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Posts Tagged ‘DES’

La matière sombre et l’énergie sombre sont bien en évidence à la conférence de physique des particules de la Société de Physique Européenne à Vienne. Bien que les physiciens et physiciennes comprennent maintenant assez bien les constituants de base de la matière, tout ce que l’on voit sur la Terre, dans les étoiles et les galaxies, cette énorme quantité de matière ne représente que 5 % du contenu total de l’Univers. Pas étonnant alors qu’autant d’efforts soient déployés pour élucider le mystère de la matière sombre (27 % de l’Univers) et de l’énergie sombre (68 %).

Depuis le Big Bang, non seulement l’Univers s’étend mais cette expansion va en accélérant. Quelle énergie alimente cette accélération ? Nous l’appelons énergie sombre. Cela demeure absolument inconnu mais l’équipe du Dark Energy Survey cherche à obtenir des éléments de réponse. Ces scientifiques vont examiner un quart du ciel de l’hémisphère sud, cataloguant l’emplacement, la forme et la distribution d’objets astronomiques tels que des amas galactiques (regroupements de galaxies) et de supernovæ (étoiles en explosion). Leur but est de recueillir de l’information sur 300 millions de galaxies et 2500 supernovæ.

Les galaxies se sont formées grâce à l’effet attractif de la gravité, qui a permis à la matière de se regrouper, malgré l’effet dispersif de l’énergie sombre, qui disperse la matière avec l’expansion de l’Univers. Les scientifiques de DES étudient essentiellement comment les grandes structures telles que les amas galactiques se sont développées dans le temps en observant des objets situés à différentes distances et dont la lumière provient de différentes époques dans le temps. Avec plus de données, ces scientifiques espèrent mieux comprendre la dynamique de l’expansion.

La matière sombre est tout aussi inconnue. Jusqu’ici, elle ne s’est manifestée qu’à travers ses effets gravitationnels. Nous pouvons “sentir” sa présence mais pas la voir, puisqu’elle n’émet aucune lumière, contrairement à la matière ordinaire contenue dans les étoiles et supernovæ. Comme si l’Univers entier était rempli de fantômes.

Une douzaine de détecteurs, utilisant des techniques différentes, essaient d’attraper ces particules fantômes. Pas facile de les traquer quand on ne sait ni comment, ni même si ces particules interagissent avec la matière. Elles doivent cependant interagir très rarement car autrement, elles auraient déjà été décelées. On utilise donc des détecteurs massifs dans l’espoir qu’une de ces particules de matière sombre frappe un noyau d’un des atomes du détecteur, induisant une petite vibration décelable. Les différentes équipes de scientifiques tentent de sonder toute la gamme de possibilités. Celles-ci dépendent de la masse possible des particules de matière sombre et leur affinité à interagir avec la matière.

Le graphe ci-dessous illustre la possibilité qu’une particule de matière sombre interagisse avec un noyau (axe vertical) en fonction de leur masse (axe horizontal). Cela couvre une vaste région de possibilités qu’il faut tester. Chaque courbe sur le graphe représente les résultats d’une expérience différente. Les régions au-dessus de ces courbes représentent les possibilités qui sont exclues. La partie gauche du graphe est la plus difficile à explorer car plus les particules de matière noire sont légères, plus la vibration induite est petite.

CRESST-limit

La Collaboration CRESST utilise de petits cristaux opérant à très basse température. Ils peuvent déceler la hausse de température minime que provoquerait une particule de matière sombre en frappant un noyau atomique. Cela leur a permis de réussir là où des dizaines d’expériences précédentes avaient échoué : la recherche de particules très légères. C’est ce que l’on peut voir sur le graphe. Toutes les possibilités au-dessus du trait continu rouge dans le coin supérieur gauche sont désormais exclues. Jusqu’ici, cette zone n’était accessible qu’aux expériences du Grand Collisionneur de Hadron (LHC) du CERN (non incluses dans ce graphe), mais au prix de plusieurs suppositions. CRESST vient d’ouvrir tout un monde de possibilités. Les particules de matière sombre légères n’ont qu’à bien se tenir.

Pauline Gagnon

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Dark matter and dark energy feature prominently at the European Physics Society conference on particle physics in Vienna. Although physicists now understand pretty well the basic constituents of matter, all what one sees on Earth, in stars and galaxies, this huge amount of matter only accounts for 5% of the whole content of the Universe. Not surprising then that much efforts are deployed to elucidate the nature of dark matter (27% of the Universe), and dark energy (68%).

Since the Big Bang, the Universe is not only expanding, but this expansion is also accelerating. So which energy fuels this acceleration? We call it dark energy. This is still something absolutely unknown but the Dark Energy Survey (DES) team is determined to get some answers. To do so, they are searching a quarter of the southern sky, mapping the location, shape and distribution of various astronomical objects such as galactic clusters (large groups of galaxies) and supernovae (exploding stars). Their goal is to record information on 300 million galaxies and 2500 supernovae.

Galaxies formed thanks to gravity that allowed matter to cluster. But this happened against the dispersive effect of dark energy, since the expansion of the Universe scattered matter away. The DES scientists essentially study how large structures such as galactic clusters evolved in time by looking at objects at various distances, and whose light comes from different times in the past. With more data, they hope to better understand the dynamic of expansion.

Dark matter is just as unknown. So far, it has only manifested itself through gravitational effects. We can “feel” its presence but we cannot see it, since it emits no light, unlike regular matter found in stars and supernovae. As if the whole Universe was full of ghosts. A dozen detectors, using different techniques, are trying to find dark matter particles.

Not easy to catch such elusive particles when no one knows how and if these particles interact with matter. Moreover, these particles must interact very rarely with regular matter (otherwise, they would already have been found), the name of the game is to use massive detectors, in the hope one nucleus from one of the detector atoms will recoil when hit by a dark matter particle, inducing a small but detectable vibration in the detector. The experiments search for a range of possibilities, depending on the mass of the dark matter particles and how often they can interact with matter.

The plot below shows how often dark matter particles could interact with a nucleus (vertical axis) as a function of their mass (horizontal axis). This spans a wide region of possibilities one must test. The various curves indicate what has been achieved so far by different experiments. All possibilites above the curves are excluded. The left part of the plot is harder to probe since the lighter the dark matter particles is, the smaller the vibration induced.

CRESST-limitThe CRESST Collaboration uses small crystals operating at extremely low temperature. They are sensitive to the temperature rise that would occur if a dark matter particle deposited the smallest amount of energy. This allowed them to succeed where tens of previous experiments had failed: looking for very light particles. This is shown on the plot by the solid red curve in the upper left corner. All possibilities above are now excluded. So far, this area was only accessible to the Large Hadron Collider (LHC) experiments (results not shown here) but only when making various theoretical hypotheses. CRESST has just opened a new world of possibilities and they will sweep nearly the entire area in the coming years. Light dark matter particles better watch out.

Pauline Gagnon

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The largest map of dark matter made with direct measurements, unveiled today by two teams of physicists at the U.S. Department of Energy’s Fermilab and Lawrence Berkeley National Laboratory (Berkeley Lab) removes a key hurdle for tracing the history of dark energy in the universe using ground-based telescopes.

This work done by members of the Sloan Digital Sky Survey collaboration points to greater successes for upcoming sky surveys, including the Dark Energy Survey, which will turn on the Dark Energy Camera on the Blanco Telescope later this year, and then the Large Synoptic Survey Telescope and the HyperSuprimeCam survey.

To find and map the invisible dark energy and dark matter that make up about 96 percent of the universe, physicists look at their effects on the matter and radiation we can see, namely galaxies.

Surveying galaxies from Earth-based telescopes is cheaper than satellite-based experiments but had traditionally had the drawback of having to make due with a less clear view of the sky. The same atmospheric distortions that make stars twinkle blurs attempts to track invisible dark matter in the universe made by measuring the distortion of background galaxy shapes, a process called weak lensing. DES and LSST will use this technique to create the largest galaxy surveys ever, covering more than one-eighth of the sky.

Layering photos of one area of sky taken at various time periods, a process called coaddition, can increase the sensitivity of the images six fold by removing errors and enhancing faint light signals. The image on the left show a single picture of galaxies from the SDSS Stripe 82 area of sky. The image on the right shows the same area with the layered effect, increasing the number of visible, distant galaxies. Credit: SDSS.

Layering photos of one area of sky taken at various time periods, a process called coaddition, can increase the sensitivity of the images six fold by removing errors and enhancing faint light signals. The image on the left show a single picture of galaxies from the SDSS Stripe 82 area of sky. The image on the right shows the same area with the layered effect, increasing the number of visible, distant galaxies. Credit: SDSS.Particle physicists and astronomers from Fermilab and Berkeley Lab have demonstrated a new technique for weak lensing that lessens the blurriness and allows researchers to see fainter galaxies, providing a younger picture of the universe. The two teams essentially layered snap shots of these distorted galaxies, in a process called coaddition, to remove errors caused by equipment or atmospheric effects and to enhance very faint light signals coming from deep in the universe.

Both teams depended upon extensive databases of cosmic images collected by the Sloan Digital Sky Survey, SDSS, which were compiled in large part with the help of Berkeley Lab and Fermilab.

“These results are very encouraging for future large sky surveys. The images produced lead to a picture of the galaxies in the universe that is about six times fainter, or further back in time, than is available from single images,” says Huan Lin, a Fermilab physicist and member of SDSS and DES.

Surveys of galaxies across large swaths of the sky track how clumps of dark matter have changed over time as dark energy exerts its repulsive push on them. Clumps of dark matter not only distort the images of galaxies behind them, but they determine how galaxies cluster around them. By combining this information with redshift data, the observed change in the color of light emitted by a star or other celestial object that is moving away from Earth, it’s possible to trace how the distribution of matter in the universe has evolved over time, offering insight into the growth of dark energy.

Researchers hope this new tool will help answer one of the largest questions for upcoming dark energy surveys and in cosmology: whether dark energy is what Einstein called a “cosmological constant”, a counterbalance to gravity’s pull on matter? Or is it something else such as gravity behaving differently at cosmic scales. The variation or lack of separation between clusters of galaxies and within the clusters across time will lead to new insight into this question.

To build one of the largest maps of dark matter and track its evolution across eras, the teams looked at two manifestations of gravitational lensing: those caused by large galaxy clusters and those caused by the overall distortion spread across the large scale structure of the universe. This second effect is called cosmic shear. Both of these distortions are caused by the gravitational fields of clumps of dark matter acting as lenses, bending the light from galaxies behind them. This distorts the shapes of these distant galaxies, making them look more elliptical. By measuring the ellipticities, or amount of distortion, physicists can infer properties of the dark matter, such as its abundance and how clumpy it is and the masses of the clusters.

“This image correction process should prove a valuable tool for the next generation of weak-lensing surveys,” Lin says.

— Tona Kunz

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A four-ton digital camera landed safely in Chile last week on its way to making history by enabling the world’s largest galaxy survey, starting next year. Getting the camera there was a worldwide feat of technlogy and transportation prowess.

Doing big science, such as building the Dark Energy Camera, takes big effort and big cooperation. Building and installing one of the world’s largest digital cameras to conduct the most extensive galaxy survey to date as part of the Dark Energy Survey experiment required scientists and manufacturers from across the globe. Researchers from more than 26 institutions enlisted the help of 129 companies in the United States and about half a dozen in foreign countries to fabricate the often one-of-a-kind components for the camera.

Most components for the camera migrated to the Department of Energy’s Fermilab for testing and assembly, as seen in this timelapse video , before being shipped to the four-meter Blanco telescope in the remote Chilean mountains. The journey required help from planes, trains, trucks and boats to traverse continents and oceans, and ended with an 11-hour drive to a mountaintop.

The DES’s combination of survey area and depth will far surpass what has come before and provide researchers for the first time with four search techniques in one powerful instrument. To find clues to the characteristics of dark energy and why the expansion of the universe is accelerating, DES will trace the history of the expanding universe roughly three-quarters of the way back to the time of the big bang.
During five years of operation, starting in 2012, the 570-megapixel camera will create in-depth color images of one-eighth of the sky, or 5000 square degrees, to measure 100,000 galaxy clusters, 4,000 supernovae, and an estimated 300 million distant galaxies, about 10 million times fainter than the dimmest star you can see from Earth with the naked eye. It will yield the largest 3-D map of the cosmic web of large-scale structures in the universe.

–Tona Kunz

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DES first-light countdown, 6 months to go

Blanco telescope, on left, at sunset in Chile. Photo: Brenna Flaugher.

I have promised to provide updates on our progress towards the first light of the Dark Energy Survey’s, or DES.  First light is the first official look at the sky after readying the camera and its detection software. If you recall, we were supposed to deliver the Dark Energy Camera, or DECam, imager this summer.

So, without further ado, I am pleased to announce: Here it is!

I have been collecting DES-related pictures and videos for a while and the picture to right by Fermilab photographer Reidar Hahn is by far my favorite shot of the imager (first published in Fermilab Today). It shows the focal plane completely populated with 74 shiny, blue CCDs, ready to catch some extragalactic photons.

Shipment arrangements and installation schedule are being worked out as I write. Our team has already set foot in Chile to assemble at the Blanco Telescope the various parts that we tested on our Fermilab telescope simulator in February. Installation will start soon.

I am joining them in November in Chile and can hardly wait. But this is when my wave-like abilities, which I mentioned in a previous post, comes to play. My wave function is now quite stretched as I perform a variety of tasks these days. Read on and see it for yourself.

Blue-tinged Charged Coupler Devices in the Dark Energy Camera imager. Photo: Reidar Hahn

Galaxy clusters are my favorite thing in the universe, and in addition to my work on the DES cluster analysis group I am now building a new catalog based on the Sloan Digital Sky Survey, or SDSS, data. Our group at Fermilab is wrapping up all the parallel threads of work on that data set, and that means that I am doing a lot of writing these days, too. Papers are coming out soon and this is terrific news, which puts my mind at ease with respect to that nightmarish pressure for publications.

I’ve also been volunteered to help in the calibration group by writing a code, which was being referred to as “George” until we found a more appropriate name. But since people now ask me, “How is George doing?” all the time, I am afraid the name has stuck. Right now I am working in the first module, “George I”, to process a series of monochromatic calibration images and create a map of the system response curve at every point of the DECam focal plane. This new task is exciting because it connects the instrument I helped build with the science I want to do (good calibration is an essential requirement for cluster science) and it also gives me the opportunity to learn more about our data management system.

The reason for my excitement about this is the fact that a reliable, fast and easy-to-use database is the key for success and productivity in our field. I use the SDSS SkyServer for all my SDSS analyses and it is just great to be able to upload a text file with sky coordinates and visualize, with a single click, all the objects you are interested in. Every time I submit a query to the SDSS database, using the CasJobs web interface or my own little scripts, I wonder what the DES equivalents for that will look like. It feels a little like waiting for the next release of your favorite gadget. And as a heavy user and big fan, I, of course, have my own wish list of improvements.

Blanco Telescope April 2011. Photo: Jose Francisco Salgado

My number one wish? Support to upload my own little codes, in addition to data tables, and run them directly on the query outputs. This way I could save only the processed tables, use them later in combination with other data, make all my plots and download only the final results. That would make my work so much easier!

Well, but I’d better stop here and go back to work. George is doing well today, but there is still a long way to go. I will be back with more updates soon. Stay tuned.

–Marcelle Soares-Santos

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A replica ring of the top-end of the Blanco telescope built at Fermilab to test assembly and operation of the dark energy camera before shipment to Chile. Credit: Fermilab/Cindy Arnold

This article ran in DOE Pulse April 4.

Building and installing one of the world’s largest digital cameras to solve the mystery of dark energy requires the collaboration of scientists and industry from across the globe. The Dark Energy Survey’s combination of survey area and depth will far surpass the scope of previous projects and provide researchers for the first time with four search techniques in one powerful instrument. More than 120 scientists are collaborating to determine the true nature of dark energy, the mysterious force that accelerates the expansion of the universe. Taking images of galaxies from the time the universe was only a few billion years old, the DES will trace the history of the expanding universe roughly three-quarters of the way back to the time of the Big Bang.

But first researchers needed to build the 570-megapixel camera at DOE’s Fermi National Accelerator Laboratory and make sure it works. Nearly all of the camera’s parts made their way to Fermilab for assembly and testing during the last 12 months. The components were assembled and operated on a full-size replica of the front end of the 4-meter Blanco telescope in Chile, built by Fermilab and Argonne National Laboratory.  Testing finished successfully in February. During the next few months, physicists will be putting the finishing touches on pieces of the camera and shipping them to the Cerro Tololo Inter-American Observatory in Chile where they will receive another round of tests before installation.

The high-tech supply chain tapped the expertise at four DOE Office of Science national laboratories and more than two dozen institutions and universities in the United States and abroad.  More than 120 companies in the United States contributed know-how and parts. Fermilab took the lead in the assembly and testing of the camera and building a cryogenics system several times larger than those used in previous ground-based sky surveys, while Berkeley and Argonne national laboratories played key roles in the camera development.

Berkeley Lab developed the Charge Coupled Devices used in the camera and did some of the processing of the silicon for the CCDs before sending the pieces to Fermilab for packaging of CCD chips. The unique design of these CCDs will give the camera unprecedented sensitivity for red and near-infrared wavelengths, allowing it to record more light for a given exposure time. The camera contains 62 CCDs for observing with 8 million pixels each, plus 12 CCDs with 4 million pixels each for guiding and focusing.

Argonne National Laboratory helped construct the calibration camera to conduct a mini-sky survey last year from a telescope adjacent to the Blanco telescope. This scaled-down version of the dark energy camera allowed for testing of the experiment hardware, software and observing strategies as well as created a baseline of celestial objects for Dark Energy Survey. Argonne also constructed several smaller components for the full-size camera and some large mechanical systems, including the heavy apparatus that installs and removes a 1-ton mirror from the front of the camera.

SLAC National Accelerator Laboratory took the lead in constructing a separate, small telescope with an infrared camera that will sit on a mountain near the Blanco telescope in a separate enclosure. This telescope will monitor cloud coverage so that the Dark Energy Camera can adapt its survey modes to various atmospheric conditions.

The DES collaboration expects to take its first astronomical images with the installed Dark Energy Camera before the end of 2011.

— Tona Kunz

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Lots of interesting particle physics news recently on the Cosmic Frontier front.

Science News reports that the National Research Council’s March 7 report for science in the coming decade recommends completion of the Large Synoptic Space Telescope.

…which will not only probe the nature of dark matter and dark energy but aid in tracking near-Earth asteroids.

LSST  is a huge public and private partnership, which includes many of the national labs, among them Fermilab, which hopes to build on its computing experience with the Sloan Digital Sky Survey to help manage the unprecedented flow of data expected from LSST. The February issue of symmetry magazine outlines the partnership needs the experiment will require.

…the LSST camera will produce 3.2-billion-pixel images and generate, on an average viewing night, about 15 terabytes of raw data, or 25,000 CDs worth. To display one of the LSST full-sky images on a television would require not just a high-definition screen, but 1500 of them.

While LSST is not expected to take data for quite sometime, its predecessor the Dark Energy Survey should start its first sky survey in October. The blog dark matter, dark energy, dark gravity explains how DES will be the first experiment to use four different methods at once to search for dark energy. Medill news services uses a great video to show physicists at Fermilab wrapping up tests on camera components before shipping the final parts to Chile for assembly on the 4-meter Blanco telescope. Sadly, the New York Times reports that the driving force behind making the telescope a bastion of U.S. science in Chile, Victor Blanco, passed away. 

Unlike DES and LSST, the holometer experiment aims not to record the sky as we see it but as Fermilab theorist Craig Hogan thinks it really is: a giant hologram.  The Little India newspaper explains Hogan’s theory and how it relates to black hole science.

Scientists have known for long time that information plays a key role in the creation of a system. Our computers and robots are just metals and wires if no information is exchanged in the form of bits. Our brain is inanimate if no information is carried by the neurons. Our genes are futile if no information is available from DNA that instructs how to function. In everything we know information is the key.

Similarly the entire information about our universe must be encoded elsewhere. Like a hologram on our credit cards, which contains the information in a thin film, and can generate 3D objects when viewed in proper light, the reality we tempt to believe is actually just one way of viewing information printed on a distant cosmic film. What we see and experience as reality are the shadows of the truth.

–Tona Kunz

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As the time for our camera’s first light approaches, workload and excitement increase exponentially among the Dark Energy Survey collaborators and it is about time we start sharing the latter. Beginning today, you will find here at Quantum Diaries an insider’s account of our fast progress, frequently updated as we countdown to first light.

So, here we go. If you haven’t heard of us yet, DES is an experiment designed to investigate dark energy, one of the most trending topics of the last 30 years, featured among the top priorities in the world-wide scientific agenda despite a recent funding blow up. DES will image an area of 5,000-square degrees (nearly 1/8 of the sky) using five optical-bands, obtaining detailed measurements of about 300 million galaxies. With this data we can shed light on the mystery of cosmic acceleration by analyzing four complementary probes: supernovae, baryonic acoustic oscillations, galaxy clusters and weak lensing.

DES will use its own powerful new instrument, the Dark Energy Camera, or DECam, which is under construction at  Fermilab.  Building an entirely new system to answer a specific question is a growing trend in astrophysics, probably a consequence of developing close ties with the field of high energy physics.

This 570-megapixel, giant camera is being tested on a telescope simulator (the yellow and red rings that you see in the video) until the end of this month. As a Fermilab postdoc, I am heavily involved in these tests, together with a team that keeps up the fast pace even during the blizzard last week.

Check out this time-lapse video of the DECam construction:

We are now getting ready for a simulated observing run, a comprehensive integration test of the full system. We will use a star projector to simulate the sky and the goal is to take one night’s worth of data. The atmosphere here at the lab is of stress and excitement as this is our last test of the full system before we bring DECam down from the telescope simulator. The results of this test will be very important to guiding us through the next steps.

So here is where we stand nine months before first light. Stay tuned for more updates here or follow us on Facebook. Leave a message in the comments if you want to know more or would like to visit us while the camera is still up on the simulator.

–Marcelle Soares-Santos

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