Since 2005, scientists have been scanning the night sky to create a three-dimensional map of our universe with the purpose of shedding light on one of the biggest mysteries in physics: the nature and identity of dark energy and dark matter. That effort is about to get a massive upgrade with the successful installation and testing of the Dark Energy Spectroscopic Instrument, or DESI.
Scientists recently installed DESI at the Kitt Peak National Observatory in Arizona. The device features 5,000 optical fibers, each one designed to collect light from a single galaxy. DESI is enabling scientists to gather 20 times more data than previous surveys.
A previous instrument on a different telescope, the Baryon Oscillation Spectroscopic Survey instrument, required collaborators to drill 1,000 holes into large metal plates that held fibers in a configuration that exactly matched the position of known galaxies in a small portion of the night sky. Each time scientists wanted to image new galaxies, a new plate had to be drilled and the fibers inserted by hand.
With DESI, researchers have relegated the grueling work of pinpointing galaxy locations to a hive of 5,000 robotic pencil-shaped tubes. The positioners have a precision of several micrometers — about one-10th the width of a human hair — and are capable of moving on their own to focus on distant galaxies.
Scientists can use these redshifted signals to create a three-dimensional map of our universe stretching back 11 billion years into its nascent past. By analyzing the distribution of galaxies through space and time, scientists can then make inferences about the nature of the unknown dark matter that pulls galaxies together and that of dark energy, which pushes them apart.
Researchers completed the first round of testing on the robotic positioners last November.
“I was pleased to see that positioners moved to where we told them to go when we turned on the instrument,” said Stephen Kent, a scientist at the Department of Energy’s Fermilab. “With a system this complex, you never know where you might run into problems.”
A second milestone was achieved in January when the positioners were accurately pointed at over 2,000 stars simultaneously.
“That was the moment we could begin working on science, not just engineering,” Kent said.
During this testing phase, researchers implemented a software package called Platemaker, which was designed by Kent and scientist Eric Neilsen at Fermilab.
The software is a key player in choreographing the movement of all 5,000 robotic positioners simultaneously, especially since the positioners can sometimes get in each other’s way.
“As a design decision for the instrument from the beginning, we allow the robots to reach into each other’s patrol zones,” said Joseph Silber, an engineer at Lawrence Berkeley National Laboratory and lead engineer on the focal plane. “That means they can collide, and they shouldn’t.”
Since then, Kent and his team have been fine-tuning the code in Platemaker to improve the accuracy to which the positioners can be located.
The software guides the robotic positioners on a multistep process to locate galaxies. First, the focal plane — a large metallic structure that holds the positioners in place — must be pointed at just the right portion of sky. Just as old maritime navigators would use the position of the stars to guide their way, 10 high-resolution cameras embedded in the focal plane capture and analyze light from stars, which allows researchers to orient the telescope.
These movements to position the focal plane have to be incredibly precise for each fiber to receive the most light that it can from its assigned galaxy. Nudged even a little off target, and the fiber will be only partially filled with its galaxy’s light. But when positioned as designed, each fiber will be filled completely with the light of its galaxy, with minimal background.
Once the telescope is pointed in the right direction, the robotic positioners begin an intricate mechanical waltz, peering deep into the sky to detect sources of light far too faint for human eyes to see.
Scientists have begun operating the Dark Energy Spectroscopic Instrument, or DESI, to create a 3-D map of over 30 million galaxies and quasars that will help them understand the nature of dark energy. Photo: Marilyn Sargent /Lawrence Berkeley National Laboratory
Their high degree of precision gets them most of the way to the desired galaxy, but the angle might still be slightly off for some. To get them the rest of the way, DESI has a CCD camera installed at the primary mirror of the telescope, which looks up at the focal plane. Researchers use a built-in light source to illuminate the fibers embedded in the robotic positioners. The fibers project the resulting small dots of light to the CCD camera, which then images them. The Platemaker software compares the positions of the fibers in the images to where they should actually be pointed based on detailed star charts from previous surveys.
The software then computes how far off each positioner is from the desired target, after which another system can move it the rest of the way toward its designated galaxy.
“It’s a very complicated modeling process, which has taken us a few years to figure out,” Kent said.
With the toughest work now complete, researchers, who are currently teleworking, plan to finish testing the software when they return to site.
DESI is scheduled to operate for a total of five years, during which time it will measure the redshifts of over 30 million galaxies and quasars — a type of massive black hole. Scientists can then use this information to determine if and how the concentration of dark energy has changed throughout the history of our universe.
Work for DESI and Fermilab astrophysics programs is supported by the DOE Office of Science.
Fermilab is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit science.energy.gov.
The discovery of the Higgs particle by the international CMS and ATLAS collaborations is the most famous discovery made to date at the Large Hadron Collider at CERN. The scientists made the announcement on July 4, 2012, and it was later recognized with a Nobel Prize: The theorists who predicted the Higgs mechanism received the award in 2013.
Most impressively, it only was publication number 183 for the CMS collaboration. On June 19, CMS scientists celebrated publishing their 1,000th peer-reviewed research paper.
It’s an unprecedented achievement. For the last 10 years, CMS scientists have been producing, testing and publishing insights arising from the spectacular particle collisions at the Large Hadron Collider, describing fundamental aspects of the quantum universe in one paper after another. Peering into the behavior of nature’s most fundamental constituents through the lens of the humming, high-tech machine known as the CMS particle detector, the CMS collaboration has contributed immensely to the very foundations of knowledge in particle physics.
Churning out raw data from a cavern located 100 meters below the French countryside, the CMS detector has produced enough data for its collaboration to publish on average more than 100 research papers per year.
On June 19, CMS scientists celebrated publishing their 1,000th peer-reviewed research paper. For the last 10 years, scientists have been producing, testing and publishing insights arising from particle collisions inside the CMS detector at the Large Hadron Collider. Photo: CERN
The CMS detector is one of four large detectors situated around the 27-kilometer ring that is the LHC. The other three are ATLAS, LHCb and ALICE. Together, a community of more than 10,000 scientists, students, engineers and technicians of all sorts keep the detectors running and analyze the data they generate.
“A thousand very high-quality scientific papers in a decade is an amazing result, testimony of the rich physics spectrum provided by the LHC data, the versatility of our experiment and the ingenuity and dedication of our collaborators,” said CERN scientist and University of Padova Professor Roberto Carlin, CMS experiment spokesperson. “We are very proud of them, and we look forward to the results we will produce in the coming decades. These will allow us to make further significant progress in the understanding of the universe.”
The papers submitted by the CMS collaboration can be sorted into seven areas of physics research. Five of these areas are measurements related to physics described by the Standard Model of particles and forces, bottom quark physics, top quark physics, Higgs boson physics, and detector performance. The CMS collaboration has rediscovered with great precision the known particles and forces of the Standard Model, confirming many of its predictions and measuring its characteristic parameters with unprecedented precision.
A sixth area is heavy-ion physics. Most of the time, the LHC produces head-on proton-proton collisions, which is the subject of about 90% of the CMS papers. But the collider goes through runs in which it sends beams of lead ions, instead of protons, into the heart of the CMS detector for study. About one in 10 of CMS’ published papers involves heavy-ion physics and data gathered during these runs.
The seventh area is the exploration of extensions of the Standard Model of elementary particles and their interactions. The Standard Model is humanity’s current best theory to describe fundamental particles and forces, but it is not able to explain some big questions in particle physics: Why is there more matter than antimatter in the universe? What is dark matter made of? Is there more than one Higgs particle? CMS scientists aim to answer these questions, which will require extensions of the Standard Model.
“We are proud of reaching the unprecedented, historic landmark with the submission of CMS’ 1,000th paper for publication,” said Boaz Klima, CMS Publications Committee chair. He added that “the scientific impact of CMS publications has been at the highest level. Their quality as well as diversity of physics topics is unparalleled.”
The LHC and CMS were built to study aspects of the universe never before probed. These investigations examine extra dimensions, mini black holes, string balls, dark matter candidates, the existence of long-lived particles and other phenomena that excite, inspire and could revolutionize our understanding of the subatomic world. Another very important chapter in the CMS program is the search for supersymmetric particles.
The collaboration’s 1,000th paper reflects significant contributions from the United States contingent, known as US CMS, and the LHC Physics Center, which is the home base of CMS scientists in the United States, hosted at the Department of Energy’s Fermilab. More than 90% of the US CMS institutions have members associated with the LHC Physics Center, which boasts a wide geographic diversity from all corners of the country. The center’s events serve 800 scientists and students every year.
“It is important to realize that while CMS is an international collaboration with members from 238 institutes from 55 countries, US CMS makes up about a third of this collaboration,” said Brown University scientist Meenakshi Narain, chair of the US CMS collaboration. “Therefore, the impact of U.S. physicists on the achievements of the CMS collaboration, including the papers published, are rather impressive and enhanced by their creativity and ingenuity in deploying cutting-edge analysis techniques to unravel the mysteries of the universe.”
About 75% of CMS publications have direct contributions to the analysis by US CMS scientists.
“The LHC has delivered only 5% of the planned collisions. The remaining 95% to be collected in between now and the mid-2030s will represent the largest proton-proton data set ever collected in history. To fully exploit the unprecedented discovery potential of the machine, the CMS detector is being upgraded these days with state-of-the-art technologies,” said scientist Anadi Canepa, head of the CMS Department at Fermilab, which is the host laboratory for the US CMS collaboration. “The breadth, scientific impact and sophistication of the LHC experiments are unparalleled. These endeavors are building the foundations of our understanding of nature for decades to come.”
Research at the Large Hadron Collider is supported by the U.S. Department of Energy Office of Science and the National Science Foundation. The Department of Energy’s Fermilab is the lead institution for U.S. participation in the CMS experiment at the LHC. With more than 1,000 participants from 49 institutions across the United States, US CMS is the largest national group in the 3,600-member international CMS collaboration.
Fermilab is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit science.energy.gov.