an astronomer at Princeton University in New Jersey and principal investigator for the ACT. "It's intrinsically a neat signal and we all believe it will become an important tool for measuring the contents of the Universe."
David Spergel, a theoretical astrophysicist also at Princeton, agrees. "It's the first time polarization has been used to trace out large-scale structure in the Universe," he says.
The SPT was switched on in 2007 and has used the cosmic microwave background to map out the positions of galaxies and star clusters. Its sensitive microwave receivers were installed in 2012 and were able to detect variations in the B-mode signal across very small scales on the sky, says John Carlstrom, an astrophysicist at the University of Chicago in Illinois and principal investigator of the SPT. To use the signal to pin down the masses of neutrinos, which make up an unknown proportion of the matter being mapped, astronomers will have to survey a patch of sky much larger than the 100 square degrees mapped by the SPT. Still, Carlstrom says it is not implausible that telescopes will determine the neutrino mass in the next few years, before planned particle-physics experiments attempt to do the same thing with beams of neutrinos on Earth.
Yet the ultimate goal of the microwave-polarization experiments is not to do particle physics but cosmology. They are chasing a different class of 'primordial' B-modes, which are thought to have been generated by the fast expansion of space during inflation. Any detection would be a definitive confirmation of inflation - one of the core theories of cosmology - and would fix its energy scale, which would be useful to physicists working to develop theories of quantum gravity. But primordial B-modes would exist as tiny variations on large scales of more than 1 degree across - too large for the SPT to find statistical significance with the relatively small patch of sky it surveyed. The European Space Agency's Planck satellite, which surveys the whole sky, might be able to make them out. It is also possible that they will be discernible in smaller data sets such as the SPT's once the gravitational B-modes have been mapped and removed, to potentially reveal any primordial signal beneath. The latest observation from the SPT suggests that this approach to detecting B-modes is a good prospect, says Spergel. "It's a good sign that they've measured this from the ground."Learn more >>
B-mode polarization spotted in cosmic microwave background
July 25, 2013
The South Pole Telescope (SPT) has made the first detection of a subtle twist in light from the cosmic microwave background (CMB), known as B-mode polarization. The signal, the existence of which has been long predicted, paves the way for a definitive test of inflation - a key theory in the Big Bang model of the universe.
"While this effect was fully expected, its detection is a milestone event in the use of the CMB to probe our universe," says Chuck Bennett, a leading expert in CMB observation based at Johns Hopkins University in Maryland, US, who was not involved with the study. "It is solid research and I believe the result."
Often called the afterglow of the Big Bang, the CMB is thought to have originated some 380,000 years into the life of the universe when neutral atoms first formed and space became transparent to light. Roughly speaking, it consists of microwaves with a temperature of about three kelvin, but it also contains details that have helped to refine our understanding of the early universe. The most noticeable of these details are variations in temperature of about 100 μK, which reveal density fluctuations in the early universe - the seeds of the stars and galaxies that we see today.
Polarized by scattering
The CMB does not only contain variations in temperature, however. Its radiation was scattered towards us from the universe's earliest atoms in the same way that blue light is scattered towards us from the atoms in the sky. And in the same way that the blue light from the sky is polarized - a fact you can check by wearing polarized sunglasses - so too is the light from the CMB polarized. Variations in CMB polarization were first detected in 2002 by the DASI interferometer in Antarctica and helped cosmologists understand the dynamics of the early universe.
These polarization variations were known as E-mode or gradient variations because they describe how the magnitude of polarization changes over the CMB. But there are even subtler variations known as B-mode variations, which describe the rotation or "curl" of CMB polarization. The majority of B-mode polarization is produced by galaxies acting as gravitational lenses, twisting the E-polarized light on its 14-billion-year journey from the other side of the observable universe. It is incredibly faint, producing temperature variations of about 0.4 μK and accounting for just one part in 10 million in the CMB temperature distribution. "B-mode polarization is very difficult to measure," says Duncan Hanson, a member of the SPT team who is based at McGill University in Canada.
The SPT has managed to detect B-mode polarization largely thanks to improvements in detector technology. Although the detection will probably have little application, it opens new doors in experimental cosmology. With more precision, B-mode signals could help cosmologists place tougher constraints on neutrino masses, which cannot be predicted in the Standard Model of particle physics.
But the biggest prize would be using B-mode signals to uncover evidence of primordial gravitational waves - gargantuan ripples in space-time. Such ripples are predicted to have been generated in inflation, a brief period prior to the formation of the CMB when the universe is thought to have undergone rapid expansion and given birth to large-scale structures.
Although most cosmologists today believe in inflation, the theory lacks crucial details such as how it started and stopped and there has been no way to test it. A detection of primordial gravitational waves would be strong evidence for the existence of inflation, which was first proposed back in 1980 by the American physicist Alan Guth.
"This possibility of detecting B modes from gravitational waves is a remarkable enough possibility that it is driving numerous experimental efforts," says cosmologist Arthur Kosowsky at the University of Pittsburgh in Pennsylvania, US. "SPT is the first to detect any B modes, [and now] several other experiments are in hot pursuit, so this is the first leg in what is shaping up to be an exciting race to the finish line over the next decade."
Others are looking
Gravitational-wave B modes could be detected by the European Space Agency's Planck observatory, which orbits the Earth, although the toughest competition will come from the BICEP telescope, which sits alongside the SPT, or the POLARBEAR or ACT telescopes in northern Chile. If the discovery is made by one of the ground-based telescopes it would continue the tradition of ground-based experimental cosmology firsts that began with the discovery of the CMB, made by the American astronomers Arno Penzias and Robert Wilson with the horn antenna at Bell Labs in Holmdel Township in New Jersey, US, in 1964.
"Results come out from space, and there's lots of press and beautiful results, and the ground-based work tends to get forgotten," says John Carlstrom, the principle investigator on the SPT team who is based at the University of Chicago in Illinois, US. "But the ground-based telescopes, balloons and short-duration flights are an extremely important part of the [experimental] program and have led the way consistently since the beginning. And they still do."
The discovery is described in the preprint arXiv:1307.5830.Learn more >>
Fermilab-University investigators receive $225,000 in collaborative seed grants
August 7, 2013
Three teams of University and Fermi National Accelerator Laboratory researchers - one group that includes a researcher from Argonne National Laboratory - recently received $225,000, collectively, in Strategic Collaborative Initiative (SCI) seed grants from the University following a rigorous competition managed by Fermilab and the University. One of the teams received second-year funding. The FY 2013 recipients include:
- "An advanced, five orders of magnitude dynamic range, wafer-scale pixel system for X-ray science", University of Chicago Investigator: John Keith Moffat, Louis Block Professor of Biochemistry and Molecular Biology; Fermilab Investigator: Grzegorz Deptuch, Engineer IV, Particle Physics Division; Argonne Investigator: Robert Bradford, Assistant Physicist, X-ray Science Division.
- "Development of low noise electronics for the first direct Dark Matter search using CCDs" (funded for a second year), University of Chicago Investigator: Paolo Privitera, Professor of Astronomy and Astrophysics; Fermilab Investigators: Juan Estrada, Scientist II, Participles Physics Division and Gustavo Cancelo, Engineer IV, Scientific Computing Division.
- "SCENE: SCintillation Efficiency of Noble Elements", University of Chicago Investigator: Luca Grandi, Assistant Professor of Physics; Fermilab Investigator: Stephen Pordes, Scientist II, Particle Physics Division.
The Strategic Collaborative Initiatives Program began in 2006 when the University renewed its contract with the DOE to manage Argonne. The SCI program includes collaborative research projects, strategic joint appointments, and joint institutes. The University extended the program to Fermilab when it became co-manager of the lab in 2007.
Giant digital camera probes cosmic 'dark energy,' the universe's deepest mystery
September 11, 2013
The Washington Post
With the whir of a giant digital camera, the biggest mystery in the universe is about to become a bit less mysterious.
Fifteen years ago, the world of science was rocked by the discovery that, contrary to our notions of gravity, distant galaxies appeared to be flying apart at an ever-accelerating rate. The observation implied that space itself was stretching apart faster and faster. It was akin to watching a dropped ball reverse course, speed upward and disappear into the sky.
The discovery made many cosmologists - the scientists who probe the very nature of nature itself - acutely uncomfortable. For either our understanding of gravity is cockeyed, or some mysterious repulsive force - quickly and glibly dubbed "dark energy" - permeates the universe.
In 2011, the Nobel Committee blessed the improbable discovery as real, handing their prize in physics to the two teams that nearly simultaneously made the observation.
"As unhappy as it made some of us, the expansion of the universe is indeed accelerating," said Marc Kamionkowski, professor of physics and astronomy at Johns Hopkins University. "That's how the universe works."
Now, after years of planning and construction, four new projects at telescopes in Chile, Hawaii and the South Pole are getting a handle on what, exactly, is doing this unseemly pushing.
Leading the way is the world's most powerful digital camera, constructed at Fermilab, the Energy Department facility in Illinois. The $50 million Dark Energy Camera took a decade to plan and build, and it sports a resolution of 570 megapixels - about a hundredfold more pixels than a smartphone camera. Technicians installed it atop a telescope in Chile last year, and after initial jitters - the camera was so heavy it made the telescope jiggle - the camera has been "tested, tweaked and fine-tuned," said Joshua Frieman, the Fermilab scientist leading the project, which has enlisted 120 scientists from 23 countries.
On Aug. 31, the big camera began snapping its way across a huge swath of the southern sky.
Each click captures light from nearly 100,000 distant galaxies. Over the next five years, the project, called the Dark Energy Survey, will catalog some 300 million galaxies and thousands of exploding stars flung across distant space and time, in what Frieman called "the biggest galactic survey yet."
Every night, scientists will beam 400 gigabytes of camera data to a supercomputing center at the University of Illinois at Urbana-Champaign, where machines will build a giant time-lapse map of the universe going back some 8 billion years - or more than half way to the Big Bang that started it all.
Frieman calls it "a movie of cosmic history."
Scrutinizing this movie will narrow down the possibilities for what's causing cosmic acceleration. Because this acceleration can't be measured directly, its nature can only be divined indirectly, by measuring, for instance, how clumps of galaxies coalesce across space and time.
One possibility: Our understanding of gravity, explained by Einstein's general theory of relativity, breaks down across huge distances. The theory marked the culmination of Einstein's hardest thinking, and since its inception in 1916 it has withstood every test thrown at it. But general relativity may be incomplete.
Another possibility: A mysterious repulsive force permeates every point in the universe. This dark energy, if revealed, would be instant Nobel Prize fodder, Kamionkowski said.
"This is the one a lot of people would bet on," said David Spergel, an astrophysicist at Princeton University. "It's where I'd put most of my money."
Beyond these two possibilities, there are a "whole bunch of crazy ideas," Kamionkowski said. Spergel called most of these notions "intellectual aardvarks," saying, "They look beautiful only to their mothers." One such idea posits that the visible universe - what we think of as everything - is only one part of a far larger cosmos.
Combined with the Dark Energy Survey, three other projects coming online will further explore cosmic acceleration. Atop Mauna Kea in Hawaii, a camera at the Subaru Telescope is mapping galaxies in much of the northern sky. And at the South Pole and in Chile, two telescopes will take another tack, peering at the glow left over from the Big Bang. Studying this "cosmic background radiation" should reveal how cosmic acceleration has sped up or slowed down over the 13.7-billion-year history of the universe.
Combining data from all four projects could lead to a big "eureka moment," said Kamionkowski, a day the world's puzzled cosmologists would welcome.
"We don't know what makes up three quarters of the universe," Spergel said. "It's a little embarrassing."Learn more >>
The Dark Energy Camera
September 27, 2013
It's the world's most powerful digital camera and it sits atop the Blanco telescope in the Andes Mountains of Chile. But it was constructed on the campus of Fermilab in far west suburban Batavia. The Dark Energy Camera officially began its work on August 31 and has already captured some amazing images of outer space. Its real mission, though, is to help scientists figure out if so-called Dark Energy is responsible for the universe's accelerating expansion. We learn how the camera is helping scientists unravel one of the greatest mysteries in the cosmos. View a slideshow of photos taken by the Dark Energy Camera.
Members of the Dark Energy Survey collaboration explain what they hope to learn by studying the southern sky with the world's most advanced digital camera in the following video.Learn more >>
South Pole Telescope helps Argonne scientists study earliest ages of the universe
November 5, 2013
Argonne National Laboratory
For physicist Clarence Chang at the U.S. Department of Energy's (DOE) Argonne National Laboratory, looking backward in time to the earliest ages of the universe is all in a day's work.
Chang helped design and operate part of the South Pole Telescope, a project that aims a giant telescope at the night sky to track tiny bits of radiation that are still traveling across the universe from the period just after it was born.
"Basically, what we're looking at is the afterglow light of the Big Bang," Chang said.
In the wake of the Big Bang, all the matter in the universe was just hot, dense particles and light. As the universe got older, it began to spread out and cool down over time, and the intense light from that period traveled across space. It's still traveling, hitting us all the time, and it has a very distinct radiation signature. "We call this the Cosmic Microwave Background, and it is essentially a snapshot of the universe as it looked about 400,000 years after the Big Bang," Chang said.
There's still a lot we don't know about the makeup of the early universe. Particularly mysterious are the dark matter and dark energy that appear to make up 95% of the universe, but about which we know very little. Mapping the Cosmic Microwave Background can shed some light on these dark forms.
"The Cosmic Microwave Background photons have traveled so far in time that some of them bumped into the early galaxy clusters along the way," Chang said. "You can detect this because they get kicked around a bit, which changes the radiation signature."
This is useful because one of the things we do know about dark energy is that it affects how galaxy clusters form. Being able to compare the distribution of distant galaxy clusters with the distribution we observe nearby helps physicists decode the role dark energy played - and continues to play - in the universe.
The majority of the Cosmic Microwave Background radiation has wavelengths of just one to two millimeters. These photons are absorbed by water, so in order to catch them, you need a very dry, flat and preferably cold space, which narrows it down to just two locations on Earth. One is the Chilean mountains, where we have a different sky mapping project underway, and the other is the South Pole.
The South Pole telescope is more than 30 feet across; Chang and colleagues at Argonne helped build its camera. ("We had to build the camera ourselves, because no sane person needs a camera that sees down to wavelengths at millimeter length," he said.) He is part of a rotation that travels to the Pole for weeks at a time to check how the camera is functioning and perform maintenance.
Developing and designing the detectors for the camera required expertise from multiple Argonne facilities and research divisions, including the Center for Nanoscale Materials.
At the core of the detector technology is an extremely thin superconducting film. Although superconductors can carry an electrical charge perfectly, they are exquisitely sensitive to changes in temperature. When thermal radiation from the Cosmic Microwave Background hits the camera, it heats the material up slightly, which changes the conductivity of the film. This lets physicists record the energy coming from that particular part of the sky.
"So far we've mapped about 2,500 square degrees of the sky," he said, "so there's just 37,500 to go."
The South Pole telescope is funded through the National Science Foundation and the DOE's Office of Science. The other institutions in the partnership are the University of Chicago, the University of California at Berkeley, Case Western Reserve University, the Harvard-Smithsonian Center for Astrophysics, McGill University, the University of Colorado at Boulder and the University of California at Davis.
Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation's first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America's scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy's Office of Science.Learn more >>
Dark Matter Experiment Has Detected Nothing, Researchers Say Proudly
November 5, 2013
The New York Times
But afterward, Juan I. Collar, a dark matter specialist at the University of Chicago who has been urging the community to take low-mass WIMPs seriously, questioned whether the LUX detector had been adequately calibrated to detect them.
"They do have a real interest in performing those calibrations, because they would settle the issue," Dr. Collar said in an email. "We just have to be patient. At the end they promised to do so, and I have no doubts they will."Learn more >>
SPT's measurement of B-mode polarization chosen as one of Physics World's Top Ten Breakthroughs of 2013
December 13, 2013
Physics World news
The award citation says: "To astronomers working on the South Pole Telescope for being the first to measure B-mode polarization in the cosmic microwave background radiation."
The IceCube collaboration may have bagged the Physics World 2013 Breakthrough of the Year award, but another discovery from the South Pole also makes it into our top-10 list. It is for the first detection of a subtle twist in light from the cosmic microwave background (CMB), known as B-mode polarization. This twist has long been predicted and its detection paves the way for a definitive test of inflation - a key theory in the Big Bang model of the universe.
The top ten was chosen by a panel of Physics World news editors and reporters using the following criteria:
Significant advance in knowledge
Strong connection between theory and experiment
General interest to all physicistsLearn more >>
Swirls in remnants of Big Bang may hold clues to universe's infancy
December 13, 2013
University of Chicago News
South Pole Telescope scientists have detected for the first time a subtle distortion in the oldest light in the universe, which may help reveal secrets about the earliest moments in the universe's formation.
The scientists observed twisting patterns in the polarization of the cosmic microwave background-light that last interacted with matter very early in the history of the universe, less than 400,000 years after the Big Bang. These patterns, known as "B modes," are caused by gravitational lensing, a phenomenon that occurs when the trajectory of light is bent by massive objects, much like a lens focuses light.
Early today, Physics World magazine heralded the result as one of the top 10 physics breakthroughs of 2013.
A multi-institutional collaboration of researchers led by John Carlstrom, the S. Chandrasekhar Distinguished Service Professor in Astronomy & Astrophysics at the University of Chicago, made the discovery. They announced their findings in a paper published in the journal Physical Review Letters-using the first data from SPTpol, a polarization-sensitive camera installed on the telescope in January 2012.
"The detection of B-mode polarization by South Pole Telescope is a major milestone, a technical achievement that indicates exciting physics to come," Carlstrom said.
The cosmic microwave background is a sea of photons (light particles) left over from the Big Bang that pervades all of space, at a temperature of minus 270 degrees Celsius-a mere 3 degrees above absolute zero. Measurements of this ancient light have already given physicists a wealth of knowledge about the properties of the universe. Tiny variations in temperature of the light have been painstakingly mapped across the sky by multiple experiments, and scientists are gleaning even more information from polarized light.
Light is polarized when its electromagnetic waves are preferentially oriented in a particular direction. Light from the cosmic microwave background is polarized mainly due to the scattering of photons off of electrons in the early universe, through the same process by which light is polarized as it reflects off the surface of a lake or the hood of a car. The polarization patterns that result are of a swirl-free type, known as "E modes," which have proven easier to detect than the fainter B modes, and were first measured a decade ago by a collaboration of researchers using the Degree Angular Scale Interferometer, another UChicago-led experiment.
Simple scattering can't generate B modes, which instead emerge through a more complex process-hence scientists' interest in measuring them. Gravitational lensing, it has long been predicted, can twist E modes into B modes as photons pass by galaxies and other massive objects on their way toward earth. This expectation has now been confirmed.
To tease out the B modes in their data, the scientists used a previously measured map of the distribution of mass in the universe to determine where the gravitational lensing should occur. They combined their measurement of E modes with the mass distribution to provide a template of the expected twisting into B modes. The scientists are currently working with another year of data to further refine their measurement of B modes.
The careful study of such B modes will help physicists better understand the universe. The patterns can be used to map out the distribution of mass, thereby more accurately defining cosmologically important properties like the masses of neutrinos, tiny elementary particles prevalent throughout the cosmos.
Similar, more elusive B modes would provide dramatic evidence of inflation, the theorized turbulent period in the moments after the Big Bang when the universe expanded extremely rapidly. Inflation is a well-regarded theory among cosmologists because its predictions agree with observations, but thus far there is not a definitive confirmation of the theory. Measuring B modes generated by inflation is a possible way to alleviate lingering doubt.
"The detection of a primordial B-mode polarization signal in the microwave background would amount to finding the first tremors of the Big Bang," said the study's lead author, Duncan Hanson, a postdoctoral scientist at McGill University in Canada.
B modes from inflation are caused by gravitational waves. These ripples in space-time are generated by intense gravitational turmoil, conditions that would have existed during inflation. These waves, stretching and squeezing the fabric of the universe, would give rise to the telltale twisted polarization patterns of B modes. Measuring the resulting polarization would not only confirm the theory of inflation - a huge scientific achievement in itself - but would also give scientists information about physics at very high energies - much higher than can be achieved with particle accelerators.
The measurement of B modes from gravitational lensing is an important first step in the quest to measure inflationary B modes. In inflationary B mode searches, lensing B modes show up as noise. "The new result shows that this noise can be accounted for and subtracted off so that scientists can search for and hopefully measure the inflationary B modes underneath," Hanson said. "The lensing signal itself can also be used by itself to learn about the distribution of mass in the universe."Learn more >>
On the dark side
December 19, 2013
University of Chicago Magazine
Astrophysicist Josh Frieman, PhD'89, works on the dark side, studying the night sky for insight into the accelerating expansion of the universe.
Josh Frieman, PhD'89, will spend the next five years photographing the night sky with a really big camera. In August the 570-megapixel Dark Energy Camera, built at Fermilab and mounted on the Victor M. Blanco Telescope at the Cerro Tololo Inter-American Observatory in Chile, began taking about 400 images of the southern sky every night. Each image captures the light of approximately 100,000 distant galaxies. The project, the Dark Energy Survey, is the largest-yet extragalactic survey and will record information on more than 300 million galaxies. Led by Frieman, UChicago professor of astronomy and astrophysics and Fermilab staff scientist, the survey enlists more than 200 scientists from 25 organizations.
The main goal of the survey is to understand why the expansion of the universe is speeding up: whether a mysterious dark energy pervades the universe or if something is amiss with the law of gravity on cosmic scales. To that end, it is measuring the history of cosmic expansion, or how fast the universe is expanding today compared to its rate billions of years ago. The survey is also measuring the history of large-scale structures: organizations of cosmic elements like clusters of galaxies, superclusters, and filaments. Galaxies tend to clump together, but the strength of that tendency changes over time. "There's this competition between gravity" - particularly the gravity of dark matter - "which is making galaxies attract to each other, and dark energy, which is pushing them apart," Frieman says. Studying this competition and the historical rates of expansion should explain more about the properties of dark energy.
Trained as a theoretical cosmologist, Frieman has worked increasingly with survey data. He previously led the Sloan Digital Sky Survey (SDSS-II) Supernova Survey, a three-year project that discovered and measured more than 500 type Ia supernovae-exploding stars that grow as bright as an entire galaxy for a short time and can be used to measure cosmic distances. Frieman is struck, he says, by the knowledge that can be gained by simply looking at the sky. "What's remarkable to me is that just by taking pictures, we can learn so much about how the universe has evolved." In an interview with the Magazine, adapted and edited below, he talked about the cosmos scientifically and philosophically.
It really wasn't until I was in college at Stanford that I caught fire with cosmology. An eminent cosmologist from Oxford, Dennis Sciama, came and gave a colloquium on the history of the universe. That was eye-opening to me, the notion that cosmology, in a way, was like archaeology on the grand scale, and that we could use the observed universe, galaxies and how they're distributed in space, similarly to how pottery shards are used by an archaeologist, to figure out what the universe looked like billions of years ago.
In the dark
We don't know what dark matter is, but we know that it obeys the ordinary laws of gravity - or we think it does. So there are experiments going on to try to detect particles of dark matter, since that's one of the leading ideas of what dark matter could be. It could just be clouds of elementary particles zipping around. Dark energy - we call them both dark because they don't emit or interact with light - is something much stranger, and it would make up about 70 percent of the universe. Unlike dark matter, it doesn't hold stuff together. Dark energy pushes stuff apart.
Filled with emptiness
One idea for what dark energy could be is the energy of empty space. If you imagine taking this coffee cup, well, it's kind of dirty, but it's filled with molecules of air, right? And imagine I sealed it, attached it to a pump to a vacuum and pumped out all of the particles that were there. It would be totally empty space. In classical physics, if there are no particles in there, there's no energy. But according to the laws of quantum mechanics, even if there are no particles in there, empty space itself can still have energy.
Before the beginning
Currently the laws of physics can take us back very close to the big bang - a tiny fraction of a second, we think, after the big bang. There is strong evidence that the early universe was very hot and very dense, and that's really what we should call the big bang. Now whether we trace that back to a single point in time, and whether it traces back somehow beyond that point in time, that becomes much more speculative because the laws of physics break down before we get there. And then there comes this question of what do we even mean by time when we get to this point? Because our classical notions of space and time themselves break down. There are certainly physicists who have worked on theories of "what happens before the big bang," ideas that before the big bang, maybe there was a previous universe that contracted and then bounced and led to the current expansion. That's certainly possible. It may be possible to theorize about that in a consistent way given the laws of physics, but at this point it's very speculative.
Where we are
Copernicus showed that we are not at the center of the universe. Now with Hubble and others, we know that not only is the sun not at the center of the universe, the sun is just one of tens of billions of stars in this rather ordinary galaxy that's one of billions of galaxies that are flying apart from each other due to the expansion of the universe. So in fact there is no center of the universe. And now with dark matter and dark energy, we're not even made of the stuff that most of the universe is made of. It's like we're this little spray on the big ocean of the universe.
On the other hand, I think what counters that is the sense that there's a real unity to the cosmos. I find some strange comfort in the fact that we're all made of stuff that was produced in the supernovae. Most of the elements in our bodies and that we construct the world out of were forged in nuclear reactions in stars when they exploded, and then were spread throughout space. So we actually have this very strange, very direct physical connection to this universe that we're studying. And the fact that we've been able to evolve and develop technologies to understand that universe doesn't give us power over the universe, but I think for me, there's comfort in that understanding of how we got here.Learn more >>