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  • richardmitnick 2:37 pm on February 22, 2017 Permalink | Reply
    Tags: , , , Dark Matter,   

    From Fermi: “NASA’s Fermi Finds Possible Dark Matter Ties in Andromeda Galaxy” 

    NASA Fermi Banner


    Feb. 21, 2017
    Claire Saravia
    NASA’s Goddard Space Flight Center, Greenbelt, Md.

    NASA’s Fermi Gamma-ray Space Telescope has found a signal at the center of the neighboring Andromeda galaxy that could indicate the presence of the mysterious stuff known as dark matter. The gamma-ray signal is similar to one seen by Fermi at the center of our own Milky Way galaxy.


    Gamma rays are the highest-energy form of light, produced by the universe’s most energetic phenomena. They’re common in galaxies like the Milky Way because cosmic rays, particles moving near the speed of light, produce gamma rays when they interact with interstellar gas clouds and starlight.

    Surprisingly, the latest Fermi data shows the gamma rays in Andromeda — also known as M31 — are confined to the galaxy’s center instead of spread throughout. To explain this unusual distribution, scientists are proposing that the emission may come from several undetermined sources. One of them could be dark matter, an unknown substance that makes up most of the universe.

    NASA’s Fermi telescope has detected a gamma-ray excess at the center of the Andromeda galaxy that’s similar to a signature Fermi previously detected at the center of our own Milky Way. Watch to learn more.
    Credits: NASA’s Goddard Space Flight Center/Scott Wiessinger, producer

    The gamma-ray excess (shown in yellow-white) at the heart of M31 hints at unexpected goings-on in the galaxy’s central region. Scientists think the signal could be produced by a variety of processes, including a population of pulsars or even dark matter.
    Credits: NASA/DOE/Fermi LAT Collaboration and Bill Schoening, Vanessa Harvey/REU program/NOAO/AURA/NSF

    “We expect dark matter to accumulate in the innermost regions of the Milky Way and other galaxies, which is why finding such a compact signal is very exciting,” said lead scientist Pierrick Martin, an astrophysicist at the National Center for Scientific Research and the Research Institute in Astrophysics and Planetology in Toulouse, France. “M31 will be a key to understanding what this means for both Andromeda and the Milky Way.”

    A paper describing the results will appear in an upcoming issue of The Astrophysical Journal.

    Another possible source for this emission could be a rich concentration of pulsars in M31’s center. These spinning neutron stars weigh as much as twice the mass of the sun and are among the densest objects in the universe. One teaspoon of neutron star matter would weigh a billion tons on Earth. Some pulsars emit most of their energy in gamma rays. Because M31 is 2.5 million light-years away, it’s difficult to find individual pulsars. To test whether the gamma rays are coming from these objects, scientists can apply what they know about pulsars from observations in the Milky Way to new X-ray and radio observations of Andromeda.

    Now that Fermi has detected a similar gamma-ray signature in both M31 and the Milky Way, scientists can use this information to solve mysteries within both galaxies. For example, M31 emits few gamma rays from its large disk, where most stars form, indicating fewer cosmic rays roaming there. Because cosmic rays are usually thought to be related to star formation, the absence of gamma rays in the outer parts of M31 suggests either that the galaxy produces cosmic rays differently, or that they can escape the galaxy more rapidly. Studying Andromeda may help scientists understand the life cycle of cosmic rays and how it is connected to star formation.

    “We don’t fully understand the roles cosmic rays play in galaxies, or how they travel through them,” said Xian Hou, an astrophysicist at Yunnan Observatories, Chinese Academy of Sciences in Kunming, China, also a lead scientist in this work. “M31 lets us see how cosmic rays behave under conditions different from those in our own galaxy.”

    The similar discovery in both the Milky Way and M31 means scientists can use the galaxies as models for each other when making difficult observations. While Fermi can make more sensitive and detailed observations of the Milky Way’s center, its view is partially obscured by emission from the galaxy’s disk. But telescopes view Andromeda from an outside vantage point impossible to attain in the Milky Way.

    “Our galaxy is so similar to Andromeda, it really helps us to be able to study it, because we can learn more about our galaxy and its formation,” said co-author Regina Caputo, a research scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “It’s like living in a world where there’s no mirrors but you have a twin, and you can see everything physical about the twin.”

    While more observations are necessary to determine the source of the gamma-ray excess, the discovery provides an exciting starting point to learn more about both galaxies, and perhaps about the still elusive nature of dark matter.

    “We still have a lot to learn about the gamma-ray sky,” Caputo said. “The more information we have, the more information we can put into models of our own galaxy.”

    NASA’s Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy and with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

    For more information on Fermi, visit:


    See the full article here .

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    NASA’s Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy and with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

  • richardmitnick 2:48 pm on February 18, 2017 Permalink | Reply
    Tags: , Dark Matter, ,   

    From Nautilus: “Dark Matter May Show Quantum Effects on a Galactic Scale” 



    David “Doddy” Marsh

    This weird type of dark matter would also puff up galaxies and make stars age prematurely.

    Microwave cavity in the ADMX axion detection experiment at the University of Washington. Credit: ADMX.

    U Washington ADMX
    U Washington ADMX

    An axion is a theoretical particle named after a laundry detergent. As particles go, it is a strange one. Its mass is tiny—somewhere between one trillionth the mass of the proton and one billion-trillion-trillionth. It is so lightweight, in fact, that it doesn’t even behave as a particle, but as a wave that could straddle a galaxy. It is also feeble—its influence extends over an almost absurdly short distance, a millionth of what the Large Hadron Collider is able to discern. These short distances stem from the possible relation between axions and very high energy physics, possibly even quantum gravity.

    When I first heard of the axion, I had no idea it would become my life’s work. I was a new grad student looking for a starter project, and I came across a paper with such a peculiar title that I couldn’t help but read it: “String Axiverse.” It was written by a group of people including John March-Russell, a theoretical physicist in my department at Oxford. Speaking to John and cosmologist Pedro Ferreira (who both later became my Ph.D. advisors), I realized that the axion was just what I wanted to work on: a fascinating theoretical construct, but with direct connection to the exciting modern progress in cosmology.

    An unknown particle that may exist in profusion: the axion is an ideal candidate for dark matter. But it is a very different beast than we’re used to thinking about, requiring us to go about the search for dark matter in a different way.

    The Nobelist Frank Wilczek gave the axion its name because it cleaned up a problem in the Standard Model of particle physics. In the 1970s, he and others puzzled over a mismatch between the two forces that govern atomic nuclei: the strong and weak nuclear forces. The strong force has a symmetry in its workings that the weak lacks, even though, a priori, there is no reason it should. Helen Quinn and Robert Peccei proposed that the force is not innately symmetrical, but develops this symmetry under the action of a new field akin to the Higgs field. The axion particle is a remnant of this field.

    To play its role, the axion must be extremely lightweight. For our current theories, that is awkward, because it creates an enormous gulf between this particle and all the others. But the low mass is entirely natural in string theory, our leading candidate for a unified theory of nature. String theory predicts there is not just one type of axion, but there are typically 30 or more different kinds, and it predicts that their masses are spread out over a wide range. Some therefore must be lightweight. String theory is often criticized for not making testable predictions, but that’s not quite right, because the theory does predict axions. Although I wouldn’t claim that discovering lots of axions would be evidence for string theory, I think it is fairly safe to say that, according to almost any theory other than string theory, it would be surprising if we discovered large numbers of them.

    If axion dark matter exists, it is completely invisible to a conventional experiment.

    Axions are like other candidates for dark matter in that they are dark—they have no electric charge and therefore do not emit or absorb light—and interact very weakly with ordinary matter. But there the resemblance stops. Compare it to the most commonly discussed type of dark matter, the WIMP, or weakly interacting massive particle.

    It is a so-called thermal relic, which, according to theory, is produced the same way as protons, neutrons, and atomic nuclei: from the collisions between particles in the hot, dense, early universe. Given the amount of missing mass that astronomers infer, this production mechanism for WIMPs sets their mass and interaction strength: 100 times the mass of the proton (hence “massive”) with an interaction strength roughly equal to the weak nuclear force (hence “weakly interacting”). These would be lumbering particles, and that is just what astronomers need to explain the distribution of galaxies. If they exist, we should be able to detect them in particle detectors similar to those we use to detect neutrinos, and we should even be able to produce them ourselves by mimicking those hot, dense conditions in the Large Hadron Collider.

    CERN/LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN

    Axions, in contrast, have a different origin story. Their production is determined not by the temperature of the plasma in the early universe, but gravitationally, by the expansion of space in the big bang. This production mechanism sets their mass and interaction strength, which are vastly different from those of WIMPs.

    Big Bang to today
    Big Bang to today. http://www.sun.org/encyclopedia/a-short-history-of-the-universe

    Axions would interact with ordinary matter to a limited degree, but only by a unique set of interactions. For this reason, if axion dark matter exists, it is completely invisible to a conventional experiment such a WIMP detector or even the Large Hadron Collider.

    The poster-child axion direct-detection experiment is ADMX, which operates at the University of Washington and relies on a concept invented by Pierre Sikivie in 1983. Though “dark”, axions do interact with electromagnetism in other ways and, in the presence of a magnetic field, can metamorphose into photons or vice versa. ADMX attempts to perform the metamorphosis inside a microwave radio-frequency cavity like those used in radar equipment and microwave relay stations. So far ADMX have observed nothing, but it is sensitive only to axions whose wavelengths are comparable to the size of the cavity, and it has still not completed its full search program. Proposed experiments such as MADMAX and CASPEr would probe a much wider range of wavelengths.

    In principle, axions might have shown up in experiments intended for other purposes. With colleagues at the University of Sussex, the Swiss Federal Institute of Technology, and the University of New South Wales, as well as two talented grad students, Nicholas Ayres and Michał Rawlik, I have been digging through the archives of the nEDM experiment, which ran for a number of years at the Institut Laue-Langevin in France and is now at the Paul Scherrer Institute in Switzerland. It has been measuring neutrons, which would oscillate in a particular way if a galactic axion wave happened to pass through it, and we are reanalyzing the data to look for this signal.


    In this field, there’s room for young theorists such as me to make headway.

    If axions exist, stars would produce them naturally. Some of the photons produced during nuclear fusion in the core could metamorphose into axions, and they would escape the star more readily than photons do. This would drain the star of energy and cause it to age faster. Astronomers have been combing through star clusters for stars that look older than they actually are, and they have found no evidence of extra cooling. This null result sets limits on how strongly axions can interact with the constituents of stars.

    With my colleagues Dan Grin and Renée Hložek, I have also been searching for axions in cosmological data. Their wavelike properties might give them away. Over distances smaller than the axion wavelength, multiple axion waves would overlap and interfere with one another, causing them to exert an outward pressure and puff up galaxies. And indeed astronomers do find that galaxies are less clumpy than WIMPs should cause them to be (although there are many possible explanations for this, not just axions). My colleagues and I have been exploring this idea further by combining galaxy data with cosmic microwave background radiation measurements, as well as conducting simulations of galaxy formation with axion dark matter.

    Finally, axions would alter what happened during cosmic inflation, the primeval period when the universe was expanding at a breakneck rate. Cosmologists generally think the inflationary process created a torrent of gravitational waves, but if dark matter is made of axions, it would have generated very few. So, the discovery of primordial gravitational waves could be taken as falsification of the axion idea, at least in a wide range of models. (If we ever detected both axion dark matter and these gravitational waves, then something would be wrong with standard inflationary theory.)

    Only a small band of devotees have given much thought to axions. That makes it a fun field to be working in. There’s room for young theorists such as me to make headway and feel like we’re adding to the understanding of the community, which is much harder to do in a more mature field such studying WIMPs.

    It should be said that there is room in the universe for both axions and WIMPs. Both have a firm grounding in fundamental physics and in cosmology, and both may exist out there. For me, one of the benefits of thinking about axions is that they force to think beyond WIMPs. If all we ever do is study and simulate WIMPs because it is relatively easy, as a community we run the risk of confirmation bias, where WIMPs always come up trumps because they are all we know. Thankfully, that doesn’t seem to be how the field of dark-matter research is going. People are exploring a huge range. Dark matter is out there and discovering it is just a matter of time. When we do discover it, whatever it is, it will revolutionize our ideas of particle physics and cosmology.

    See the full article here .

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  • richardmitnick 10:02 pm on February 13, 2017 Permalink | Reply
    Tags: , Dark Matter, , LUX-ZEPLIN (LZ) dark matter-hunting experiment, ,   

    From LBNL: “Next-Gen Dark Matter Detector in a Race to Finish Line” 

    Berkeley Logo

    Berkeley Lab

    February 13, 2017
    Glenn Roberts Jr.

    Light-amplifying devices known as photomultiplier tubes (PMTs), developed for use in the LUX-ZEPLIN (LZ) dark matter-hunting experiment, are prepared for a test at Brown University. This test bed, dubbed PATRIC, will be used to test over 600 PMTs in conditions simulating the temperature and pressure of the liquid xenon that will be used for LZ. (Credit: Brown University)

    The race is on to build the most sensitive U.S.-based experiment designed to directly detect dark matter particles. Department of Energy officials have formally approved a key construction milestone that will propel the project toward its April 2020 goal for completion.

    The LUX-ZEPLIN (LZ) experiment, which will be built nearly a mile underground at the Sanford Underground Research Facility (SURF) in Lead, S.D., is considered one of the best bets yet to determine whether theorized dark matter particles known as WIMPs (weakly interacting massive particles) actually exist. There are other dark matter candidates, too, such as “axions” or “sterile neutrinos,” which other experiments are better suited to root out or rule out.

    SURF logo
    SURF – Sanford Underground Research Facility at Lead, SD, USA

    The fast-moving schedule for LZ will help the U.S. stay competitive with similar next-gen dark matter direct-detection experiments planned in Italy and China.

    This image shows a cutaway rendering of the LUX-ZEPLIN (LZ) detector that will search for dark matter nearly a mile below ground. An array of detectors, known as photomultiplier tubes, at the top and bottom of the liquid xenon tank are designed to pick up particle signals. (Credit: Matt Hoff/Berkeley Lab)

    On Feb. 9, the project passed a DOE review and approval stage known as Critical Decision 3 (CD-3), which accepts the final design and formally launches construction.

    “We will try to go as fast as we can to have everything completed by April 2020,” said Murdock “Gil” Gilchriese, LZ project director and a physicist at the DOE’s Lawrence Berkeley National Laboratory (Berkeley Lab), the lead lab for the project. “We got a very strong endorsement to go fast and to be first.” The LZ collaboration now has about 220 participating scientists and engineers who represent 38 institutions around the globe.

    The nature of dark matter—which physicists describe as the invisible component or so-called “missing mass” in the universe that would explain the faster-than-expected spins of galaxies, and their motion in clusters observed across the universe—has eluded scientists since its existence was deduced through calculations by Swiss astronomer Fritz Zwicky in 1933.

    The quest to find out what dark matter is made of, or to learn whether it can be explained by tweaking the known laws of physics in new ways, is considered one of the most pressing questions in particle physics.

    Successive generations of experiments have evolved to provide extreme sensitivity in the search that will at least rule out some of the likely candidates and hiding spots for dark matter, or may lead to a discovery.

    The underground home of LZ and its supporting systems are shown in this computerized rendering. (Credit: Matt Hoff/Berkeley Lab)

    LZ will be at least 50 times more sensitive to finding signals from dark matter particles than its predecessor, the Large Underground Xenon experiment (LUX), which was removed from SURF last year to make way for LZ. The new experiment will use 10 metric tons of ultra-purified liquid xenon, to tease out possible dark matter signals. Xenon, in its gas form, is one of the rarest elements in Earth’s atmosphere.

    “The science is highly compelling, so it’s being pursued by physicists all over the world,” said Carter Hall, the spokesperson for the LZ collaboration and an associate professor of physics at the University of Maryland. “It’s a friendly and healthy competition, with a major discovery possibly at stake.”

    This chart shows the sensitivity limits (solid-line curves) of various experiments searching for signs of theoretical dark matter particles known as WIMPs, with LZ (green dashed line) set to expand the search range. (Credit: Snowmass report, 2013)

    A planned upgrade to the current XENON1T experiment at National Institute for Nuclear Physics’ Gran Sasso Laboratory (the XENONnT experiment) in Italy, and China’s plans to advance the work on PandaX-II, are also slated to be leading-edge underground experiments that will use liquid xenon as the medium to seek out a dark matter signal.

    Assembly of the XENON1T TPC in the cleanroom. (Image: INFN)

    Gran Sasso LABORATORI NAZIONALI del GRAN SASSO, located in the Abruzzo region of central Italy
    Gran Sasso LABORATORI NAZIONALI del GRAN SASSO, located in the Abruzzo region of central Italy


    Both of these projects are expected to have a similar schedule and scale to LZ, though LZ participants are aiming to achieve a higher sensitivity to dark matter than these other contenders.

    Hall noted that while WIMPs are a primary target for LZ and its competitors, LZ’s explorations into uncharted territory could lead to a variety of surprising discoveries. “People are developing all sorts of models to explain dark matter,” he said. “LZ is optimized to observe a heavy WIMP, but it’s sensitive to some less-conventional scenarios as well. It can also search for other exotic particles and rare processes.”

    LZ is designed so that if a dark matter particle collides with a xenon atom, it will produce a prompt flash of light followed by a second flash of light when the electrons produced in the liquid xenon chamber drift to its top. The light pulses, picked up by a series of about 500 light-amplifying tubes lining the massive tank—over four times more than were installed in LUX—will carry the telltale fingerprint of the particles that created them.

    Inside LZ: When a theorized dark matter particle known as a WIMP collides with a xenon atom, the xenon atom emits a flash of light (gold) and electrons. The flash of light is detected at the top and bottom of the liquid xenon chamber. An electric field pushes the electrons to the top of the chamber, where they generate a second flash of light (red). (Credit: SLAC National Accelerator Laboratory)

    Daniel Akerib, Thomas Shutt, and Maria Elena Monzani are leading the LZ team at SLAC National Accelerator Laboratory. The SLAC effort includes a program to purify xenon for LZ by removing krypton, an element that is typically found in trace amounts with xenon after standard refinement processes. “We have already demonstrated the purification required for LZ and are now working on ways to further purify the xenon to extend the science reach of LZ,” Akerib said.

    SLAC and Berkeley Lab collaborators are also developing and testing hand-woven wire grids that draw out electrical signals produced by particle interactions in the liquid xenon tank. Full-size prototypes will be operated later this year at a SLAC test platform. “These tests are important to ensure that the grids don’t produce low-level electrical discharge when operated at high voltage, since the discharge could swamp a faint signal from dark matter,” said Shutt.

    Assembly of the prototype for the LZ detector’s core, known as a time projection chamber (TPC). From left: Jeremy Mock (State University of New York/Berkeley Lab), Knut Skarpaas, and Robert Conley. (Credit: SLAC National Accelerator Laboratory)

    Hugh Lippincott, a Wilson Fellow at Fermi National Accelerator Laboratory (Fermilab) and the physics coordinator for the LZ collaboration, said, “Alongside the effort to get the detector built and taking data as fast as we can, we’re also building up our simulation and data analysis tools so that we can understand what we’ll see when the detector turns on. We want to be ready for physics as soon as the first flash of light appears in the xenon.” Fermilab is responsible for implementing key parts of the critical system that handles, purifies, and cools the xenon.

    All of the components for LZ are painstakingly measured for naturally occurring radiation levels to account for possible false signals coming from the components themselves. A dust-filtering cleanroom is being prepared for LZ’s assembly and a radon-reduction building is under construction at the South Dakota site—radon is a naturally occurring radioactive gas that could interfere with dark matter detection. These steps are necessary to remove background signals as much as possible.

    A rendering of the Surface Assembly Laboratory in [at SURF] South Dakota where LZ components will be assembled before they are relocated underground. (Credit: LZ collaboration)

    The vessels that will surround the liquid xenon, which are the responsibility of the U.K. participants of the collaboration, are now being assembled in Italy. They will be built with the world’s most ultra-pure titanium to further reduce background noise.

    To ensure unwanted particles are not misread as dark matter signals, LZ’s liquid xenon chamber will be surrounded by another liquid-filled tank and a separate array of photomultiplier tubes that can measure other particles and largely veto false signals. Brookhaven National Laboratory is handling the production of another very pure liquid, known as a scintillator fluid, that will go into this tank.

    A production prototype of highly purified, gadolinium-doped scintillator fluid, viewed under ultraviolet light. Scintillator fluid will surround LZ’s xenon tank and will help scientists veto the background “noise” of unwanted particle signals. (Credit: Brookhaven National Laboratory)

    The cleanrooms will be in place by June, Gilchriese said, and preparation of the cavern where LZ will be housed is underway at SURF. Onsite assembly and installation will begin in 2018, he added, and all of the xenon needed for the project has either already been delivered or is under contract. Xenon gas, which is costly to produce, is used in lighting, medical imaging and anesthesia, space-vehicle propulsion systems, and the electronics industry.

    “South Dakota is proud to host the LZ experiment at SURF and to contribute 80 percent of the xenon for LZ,” said Mike Headley, executive director of the South Dakota Science and Technology Authority (SDSTA) that oversees SURF. “Our facility work is underway and we’re on track to support LZ’s timeline.”

    UK scientists, who make up about one-quarter of the LZ collaboration, are contributing hardware for most subsystems. Henrique Araújo, from Imperial College London, said, “We are looking forward to seeing everything come together after a long period of design and planning.”

    LZ participants conduct a quality-control inspection of photomultiplier tube bases that are being manufactured at Imperial College London. (Credit: Henrique Araújo /Imperial College London)

    Kelly Hanzel, LZ project manager and a Berkeley Lab mechanical engineer, added, “We have an excellent collaboration and team of engineers who are dedicated to the science and success of the project.” The latest approval milestone, she said, “is probably the most significant step so far,” as it provides for the purchase of most of the major components in LZ’s supporting systems.

    For more information about LZ and the LZ collaboration, visit: http://lz.lbl.gov/.

    Major support for LZ comes from the DOE Office of Science’s Office of High Energy Physics, South Dakota Science and Technology Authority, the UK’s Science & Technology Facilities Council, and by collaboration members in South Korea and Portugal.

    Both of these projects are expected to have a similar schedule and scale to LZ, though LZ participants are aiming to achieve a higher sensitivity to dark matter than these other contenders.

    See the full article here .

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  • richardmitnick 9:29 am on January 30, 2017 Permalink | Reply
    Tags: , Dark Matter, , ,   

    From The Conversation: “Giant atoms could help unveil ‘dark matter’ and other cosmic secrets” 

    The Conversation

    January 5, 2017
    Diego A. Quiñones

    Composite image showing the galaxy cluster 1E 0657-56. Chandra X-Ray Observatory/NASA

    The universe is an astonishingly secretive place. Mysterious substances known as dark matter and dark energy account for some 95% of it. Despite huge effort to find out what they are, we simply don’t know.

    We know dark matter exists because of the gravitational pull of galaxy clusters – the matter we can see in a cluster just isn’t enough to hold it together by gravity. So there must be some extra material there, made up by unknown particles that simply aren’t visible to us. Several candidate particles have already been proposed.

    Scientists are trying to work out what these unknown particles are by looking at how they affect the ordinary matter we see around us. But so far it has proven difficult, so we know it interacts only weakly with normal matter at best. Now my colleague Benjamin Varcoe and I have come up with a new way to probe dark matter that may just prove successful: by using atoms that have been stretched to be 4,000 times larger than usual.

    Advantageous atoms

    We have come a long way from the Greeks’ vision of atoms as the indivisible components of all matter. The first evidence-based argument for the existence of atoms was presented in the early 1800s by John Dalton. But it wasn’t until the beginning of the 20th century that JJ Thomson and Ernest Rutherford discovered that atoms consist of electrons and a nucleus. Soon after, Erwin Schrödinger described the atom mathematically using what is today called quantum theory.

    Modern experiments have been able to trap and manipulate individual atoms with outstanding precision. This knowledge has been used to create new technologies, like lasers and atomic clocks, and future computers may use single atoms as their primary components.

    Individual atoms are hard to study and control because they are very sensitive to external perturbations. This sensitivity is usually an inconvenience, but our study suggests that it makes some atoms ideal as probes for the detection of particles that don’t interact strongly with regular matter – such as dark matter.

    Our model is based on the fact that weakly interacting particles must bounce from the nucleus of the atom it collides with and exchange a small amount of energy with it – similar to the collision between two pool balls. The energy exchange will produce a sudden displacement of the nucleus that will eventually be felt by the electron. This means the entire energy of the atom changes, which can be analysed to obtain information about the properties of the colliding particle.

    However the amount of transferred energy is very small, so a special kind of atom is necessary to make the interaction relevant. We worked out that the so-called “Rydberg atom” would do the trick. These are atoms with long distances between the electron and the nucleus, meaning they possess high potential energy. Potential energy is a form of stored energy. For example, a ball on a high shelf has potential energy because this could be converted to kinetic energy if it falls off the shelf.

    In the lab, it is possible to trap atoms and prepare them in a Rydberg state – making them as big as 4,000 times their original size. This is done by illuminating the atoms with a laser with light at a very specific frequency.

    This prepared atom is likely much heavier than the dark matter particles. So rather than a pool ball striking another, a more appropriate description will be a marble hitting a bowling ball. It seems strange that big atoms are more perturbed by collisions than small ones – one may expect the opposite (smaller things are usually more affected when a collision occurs).

    The explanation is related to two features of Rydberg atoms: they are highly unstable because of their elevated energy, so minor perturbations would disturb them more. Also, due to their big area, the probability of the atoms interacting with particles is increased, so they will suffer more collisions.

    Spotting the tiniest of particles

    Current experiments typically look for dark matter particles by trying to detect their scattering off atomic nuclei or electrons on Earth. They do this by looking for light or free electrons in big tanks of liquid noble gases that are generated by energy transfer between the dark matter particle and the atoms of the liquid.

    The Large Underground Xenon experiment installed 4,850 ft underground inside a 70,000-gallon water tank shield. Gigaparsec at English Wikipedia, CC BY-SA

    But, according to the laws of quantum mechanics, there needs to be a certain a minimum energy transfer for the light to be produced. An analogy would be a particle colliding with a guitar string: it will produce a note that we can hear, but if the particle is too small the string will not vibrate at all.

    So the problem with these methods is that the dark matter particle has to be big enough if we are to detect it in this way. However, our calculations show that the Rydberg atoms will be disturbed in a significant way even by low-mass particles – meaning they can be applied to search for candidates of dark matter that other experiments miss. One of such particles is the Axion, a hypothetical particle which is a strong candidate for dark matter.

    Experiments would require for the atoms to be treated with extreme care, but they will not require to be done in a deep underground facility like other experiments, as the Rydberg atoms are expected to be less susceptible to cosmic rays compared to dark matter.

    We are working to further improve the sensitivity of the system, aiming to extend the range of particles that it may be able to perceive.

    Beyond dark matter we are also aiming to one day apply it for the detection of gravitational waves, the ripples in the fabric of space predicted by Einstein long time ago. These perturbations of the space-time continuum have been recently discovered, but we believe that by using atoms we may be able to detect gravitational waves with a different frequency to the ones already observed.

    See the full article here .

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    • gregoriobaquero 9:46 am on January 30, 2017 Permalink | Reply

      Precisely to the point of my paper. If I am right nothing is going to be found. No new particles. The density of neutrinos”hot Dark Matter”) we can measure in our frame of reference does not tell the whole picture since we have the same local time with neutrinos passing by. What had not been taken into account is that gravitational time dilation is accumulating neutrinos when compared to neutrinos passing far away from the galaxy. Sent from my iPhone



    • gregoriobaquero 9:48 am on January 30, 2017 Permalink | Reply

      Also, this phenomenon is similar to how relativity explains electromagnetism. Veritasium has a good video about it.

      Sent from my iPhone



    • gregoriobaquero 9:54 am on January 30, 2017 Permalink | Reply

      Precisely to the point of my paper. If I am right nothing is going to be found. No new particles. The density of neutrinos”hot Dark Matter”) we can measure in our frame of reference does not tell the whole picture since we have the same local time with neutrinos passing by. What had not been taken into account is that gravitational time dilation is accumulating neutrinos when compared to neutrinos passing far away from the galaxy.

      Also, this phenomenon is similar to how relativity explains electromagnetism. Veritasium has a good video about it.


    • richardmitnick 10:19 am on January 30, 2017 Permalink | Reply

      Thank you so much for coming on to comment. I appreciate it very much.


  • richardmitnick 3:52 pm on January 11, 2017 Permalink | Reply
    Tags: , , , , Dark Matter, , ,   

    From PI via Motherboard: “Dark Matter Hunters Are Hoping 2017 is Their Year” 

    Perimeter Institute
    Perimeter Institute


    January 3, 2017
    Kate Lunau

    It can be unsettling to realize that only five percent of the universe is made of the kind of matter we know and understand—everything from the planets and stars, to trees and animals and your dining room table.

    Roughly one-quarter is dark matter. This is thought to knit the galaxies together, and has been called the “scaffolding” of the universe, but we’ve never detected it directly. Scientists believe they can see dark matter’s traces in the way that galaxies rotate, but they still have no idea what it is. (Most of the universe, about 70 percent, is dark energy, a mysterious force that permeates space and time. It’s even less well-understood than dark matter.)

    Confirming dark matter’s existence would change humankind’s perspective on the universe. 2016 was a year of dark matter disappointments, as big searches came up empty. Most are looking for WIMPs—weakly interacting massive particles, the leading contender for a dark matter particle.

    2017 might just be the year we finally catch one. And if we don’t, well, it may be that our best theories about dark matter are wrong—that we’re looking in the wrong places, with the wrong instruments. Maybe dark matter, whatever it is, will turn out to be even weirder and more surprising than anyone has so far predicted. Maybe it’s not a WIMP, but some other bizarre kind of particle.

    Then there’s the outside possibility that dark matter doesn’t exist, that it’s an illusion. If that’s the case, we’ll have to consider whether we’ve been fundamentally misreading the universe’s clues.

    Buried deep in a mine near Sudbury in northern Ontario is SNOLAB, a vast underground laboratory where scientists are performing a range of experiments, including looking for dark matter. Often compared to the lair of a Bond villain, it’s an ultra-clean, high-tech facility. Two kilometers of solid rock overhead shield its detectors from cosmic radiation, allowing them to sift for bits of matter from dying stars and the Sun: science done here won the Nobel Prize in Physics, in 2015.

    A scientist works on the deck of DEAP-3600, a dark matter search at SNOLAB. Image: SNOLAB

    I recently travelled to SNOLAB. To get there, I had to don full mining gear (including a hardhat and headlamp), drop down underground in a rattling dark cage, and hike a kilometre or so to reach the gleaming white facility, which is cleaner inside than an operating room—a startling contrast to the dirty nickel mine that surrounds it.

    After the long hike through the mine, anyone who wants to enter SNOLAB has to undress, shower (with soap and shampoo), and put on lint-free clothing and a hairnet. Any bit of dust from the mine, which is naturally radioactive, can mess up the experiments.

    There, I met research scientist Ken Clark, a congenial physicist with a sandy-coloured beard. Like me, he was wearing safety goggles and a hardhat. Clark has worked on high-profile dark matter searches like CDMS and LUX, and collaborates on the IceCube detector at the South Pole in Antarctica.

    LBL SuperCDMS
    LBL SuperCDMS, at SNOLAB (Vale Inco Mine, Sudbury, Canada)
    LBL SuperCDMS, at SNOLAB (Vale Inco Mine, Sudbury, Canada)

    LUX Xenon experiment at SURF
    LUX Xenon experiment at SURF, Lead, SD, USA

    U Wisconsin ICECUBE neutrino detector at the South Pole
    IceCube neutrino detector interior
    U Wisconsin ICECUBE neutrino detector at the South Pole

    Now he’s with PICO, a dark matter search that targets the WIMP particle.


    It was launched in 2013 when two other collaborations, called PICASSO and COUPP, merged.

    A multi-bubble image of a neutron scattering in the PICO detector. Image: PICO Collaboration

    PICO is a bubble detector: a tank of superheated fluid kept higher than its natural boiling point. If dark matter bumps into the nucleus of another particle in the detector, it should cause a tiny bubble to form. Dark matter courses through the Earth and right through our bodies, so it will reach the detector underground, even through all that rock overhead. But that’s also part of the challenge—dark matter is thought to only rarely interact with normal matter, if at all, so it’s really tricky to catch.

    Clark believes we might just find dark matter in the next year or two. “It’s exciting times,” he said.

    Other searches are due to turn on soon, he explained, and those that are already up-and-working are getting increasingly sensitive. In 2017, Clark said it’s possible we’ll see new results from PICO, DEAP (a different detector, also at SNOLAB), as well as China’s ambitious PandaX project, and another in Italy called XENON1T. Even more searches will turn on in 2018.

    “Provided the models are correct, we should see something soon,” Clark told me.

    A scientist works on the steel vessel of DEAP-3600. Image: DEAP Collaboration

    Still, there’s no guarantee, and WIMP searches keep turning up empty-handed. For example, in the summer, the highly sensitive LUX—which uses liquid xenon in a South Dakota mine as its detector—announced it had seen zero WIMPs, after looking for more than a year.

    I phoned Lisa Randall, a prominent theoretical physicist and professor at Harvard University, to ask whether she thinks there’s a chance we’ll find dark matter in the next year or two.

    “I would say kind of the opposite,” said Randall, author of Dark Matter and the Dinosaurs. While she agrees that if dark matter is indeed a WIMP, these searches could find it soon, “that’s just one possibility,” she said.

    The WIMP is “lowest-hanging fruit,” Randall continued: this theoretical particle fits snugly within what’s already known about the Standard Model of physics, which explains how the building blocks of the universe interact. And scientists can imagine ways to actually look for WIMPs, unlike some of the more far-out theories, which are much harder to test in experiments.

    “What if it’s not a WIMP?” Randall said. “Could we still learn something about what dark matter is?”

    Other scientists have different strategies for solving the dark matter puzzle.

    Leslie Rosenberg, a professor of physics at the University of Washington in Seattle, is project scientist on the Axion Dark Matter Experiment, or ADMX, which is looking for a theoretical particle called the axion, which is thought to be much lighter than a WIMP.

    ADMX Axion Dark Matter Experiment
    U Washington ADMX
    U Washington ADMX

    It’s being targeted by other searches under development around the world, Rosenberg told me. ADMX, though, is “the only high-sensitivity axion search now,” he said.

    Maybe we’re being fooled into thinking that dark matter is there.

    ADMX, which uses a resonant microwave cavity nested inside a huge superconducting magnet, started out of a collaboration that began in the mid-nineties. It’s been at full sensitivity for about a year now, Rosenberg told me, and will only get better as the team continues to tweak it. He’s hoping they turn up something soon: their next update should come in the summer of 2017.

    “Axions are bound up in our galaxy,” Rosenberg said. “There [should be] an awful lot of them, and we depend on that as the source of our signal.”

    Axions are a mainstream dark matter candidate. Other ideas get weirder.

    “Personally, I’m interested in the idea that dark matter might have nothing to do with the Standard Model,” Randall told me. “One of the possibilities is that it could be some other type of particle. Maybe it interacts [with itself] via its own light, a dark photon.”

    ESA/Gaia’s first sky map of the Milky Way, based on data collected from July 2014 to Sept. 2015. Image: ESA/Gaia/DPAC

    Randall thinks that one of the best ways to learn about dark matter may be to study the structure of galaxies, and watching the universe at work, to understand how it interacts with itself. The European Space Agency’s Gaia mission, which is making a three-dimensional map of over a thousand million stars, could give insight into some of this, Randall said.

    Asimina Arvanitaki, a theoretical physicist at the Perimeter Institute for Theoretical Physics, suggested to me in a Skype call that dark matter might be detectable through resonant-mass detectors, which are used to hunt for gravitational waves. These ripples in spacetime were detected for the first time in 2016, a hundred years after Albert Einstein predicted their existence.

    Dark matter could also be behaving like a wave, “trapped by gravity and oscillat[ing] at a frequency set by the mass,” she said.

    “The funny thing is you could perhaps even hear dark matter,” Arvanitaki said, “depending on the frequency.”

    Over millions of years, humans have come up with ingenious ways to probe the world around us, from Copernicus and Kepler, through the thousands of scientists involved in the search for the Higgs boson particle at the Large Hadron Collider, and those who are now shaking out the endless diversity of exoplanets that populate our galaxy.

    Because of them, our perspective has changed. When we look up at the night sky today, we understand that just about every star we see hosts at least one planet. The first confirmed exoplanet was announced just over two decades ago.

    Nature can still surprise us.

    The Bullet cluster, formed by the collision of two large galaxy clusters, provides some of the best evidence yet for dark matter. Image: X-ray: NASA/CXC/CfA/M.Markevitch et al.; Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.; Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/D.Clowe et al.

    “There’s a chance that dark matter isn’t necessarily a particle at all,” Clark told me. “Some [theorists] say there’s no dark matter. It’s just that we don’t understand how gravity works at large scales,” he continued. “If that’s the case, we’re being fooled into thinking that dark matter is there.”

    Clark and the other dark matter hunters continue their search. If it’s real, “we’re not even made of what most of the universe is made of,” Rosenberg told me. In the grand scheme of things, then, it isn’t dark matter that’s really so exotic and strange—it’s us.

    See the full article here .

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    About Perimeter

    Perimeter Institute is the world’s largest research hub devoted to theoretical physics. The independent Institute was founded in 1999 to foster breakthroughs in the fundamental understanding of our universe, from the smallest particles to the entire cosmos. Research at Perimeter is motivated by the understanding that fundamental science advances human knowledge and catalyzes innovation, and that today’s theoretical physics is tomorrow’s technology. Located in the Region of Waterloo, the not-for-profit Institute is a unique public-private endeavour, including the Governments of Ontario and Canada, that enables cutting-edge research, trains the next generation of scientific pioneers, and shares the power of physics through award-winning educational outreach and public engagement.

  • richardmitnick 8:37 am on December 21, 2016 Permalink | Reply
    Tags: , Cryogenic Dark Matter Search (CDMS), Dark Matter, ,   

    From FNAL: “SuperCDMS: An end and a beginning” 

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    December 15, 2016
    Dan Bauer

    One year ago, the Cryogenic Dark Matter Search (CDMS) collaboration warmed up its apparatus at the Soudan Underground Laboratory in northern Minnesota, after 12 years of successful operation.


    Soudan Underground Lab at the site of te Soudan Underground Mine on the South Shore of Lake Vermillion in the Vermillian Range, Minnesota, USA

    The CDMS II and SuperCDMS Soudan experiments produced many world-leading limits on dark matter particle detection during that time, covering masses from a few GeV to a few TeV. However, the sensitivity was limited by backgrounds and by environmental noise from the design of the facility.

    Meanwhile, based on the success of the CDMS experiments at Soudan, DOE and NSF selected the SuperCDMS collaboration to develop a next-generation experiment to be based at SNOLAB, a deeper and cleaner environment located near Sudbury in Ontario, Canada.

    SNOLAB, Sudbury, Ontario, Canada.
    SNOLAB, Sudbury, Ontario, Canada

    The focus of the new experiment will be a search for dark matter particles with masses less than 10 GeV/c2, based on the demonstrated SuperCDMS Soudan detector technologies. Such light dark matter is a feature of theoretical models that postulate a “dark sector” of particles that interact only very weakly with normal matter. The ultimate goal for SuperCDMS SNOLAB is to search for such light dark matter to sensitivities where the experiment will begin to see elastic scattering of solar neutrinos with its germanium and silicon targets.

    Thus, to focus its attention on developing the new experiment, the collaboration took the painful step of turning off a running experiment at Soudan, saying goodbye to the incredibly helpful staff from the University of Minnesota and recovering its equipment, much of which will be reused for SuperCDMS SNOLAB. To facilitate the recovery of equipment from Soudan, and provide a space for SuperCDMS SNOLAB to be built, PPD renovated an existing hall at Fermilab with the rather pedestrian designation Lab G. Lighting, HVAC and other utilities have been modernized, and a large cleanroom has been installed. The photographs shows this new clean space, which will be the temporary home for SuperCDMS SNOLAB over the next couple of years.

    This panoramic view shows the new SuperCDMS SNOLAB cleanroom at Lab G, with SuperCDMS spokesperson Dan Bauer and senior technical specialist Mark Ruschman. Photo: Reidar Hahn

    The cleanroom in Lab G will be used in the development of SuperCDMS detectors. Photo: Reidar Hahn

    Starting in 2017, with the arrival of a large new dilution refrigerator, the SuperCDMS group at Fermilab will build and commission the cryogenic apparatus that will allow SuperCDMS SNOLAB to cool its detectors to less than 30 milliKelvin. In 2019, the experiment will be installed at SNOLAB and will begin operations starting in 2020. If light dark matter particles exist, SuperCDMS SNOLAB should detect them sometime in the next decade.

    Dan Bauer is the spokesperson for SuperCDMS and the deputy head of the Fermilab Center for Particle Astrophysics.

    See the full article here .

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    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

  • richardmitnick 9:46 am on December 14, 2016 Permalink | Reply
    Tags: , , , Dark Matter, Einstein’s General Relativity (GR), Emergent Gravity, , , Hubble Constant, , Weak Gravitational Lensing   

    From astrobites: “Emergent Gravity faces its First Test in Galaxy Lensing” 

    Astrobites bloc


    Dec 13, 2016
    Gourav Khullar

    Title: First test of Verlinde’s theory of Emergent Gravity using Weak Gravitational Lensing measurements
    Authors: M. M. Brower, M.R. Visser, A Dvornik, et al.
    First Author’s Institution: Leiden Observatory, Leiden, The Netherlands
    Status: Submitted to The Monthly Notices of the Royal Astronomical Society (MNRAS), December 2016 [open access]

    Despite being a near-perfect model and explaining everything ranging from galactic rotation curves to high-redshift supernovae observations, Lambda-CDM has its problems. A lack of clear candidates for a dark matter particle and dark energy are two that certainly keep physicists up at night. This leads us towards alleys unexplored – theories that are creative, innovative and crucial to the scientific process, theories that could lead us to the eventual model of the universe with a clear explanations of all observations. One such theory that garnered some attention in the last few years is Emergent Gravity.

    Fig 1. Galaxy rotation curves observed over the last few years indicate a dominant matter halo on the outskirts of galaxies, something that’s explained concretely by dark matter.

    What is ‘Emergent’ in Emergent Gravity?

    The idea is pretty radical yet basic – gravity isn’t a manifestation of mass in spacetime as proposed by Einstein’s General Relativity (GR) or a fundamental force that fits perfectly in a four-force model of the universe. Instead, gravity is proposed to be ’emerging’ from interactions between even more fundamental particles. This is akin to seeing thermodynamical parameters like pressure and temperature arising from interactions between atoms and molecules – what’s crucial to our discussion is the macroscopic quantity. In the case here, that quantity would be gravity. This idea has been developing over the last few decades, with Theodore Jacobson, Thanu Padmanabhan and more recently, Erik Verlinde contributing heavily to its development.

    Erik Verlinde

    Fig 2. High speeds of particle collision against the walls of a container lead to higher temperature, since the system possesses more kinetic energy that gets converted to thermal energy.

    Diving deep into Entropy and Gravity

    One aspect of a theoretical model like emergent gravity (EG) is that we are allowed to derive macroscopic results without having to worry about the underlying fundamental particles that could lead to gravity ’emerging’ – at least for now. This ’emergence’ can be thought of as the result of the tendency of a physical system to increase its entropy. Early work in the field towards a ‘thermodynamics-like theory of gravity’ used something called ‘holographic scaling of entropy’, which essentially scales with surface area of an enclosed volume of spacetime. Verlinde’s new work insists that due to dark energy, we see deviations in GR at long distances that can be resolved if this entropy scaling scales as volume instead of area. Keeping details aside, this leads to a different ‘force-law’, that has additional dominant matter terms that could explain dark matter (called ‘apparent dark matter’ in this case). This and this piece are excellent sources for details on the model. It can be seen that in some sense, this model combines the origin of dark matter and dark energy in a novel way.

    Basics of Weak Gravitational Lensing

    Well, how do we test this theory? Perhaps, passing it through the same standards as GR would seem appropriate.

    The idea of gravitational lensing was one of the first tests of GR i.e. the idea that light’s path gets distorted when traveling through curved spacetime surrounding massive objects. This distortion can change the light ray received from background galaxies (and hence, apparent shape and size) due to a foreground massive object like a galaxy or a galaxy cluster, leading to weak gravitational lensing. This galaxy-galaxy lensing signal is a massive success story of GR, as observations of this phenomena in the Universe fit into the model very well.

    Fig 3. Gravitational lensing leading to a drastic distortion in light coming from background galaxies. Credit: NASA-Hubble Space Telescope.

    Since EG still gives rise to ‘apparent dark matter’, it is safe to say that the gravitational lensing formalism stays the same, since we do apply this formalim to our universe’s dark matter-dominated objects like galaxy clusters (if we believe Lambda-CDM and its predictions). This allows us to use weak lensing as a test for emergent gravity, and match observations against the predictions of this theory.

    This work

    The regime studied in this work is the low-redshift universe, or the relatively local universe, where the Hubble Constant can be treated as a constant. This is almost true because of the dominance of dark energy after redshift ~0.7-0.9. Since Verlinde’s EG isn’t evolved enough as a theory to quantify cosmology before this epoch, this work assumes a background Lambda-CDM cosmology. For studying galaxy-galaxy lensing, Brower et al. select ~33,000 galaxies from the Galaxy And Mass Assembly (GAMA) survey as ‘lenses’ and KiDS survey galaxies as background galaxies that get lensed. They model these galaxies as having a static, spherically symmetric distribution of mass- something like a point mass or an extended source resembling a point mass- because that’s what EG can handle so far.

    This work calculates the lensing effect by measuring distortions in the background galaxies’ images, termed as a ‘shear’. In the framework of GR, this quantity is comprised in something called the Extended Surface Density (ESD) profile. Brower et al. calculated the ESD for these galaxies under the many assumptions of this model, compared them with Navarror-Frenk-White (NFW) profiles of galaxies from Lambda-CDM, and found that there was general agreement in the ESD progression between the two.

    Fig 4. From the paper, a model-fit of Emergent Gravity(Point mass model), Emergent Gravity (Extended model) and Dark Matter(NFW model). The lensing signal measured in the form of an ESD is plotted for four different galactic mass bins. It can be seen that Verlinde’s Emergent Gravity model assisted by teh assumptions made by Brower et al. match NFW profile predictions very well.

    Conclusion and Summary

    So what are the assumptions? For one, EG cannot deal with evolution of the universe at the moment. Moreover, the theory isn’t developed enough to have a basic framework of what causes gravity to ’emerge’ from fundamental interactions. The paper agrees that a more ‘sophisticated implementation of both theories’ is needed to make a statement about whether apparent dark matter explains observations better than Lambda-CDM dark matter. Till then, EG shall keep on evolving and observations shall keep on being pitted against these evolving frameworks. A very exciting space to watch!

    See the full article here .

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    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

  • richardmitnick 2:55 pm on December 9, 2016 Permalink | Reply
    Tags: , , Dark Matter   

    From New Science: “Dark matter that talks to itself could explain galaxy mystery” 


    New Scientist

    7 December 2016
    Shannon Hall

    Spinning puzzle. Robert Gendler/Science Photo Library

    DARK matter might talk to itself. The mysterious substance that outweighs all visible matter in the cosmos might be best explained if it’s able to interact with itself via an invisible force.

    Take a look at any image of a galaxy and you will see that the centre is the brightest. With so much light – and therefore mass – concentrated there, astronomers expected central objects to orbit faster than those on the outer rim.

    But in the early 20th century, astronomers were surprised to find that galaxies’ outer stars appear to move about as fast as their inner stars, suggesting that there is more matter that doesn’t meet the eye. The name given to the invisible stuff is dark matter, and the standard paradigm suggests it is composed of weakly interacting massive particles, or WIMPs.

    Now new research on galactic rotation curves – graphs showing the orbital speeds of stars versus their distance from the centre of the galaxy – suggests the story might not be so simple.

    Not all rotation curves look alike – before they reach that characteristic plateau, some rise gradually, and others rise rapidly. But WIMP models struggle to explain this. Also, there has been no direct evidence of WIMPs, despite decades of searching. So Ayuki Kamada at the University of California, Riverside, and his colleagues set about finding an alternative.

    The team looked at 30 galaxies with strange rotation curves, and found that they could better explain them using a different type of dark matter: the self-interacting sort. These particles do something similar to how ordinary matter particles, like protons, interact with one another via the electromagnetic force.

    “It’s a very minimal modification,” says Manoj Kaplinghat at the University of California, Irvine. “But it’s amazing how well it actually fits. You don’t have to bend over backwards.”

    When galaxies form, cold dark matter falls to the centre and hot dark matter flows toward the outer edges. But if dark matter is allowed to interact with itself, then the particles will exchange energy and end up at the same temperature, just like the air molecules in a room. In some cases, the cool dark matter particles in the centre will grow hotter and flow toward the outer edges, building a centre less dominated by dark matter – explaining the rotation curves that rise gradually (arxiv.org/abs/1611.02716).

    Stacy McGaugh at Case Western Reserve University in Ohio is a critic of the standard dark matter paradigm, so he thinks all alternatives are worth exploring. However, adding new unseen forces to unseen particles complicates the picture unnecessarily, he says.

    “It’s what the philosophers of science would call an auxiliary hypothesis on top of an auxiliary hypothesis,” he says. “It’s already ad hoc and we’re adding more.”

    McGaugh’s favourite explanation is Modified Newtonian Dynamics (MOND), a theory that doesn’t add invisible matter but tweaks our understanding of gravity.

    An answer might come with direct detection of dark matter – whether WIMPs or the self-interacting kind.

    See the full article here .

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  • richardmitnick 8:52 am on December 7, 2016 Permalink | Reply
    Tags: , , Dark Matter, , Kilo Degree Survey (KiDS)   

    From ESO: “Dark Matter May be Smoother than Expected” 

    ESO 50 Large

    European Southern Observatory

    7 December 2016
    Hendrik Hildebrandt
    Head of Emmy Noether-Research Group
    Bonn, Germany
    Tel: +49 228 73 1772
    Email: hendrik@astro.uni-bonn.de

    Massimo Viola
    Leiden Observatory
    Leiden, The Netherlands
    Tel: +31 (0)71 527 8442
    Email: viola@strw.leidenuniv.nl

    Catherine Heymans
    Institute for Astronomy, University of Edinburgh
    Edinburgh, United Kingdom
    Tel: +44 131 668 8301
    Email: heymans@roe.ac.uk

    Konrad Kuijken
    Leiden Observatory
    Leiden, The Netherlands
    Tel: +31 715275848
    Cell: +31 628956539
    Email: kuijken@strw.leidenuniv.nl

    Richard Hook
    ESO Public Information Officer
    Garching bei Munchen, Germany
    Tel: +49 89 3200 6655
    Cell: +49 151 1537 3591
    Email: rhook@eso.org


    Analysis of a giant new galaxy survey, made with ESO’s VLT Survey Telescope in Chile, suggests that dark matter may be less dense and more smoothly distributed throughout space than previously thought. An international team used data from the Kilo Degree Survey (KiDS) to study how the light from about 15 million distant galaxies was affected by the gravitational influence of matter on the largest scales in the Universe. The results appear to be in disagreement with earlier results from the Planck satellite.

    Hendrik Hildebrandt from the Argelander-Institut für Astronomie in Bonn, Germany and Massimo Viola from the Leiden Observatory in the Netherlands led a team of astronomers [1] from institutions around the world who processed images from the Kilo Degree Survey (KiDS), which was made with ESO’s VLT Survey Telescope (VST) in Chile. For their analysis, they used images from the survey that covered five patches of the sky covering a total area of around 2200 times the size of the full Moon [2], and containing around 15 million galaxies.

    By exploiting the exquisite image quality available to the VST at the Paranal site, and using innovative computer software, the team were able to carry out one of the most precise measurements ever made of an effect known as cosmic shear. This is a subtle variant of weak gravitational lensing, in which the light emitted from distant galaxies is slightly warped by the gravitational effect of large amounts of matter, such as galaxy clusters.

    In cosmic shear, it is not galaxy clusters but large-scale structures in the Universe that warp the light, which produces an even smaller effect. Very wide and deep surveys, such as KiDS, are needed to ensure that the very weak cosmic shear signal is strong enough to be measured and can be used by astronomers to map the distribution of gravitating matter. This study takes in the largest total area of the sky to ever be mapped with this technique so far.

    Intriguingly, the results of their analysis appear to be inconsistent with deductions from the results of the European Space Agency’s Planck satellite, the leading space mission probing the fundamental properties of the Universe.


    CMB per ESA/Planck
    CMB per ESA/Planck

    In particular, the KiDS team’s measurement of how clumpy matter is throughout the Universe — a key cosmological parameter — is significantly lower than the value derived from the Planck data [3].

    Massimo Viola explains: “This latest result indicates that dark matter in the cosmic web, which accounts for about one-quarter of the content of the Universe, is less clumpy than we previously believed.”

    Dark matter remains elusive to detection, its presence only inferred from its gravitational effects. Studies like these are the best current way to determine the shape, scale and distribution of this invisible material.

    The surprise result of this study also has implications for our wider understanding of the Universe, and how it has evolved during its almost 14-billion-year history. Such an apparent disagreement with previously established results from Planck means that astronomers may now have to reformulate their understanding of some fundamental aspects of the development of the Universe.

    Hendrik Hildebrandt comments: “Our findings will help to refine our theoretical models of how the Universe has grown from its inception up to the present day.”

    The KiDS analysis of data from the VST is an important step but future telescopes are expected to take even wider and deeper surveys of the sky.

    The co-leader of the study, Catherine Heymans of the University of Edinburgh in the UK adds: “Unravelling what has happened since the Big Bang is a complex challenge, but by continuing to study the distant skies, we can build a picture of how our modern Universe has evolved.”

    “We see an intriguing discrepancy with Planck cosmology at the moment. Future missions such as the Euclid satellite and the Large Synoptic Survey Telescope will allow us to repeat these measurements and better understand what the Universe is really telling us,” concludes Konrad Kuijken (Leiden Observatory, the Netherlands), who is principal investigator of the KiDS survey.

    ESA/Euclid spacecraft
    ESA/Euclid spacecraft


    LSST/Camera, built at SLAC
    LSST/Camera, built at SLAC

    LSST Interior
    LSST telescope, currently under construction at Cerro Pachón Chile
    LSST telescope, currently under construction at Cerro Pachón Chile


    [1] The international KiDS team of researchers includes scientists from Germany, the Netherlands, the UK, Australia, Italy, Malta and Canada.

    [2] This corresponds to about 450 square degrees, or a little more than 1% of the entire sky.

    [3] The parameter measured is called S8. Its value is a combination of the size of density fluctuations in, and the average density of, a section of the Universe. Large fluctuations in lower density parts of the Universe have an effect similar to that of smaller amplitude fluctuations in denser regions and the two cannot be distinguished by observations of weak lensing. The 8 refers to a cell size of 8 megaparsecs, which is used by convention in such studies.

    More information

    This research was presented in the paper entitled “KiDS-450: Cosmological parameter constraints from tomographic weak gravitational lensing”, by H. Hildebrandt et al., to appear in Monthly Notices of the Royal Astronomical Society.

    The team is composed of H. Hildebrandt (Argelander-Institut für Astronomie, Bonn, Germany), M. Viola (Leiden Observatory, Leiden University, Leiden, the Netherlands), C. Heymans (Institute for Astronomy, University of Edinburgh, Edinburgh, UK), S. Joudaki (Centre for Astrophysics & Supercomputing, Swinburne University of Technology, Hawthorn, Australia), K. Kuijken (Leiden Observatory, Leiden University, Leiden, the Netherlands), C. Blake (Centre for Astrophysics & Supercomputing, Swinburne University of Technology, Hawthorn, Australia), T. Erben (Argelander-Institut für Astronomie, Bonn, Germany), B. Joachimi (University College London, London, UK), D Klaes (Argelander-Institut für Astronomie, Bonn, Germany), L. Miller (Department of Physics, University of Oxford, Oxford, UK), C.B. Morrison (Argelander-Institut für Astronomie, Bonn, Germany), R. Nakajima (Argelander-Institut für Astronomie, Bonn, Germany), G. Verdoes Kleijn (Kapteyn Astronomical Institute, University of Groningen, Groningen, the Netherlands), A. Amon (Institute for Astronomy, University of Edinburgh, Edinburgh, UK), A. Choi (Institute for Astronomy, University of Edinburgh, Edinburgh, UK), G. Covone (Department of Physics, University of Napoli Federico II, Napoli, Italy), J.T.A. de Jong (Leiden Observatory, Leiden University, Leiden, the Netherlands), A. Dvornik (Leiden Observatory, Leiden University, Leiden, the Netherlands), I. Fenech Conti (Institute of Space Sciences and Astronomy (ISSA), University of Malta, Msida, Malta; Department of Physics, University of Malta, Msida, Malta), A. Grado (INAF – Osservatorio Astronomico di Capodimonte, Napoli, Italy), J. Harnois-Déraps (Institute for Astronomy, University of Edinburgh, Edinburgh, UK; Department of Physics and Astronomy, University of British Columbia, Vancouver, Canada), R. Herbonnet (Leiden Observatory, Leiden University, Leiden, the Netherlands), H. Hoekstra (Leiden Observatory, Leiden University, Leiden, the Netherlands), F. Köhlinger (Leiden Observatory, Leiden University, Leiden, the Netherlands), J. McFarland (Kapteyn Astronomical Institute, University of Groningen, Groningen, the Netherlands), A. Mead (Department of Physics and Astronomy, University of British Columbia, Vancouver, Canada), J. Merten (Department of Physics, University of Oxford, Oxford, UK), N. Napolitano (INAF – Osservatorio Astronomico di Capodimonte, Napoli, Italy), J.A. Peacock (Institute for Astronomy, University of Edinburgh, Edinburgh, UK), M. Radovich (INAF – Osservatorio Astronomico di Padova, Padova, Italy), P. Schneider (Argelander-Institut für Astronomie, Bonn, Germany), P. Simon (Argelander-Institut für Astronomie, Bonn, Germany), E.A. Valentijn (Kapteyn Astronomical Institute, University of Groningen, Groningen, the Netherlands), J.L. van den Busch (Argelander-Institut für Astronomie, Bonn, Germany), E. van Uitert (University College London, London, UK) and L. van Waerbeke (Department of Physics and Astronomy, University of British Columbia, Vancouver, Canada).

    See the full article here .

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  • richardmitnick 1:35 pm on December 2, 2016 Permalink | Reply
    Tags: , , , Dark Interactions Workshop, Dark Matter   

    From BNL: “Dark Interactions Workshop Hosts Physicists from Around the World” 

    Brookhaven Lab

    November 23, 2016
    Chelsea Whyte

    Dozens of experimental and theoretical physicists convened at the U.S. Department of Energy’s Brookhaven National Laboratory in October for the second biennial Dark Interactions Workshop. Attendees came from universities and laboratories worldwide to discuss current research and possible future searches for dark sector states such as dark matter.


    Two great cosmic mysteries – dark energy and dark matter — make up nearly 95% of the universe’s energy budget. Dark energy is the proposed agent behind the ever-increasing expansion of the universe. Some force must propel the accelerating rate at which the fabric of space is stretching, but its origin and makeup are still unknown. Dark matter, first proposed over 80 years ago, is theorized to be the mass responsible for most of the immense gravitational pull that galaxy clusters exert. Without its presence, galaxies and galaxy clusters shouldn’t hang together as they do, according to the laws of gravity that permeate our cosmos.

    Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey
    Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey

    Scientists know this much. It’s a bit like a map of a continent with the outlines drawn, but large holes that need a lot of filling in. “There are a lot of things we know that we don’t know,” said Brookhaven physicist Ketevi Assamagan, who organized the workshop along with Brookhaven physicists Hooman Davoudiasl and Mary Bishai, and Stony Brook University physicist Rouven Essig.

    The Dark Interactions Workshop was created to gather great minds in search of answers to these cosmic questions, and to share knowledge across the many different types of experiments searching for dark-sector particles. “The goals are to search for several well-motivated dark-sector particles with existing and upcoming experiments, but also to propose new experiments that can lead the search for dark forces in the coming decade. This requires in-depth discussions among theorists and experimentalists,” Essig said.

    The sessions ranged from discussing theories to status updates from dark-particle searches following the first workshop two years ago. Attendees included post-docs as well as tenured scientists, and Assamagan said workshops like this are crucial for allowing a diverse and somewhat disparate group of scientists in a dense field of study to get to know each other’s work and build collaborations.

    “Dark matter is one of the hot topics in particle and astrophysics today. We know that we don’t have the complete story when it comes to our universe. Understanding the nature of dark matter would be a revolution,” Assamagan said.

    While tantalizing theories have directed physicists to build new ways to search for dark sector states, conclusive evidence still eludes scientists. “Since there is currently a vast range of possibilities for what could constitute the dark sector, a variety of innovative approaches for answering this question need to be considered,” Davoudiasl said. “To that end, meetings like this are quite helpful as they facilitate the exchange of new ideas.”

    “There’s still a lot of hope. Meetings like this one show that there are a lot of clever people working in this field and a lot of collaboration between them. Hopefully at our next workshop, we’ll be sharing evidence that we’ve discovered something of the dark sector,” said Assamagan.

    See the full article here .

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