POLARBEAR Detects Curls in the Universe’s Oldest Light CMB

Measurements of polarization of the cosmic microwave background. 

Credit: POLARBEAR

Cosmologists have made the most sensitive and precise measurements yet of the polarisation of the Cosmic Microwave Background (CMB).

The report, published October 20 in the Astrophysical Journal, marks an early success for POLARBEAR, a collaboration of more than 70 scientists using a telescope high in Chile's Atacama desert designed to capture the universe's oldest light.

"It's a really important milestone," said Kam Arnold, the corresponding author of the report who has been working on the instrument for a decade.

"We're in a new regime of more powerful, precision cosmology." Arnold is a research scientist at UC San Diego's Center for Astrophysics and Space Sciences and part of the cosmology group led by physics professor Brian Keating.

POLARBEAR measures remnant radiation from the Big Bang, which has cooled and stretched with the expansion of the universe to microwave lengths.

This cosmic microwave background, the CMB, acts as an enormous backlight, illuminating the large-scale structure of the universe and carrying an imprint of cosmic history.

Arnold and many others have developed sensitive instruments called bolometers to measure this light.

Arrayed in the telescope, the bolometers record the direction of the light's electrical field from multiple points in the sky.

"It's a map of all these little directions that the light's electric field is pointing," Arnold explained.
POLARBEAR has now mapped these angles with resolution on a scale of about 3 arcminutes, just one-tenth the diameter of the full moon.

The team found telling twists called B-modes in the patterns of polarization, signs that this cosmic backlight has been warped by intervening structures in the universe, including such mysteries as dark matter, composed of substance that remains unknown, and the famously aloof particles called neutrinos, which elude capture making them difficult to study.

This initial report, the result of the first season of observation, maps B-modes in three small patches of sky.

Dust in our own galaxy also emits polarized radiation like the CMB and has influenced other measurements, but these patches are relatively clean, Arnold says. and variations in the CMB polarization due to dust occur on so broad a scale that they do not significantly influence the finer resolution B-modes in this report.

"We are confident that these B-modes are cosmological rather than galactic in origin," Arnold said.

Observations continue, and the data stream will ultimately be fed by additional telescopes comprising the Simons Array. Together they will map wider swaths of the sky, making fundamental discoveries possible.

"POLARBEAR is a real tour de force. With a relatively small, but strong, UC-led team we have surpassed the next-nearest competitors by an order of magnitude in sensitivity."

"We have paved the way towards solving the deepest mysteries in the quest to understand matter and energy at the beginning of time," said Brian Keating.

POLARBEAR is a collaboration of scientists from many institutions including experiment founder, Adrian Lee, professor of physics at UC Berkeley.

SPIDER: 'Spacecraft' seeks traces of the early universe over Antartica

Constructed primarily in Princeton's Jadwin Hall, SPIDER is a stratospheric spacecraft that in December will begin a 20-day orbit in Earth's stratosphere at an altitude of roughly 110,000 feet.

During that period, SPIDER's six large cameras will look for the pattern, or polarization, of gravitational waves produced by the fluctuation of energy and density that resulted from the Big Bang.

These waves, explained William Jones a Princeton University assistant professor of physics, are a "statistically unique fingerprint" that can be traced back to the beginning of the universe.

Many astronomical instruments measure various characteristics of this fingerprint, SPIDER is designed to characterize the "shape" of it, said Jones, who is the project's principal investigator.

"The ultimate goal of SPIDER is to see to what extent we can identify a very characteristic feature in that polarization that's expected to come from the earliest stages of the evolutionary growth of our universe," Jones said.

"There's a very particular pattern than can be generated only by something like a gravitational wave propagating through the surface of the cosmic microwave background [which is the glow of the heat left over from the Big Bang]," Jones said.

"That is a very particular pattern commonly referred to as a 'pinwheel' pattern on the sky. It's that particular pinwheel pattern that we're really after."

SPIDER, which used to be an acronym, but now is the project's formal name, is a multi-institutional project funded largely by a grant from NASA, as well as the David and Lucille Packard Foundation.

In addition to Princeton, the primary institutions involved are the University of Toronto; Case Western Reserve University; the California Institute of Technology and the Jet Propulsion Laboratory, a NASA-funded research center managed by Caltech; and the University of British Columbia.

The project was proposed in 2006 while Jones, who joined Princeton's faculty in 2008, was a scientist at the Jet Propulsion Laboratory.

South Pole Telescope: Monitoring Cosmic Microwave Background using Superconductors

At the South Pole Telescope, scientists measure Cosmic Microwave Background still traveling across space from the early days of the universe, using superconductors. 

Credit: Daniel Luong-Van, National Science Foundation.

For Argonne physicist Clarence Chang, looking backward in time to the earliest ages of the universe is all in a day's work.

Clarence Chang

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 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 High Energy Physics Dept. helped build its camera.

At the core of the detector technology is an extremely thin superconducting film. Although superconductors can carry an electrical charge perfectly, they are extremely 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."

Massive neutrinos solve a cosmological conundrum

UK Scientists have solved a major problem with the current standard model of cosmology identified by combining results from the Planck spacecraft and measurements of gravitational lensing in order to deduce the mass of ghostly sub-atomic particles called neutrinos.

The UK team, from the universities of Manchester and Nottingham, used observations of the Big Bang and the curvature of space-time to accurately measure the mass of these elementary particles for the first time.

Planck spacecraft

The recent Planck spacecraft observations of the Cosmic Microwave Background (CMB) - the fading glow of the Big Bang - highlighted a discrepancy between these cosmological results and the predictions from other types of observations.

The CMB is the oldest light in the Universe, and its study has allowed scientists to accurately measure cosmological parameters, such as the amount of matter in the Universe and its age.

But an inconsistency arises when large-scale structures of the Universe, such as the distribution of galaxies, are observed.

Professor Richard Battye, from the University of Manchester's School of Physics and Astronomy, said: "We observe fewer galaxy clusters than we would expect from the Planck results and there is a weaker signal from gravitational lensing of galaxies than the CMB would suggest.

"A possible way of resolving this discrepancy is for neutrinos to have mass. The effect of these massive neutrinos would be to suppress the growth of dense structures that lead to the formation of clusters of galaxies."

Cosmic Microwave Background (CMB)

Neutrinos interact very weakly with matter and so are extremely hard to study.

They were originally thought to be massless but particle physics experiments have shown that neutrinos do indeed have mass and that there are several types, known as flavours by particle physicists.

The sum of the masses of these different types has previously been suggested to lie above 0.06 eV (much less than a billionth of the mass of a proton).

Adam Moss

In this paper, Professor Battye and co-author Dr Adam Moss, from the University of Nottingham, have combined the data from Planck with gravitational lensing observations in which images of galaxies are warped by the curvature of space-time.

They conclude that the current discrepancies can be resolved if massive neutrinos are included in the standard cosmological model.

They estimate that the sum of masses of neutrinos is 0.320 +/- 0.081 eV (assuming active neutrinos with three flavours).

Dr Moss said: "If this result is borne out by further analysis, it not only adds significantly to our understanding of the sub-atomic world studied by particle physicists, but it would also be an important extension to the standard model of cosmology which has been developed over the last decade."

More Information: 'Evidence for Massive Neutrinos from Cosmic Microwave Background and Lensing Observations' DOI:10.1103/PhysRevLett.112.051303