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14,000 Quasars Shine a Light on the Distant Universe

Monday, May 2nd, 2011

The following news release from the Sloan Digital Sky Survey-III (SDSS-III) collaboration was first posted on Brookhaven’s website.

Scientists from the Sloan Digital Sky Survey III (SDSS-III) have created the largest ever three-dimensional map of the distant universe by using the light of the brightest objects in the cosmos to illuminate ghostly clouds of intergalactic hydrogen. The map provides an unprecedented view of what the universe looked like 11 billion years ago.

A slice through the three-dimensional map of the universe. SDSS-III scientists are looking out from the Milky Way, at the bottom tip of the wedge. Distances are labeled on the right in billions of light-years. The black dots going out to about 7 billion light years are nearby galaxies. The red cross-hatched region could not be observed with the SDSS telescope, but the future BigBOSS survey, the proposed successor to BOSS, could observe it. The colored region shows the map of intergalactic hydrogen gas in the distant universe. Red areas have more gas; blue areas have less gas.

The new findings were presented on May 1 at a meeting of the American Physical Society by Anže Slosar, a physicist at the U.S. Department of Energy’s Brookhaven National Laboratory, and described in an article posted online on the arXiv astrophysics preprint server.

The new technique used by Slosar and his colleagues turns the standard approach of astronomy on its head. “Usually we make our maps of the universe by looking at galaxies, which emit light,” Slosar explained. “But here, we are looking at intergalactic hydrogen gas, which blocks light. It’s like looking at the moon through clouds — you can see the shapes of the clouds by the moonlight that they block.”

Instead of the moon, the SDSS team observed quasars, brilliantly luminous beacons powered by giant black holes. Quasars are bright enough to be seen billions of light years from Earth, but at these distances they look like tiny, faint points of light. As light from a quasar travels on its long journey to Earth, it passes through clouds of intergalactic hydrogen gas that absorb light at specific wavelengths, which depend on the distances to the clouds. This patchy absorption imprints an irregular pattern on the quasar light known as the “Lyman-alpha forest.”

An observation of a single quasar gives a map of the hydrogen in the direction of the quasar, Slosar explained. The key to making a full, three-dimensional map is numbers. “When we use moonlight to look at clouds in the atmosphere, we only have one moon. But if we had 14,000 moons all over the sky, we could look at the light blocked by clouds in front of all of them, much like what we can see during the day. You don’t just get many small pictures — you get the big picture.”

The big picture shown in Slosar’s map contains important clues to the history of the universe. The map shows a time 11 billion years ago, when the first galaxies were just starting to come together under the force of gravity to form the first large clusters. As the galaxies moved, the intergalacitc hydrogen moved with them. Andreu Font-Ribera, a graduate student at the Institute of Space Sciences in Barcelona, created computer models of how the gas likely moved as those clusters formed. The results of his computer models matched well with the map. “That tells us that we really do understand what we’re measuring,” Font-Ribera said. “With that information, we can compare the universe then to the universe now, and learn how things have changed.”

A zoomed-in view of the map slice shown in the previous image. Red areas have more gas; blue areas have less gas. The black scalebar in the bottom right measures one billion light years. Image credit: A. Slosar and the SDSS-III collaboration.

The quasar observations come from the Baryon Oscillation Spectroscopic Survey (BOSS), the largest of the four surveys that make up SDSS-III. Eric Aubourg, from the University of Paris, led a team of French astronomers who visually inspected every one of the 14,000 quasars individually. “The final analysis is done by computers,” Aubourg said, “but when it comes to spotting problems and finding surprises, there are still things a human can do that a computer can’t.”

“BOSS is the first time anyone has used the Lyman-alpha forest to measure the three-dimensional structure of the universe,” said David Schlegel, a physicist at Lawrence Berkeley National Laboratory in California and the principal investigator of BOSS. “With any new technique, people are nervous about whether you can really pull it off, but now we’ve shown that we can.” In addition to BOSS, Schlegel noted, the new mapping technique can be applied to future, still more ambitious surveys, like its proposed successor BigBOSS.

When BOSS observations are completed in 2014, astronomers can make a map ten times larger than the one being released today, according to Patrick McDonald of Lawrence Berkeley National Laboratory and Brookhaven National Laboratory, who pioneered techniques for measuring the universe with the Lyman-alpha forest and helped design the BOSS quasar survey. BOSS’s ultimate goal is to use subtle features in maps like Slosar’s to study how the expansion of the universe has changed during its history. “By the time BOSS ends, we will be able to measure how fast the universe was expanding 11 billion years ago with an accuracy of a couple of percent. Considering that no one has ever measured the cosmic expansion rate so far back in time, that’s a pretty astonishing prospect.”

Quasar expert Patrick Petitjean of the Institut d’Astrophysique de Paris, a key member of Aubourg’s quasar-inspecting team, is looking forward to the continuing flood of BOSS data. “Fourteen thousand quasars down, one hundred and forty thousand to go,” he said. “If BOSS finds them, we’ll be happy to look at them all, one by one. With that much data, we’re bound to find things that we never expected.”


Pumping Up Proton Polarization

Thursday, April 7th, 2011

Brookhaven Lab’s oldest and most-trophied workhorse, the Alternating Gradient Synchrotron (AGS), has broke its own world record for producing intense beams of polarized protons – particles that “spin” in the same direction.

Spin, a quantum property that describes a particle’s intrinsic angular momentum,  is used in a wide range of fields, from astronomy to medical imaging. But where spin comes from is still unknown.

In this picture of a proton-proton collision, the spin of the particles is shown as arrows circling the spherical particles. The red and green particles represent reaction products from the collision that are "seen" and analyzed by RHIC detectors.

To explore the mystery of spin, Brookhaven’s Relativistic Heavy Ion Collider (RHIC) smashes beams of polarized protons at close to the speed of light. RHIC is the only machine in the world with this capability. But before reaching RHIC’s high-speed collision course, the protons travel about one million miles through a series of linear and circular accelerators, including the AGS, a 41-year old circular accelerator more than a half mile around. Home to three of BNL’s seven Nobel Prize-winning discoveries, the AGS is Brookhaven’s longest-running accelerator.

Now, with a new upgrade, the AGS can keep up to 75 percent of those particles in the beam polarized while they accelerate – a 5 to 8 percent increase over the previous record. This feat was accomplished with custom-built power supplies created from old inventory and two revamped 1960s quadrupole magnets pulled from storage.

The two refurbished quadrupole magnets before being installed at the AGS

As the particles race through the AGS, two of the customized power supplies quickly pulse, hold, and pull back surges of power for each of the quadrupoles in a matter of milliseconds. Forty-two times within half a second, these pulsed currents produce magnetic kicks that keep the particles spinning in the correct direction.

For more details, see this story.

-Kendra Snyder, BNL Media & Communications


Going in Circles

Wednesday, February 23rd, 2011

RHIC's main control room

If you were expecting this blog entry to be about the great song from the Friends of Distinction, it unfortunately won’t be the case. Instead, I’m taking you on the first trip this year of RHIC’s Yellow beam, one of two oppositely circulating particle beams that collide in the center of RHIC’s detectors. Why? Because the main goal of my first shift of Run11 was to get our particles to circulate in a closed orbit in the Yellow beamline. This will also give me the opportunity to get back to some of the technical terms I used in my previous post. So allow me to go over a little bit of accelerator physics theory for a minute.

RHIC, which stands for Relativistic Heavy Ion Collider, is the name given to the large circular collider at Brookhaven National Laboratory; in order for particles to actually reach the collider from their source, they need travel through a series of other accelerators:

  1. the LINAC for protons, the Tandem-to-Booster beamline for heavy ions
  2. the Booster synchrotron
  3. the Booster-to-AGS (BtA) line
  4. the Alternating Gradient Synchrotron (AGS)
  5. the AGS-to-RHIC (AtR) line



New Tool Puts a Different “Spin” on Proton Mystery

Tuesday, February 15th, 2011

Scientists hoping to unravel the mystery of proton spin at the Relativistic Heavy Ion Collider (RHIC) have a new tool at their disposal — the first to directly explore how quarks of different types, or “flavors,” contribute to the overall spin of the proton. The technique, described in papers just published by RHIC’s STAR and PHENIX collaborations in Physical Review Letters, relies on the measurement of particles called W bosons, the mediators of the weak force responsible for the decay of radioactive nuclei.

Illustration of a new measurement using W boson production in polarized proton collisions at RHIC. Collisions of polarized protons (beam entering from left) and unpolarized protons (right) result in the production of W bosons (in this case, W-). RHIC's detectors identify the particles emitted as the W bosons decay (in this case, electrons, e-) and the angles at which they emerge. The colored arrows represent different possible directions, which probe how different quark flavors (e.g., “anti-up,” ū; and “down,” d) contribute to the proton spin.

Spin is a quantum property that describes a particle’s intrinsic angular momentum. Like charge and mass, it’s part of a particle’s identity, whose magnitude is the same for all particles of a given type. But unlike charge and mass, spin has a direction that can be oriented differently for individual particles of a given species.

Spin is used by a wide range of people, from astronomers studying the contents of the universe to doctors using an MRI (magnetic resonance imaging) machine to see inside the human body. But where spin comes from is still a mystery.

Physicists have long thought that the spin of a proton was simply the sum of the spins of its three component quarks. But experiments have shown that the quarks account for only about 25 percent of the proton’s spin. What accounts for the missing 75 percent? RHIC is the world’s only machine capable of colliding high-energy beams of polarized protons — a useful approach for investigating this question.

After beginning polarized proton collisions at RHIC late in 2001, scientists first looked for the missing spin in the gluons, the particles that hold a proton’s quarks together via the strong force. But so far, gluons have been found to contribute much less than originally speculated to proton spin.

Now, RHIC scientists have a new tool to guide their search. Thanks to new detection techniques and the ability to run polarized proton collisions at very high energies — 500 GeV, or 500 billion electron volts — scientists at both PHENIX and STAR are able to directly probe the polarization contributions from different flavored quarks (known by the names “up” and “down”) inside protons for the first time.

Read more about this new technique here.

-Karen McNulty Walsh, BNL Media & Communications


Taking Pictures of the Sky with LSST

Monday, February 7th, 2011

Hello again,

One of the commenters on our very first post wanted to hear more about the Large Synoptic Survey Telescope (LSST), one of the three cosmological projects that involve Brookhaven Lab. Set high on a mountaintop in Chile, LSST will be a very big and expensive ground-based telescope. Planning for the project started near the end of the 20th century and the experiment probably won’t start taking data in a scientific manner until 2020.

Artist rendering of LSST on Cerro Pachon, Chile. (Image Credit: Michael Mullen Design, LSST Corporation)

The story is that at a decadal survey 10 years ago, the person who first proposed that the word “synoptic” be used in the project’s name had a misunderstanding about what synoptic really means. Either way, the name has stuck. Synoptic, by the way, comes from Greek word “synopsis” and refers to looking at something from all possible aspects, which is precisely what LSST will do.

Astronomical survey instruments fall broadly under two categories: imaging instruments that take photos of the sky, and spectroscopic instruments that take spectra (that is, distribution of light across wavelengths) of a selected few objects in the sky. LSST falls into the first category — it will take many, many images of the sky in the five bands, which are a bit like colors, from ultra-violet light to infrared light.



Quark Matter at RHIC: It’s in the Cards

Tuesday, January 25th, 2011

Quark Matter game cards

Want to “play” with subatomic particles? You could work at Brookhaven Lab’s Relativistic Heavy Ion Collider (RHIC) or the LHC — or you could play a new card game invented by a group of Hungarian students and RHIC/PHENIX collaborator Tamás Csörgő.

The students — Csaba Török and his friend Judit Csörgő (Tamás’ daughter) — invented the game as an entertaining way to learn about subatomic particles and their interactions, inspired by physics presentations in the science club at their secondary school, where Tamás was a frequent presenter.

The game, now available for purchase in both Hungarian and English, “provides a great opportunity for all people — not just physicists — to get acquainted with some of the elementary particles and concepts of the Standard Model,” said Csaba.

The deck consists of cards that represent particles and anti-particles from neutrinos, to electrons, positrons, muons, and quarks, which can be used for four different games. In “Quark Matter,” a game that models RHIC physics, the cards are mixed face up on a table, packed closely together to represent matter at the instant of collision — a quark-gluon plasma (QGP). The object for each player is to quickly extract particles as they would emerge from the collision, in order: non-interacting neutrinos and antineutrinos first, followed by electron/positron and muon/anti-muon pairs, and then quarks and anti-quarks as they hadronize, or freeze out, to form mesons, baryons, and anti-baryons — all while maintaining a neutral color charge.

Brookhaven's Educational Programs staff introduced the card game to students at Rocky Point Middle School.

As players race to extract cards, the “system” expands just as it does in a real RHIC collision. Players score points for each correct particle pick. More sophisticated players can name the particles as they extract them. Additional games teach and reinforce deeper concepts, such as weak decays and several laws of conservation.

For more information, visit particles card game.

-Karen McNulty Walsh, BNL Media & Communications


Behind the Scenes: RHIC

Monday, January 10th, 2011

Hello, everyone. I’m Guillaume Robert-Demolaize, an accelerator physicist at Brookhaven National Laboratory, working on the Relativistic Heavy Ion Collider (RHIC). I work as a shift leader on the collider during the beam development period, which means that I have to study the behavior of the particles circulating in our two rings and change some of the machine parameters in order to steer both beams into collision for our two detectors (STAR and PHENIX) to acquire data in the best possible conditions. When RHIC is not running, I participate in the design and setup of some of the tools required to run the machine. I am mainly in charge of the RHIC online model, a server that allows converting the optic functions of the machine into values of current for the power supplies of the RHIC magnets. This might be a lot of technical terms for a simple description of my job; so one of my next posts in this blog will be dedicated to go over these terms in further details.

I was born in 1981 in Aix-en-Provence, in the south of France. I got interested in science as a teenager when the first physics and chemistry classes started, and physics won me over very quickly. I thought it was impressive that I could describe and/or predict how something would move with just a series of equations. By the time I reached 19 and had to select an engineering school, I read an article about SLAC National Accelerator Laboratory and its collider for a school project; I got hooked instantly and never looked back. I then went to the ENSPG, a nuclear energy engineering school in Grenoble, France and graduated in 2003 with a specialization in accelerator physics after an internship at the SOLEIL synchrotron in Paris, France.



Looking Up: Cosmology and Me

Friday, January 7th, 2011

Welcome to Quantum Diaries. I’m Anže Slosar, a scientist living in New York and working at Brookhaven National Laboratory. I’ll also be occasionally blogging on this site. Let me tell you a little about myself.

I am originally from Slovenia, a small country with population of 2 
million, which was created in 1991 after the disintegration of
 Yugoslavia. I studied physics as an undergrad at the University of Cambridge, UK, and, in a typical 
Oxbridge fashion, continued my graduate studies at Cambridge. My Ph.D. 
thesis was on the Very Small Array, an interferometric radio telescope 
designed to measure fluctuations in the cosmic microwave 
background. After receiving my Ph.D., I spent six years doing postdocs at the University of Ljubljana (in the
 capital of Slovenia), Oxford University, and Lawrence Berkeley National Laboratory before moving to Brookhaven

Here, I work on a mixed salad of projects, both theoretical and
 experimental, but inevitably connected to the universe we live 
in. These days, my scientific focus is on the Lyman-alpha forest, part 
of a dark energy project called BOSS (Baryonic Oscillation Spectroscopic Survey), a topic
 that takes more than a healthy amount of my time and nerves but holds
 promise of being truly revolutionary. I will no doubt write more about 
it in the coming posts.

In my spare time, I do a lot of things at a very low level: real ales,
 real food, yoga, classical guitar. And then I do things New Yorkers do, 
namely following the real estate and thinking about cunning ways 
of getting rich while burning cash on restaurants, theaters, clubs,
 galleries, and a myriad other places.

More to come.



Brookhaven Lab Welcomes You to the New Quantum Diaries

Friday, January 7th, 2011

“Hello” from Brookhaven National Laboratory, the land of quarks, nanoparticles, proteins, superconductors, and lots of deer and wild turkeys. We’re really excited to be a part of this new version of Quantum Diaries along with our friends from CERN, Fermilab, and TRIUMF. Through this blog, we’ll focus on one very important piece of Brookhaven’s multidisciplinary research portfolio: physics.

The independent discovery of the J/psi by Samuel Ting (front) of the Massachusetts Institute of Technology, at BNL's Alternating Gradient Synchrotron, and by Burton Richter, of the Stanford Linear Accelerator Center, earned its co-discoverers the 1976 Nobel Prize in physics. Shown with Ting in this photo are members of his experimental team.

From its early history, Brookhaven Lab has played a leading role in the exploration of matter and the early universe through groundbreaking nuclear and particle physics experiments. In fact, five of the Lab’s seven Nobel Prizes were awarded for physics research.

Today, Brookhaven continues this leadership role through several large-scale facilities on our site and around the world. At the Relativistic Heavy Ion Collider (RHIC), a 2.4-mile particle racetrack, scientists collide beams of “heavy ions” – the nuclei of atoms as heavy as gold – to replicate conditions microseconds after the Big Bang. This research has led to a series of stunning discoveries, including quark-gluon plasma, a “perfect”-liquid state of matter that permeated the early universe.  In addition to colliding heavy ions, RHIC is able to collide single protons to reveal details about a puzzling property called “spin.”