Next-Generation Camera Takes Data of Early Universe

 Deep in Antarctica, at the southernmost point on our planet, sits a 33-foot telescope designed for a single purpose: to make images of the oldest light in the universe.

This light, known as the cosmic microwave background, or CMB, has journeyed across the cosmos for 14 billion years—from the moments immediately after the Big Bang until now. Because it is brightest in the microwave part of the spectrum, the CMB is impossible to see with our eyes and requires specialized telescopes.

The South Pole Telescope, specially designed to measure the CMB, has recently opened its third-generation camera for a multiyear survey to observe the earliest instants of the universe. Since 2007, the SPT has shed light on the physics of black holes, discovered a galaxy cluster that is making stars at the highest rate ever seen, redefined our picture of when the first stars formed In the universe, provided new insights into dark energy and homed in on the masses of neutrinos. This latest upgrade improves its sensitivity by nearly an order of magnitude—making it among the most sensitive CMB instruments ever built.

“Being able to detect and analyze the CMB, especially with this level of detail, is like having a time machine to go back to the first moments of our universe,” says University of Chicago Professor John Carlstrom, the principal investigator for the South Pole Telescope project.

Image courtesy : Jason Gallicchio

“Encoded in images of the CMB light that we capture is the history of what that light has encountered in its 14 billion-year journey across the cosmos,” he says. “From these images, we can tell what the universe is made up of, how the universe looked when it was extremely young and how the universe has evolved.”

Located at the National Science Foundation’s Amundsen-Scott South Pole Station, the South Pole Telescope is funded and maintained by the National Science Foundation in its role as manager of the US Antarctic Program, the national program of research on the southernmost continent.

“The ability to operate a 10-meter telescope, literally at the end of the Earth, is a testament to the scientific capabilities of the researchers that NSF supports and the sophisticated logistical support that NSF and its partners are able to provide in one of the harshest environments on Earth,” says Vladimir Papitashvili, Antarctic astrophysics and geospace sciences program director in NSF’s Office of Polar Programs. “This new camera will extend the abilities of an already impressive instrument.”

The telescope is operated by a collaboration of more than 80 scientists and engineers from a group of universities and US Department of Energy national laboratories, including three institutions in the Chicago area. These research organizations—the University of Chicago, Argonne National Laboratory and Fermi National Accelerator Laboratory—have worked together to build a new, ultrasensitive camera for the telescope, containing 16,000 specially manufactured detectors.

“Built with cutting-edge detector technology, this new camera will significantly advance the search for the signature of early cosmic inflation in the cosmic microwave background and allow us to make inroads into other fundamental mysteries of the universe, including the masses of neutrinos and the nature of dark energy,” says Kathy Turner of DOE’s Office of Science.

“Baby pictures” of the cosmos

Image courtesy : The Aurora Australis above the South Pole Telescope.
Photo: Robert Schwarz

The CMB is the oldest light in our universe, produced in the intensely hot aftermath of the Big Bang before even the formation of atoms. These primordial particles of light, which have remained nearly untouched for nearly 14 billion years, provide unique clues about how the universe looked at the beginning of time and how it has changed since.

“This relic light is still incredibly bright—literally outshining all the stars that have ever existed in the history of the universe by over an order of magnitude in energy,” says University of Chicago professor and Fermilab scientist Bradford Benson, who headed the effort to build this new camera.

However, because most of the energy is in the microwave part of the spectrum, to observe it we need to use special detectors at observatories in high and dry locations. The South Pole Station is better than anyplace else on Earth for this: It is located atop a two-mile-thick ice sheet, and the extremely low temperatures in Antarctica mean there is almost no atmospheric water vapor.

Scientists are hoping to plumb this data for information on a number of physical processes and even new particles.

“The cosmic microwave background is a remarkably rich source for science,” Benson says. “The third-generation camera survey can give us clues on everything from dark energy to the physics of the Big Bang to locating the most massive clusters of galaxies in the universe.”

The details of this “baby picture” of the cosmos will allow scientists to better understand the different kinds of matter and energy that make up our universe, such as neutrinos and dark energy. They may even find evidence of the gravitational waves from the beginning of the universe, regarded by many as the “smoking gun” for the theory of inflation. It also serves as a rich astronomical survey; one of the things they’ll be looking for are some of the first massive galaxies in the universe. These massive galaxies are increasingly of interest to astronomers as “star farms,” forming the first stars in the universe, and since they are nearly invisible to typical optical telescopes, the South Pole Telescope is perhaps the most efficient way to find them.

“Nothing that comes out of a box”

The South Pole Telescope team, led by the University of Chicago, Fermilab and Argonne National Laboratory. Photo: Brad Benson

The South Pole Telescope collaboration has operated the telescope since its construction in 2007. Grants from multiple sources—the National Science Foundation, the US Department of Energy and the Kavli and Moore foundations—supported a second-generation polarization-sensitive camera. The latest third-generation focal plane contains 10 times as many detectors as the previous experiment, requiring new ideas and solutions in materials and nanoscience.

“From a technology perspective, there is virtually nothing that comes ‘out of a box,’” says Clarence Chang, an assistant professor at the University of Chicago and physicist at Argonne involved with the experiment.

For the South Pole Telescope, scientists needed equipment far more sensitive than anything made commercially. They had to develop their own detectors, which use special materials for sensing tiny changes in temperature when they absorb light. These custom detectors were developed and manufactured from scratch in ultraclean rooms at Argonne.

The detectors went to Fermilab to be assembled into modules, which included small lenses for each pixel made at the University of Illinois at Urbana-Champaign. After being tested at multiple collaborating universities around the country, the detectors made their way back to Fermilab to be integrated into the South Pole Telescope camera cryostat, designed by Benson. The camera looks like an 8-foot-tall, 2500-pound optical camera with a telephoto lens on the front, but with the added complication that the lenses need to be cooled to just a few degrees above absolute zero. (Even the Antarctic isn’t that cold, so it needs this special cryostat to cool it down further.)

Finally, the new camera was ready for its 10,000-mile journey to Antarctica by way of land, air and sea. On the final leg, from NSF’s McMurdo Station to the South Pole, it flew aboard a specialized LC130 cargo plane outfitted with skis so that it could land on snow near the telescope site, since the station sits atop an ice sheet. The components were carefully unloaded, and a team of more than 30 scientists raced to reassemble the camera during the brief three-month Antarctic summer—since the South Pole is not accessible by plane for most of the year due to temperatures that can drop to minus 100 degrees Fahrenheit.

The South Pole Telescope’s multiyear observing campaign brings together researchers from across North America, Europe and Australia. With the upgraded telescope taking data, the exploration of the cosmic microwave background radiation enters a new era with a powerful collaboration and an extremely sensitive instrument.

“The study of the CMB involves so many different kinds of scientific journeys,” Chang says. “It’s exciting to watch efforts from all over come together to push the frontiers of what we know.”

Editor's note: This article is adapted from a Fermilab press release.

Image courtesy: Dunlap Institue - University of Toronto

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Gravity's Waterfall !!

 Physicists are using analog black holes to better understand gravity.

A0620-00, a binary star system 3300 light-years away, holds a dark secret: One of its stars isn’t a star at all, but a black hole. As far as we know, this is the black hole closest to our planet. Astronomers know it’s there only because its partner star appears to be dancing alone, pulled along by an invisible lead.In recent years, scientists have found ways to study black holes, listening to the gravitational waves they unleash when they collide, and even creating an image of one by combining information from radio telescopes around the world.Bu your knowledge of black holes remains limited. No one will ever be able to test a real one in a lab, and with current technology, it would take about 50 million years for a probe to reach A0620-00.So scientists are figuring out how to make do with substitutes—analogs to black holes that may hold answers to mysteries about gravity and quantum mechanics.

Building black hole models

In 1972, William “Bill” Unruh, a physicist at the University of British Columbia, Vancouver, connected gravity to fluid dynamics in an analogy: “Imagine that you are a blind fish, and are also a physicist, living in a river,” Unruh wrote.Along Unruh’s imaginary river, a waterfall plunges at a supersonic speed—faster than the speed of sound in water. What happens if a fellow fish goes over the falls? You, a blind fish, cannot know; you will never hear it scream because the waterfall will drag the sound down faster than it can travel up.

Unruh used this piscine drama to explain a property of black holes: Like sound that passes over the edge of the supersonic waterfall, light that crosses the horizon of a black hole cannot escape.The analogy turned out to be more accurate than Unruh initially thought. Eight years later, in 1980, he realized that the equations of motion for sound in the waterfall analogy were identical to those describing light at the horizon of a black hole.At the time, his research drew little attention—it was cited just four times in the decade after it was published. But in the ’90s, Unruh’s work was rediscovered as physicists began probing gravity theoretically and experimentally with analog models.Today, physicists use everything from water to exotic ultracold states of matter to mimic black holes. Proponents of the analogs say that these models have confirmed theoretical predictions about black holes. But many physicists still doubt that analogs can predict what happens where gravity warps spacetime so violently.

Black holes were first theorized in 1784, by English clergyman and astronomer John Michell, who calculated that for a large enough star, “all light emitted from such a body would be made to return towards it, by its own proper gravity.”The idea was mostly put aside until the 20th century, when Einstein’s general theory of relativity overturned the paradigm of Newtonian gravity. Luminaries like Karl Schwarzchild, Subrahmanyan Chandrasekhar and John Archibald Wheeler developed theory about these monsters from which nothing could escape. But in 1974, a young physicist named Stephen Hawking revolutionized the field by proposing that that something could, in fact, escape from a black hole.

Due to random quantum fluctuations in the fabric of spacetime, pairs of virtual particles and antiparticles pop into existence all the time, throughout the universe. Most of the time, these pairs annihilate instantly, disappearing back into the void. But, Hawking theorized, the horizon of a black hole could separate a pair: One particle would be sucked in, while the other would zoom away as a now real particle because of a mathematical quirk in Hawking radiation, swallowed virtual particles effectively have negative energy. Black holes that gobble up these particles shrink. To an observer, Hawking radiation would look a lot like a black hole spitting up what it swallowed and getting smaller.However, Hawking radiation is random and carries no information about the inside of a black hole—remember that the emitted particle comes from just outside the horizon. This creates a paradox: Quantum mechanics rests on the premise that information is never destroyed, but if particles emitted as Hawking radiation are truly random, information would be lost forever.

Most physicists believe that black holes don’t truly destroy information and that information is preserved in Hawking radiation, but that conjecture may be impossible to test directly. “The temperature of Hawking radiation is very small—it’s much smaller than the background radiation of the universe,” says Hai Son Nguyen, a physicist at the Institute of Nanotechnology of Lyon. “That’s why we will never be able to observe Hawking radiation from a real black hole.”What about something that behaved a lot like a black hole? In his 1980 paper, Unruh calculated that phonons—quantum units of sound analogous to photons, quantum units of light—would be the Hawking radiation emitted from his analog black hole.

Unruh was initially bleak about the prospects of actually making such a measurement, calling it “an extremely slim possibility.” But as more physicists joined Unruh in theorizing about analogs to black holes in the ’90s, the possibility of measuring Hawking radiation became a difficult, but achievable goal.

Over the waterfall

No its not this waterfall at all.

There are many different analog models of black holes, but they all have one aspect in common: a horizon. Mathematically, horizons are defined as the boundary beyond which events cannot escape—like the edge of Unruh’s waterfall. Because they can separate pairs of particles, any horizon creates a form of Hawking radiation. "Understanding" the phenomenology associated with the presence of horizons in different analog systems provides hints about phenomena that might also be present in the gravitational realm,” writes Carlos Barceló, a theoretical physicist at the Astrophysical Institute of Andalucia.

Often, it’s useful to start with a simple analog like water, says Silke Weinfurtner, a physicist at the University of Nottingham. It’s possible to create a horizon by running water quickly enough over an obstacle; if the conditions are just right, surface waves are thwarted at the obstacle.But to properly measure the smallest—quantum-level—effects of a black hole, you need a quantum analog. Bose-Einstein condensates, or BECs, are typically ultracold gases like rubidium that are ruled by quantum effects odd enough to qualify them as another state of matter. Subtle quantum effects like Hawking radiation hidden by the noise present in normal fluids become apparent in BECs.

Analog black holes can even use light as a fluid. The fluid is made of quasiparticles called polaritons, which are the collective state of a photon that couples to an electric field. Enough polaritons behave as a quantum fluid of light. So when the flow of polaritons goes faster than the speed of sound in the polariton fluid, just like Unruh’s waterfall, a horizon forms. Hawking radiation from this fluid of light still comes in the form of phonons.Some black hole analogs are “optical” because their Hawking radiation comes in photons. In optical fibers—like the type we send data through—intense laser pulses can create a horizon. The pulse changes the physical properties of the fiber, slowing down the speed of light within the fiber. This makes the leading edge of the pulse a horizon: Slowed light cannot escape past the pulse any more than sound can escape up out of Unruh’s waterfall.

To date, though, experimental evidence of Hawking radiation in any of these analogs has been lacking in support—with one exception.

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Does God, Play Dice ???

There's a Famous Quote from Albert Einstein

"God Does Not Play with Universe"

What does it mean ?

The common interpretation of this statement contains two myths (perhaps misunderstandings).

The first is that his use of the word ‘God’ implies that he was a religious person who believed in the existence of God. Nothing could be further from the truth; indeed, Einstein can be described more accurately as an outright atheist. Although his early up-bringing was in a highly religious Jewish environment, he soon realized that many of the things described in the Old Testament were not consistent with physical laws. His great contributions to physics came from his belief in precise mathematical laws that govern the natural world. This rational approach is antithetical to the common religious notion of a supernatural God with powers that can overcome natural laws.

We can go as far as saying that, deep down, every person (and certainly every practising scientist) must have this rational streak. You cannot do good science if you do not believe in fundamental immutable laws that govern Nature. Tomorrow, if your computer breaks down, you know it is because some part of the system failed. You call a technician hoping he/she will find out what is wrong and fix it; you certainly don’t pray to a God or go to a temple to get it fixed, though you might pray to God that the technician comes quickly ! It is interesting that we are born with this rational bent of mind.

Einstein believes about God might not be what you think of God. So what did Einstein really mean by the word ‘God’ in his statement ? Einstein of course believed in mathematical laws of nature, so his idea of a God was at best someone who formulated the laws and then left universe a-lone to evolve according to these laws. To him, the very fact that there were natural laws that the human mind could discover was evidence of a God, not a God who superseded these laws but one who created them. Thus his use of the word God is to be interpreted as the existence of natural laws of great mathematical beauty, whatever form they might take.

Which brings us to the second part of Einstein’s statement, the part about not playing dice. This relates to Einstein’s reaction to the part of Nature described by Quantum Mechanics, which is undoubtedly one of the pillars of modern physics. He felt that natural laws could not be like the throw of dice, with inherent randomness or probability. But this is exactly what QuantumMechanics tells us – that at the fundamental level Nature is inherently random, codified in Heisenberg’s famous Uncertainty Principle. Thus, the second misunderstanding about Einstein’s  statement is that his opposition to Quantum Mechanics was the raving of an old man, a man well beyond his prime who did not understand the new physics. Well, we will see below why this is all a myth.

There were thus three features of QuantumMechanics that Einstein disapproved of – it was probabilistic, nonlocal, and linear. Despite this opposition, Einstein realized that it was a successful theory within its domain of applicability. He believed that a future unified field theory would have to reproduce the results of Quantum Mechanics, perhaps as a Linear approximation to a deeper nonlinear theory. This was similar to how the relativistic gravitational field of General Relativity (with a finite propagation speed of the gravitational force) led to Newton’s law of gravitation (with its action-at-a-distance force) in the nonrelativistic limit. But Einstein was convinced that Quantum Mechanics was  no the correct approach to deducing the fundamental laws of physics.

Today, 50 years after his death, the mainstream of physics does not take Einstein’s approach seriously. The popular notion is that he was unreasonably opposed to the highly successful Quantum Mechanics. While I have tried to correct this misconception by presenting Einstein’s cogent reasoning behind his stand, only time (and perhaps future brilliant scientists who take up his approach) will tell us if he was justified. Let us not forget that Newton’s theory of gravity was enormously successful  came until Einstein along. We await the next Einstein.

 

"GOD NOT ONLY PLAYS DICE WITH THE UNIVERSE, BUT SOMETIMES THROUGH THEM BUT THEY CAN'T BE SEEN"

- Stephen Hawking

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Expanding the Cosmic search...

Down at the South Pole, where temperatures drop below negative 100 degrees Fahrenheit and darkness blankets the land for six months at a time, the South Pole Telescope (SPT) searches the skies for answers to the mysteries of our universe.

This mighty scavenger is about to get a major upgrade — a new camera that will help scientists further understand neutrinos, the ghost-like particles without electric charge that rarely interact with matter.

The 10-meter SPT is the largest telescope ever to make its way to the South Pole. It stands atop a two-mile thick plateau of ice, mapping the cosmic microwave background (CMB), the light left over from the big bang. Astrophysicists use these observations to understand the composition and evolution of the universe, all the way back to the first fraction of a second after the big bang, when scientists believe the universe quickly expanded during a period called inflation.

One of the goals of the SPT is to determine the masses of the neutrinos, which were produced in great abundance soon after the big bang. Though nearly massless, because neutrinos exist in huge numbers, they contribute to the total mass of the universe and affect its expansion. By mapping out the mass density of the universe through measurements of CMB lensing, the bending of light caused by immense objects such as large galaxies, astrophysicists are trying to determine the masses of these elusive particles.

A wafer of detectors for the SPT-3G camera undergoes inspection at Fermilab. Photo: Bradford Benson, University of Chicago

To conduct these extremely precise measurements, scientists are installing a bigger, more sensitive camera on the telescope. This new camera, SPT-3G, will be four times heavier and have a factor of about 10 more detectors than the current camera. Its higher level of sensitivity will allow researchers to make extremely precise measurements of the CMB that will hopefully make it possible to cosmologically detect neutrino mass.

SPT-3G is being completed by a collaboration of scientists spanning the DOE national laboratories, including Fermilab and Argonne, and universities including the University of Chicago and University of California, Berkeley. The national laboratories provide the resources needed for the bigger camera and larger detector array while the universities bring years of expertise in CMB research.
“In the next several years, we should be able to get to the sensitivity level where we can measure the number of neutrinos and derive their mass, which will tell us how they contribute to the overall density of the universe,” explained Bradford Benson, the head of the CMB Group at Fermilab. “This measurement will also enable even more sensitive constraints on inflation and has the potential to measure the energy scale of the associated physics that caused it.”

This photo shows an up-close look at a single SPT-3G detector. Photo: Volodymyr Yefremenko, Argonne National Laboratory

“The national labs are getting involved because we need to scale up our infrastructure to support the big experiments the field needs for the next generation of science goals,” Benson said. Fermilab’s main role is the initial construction and assembly of the camera, as well as its integration with the detectors. This upgrade is being supported mainly by the Department of Energy and the National Science Foundation, which also supports the operations of the experiment at the South Pole.

Once the camera is complete, scientists will bring it to the South Pole, where conditions are optimal for these experiments. The extreme cold prevents the air from holding much water vapor, which can absorb microwave signals, and the sun, another source of microwaves, does not rise between March and September.

The South Pole is accessible only for about three months during the year, starting in November. This fall, about 20 to 30 scientists will head down to the South Pole to assemble the camera on the telescope and make sure everything works before leaving in mid-February. Once installed, scientists will use it to observe the sky over four years.

“For every project I’ve worked on, it’s that beginning — when everyone is so excited not knowing what we’re going to find, then seeing things you’ve been dreaming about start to show up on the computer screen in front of you — that I find really exciting,” said University of Chicago’s John Carlstrom, the principal investigator for the SPT-3G project.

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Absence of gravitational-wave signal extends limit on knowable universe

Imagine an instrument that can measure motions a billion times smaller than an atom that last a millionth of a second. Fermilab’s Holometer is currently the only machine with the ability to take these very precise measurements of space and time, and recently collected data has improved the limits on theories about exotic objects from the early universe.
Our universe is as mysterious as it is vast. According to Albert Einstein’s theory of general relativity, anything that accelerates creates gravitational waves, which are disturbances in the fabric of space and time that travel at the speed of light and continue infinitely into space. Scientists are trying to measure these possible sources all the way to the beginning of the universe.
The Holometer experiment, based at the Department of Energy’s Fermilab, is sensitive to gravitational waves at frequencies in the range of a million cycles per second. Thus it addresses a spectrum not covered by experiments such as the Laser Interferometer Gravitational-Wave Observatory, which searches for lower-frequency waves to detect massive cosmic events such as colliding black holes and merging neutron stars.
“It’s a huge advance in sensitivity compared to what anyone had done before,” said Craig Hogan, director of the Center for Particle Astrophysics at Fermilab.
This unique sensitivity allows the Holometer to look for exotic sources that could not otherwise be found. These include tiny black holes and cosmic strings, both possible phenomena from the early universe that scientists expect to produce high-frequency gravitational waves. Tiny black holes could be less than a meter across and orbit each other a million times per second; cosmic strings are loops in space-time that vibrate at the speed of light.
The Holometer is composed of two Michelson interferometers that each split a laser beam down two 40-meter arms. The beams reflect off the mirrors at the ends of the arms and travel back to reunite. Passing gravitational waves alter the lengths of the beams’ paths, causing fluctuations in the laser light’s brightness, which physicists can detect.
The Holometer team spent five years building the apparatus and minimizing noise sources to prepare for experimentation. Now the Holometer is taking data continuously, and with an hour’s worth of data, physicists were able to confirm that there are no high-frequency gravitational waves at the magnitude where they were searching.
The absence of a signal provides valuable information about our universe. Although this result does not prove whether the exotic objects exist, it has eliminated the region of the universe where they could be present.

“It means that if there are primordial cosmic string loops or tiny black hole binaries, they have to be far away,” Hogan said. “It puts a limit on how much of that stuff can be out there.”
Detecting these high-frequency gravitational waves is a secondary goal of the Holometer. Its main purpose is to determine whether our universe acts like a 2-D hologram, where information is coded into two-dimensional bits at the Planck scale, a length around ten trillion trillion times smaller than an atom. That investigation is still in progress.
“For me, it’s gratifying to be able to contribute something new to science,” said researcher Bobby Lanza, who recently earned his Ph.D. conducting research on the Holometer. He is the lead author on an upcoming paper about the result. “It’s part of chipping away at the whole picture of the universe.”

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Dark Energy Spectroscopic Instrument (DESI)Opens its 5000 Eyes

With its installation near to completing, the new sky-surveying instrument has begun for its final testing series.

A instrument is mounted at the top a telescope in Arizona aimed its Robotic Array of 5000 fiber-optic called as "eyes" at the night sky on October 22, 2019 to capture the first images showing Galaxy Lights ij its own unique way.

It was the first test of the Dark Energy Spectroscopic Instrument (DESI), with its nearly complete components. The long awaited Spectroscopic Instrument is designed to explore the mystery of dark energy, which makes up about 68-70% of the universe.

DESI’s components are designed to automatically point at preselected sets of galaxies, gather their light, and then split that light into narrow bands of colour to precisely map their distance from Earth and Gauge how much the universe expanded as this light travelled to Earth. In ideal conditions DESI can cycle through a new set of 5000 galaxies every 20 minutes.

Like a powerful time machine, this Spectroscopic Instrument will peer deeply into the universe’s early development stated to be up to about 11 billion years ago to create the most detailed 3-D map of the universe.

By repeatedly mapping the distance to 35 million galaxies and 2.4 million Quasars across ⅓ of the area of the sky over its run for every five-year. It will give us more information about dark energy. Quasars, among the brightest objects in the universe, allow instrument to look deeply into the universe’s past.

DESI will provide very precise measurements of the universe’s expansion rate. Gravity had slowed this rate of expansion in the early universe, and dark energy has since been responsible for speeding up its expansion.

“After a decade in planning and R&D, installation and assembly, we are delighted that DESI can soon begin its quest to unravel the mystery of dark energy,” says DESI Director Michael Levi of the Department of Energy’s Lawrence Berkeley National Laboratory, the lead institution for DESI’s construction and operations.

"Most of the universe’s matter and energy are dark and unknown, and next-generation experiments like DESI are our best bet for unraveling these mysteries,” Levi says. “I am thrilled to see this new experiment come to life."

The DESI collaboration has participation from nearly 500 researchers at 75 institutions in 13 countries.

Installation of DESI began in February 2018 at the Nicholas U. Mayall Telescope at Kitt Peak National Observatory near Tucson, Arizona.

“With DESI we are combining a modern instrument with a venerable old telescope to make a state-of-the-art survey machine,” says Lori Allen, director of Kitt Peak National Observatory at the National Science Foundation’s National Optical-Infrared Astronomy Research Laboratory. 

Over the past 18 months, a bevy of DESI components were shipped to the site from institutions around the globe and installed on the telescope.
Among the early arrivals was an assembly of lenses packaged in a large steel barrel, together weighing in at three tons. This corrector barrel sits over the 4-meter primary mirror of the Mayall Telescope and provides an expansive field of view. The lenses, each measuring about a meter across, were successfully tested in April.
DESI’s focal plane, which carries 5,000 robotic positioners that swivel in a choreographed “dance” to individually focus on galaxies, is at the top of the telescope.

These little robots—which each hold a light-gathering fiber-optic cable that is about the average width of a human hair—serve as DESI’s eyes. It takes about 10 seconds for the positioners to swivel to a new sequence of targeted galaxies. With its unprecedented surveying speed, DESI will map over 20 times more objects than any predecessor experiment.

The focal plane, which is comprised of a half-million individual parts, is arranged in a series of 10 wedge-shaped petals that each contain 500 positioners and a little camera to help the telescope point and focus.
The focal plane, corrector barrel and other DESI components weigh 11 tons, and the Mayall telescope’s movable arm that DESI is installed on weighs 250 tons and rises 90 feet above the floor in the Mayall’s 14-story dome.

Among the more recent arrivals at Kitt Peak is the collection of spectrographs that are designed to split up the gathered light into three separate color bands to allow precise distance measurements of the observed galaxies across a broad range of colors.
These spectrographs, which allow DESI’s robotic eyes to “see” even faint, distant galaxies, are designed to measure redshift, which is a shift in the color of objects to longer, redder wavelengths due to the objects’ movement away from us. Redshift is analogous to how the sound of a fire engine’s siren shifts to lower tones as it moves away from us.

Postioner for Dark Energy Spectroscopic Instrument

There are now eight spectrographs installed, with the final two arriving before year-end. To connect the focal plane with the spectrographs, which are located beneath the telescope, DESI is equipped with about 150 miles of fiber-optic cabling.

“This is a very exciting moment,” says Nathalie Palanque-Delabrouille, a DESI spokesperson and an astrophysics researcher at France’s Atomic Energy Commission who has participated in the selection process to determine which galaxies and other objects DESI will observe.

“The instrument is all there. It has been very exciting to be a part of this from the start,” she says. “This is a very significant advance compared to previous experiments. By looking at objects very far away from us, we can actually map the history of the universe and see what the universe is composed of by looking at very different objects from different eras.”

Palanque-Delabrouille’s institution, CEA, contributed a specialized cooling system to optimize the performance of the light sensors (known as CCDs or charge-coupled devices) that enable DESI’s broad color-sampling range.
Gregory Tarlé, a physics professor at the University of Michigan (UM) who led the student teams that assembled the robotic positioners for DESI and related components, said it’s gratifying to reach a stage in the project where all of DESI’s complex components are functioning together. UM delivered a total of 7300 robotic positioners, including spares. During the production peak, the teams were churning out about 50 positioners a day.

“It was quite a process,” Tarlé says. “We were at the limits of precision for these production parts.”
The positioners were installed in the focal plane petals at Berkeley Lab, and after assembly and testing the completed petals were shipped to Kitt Peak and installed one at a time on the Mayall Telescope.Now that the hard work of building DESI is largely done, Tarlé said he looks forward to DESI discoveries.
“I want to find out what the nature of dark energy is,” he says. “We finally have a shot at really trying to understand the nature of this stuff that dominates the universe.”

Editor's note: This article is adapted from an article originally published by Lawrence Berkeley National Laboratory

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