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  • richardmitnick 11:41 am on April 18, 2019 Permalink | Reply
    Tags: "What gravitational waves can say about dark matter", , , , , , , , , , Vera Rubin   

    From Symmetry: “What gravitational waves can say about dark matter” 

    Symmetry Mag
    From Symmetry

    04/18/19
    Caitlyn Buongiorno

    Scientists think that, under some circumstances, dark matter could generate powerful enough gravitational waves for equipment like LIGO to detect.

    1
    Artwork by Sandbox Studio, Chicago

    In 1916, Albert Einstein published his theory of general relativity, which established the modern view of gravity as a warping of the fabric of spacetime. The theory predicted that objects that interact with gravity could disturb that fabric, sending ripples across it.

    Any object that interacts with gravity can create gravitational waves. But only the most catastrophic cosmic events make gravitational waves powerful enough for us to detect. Now that observatories have begun to record gravitational waves on a regular basis, scientists are discussing how dark matter—only known so far to interact with other matter only through gravity—might create gravitational waves strong enough to be found.

    Fritz Zwicky discovered Dark Matter when observing the movement of the Coma Cluster. But , Vera Rubin a Woman in STEM denied the Nobel, did most of the work on Dark Matter.

    Fritz Zwicky from http:// palomarskies.blogspot.com

    Coma cluster via NASA/ESA Hubble

    Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science)


    Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL)


    Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu

    The spacetime blanket

    In the universe, space and time are invariably linked as four-dimensional spacetime. For simplicity, you can think of spacetime as a blanket suspended above the ground.

    Spacetime with Gravity Probe B. NASA

    Jupiter might be a single Cheerio on top of that blanket. The sun could be a tennis ball. R136a1—the most massive known star—might be a 40-pound medicine ball.

    Each of these objects weighs down the blanket where it sits: the heavier the object, the bigger the dip in the blanket. Like objects of different weights on a blanket, objects of different masses have different effects on the fabric of spacetime. A dip in spacetime is gravitational field.

    The gravitational field of one object can affect another object. The other object might fall into the first object’s gravitational field and orbit around it, like the moon around Earth, or Earth around the sun.

    Alternatively, two bodies with gravitational fields might spiral toward each other, getting closer and closer until they collide. As this happens, they create ripples in spacetime—gravitational waves.

    On September 14, 2015, scientists used the Laser Interferometer Gravitational-Wave Observatory, or LIGO, to make the first direct observation of gravitational waves, part of the buildup to the crash between two massive black holes.

    Since that first detection, the LIGO collaboration—together with the collaboration that runs a partner gravitational-wave observatory called Virgo—has detected gravitational waves from at least 10 more mergers of black holes and, in 2017, the first merger between two neutron stars.


    VIRGO Gravitational Wave interferometer, near Pisa, Italy


    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger

    Gravity is talking. Lisa will listen. Dialogos of Eide

    ESA/eLISA the future of gravitational wave research

    Localizations of gravitational-wave signals detected by LIGO in 2015 (GW150914, LVT151012, GW151226, GW170104), more recently, by the LIGO-Virgo network (GW170814, GW170817). After Virgo came online in August 2018


    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    Dark matter is believed to be five times as prevalent as visible matter. Its gravitational effects are seen throughout the universe. Scientists think they have yet to definitively see gravitational waves caused by dark matter, but they can think of numerous ways this might happen.

    Primordial black holes

    Scientists have seen the gravitational effects of dark matter, so they know it must be there—or at least, something must be going on to cause those effects. But so far, they’ve never directly detected a dark matter particle, so they’re not sure exactly what dark matter is like.

    One idea is that some of the dark matter could actually be primordial black holes.

    Imagine the universe as an infinitely large petri dish. In this scenario, the Big Bang is the point where matter-bacteria begins to grow. That point quickly expands, moving outward to encompass more and more of the petri dish. If that growth is slightly uneven, certain areas will become more densely inhabited by matter than others.

    These pockets of dense matter—mostly photons at this point in the universe—might have collapsed under their own gravity and formed early black holes.

    “I think it’s an interesting theory, as interesting as a new kind of particle,” says Yacine Ali-Haimoud, an assistant professor of physics at New York University. “If primordial black holes do exist, it would have profound implications on the conditions in the very early universe.”

    By using gravitational waves to learn about the properties of black holes, LIGO might be able to prove or constrain this dark matter theory.

    Unlike normal black holes, primordial black holes don’t have a minimum mass threshold they need to reach in order to form. If LIGO were to see a black hole less massive than the sun, for example, it might be a primordial black hole.

    Even if primordial black holes do exist, it’s doubtful that they account for all of the dark matter in the universe. Still, finding proof of primordial black holes would expand our fundamental understanding of dark matter and how the universe began.

    Neutron star rattles

    Dark matter seems to interact with normal matter only through gravity, but, based on the way known particles interact, theorists think it’s possible that dark matter might also interact with itself.

    If that is the case, dark matter particles might bind together to form dark objects that are as compact as a neutron star.

    We know that stars drastically “weigh down” the fabric of spacetime around them. If the universe were populated with compact dark objects, there would be a chance that at least some of them would end up trapped inside of ordinary matter stars.

    A normal star and a dark object would interact only through gravity, allowing the two to co-exist without much of a fuss. But any disruption to the star—for example, a supernova explosion—could create a rattle-like disturbance between the resulting neutron star and the trapped dark object. If such an event occurred in our galaxy, it would create detectable gravitational waves

    “We understand neutron stars quite well,” says Sanjay Reddy, University of Washington physics professor and senior fellow with the Institute for Nuclear Theory. “If something ‘odd’ happens with gravitational waves, we would know there was potentially something new going on that might involve dark matter.”

    The likelihood that any exist in our solar system is limited. Chuck Horowitz, Maria Alessandra Papa and Reddy recently analyzed LIGO’s data and found no indication of compact dark objects of a specific mass range within Earth, Jupiter or the sun.

    Further gravitational-wave studies could place further constraints on compact dark objects. “Constraints are important,” says Ann Nelson, a physics professor at the University of Washington. “They allow us to improve existing theories and even formulate new ones.”

    Axion stars

    One light dark matter candidate is the axion, named by physicist Frank Wilczek after a brand of detergent, in reference to its ability to tidy up a problem in the theory of quantum chromodynamics.

    Scientists think it could be possible for axions to bind together into axion stars, similar to neutron stars but made up of extremely compact axion matter.

    “If axions exist, there are scenarios where they can cluster together and form stellar objects, like ordinary matter,” says Tim Dietrich, a LIGO-Virgo member and physicist. “We don’t know if axion stars exist, and we won’t know for sure until we find constraints for our models.”

    If an axion star merged with a neutron star, scientists might not be able to tell the difference between the two with their current instruments. Instead, scientists would need to rely on electromagnetic signals accompanying the gravitational wave to identify the anomaly.

    It’s also possible that axions could bunch around a binary black hole or neutron star system. If those stars then merged, the changes in the axion “cloud” would be visible in the gravitational wave signal. A third possibility is that axions could be created by the merger, an action that would be reflected in the signal.

    This month, the LIGO-Virgo collaborations began their third observing run and, with new upgrades, expect to detect a merger event every week.

    Gravitational-wave detectors have already proven their worth in confirming Einstein’s century-old prediction. But there is still plenty that studying gravitational waves can teach us. “Gravitational waves are like a completely new sense for science,” Ali-Haimoud says. “A new sense means new ways to look at all the big questions in physics.”

    See the full article here .


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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 11:00 am on November 29, 2018 Permalink | Reply
    Tags: , , , , , , , , Vera Rubin   

    From NASA/ESA Hubble Telescope: “Hubble Uncovers Thousands of Globular Star Clusters Scattered Among Galaxies” 

    NASA Hubble Banner

    NASA/ESA Hubble Telescope

    From NASA/ESA Hubble Telescope

    Nov 29, 2018

    Ray Villard
    Space Telescope Science Institute, Baltimore, Maryland
    410-338-4514
    villard@stsci.edu

    Juan Madrid
    Australian Telescope National Facility, Sydney, Australia
    jmadrid@astro.swin.edu.au

    1
    Survey will allow for mapping of dark matter in huge galaxy cluster

    Gazing across 300 million light-years into a monstrous city of galaxies, astronomers have used NASA’s Hubble Space Telescope to do a comprehensive census of some of its most diminutive members: a whopping 22,426 globular star clusters found to date.

    The survey, published in the November 9, 2018, issue of The Astrophysical Journal, will allow for astronomers to use the globular cluster field to map the distribution of matter and dark matter in the Coma galaxy cluster, which holds over 1,000 galaxies that are packed together.

    Because globular clusters are much smaller than entire galaxies – and much more abundant – they are a much better tracer of how the fabric of space is distorted by the Coma cluster’s gravity. In fact, the Coma cluster is one of the first places where observed gravitational anomalies were considered to be indicative of a lot of unseen mass in the universe – later to be called “dark matter.”

    Fritz Zwicky discovered Dark Matter when observing the movement of the Coma Cluster.

    Fritz Zwicky from http:// palomarskies.blogspot.com

    Coma cluster via NASA/ESA Hubble

    But most of the real work was done by Vera Rubin a Woman in STEM

    Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science)


    Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL)


    Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu

    Among the earliest homesteaders of the universe, globular star clusters are snow-globe-shaped islands of several hundred thousand ancient stars. They are integral to the birth and growth of a galaxy. About 150 globular clusters zip around our Milky Way galaxy, and, because they contain the oldest known stars in the universe, were present in the early formative years of our galaxy.

    Some of the Milky Way’s globular clusters are visible to the naked eye as fuzzy-looking “stars.” But at the distance of the Coma cluster, its globulars appear as dots of light even to Hubble’s super-sharp vision. The survey found the globular clusters scattered in the space between the galaxies. They have been orphaned from their home galaxy due to galaxy near-collisions inside the traffic-jammed cluster. Hubble revealed that some globular clusters line up along bridge-like patterns. This is telltale evidence for interactions between galaxies where they gravitationally tug on each other like pulling taffy.

    Astronomer Juan Madrid of the Australian Telescope National Facility in Sydney, Australia first thought about the distribution of globular clusters in Coma when he was examining Hubble images that show the globular clusters extending all the way to the edge of any given photograph of galaxies in the Coma cluster.

    He was looking forward to more data from one of the legacy surveys of Hubble that was designed to obtain data of the entire Coma cluster, called the Coma Cluster Treasury Survey. However, halfway through the program, in 2006, Hubble’s powerful Advanced Camera for Surveys (ACS) had an electronics failure. (The ACS was later repaired by astronauts during a 2009 Hubble servicing mission.)

    NASA Hubble Advanced Camera forSurveys

    To fill in the survey gaps, Madrid and his team painstakingly pulled numerous Hubble images of the galaxy cluster taken from different Hubble observing programs. These are stored in the Space Telescope Science Institute’s Mikulski Archive for Space Telescopes in Baltimore, Maryland. He assembled a mosaic of the central region of the cluster, working with students from the National Science Foundation’s Research Experience for Undergraduates program. “This program gives an opportunity to students enrolled in universities with little or no astronomy to gain experience in the field,” Madrid said.

    The team developed algorithms to sift through the Coma mosaic images that contain at least 100,000 potential sources. The program used globular clusters’ color (dominated by the glow of aging red stars) and spherical shape to eliminate extraneous objects – mostly background galaxies unassociated with the Coma cluster.

    Though Hubble has superb detectors with unmatched sensitivity and resolution, their main drawback is that they have tiny fields of view. “One of the cool aspects of our research is that it showcases the amazing science that will be possible with NASA’s planned Wide Field Infrared Survey Telescope (WFIRST) that will have a much larger field of view than Hubble,” said Madrid.

    NASA/WFIRST

    “We will be able to image entire galaxy clusters at once.”

    See the full article here .


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    The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA’s Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI), is a free-standing science center, located on the campus of The Johns Hopkins University and operated by the Association of Universities for Research in Astronomy (AURA) for NASA, conducts Hubble science operations.

    ESA50 Logo large

    AURA Icon

     
  • richardmitnick 10:43 am on November 14, 2018 Permalink | Reply
    Tags: , , , , , The search for Dark Matter, Vera Rubin,   

    From Sanford Underground Research Facility: “Success of experiment requires testing” 

    SURF logo
    Sanford Underground levels

    From Sanford Underground Research Facility

    November 13, 2018
    Erin Broberg

    1
    Tomasz Biesiadzinski, project scientist for SLAC National Accelerator Laboratory (SLAC), works on the mock PMT [photomultiplier tubes] array. Erin Broberg

    “The LZ detector is kind of like a spacecraft,” said Tomasz Biesiadzinski, project scientist for SLAC National Accelerator Laboratory (SLAC). “Repairing it after it’s installed would be very difficult, so we do everything we can to make sure it works correctly the first time.”

    LZ Dark Matter Experiment at SURF lab

    LBNL LZ project at SURF, Lead, SD, USA

    Biesiadzinski himself is responsible for planning and carrying out tests during the assembly of time projection chamber (TPC), the main detector for LUX-ZEPLIN experiment (LZ). Currently being constructed on the 4850 Level at Sanford Underground Research Facility (Sanford Lab), this main detector consists of a large tank that will hold 7 tonnes of ultra-pure, cryogenic liquid xenon maintained at -100o C. All the pieces of this detector are designed to function with precision; it’s Biesiadzinski job to verify that each part continues to work correctly as they are integrated. That includes hundreds of photomultiplier tubes (PMT).

    Test run

    The most recent test was piecing together an intricate mock array for the PMTs, which will detect light signals created by the collision of a dark matter particle and a xenon atom, inside the main detector. In a soft-wall cleanroom in the Surface Laboratory at Sanford Lab, Biesiadzinski and his team carefully practiced placing instruments like thermometers, sensors and reflective covering. They practiced installing routing cabling, including PMT high voltage power cables, PMT signal cables and thermometer cables.

    “Essentially, we wanted to gain experience so we could be faster during the actual assembly. The faster we work, the more we limit dust exposure and therefore potential backgrounds,” said Biesiadzinski. “It was also an opportunity to test fit real components. We did find that there were some very tight places that motivated us to slightly redesign some small parts to make assembly easier.”

    These tests will make the installment of the actual LZ arrays much smoother.

    “LZ’s main detector will have two PMT arrays, one on the top of the tank and one on the bottom,” Biesiadzinski explained. “The bottom array will hold 241 PMTs pointing up into the liquid Xenon volume of the main detector. The top array will hold PMTs 253 pointing down on the liquid Xenon and the gas layer above it in the main detector.”

    In total, there will be 494 PMTs lining the main detector. If a WIMP streaks through the tank and strikes a xenon nucleus, two things will happen. First, the xenon will emit a flash of light. Then, it will release electrons, which drift in an electric field to the top of the tank, where they will produce a second flash of light. Hundreds of PMTs will be waiting to detect a characteristic combination of flashes from inside the tank—a WIMPs’ telltale signature.

    “Both arrays—top and bottom—record the light from particle interactions inside the detector, including, hopefully, dark matter,” said Biesiadzinski. “This data allows us to estimate both the energy created and 3D location of the interaction.”

    Catching light

    The PMTs used for LZ are extremely sensitive. Not only can they distinguish individual photons of light arriving just a few tens of nanoseconds apart, they can also see the UV light produced by xenon that is far outside the human vision range. The X-Y location of events in the detector can be measured using the top PMT array to within a few millimeters for sufficiently energetic events.

    To insure every bit of light makes its way to a PMT, the inside surfaces of the arrays are covered with Polytetrafluoroethylene (PTFE or teflon), a material highly reflective to xenon scintillation light, in between the PMT faces.

    “This way, photons that don’t enter the PMTs right away—and are therefore not recorded—are reflected and will get a second, third, and so on, chance of being detected as they bounce around the detector,” said Biesiadzinski.

    Researchers will also cover the outside of the bottom array, including all of the cables, with PTFE to maximize light collection there. Light recorded there by additional PMTs that are not part of the array, allow us to measure radioactive backgrounds that can contaminate the main detector.

    Keeping it “clean”

    In addition to being very specific, these PMTs are also ultra-clean.

    “By clean, we mean radio-pure,” said Briana Mount, director of the BHUC, where 338 of LZ’s PMTs have already been tested for radio-purity.

    The tiniest amounts of radioactive elements in the very materials used to construct LZ can also overwhelm the rare-event signal. Radioactive elements can be found in rocks, titanium—even human sweat. As these elements decay, they emit signals that quickly light up ultra-sensitive detectors. To lessen these misleading signatures, researchers assay, or test, their materials for radio-purity using low-background counters (LBCs).

    “Our PMTs are special made to have very low radioactivity so as to not overwhelm a very sensitive detector like LZ with background signal,” said Biesiadzinski.

    Testing the PMTs at the BHUC allows researchers to understand exactly how much of a remaining background they can expect to see from these materials during the experiment. Mount explained that most of the samples currently being assayed at the BHUC are LZ samples, including cable ties, wires, nuts and bolts.

    “We have assayed every component that will make up LZ,” said Kevin Lesko, senior physicist at Lawrence Berkeley National Lab (Berkeley Lab) and a spokesperson for LZ. “At this point we have performed over 1300 assays with another 800 assays planned. These have kept BHUC and the UK’s Boulby LBCs fully occupied for approximately 4 years. These assays permit us ensure no component contributes a major background to the detector and also allows us to assemble a model of the backgrounds for the entire detector before we turn on a single PMT.”

    For a visual description and breakdown of LZ’s design, watch this video created by SLAC.

    Fritz Zwicky discovered Dark Matter when observing the movement of the Coma Cluster.

    Fritz Zwicky from http:// palomarskies.blogspot.com

    Coma cluster via NASA/ESA Hubble

    But most of the real work was done by Vera Rubin a Woman in STEM

    Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science)


    Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL)


    Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    Stem Education Coalition

    About us.
    The Sanford Underground Research Facility in Lead, South Dakota, advances our understanding of the universe by providing laboratory space deep underground, where sensitive physics experiments can be shielded from cosmic radiation. Researchers at the Sanford Lab explore some of the most challenging questions facing 21st century physics, such as the origin of matter, the nature of dark matter and the properties of neutrinos. The facility also hosts experiments in other disciplines—including geology, biology and engineering.

    The Sanford Lab is located at the former Homestake gold mine, which was a physics landmark long before being converted into a dedicated science facility. Nuclear chemist Ray Davis earned a share of the Nobel Prize for Physics in 2002 for a solar neutrino experiment he installed 4,850 feet underground in the mine.

    Homestake closed in 2003, but the company donated the property to South Dakota in 2006 for use as an underground laboratory. That same year, philanthropist T. Denny Sanford donated $70 million to the project. The South Dakota Legislature also created the South Dakota Science and Technology Authority to operate the lab. The state Legislature has committed more than $40 million in state funds to the project, and South Dakota also obtained a $10 million Community Development Block Grant to help rehabilitate the facility.

    In 2007, after the National Science Foundation named Homestake as the preferred site for a proposed national Deep Underground Science and Engineering Laboratory (DUSEL), the South Dakota Science and Technology Authority (SDSTA) began reopening the former gold mine.

    In December 2010, the National Science Board decided not to fund further design of DUSEL. However, in 2011 the Department of Energy, through the Lawrence Berkeley National Laboratory, agreed to support ongoing science operations at Sanford Lab, while investigating how to use the underground research facility for other longer-term experiments. The SDSTA, which owns Sanford Lab, continues to operate the facility under that agreement with Berkeley Lab.

    The first two major physics experiments at the Sanford Lab are 4,850 feet underground in an area called the Davis Campus, named for the late Ray Davis. The Large Underground Xenon (LUX) experiment is housed in the same cavern excavated for Ray Davis’s experiment in the 1960s.
    LUX/Dark matter experiment at SURFLUX/Dark matter experiment at SURF

    In October 2013, after an initial run of 80 days, LUX was determined to be the most sensitive detector yet to search for dark matter—a mysterious, yet-to-be-detected substance thought to be the most prevalent matter in the universe. The Majorana Demonstrator experiment, also on the 4850 Level, is searching for a rare phenomenon called “neutrinoless double-beta decay” that could reveal whether subatomic particles called neutrinos can be their own antiparticle. Detection of neutrinoless double-beta decay could help determine why matter prevailed over antimatter. The Majorana Demonstrator experiment is adjacent to the original Davis cavern.

    LUX’s mission was to scour the universe for WIMPs, vetoing all other signatures. It would continue to do just that for another three years before it was decommissioned in 2016.

    In the midst of the excitement over first results, the LUX collaboration was already casting its gaze forward. Planning for a next-generation dark matter experiment at Sanford Lab was already under way. Named LUX-ZEPLIN (LZ), the next-generation experiment would increase the sensitivity of LUX 100 times.

    SLAC physicist Tom Shutt, a previous co-spokesperson for LUX, said one goal of the experiment was to figure out how to build an even larger detector.
    “LZ will be a thousand times more sensitive than the LUX detector,” Shutt said. “It will just begin to see an irreducible background of neutrinos that may ultimately set the limit to our ability to measure dark matter.”
    We celebrate five years of LUX, and look into the steps being taken toward the much larger and far more sensitive experiment.

    Another major experiment, the Long Baseline Neutrino Experiment (LBNE)—a collaboration with Fermi National Accelerator Laboratory (Fermilab) and Sanford Lab, is in the preliminary design stages. The project got a major boost last year when Congress approved and the president signed an Omnibus Appropriations bill that will fund LBNE operations through FY 2014. Called the “next frontier of particle physics,” LBNE will follow neutrinos as they travel 800 miles through the earth, from FermiLab in Batavia, Ill., to Sanford Lab.

    Fermilab LBNE
    LBNE

    U Washington Majorana Demonstrator Experiment at SURF

    The MAJORANA DEMONSTRATOR will contain 40 kg of germanium; up to 30 kg will be enriched to 86% in 76Ge. The DEMONSTRATOR will be deployed deep underground in an ultra-low-background shielded environment in the Sanford Underground Research Facility (SURF) in Lead, SD. The goal of the DEMONSTRATOR is to determine whether a future 1-tonne experiment can achieve a background goal of one count per tonne-year in a 4-keV region of interest around the 76Ge 0νββ Q-value at 2039 keV. MAJORANA plans to collaborate with GERDA for a future tonne-scale 76Ge 0νββ search.

    LBNL LZ project at SURF, Lead, SD, USA

     
  • richardmitnick 8:52 pm on November 12, 2018 Permalink | Reply
    Tags: , , , , Dark matter hurricane, , S1 stream, Vera Rubin   

    From Discover Magazine: “A ‘Dark Matter Hurricane’ is Storming Past Earth. It Could Help Scientists Detect the Strange Substance” 

    DiscoverMag

    From Discover Magazine

    November 12, 2018
    Chelsea Gohd

    1
    The Milky Way is shown on a collision course with a smaller galaxy in this simulation. (Credit: Koppelman, Villalobos; Helmi, Kapteyn Astronomical Institute, University of Groningen, The Netherlands)

    There’s a “dark matter hurricane” blowing through our corner of the Milky Way galaxy. Right this second, it’s passing over Earth. And this fast-moving stream could reveal major details about dark matter, a new study finds.

    The dark matter is traveling in what is known as the S1 stream. Scientists think that streams like this one are the cosmic debris leftover when small galaxies stray too close to the Milky Way. Our gravitational forces tear the smaller galaxy apart, leaving behind a traveling, elliptical stream of stars, dark matter and other debris.

    Dark Matter Hurricane

    Dark matter is an elusive material that scientists think, if the Standard Model is correct, exists in large quantities throughout space. Scientists still don’t know what dark matter actually is — there are a number of leading theories, but no one knows for sure.

    Women in STEM – Vera Rubin
    Fritz Zwicky discovered Dark Matter when observing the movement of the Coma Cluster

    Coma cluster via NASA/ESA Hubble

    But most of the real work was done by Vera Rubin

    Fritz Zwicky from http:// palomarskies.blogspot.com


    Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science)


    Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL)


    Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu

    But the S1 stream is predicted to be blowing dark matter past us at about 310 miles per second (500 km/s) right this moment, and that could provide an opportunity for detection.

    Galactic Streams

    Dozens of such streams have been found in the Milky Way. And like the galaxies they’re stripped from, these streams are typically made of stars and dark matter all traveling along together at the same velocity. “(There are) tons of these streams all over the galaxy, some of them are really huge and you can see them in the sky,” said Ciaran O’Hare of the University of Zaragoza in Spain.

    The European Space Agency’s billion-star survey using the Gaia spacecraft is reaching far out into our galaxy to discover and observe stars.

    ESA/GAIA satellite

    And Gaia picked out the S1 stream because its some 30,000 stars have a different chemical composition than those native to our galaxy. And they’re traveling along a similar, elliptical path.

    And, while there are over 30 such streams known in our galaxy, S1 still surprised astronomers because our solar system is actually inside this stream. And our paths will intersect for millions of more years. Now, this will not affect our lives or planet in any physical way – there is still only one star (the sun) in our solar system.

    But O’Hare and his colleagues calculated the affect of the S1 stream in our part of the galaxy and predicted possible signatures of the dark matter, which could help inform and support efforts to locate and study the elusive substance.

    “What we want to do is add the stream as part of our kind of main prediction for the types of signal that should show up in a dark matter experiment,” O’Hare said. According to a statement, current detectors searching for weakly interacting massive particles (WIMPs) (one popular idea of what dark matter might be) probably won’t see anything from S1, but future tech might.

    Their study was published in the journal Physical Review D.

    See the full article here .

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  • richardmitnick 9:44 pm on August 30, 2018 Permalink | Reply
    Tags: An endowed chair named in honor of Faber's mentor distinguished astronomer Vera Rubin, Sandra Faber professor emerita of astronomy and astrophysics at UC Santa Cruz and her husband Andrew Faber launched the campaign for the Rubin Chair with an initial gift of $250000, Sandy Faber, , Vera Rubin   

    From UC Santa Cruz: “Gifts to UC Santa Cruz fund new presidential chair for diversity in astronomy” 

    UC Santa Cruz

    From UC Santa Cruz

    August 29, 2018
    Tim Stephens
    stephens@ucsc.edu

    UCSC astronomer Sandra Faber and her husband made the lead gift to establish an endowed chair named in honor of Faber’s mentor, distinguished astronomer Vera Rubin.

    1
    Sandra Faber and Vera Rubin (Photo by Lars Hagberg for the National Post)

    UC Santa Cruz has received gifts and matching funds to establish a $1.5 million endowment for the Vera Rubin Presidential Chair for Diversity in Astronomy.

    The endowed chair was created to advance the cause of diversity, equity, and inclusive excellence in astronomy. The holder of the chair will embody the spirit of diversity in one of a variety of ways, such as their proven ability to attract and train new astronomers from all walks of life.

    Sandra Faber, professor emerita of astronomy and astrophysics at UC Santa Cruz, and her husband Andrew Faber launched the campaign for the Rubin Chair with an initial gift of $250,000. The chair is named for the distinguished astronomer Vera Rubin (1928-2016), who was a champion of inclusivity in science.

    For Sandra Faber, who worked with Rubin at the Carnegie Institution of Washington early in her career, the more experienced astronomer served as a model of a successful woman in a field dominated by men. “At a time when few women succeeded in science, especially astrophysics, Rubin began to pave the way for all members of underrepresented groups,” Faber said.

    Vera Rubin measuring spectra (Emilio Segre Visual Archives AIP SPL)


    Astronomer Vera Rubin at the Lowell Observatory in 1965. (The Carnegie Institution for Science)

    Rubin helped transform modern astrophysics through her research on the rotation rates of galaxies, making crucial contributions to the evidence that galaxies and stars are immersed in the gravitational grip of vast clouds of dark matter. Faber said she learned a lot about how to be an astronomer while working alongside Rubin, from how to give a scientific talk to the importance of careful measurements and respect for the data.

    “She was playing in the big leagues, and she was also raising a family. It told me that I could do this too,” Faber said.

    Dozens of astronomers from varied backgrounds remember with gratitude Rubin’s deep interest and encouragement of their budding careers. Her passion to open doors to all qualified persons makes her the perfect namesake for UC Santa Cruz’s newest endowed chair, according to Enrico Ramirez-Ruiz, professor and chair of the Department of Astronomy and Astrophysics.

    A novel feature of the Rubin Chair is its emphasis on using the proceeds from the endowment to enhance the department’s ability to attract and support aspiring astronomers from underrepresented groups, he said. Endowed chairs are typically used to pay the salary or support the research of the chair holder, whereas the holder of the Rubin Chair might use the funds for graduate and postdoctoral fellowships or undergraduate research internships.

    “The Rubin Chair will be a bridge of support across cultural, ethnic, and economic hurdles to engage the brightest minds in astronomy,” said Ramirez-Ruiz, adding that diversity is a source of strength and excellence for the astronomy department.

    Women have composed half of UC Santa Cruz astronomy Ph.D. students for more than a decade, and 30 percent of current graduate students come from underrepresented backgrounds. The department’s six active women professors are the largest tenured cohort of female astronomers in the nation, led by eminent scientists such as Faber and Claire Max, director of UC Observatories.

    Faber, like Rubin before her, has been honored with the National Medal of Science, the Gruber Prize for Cosmology, and many other awards and honors. Her research interests include cosmology, galaxy formation, and astronomical instrumentation. Faber has also been a driving force in the development and evolution of the Osterbrock Leadership Program, which offers leadership lectures, workshops, field trips, and other opportunities to all interested graduate students in the Department of Astronomy and Astrophysics. This program is unique to UC Santa Cruz and sets the department apart from all other top astronomy programs. It is also testament to Faber’s commitment to advancing the careers of young women and students from diverse backgrounds.

    In addition to the gift from the Fabers, which came from a significant portion of the Gruber Prize, the Rubin Chair endowment fund has received major contributions from the Heising-Simons Foundation, John and Barbara Crary, and an anonymous donor. Other donors include the Rubin family, Mark Headley, Claudia Webster, Joanna Miller, and Loren Kinczel. The UC Office of the President provided matching funds of $500,000.

    See the full article here .


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    Please help promote STEM in your local schools.

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    UCO Lick Shane Telescope
    UCO Lick Shane Telescope interior
    Shane Telescope at UCO Lick Observatory, UCSC

    Lick Automated Planet Finder telescope, Mount Hamilton, CA, USA

    Lick Automated Planet Finder telescope, Mount Hamilton, CA, USA

    UC Santa Cruz campus
    The University of California, Santa Cruz, opened in 1965 and grew, one college at a time, to its current (2008-09) enrollment of more than 16,000 students. Undergraduates pursue more than 60 majors supervised by divisional deans of humanities, physical & biological sciences, social sciences, and arts. Graduate students work toward graduate certificates, master’s degrees, or doctoral degrees in more than 30 academic fields under the supervision of the divisional and graduate deans. The dean of the Jack Baskin School of Engineering oversees the campus’s undergraduate and graduate engineering programs.

    UCSC is the home base for the Lick Observatory.

    Lick Observatory's Great Lick 91-centimeter (36-inch) telescope housed in the South (large) Dome of main building
    Lick Observatory’s Great Lick 91-centimeter (36-inch) telescope housed in the South (large) Dome of main building

    Search for extraterrestrial intelligence expands at Lick Observatory
    New instrument scans the sky for pulses of infrared light
    March 23, 2015
    By Hilary Lebow
    1
    The NIROSETI instrument saw first light on the Nickel 1-meter Telescope at Lick Observatory on March 15, 2015. (Photo by Laurie Hatch) UCSC Lick Nickel telescope

    Astronomers are expanding the search for extraterrestrial intelligence into a new realm with detectors tuned to infrared light at UC’s Lick Observatory. A new instrument, called NIROSETI, will soon scour the sky for messages from other worlds.

    “Infrared light would be an excellent means of interstellar communication,” said Shelley Wright, an assistant professor of physics at UC San Diego who led the development of the new instrument while at the University of Toronto’s Dunlap Institute for Astronomy & Astrophysics.

    Wright worked on an earlier SETI project at Lick Observatory as a UC Santa Cruz undergraduate, when she built an optical instrument designed by UC Berkeley researchers. The infrared project takes advantage of new technology not available for that first optical search.

    Infrared light would be a good way for extraterrestrials to get our attention here on Earth, since pulses from a powerful infrared laser could outshine a star, if only for a billionth of a second. Interstellar gas and dust is almost transparent to near infrared, so these signals can be seen from great distances. It also takes less energy to send information using infrared signals than with visible light.

    Frank Drake, professor emeritus of astronomy and astrophysics at UC Santa Cruz and director emeritus of the SETI Institute, said there are several additional advantages to a search in the infrared realm.

    “The signals are so strong that we only need a small telescope to receive them. Smaller telescopes can offer more observational time, and that is good because we need to search many stars for a chance of success,” said Drake.

    The only downside is that extraterrestrials would need to be transmitting their signals in our direction, Drake said, though he sees this as a positive side to that limitation. “If we get a signal from someone who’s aiming for us, it could mean there’s altruism in the universe. I like that idea. If they want to be friendly, that’s who we will find.”

    Scientists have searched the skies for radio signals for more than 50 years and expanded their search into the optical realm more than a decade ago. The idea of searching in the infrared is not a new one, but instruments capable of capturing pulses of infrared light only recently became available.

    “We had to wait,” Wright said. “I spent eight years waiting and watching as new technology emerged.”

    Now that technology has caught up, the search will extend to stars thousands of light years away, rather than just hundreds. NIROSETI, or Near-Infrared Optical Search for Extraterrestrial Intelligence, could also uncover new information about the physical universe.

    “This is the first time Earthlings have looked at the universe at infrared wavelengths with nanosecond time scales,” said Dan Werthimer, UC Berkeley SETI Project Director. “The instrument could discover new astrophysical phenomena, or perhaps answer the question of whether we are alone.”

    NIROSETI will also gather more information than previous optical detectors by recording levels of light over time so that patterns can be analyzed for potential signs of other civilizations.

    “Searching for intelligent life in the universe is both thrilling and somewhat unorthodox,” said Claire Max, director of UC Observatories and professor of astronomy and astrophysics at UC Santa Cruz. “Lick Observatory has already been the site of several previous SETI searches, so this is a very exciting addition to the current research taking place.”

    NIROSETI will be fully operational by early summer and will scan the skies several times a week on the Nickel 1-meter telescope at Lick Observatory, located on Mt. Hamilton east of San Jose.

    The NIROSETI team also includes Geoffrey Marcy and Andrew Siemion from UC Berkeley; Patrick Dorval, a Dunlap undergraduate, and Elliot Meyer, a Dunlap graduate student; and Richard Treffers of Starman Systems. Funding for the project comes from the generous support of Bill and Susan Bloomfield.

     
  • richardmitnick 5:34 pm on August 30, 2018 Permalink | Reply
    Tags: , Borexino observatory, , , , , DarkSide experiment, Davide D’Angelo-physical scientist, , , , , , , Pobbile dark matter candidates-axions gravitinos Massive Astrophysical Compact Halo Objects (MACHOs) and Weakly Interacting Massive Particles (WMIPs.)), SABRE-Sodium Iodide with Active Background Rejection Experiment, , Solar neutrinos-recently caught at U Wisconsin IceCube at the South Pole, , , , , Vera Rubin, WIMPs that go by names like the gravitino sneutrino and neutralino   

    From Gran Sasso via Motherboard: “The New Hunt for Dark Matter Is Taking Place Under a Mountain” 

    From Gran Sasso

    via

    Motherboard

    1

    Aug 30 2018
    Daniel Oberhaus

    Davide D’Angelo wasn’t always interested in dark matter, but now he’s at the forefront of the hunt to find the most elusive particle in the universe.

    About an hour outside of Rome there’s a dense cluster of mountains known as the Gran Sasso d’Italia. Renowned for their natural beauty, the Gran Sasso are a popular tourist destination year round, offering world-class skiing in the winter and plenty of hiking and swimming opportunities in the summer. For the 43-year old Italian physicist Davide D’Angelo, these mountains are like a second home. Unlike most people who visit Gran Sasso, however, D’Angelo spends more time under the mountains than on top of them.

    It’s here, in a cavernous hall thousands of feet beneath the earth, that D’Angleo works on a new generation of experiments dedicated to the hunt for dark matter particles, an exotic form of matter whose existence has been hypothesized for decades but never proven experimentally.

    Dark matter is thought to make up about 27 percent of the universe and characterizing this elusive substance is one of the most profound problems in contemporary physics. Although D’Angelo is optimistic that a breakthrough will occur in his lifetime, so was the last generation of physicists. In fact, there’s a decent chance that the particles D’Angelo is looking for don’t exist at all. Yet for physicists probing the fundamental nature of the universe, the possibility that they might spend their entire career “hunting ghosts,” as D’Angelo put it, is the price of advancing science.

    WHAT’S UNDER THE ‘GREAT STONE’?

    In 1989, Italy’s National Institute for Nuclear Physics opened the Gran Sasso National Laboratory, the world’s largest underground laboratory dedicated to astrophysics. Gran Sasso’s three cavernous halls were purposely built for physics, which is something of a luxury as far as research centers go. Most other underground astrophysics laboratories like SNOLAB are ad hoc facilities that repurpose old or active mine shafts, which limits the amount of time that can be spent in the lab and the types of equipment that can be used.


    SNOLAB, Sudbury, Ontario, Canada.

    Buried nearly a mile underground to protect it from the noisy cosmic rays that bathe the Earth, Gran Sasso is home to a number of particle physics experiments that are probing the foundations of the universe. For the last few years, D’Angelo has divided his time between the Borexino observatory and the Sodium Iodide with Active Background Rejection Experiment (SABRE), which are investigating solar neutrinos and dark matter, respectively.

    Borexino Solar Neutrino detector

    SABRE experiment at INFN Gran Sasso

    2
    Davide D’Angelo with the SABRE proof of concept. Image: Xavier Aaronson/Motherboard

    Over the last 100 years, characterizing solar neutrinos and dark matter was considered to be one of the most important tasks of particle physics. Today, the mystery of solar neutrinos is resolved, but the particles are still of great interest to physicists for the insight they provide into the fusion process occurring in our Sun and other stars. The composition of dark matter, however, is still considered to be one of the biggest questions in particle physics. Despite the radically different nature of the particles, they are united insofar as they both can only be discovered in environments where the background radiation is at a minimum: Thousands of feet beneath the Earth’s surface.

    “The mountain acts as a shield so if you go below it, you have so-called ‘cosmic silence,’” D’Angelo said. “That’s the part of my research I like most: Going into the cave, putting my hands on the detector and trying to understand the signals I’m seeing.”

    After finishing grad school, D’Angelo got a job with Italy’s National Institute for Nuclear Physics where his research focused on solar neutrinos, a subatomic particle with no charge that is produced by fusion in the Sun. For the better part of four decades, solar neutrinos [recently caught at U Wisconsin IceCube at the South Pole] were at the heart of one of the largest mysteries in astrophysics.

    IceCube neutrino detector interior


    U Wisconsin ICECUBE neutrino detector at the South Pole

    The problem was that instruments measuring the energy from solar neutrinos returned results much lower than predicted by the Standard Model, the most accurate theory of fundamental particles in physics.

    Given how accurate the Standard Model had proven to be for other aspects of cosmology, physicists were reluctant to make alterations to it to account for the discrepancy. One possible explanation was that physicists had faulty models of the Sun and better measurements of its core pressure and temperature were needed. Yet after a string of observations in the 60s and 70s demonstrated that the models of the sun were essentially correct, physicists sought alternative explanations by turning to the neutrino.

    A TALE OF THREE NEUTRINOS

    Ever since they were first proposed by the Austrian physicist Wolfgang Pauli in 1930, neutrinos have been called upon to patch holes in theories. In Pauli’s case, he first posited the existence of an extremely light, chargeless particle as a “desperate remedy” to explain why the law of the conservation of energy appeared to be violated during radioactive decay. Three years later, the Italian physicist Enrico Fermi gave these hypothetical particles a name. He called them “neutrinos,” Italian for “little neutrons.”

    A quarter of a century after Pauli posited their existence, two American physicists reported the first evidence of neutrinos produced in a fission reactor. The following year, in 1957, Bruno Pontecorvo, an Italian physicist working in the Soviet Union, developed a theory of neutrino oscillations. At the time, little was known about the properties of neutrinos and Pontecorvo suggested that there might be more than one type of neutrino. If this were the case, Pontecorvo theorized that it could be possible for the neutrinos to switch between types.

    By 1975, part of Pontecorvo’s theory had been proven correct. Three different types, or “flavors,” of neutrino had been discovered: electron neutrinos, muon neutrinos, and tau neutrinos. Importantly, observations from an experiment in a South Dakota mineshaft had confirmed that the Sun produced electron neutrinos. The only issue was that the experiment detected far fewer neutrinos than the Standard Model predicted.

    FNAL LBNF/DUNE from FNAL to SURF, Lead, South Dakota, USA


    FNAL DUNE Argon tank at SURF


    Surf-Dune/LBNF Caverns at Sanford



    SURF building in Lead SD USA

    Prior to the late 90s, there was scant indirect evidence that neutrinos could change from one flavor to another. In 1998, a group of researchers working in Japan’s Super-Kamiokande Observatory observed oscillations in atmospheric neutrinos, which are mostly produced by the interactions between photons and the Earth’s atmosphere.

    Super-Kamiokande experiment. located under Mount Ikeno near the city of Hida, Gifu Prefecture, Japan

    Three years later, Canada’s Sudbury Neutrino Observatory (SNO) provided the first direct evidence of oscillations from solar neutrinos.

    Sudbury Neutrino Observatory, no longer operating

    This was, to put it lightly, a big deal in cosmological physics. It effectively resolved the mystery of the missing solar neutrinos, or why experiments only observed about a third as many neutrinos radiating from the Sun compared to predictions made by the Standard Model. If neutrinos could oscillate between flavors, this means a neutrino that is emitted in the Sun’s core could be a different type of neutrino by the time it reaches Earth. Prior to the mid-80s, most experiments on Earth were only looking for electron neutrinos, which meant they were missing the other two flavors of neutrinos that were created en route from the Sun to the Earth.

    When SNO was dreamt up in the 80s, it was designed so that it would be capable of detecting all three types of neutrinos, instead of just electron neutrinos. This decision paid off. In 2015, the directors of the experiments at Super-Kamiokande and SNO shared the Nobel Prize in physics for resolving the mystery of the missing solar neutrinos.

    Although the mystery of solar neutrinos has been solved, there’s still plenty of science to be done to better understand them. Since 2007, Gran Sasso’s Borexino observatory has been refining the measurements of solar neutrino flux, which has given physicists unprecedented insight into the fusion process powering the Sun. From the outside, the Borexino observatory looks like a large metal sphere, but on the inside it looks like a technology transplanted from an alien world.

    Borexino detector. Image INFN

    In the center of the sphere is basically a large, transparent nylon sack that is almost 30 feet in diameter and only half a millimeter thick. This sack contains a liquid scintillator, a chemical mixture that releases energy when a neutrino passes through it. This nylon sphere is suspended in 1,000 metric tons of a purified buffer liquid and surrounded by 2,200 sensors to detect energy released by electrons that are freed when neutrinos interact with the liquid scintillator. Finally, an outer buffer of nearly 3,000 tons of ultrapure water helps provide additional shielding for the detector. Taken together, the Borexino observatory has the most protection from outside radiation interference of any liquid scintillator in the world.

    For the last decade, physicists at Borexino—including D’Angelo, who joined the project in 2011—have been using this one-of-a-kind device to observe low energy solar neutrinos produced by proton collisions during the fusion process in the Sun’s core. Given how difficult it is to detect these chargless, ultralight particles that hardly ever interact with matter, detecting the low energy solar neutrinos would be virtually impossible without such a sensitive machine. When SNO directly detected the first solar neutrino oscillations, for instance, it could only observe the highest energy solar neutrinos due to interference from background radiation. This amounted to only about 0.01 percent of all the neutrinos emitted by the Sun. Borexino’s sensitivity allows it to observe solar neutrinos whose energy is a full order of magnitude lower than those detected by SNO, opening the door for an incredibly refined model of solar processes as well as more exotic events like supernovae.

    “It took physicists 40 years to understand solar neutrinos and it’s been one of the most interesting puzzles in particle physics,” D’Angelo told me. “It’s kind of like how dark matter is now.”

    SHINING A LIGHT ON DARK MATTER

    If neutrinos were the mystery particle of the twentieth century, then dark matter is the particle conundrum for the new millenium. Just like Pauli proposed neutrinos as a “desperate remedy” to explain why experiments seemed to be violating one of the most fundamental laws of nature, the existence of dark matter particles is inferred because cosmological observations just don’t add up.

    In the early 1930s, the American astronomer Fritz Zwicky was studying the movement of a handful of galaxies in the Coma cluster, a collection of over 1,000 galaxies approximately 320 million light years from Earth.

    Fritz Zwicky, the Father of Dark Matter research.No image credit after long search

    Vera Rubin did much of the work on proving the existence of Dark Matter. She and Fritz were both overlooked for the Nobel prize.

    Vera Rubin measuring spectra (Emilio Segre Visual Archives AIP SPL)


    Astronomer Vera Rubin at the Lowell Observatory in 1965. (The Carnegie Institution for Science)

    Using data published by Edwin Hubble, Zwicky calculated the mass of the entire Coma galaxy cluster.

    Coma cluster via NASA/ESA Hubble

    When he did, Zwicky noticed something odd about the velocity dispersion—the statistical distribribution of the speeds of a group of objects—of the galaxies: The velocity distribution was about 12 times higher than it should be based on the amount of matter in the galaxies.

    Inside Gran Sasso- Image- Xavier Aaronson-Motherboard

    This was a surprising calculation and its significance wasn’t lost on Zwicky. “If this would be confirmed,” he wrote, “we would get the surprising result that dark matter is present in much greater amount than luminous matter.”

    The idea that the universe was made up mostly of invisible matter was a radical idea in Zwicky’s time and still is today. The main difference, however, is that astronomers now have much stronger empirical evidence pointing to its existence. This is mostly due to the American astronomer Vera Rubin, whose measurement of galactic rotations in the 1960s and 70s put the existence of dark matter beyond a doubt. In fact, based on Rubin’s measurements and subsequent observations, physicists now think dark matter makes up about 27 percent of the “stuff” in the universe, about seven times more than the regular, baryonic matter we’re all familiar with. The burning question, then, is what is it made of?

    Since Rubin’s pioneering observations, a number of dark matter candidate particles have been proposed, but so far all of them have eluded detection by some of the world’s most sensitive instruments. Part of the reason for this is that physicists aren’t exactly sure what they’re looking for. In fact, a small minority of physicists think dark matter might not be a particle at all and is just an exotic gravitational effect. This makes designing dark matter experiments kind of like finding a car key in a stadium parking lot and trying to track down the vehicle it pairs with. There’s a pretty good chance the car is somewhere in the parking lot, but you’re going to have to try a lot of doors before you find your ride—if it even exists.

    Among the candidates for dark matter are subatomic particles with goofy names like axions, gravitinos, Massive Astrophysical Compact Halo Objects (MACHOs), and Weakly Interacting Massive Particles (WMIPs.) D’Angelo and his colleagues at Gran Sasso have placed their bets on WIMPs, which until recently were considered to be the leading particle candidate for dark matter.

    Over the last few years, however, physicists have started to look at other possibilities after some critical tests failed to confirm the existence of WIMPs. WIMPs are a class of hypothetical elementary particles that hardly ever interact with regular baryonic matter and don’t emit light, which makes them exceedingly hard to detect. This problem is compounded by the fact that no one is really sure how to characterize a WIMP. Needless to say, it’s hard to find something if you’re not even really sure what you’re looking for.

    So why would physicists think WIMPs exist at all? In the 1970s, physicists conceptualized the Standard Model of particle physics, which posited that everything in the universe was made out of a handful of fundamental particles.

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.


    Standard Model of Particle Physics from Symmetry Magazine

    The Standard Model works great at explaining almost everything the universe throws at it, but it’s still incomplete since it doesn’t incorporate gravity into the model.

    Gravity measured with two slightly different torsion pendulum set ups and slightly different results

    In the 1980s, an extension of the Standard Model called Supersymmetry emerged, which hypothesizes that each fundamental particle in the Standard Model has a partner.

    Standard model of Supersymmetry DESY

    These particle pairs are known as supersymmetric particles and are used as the theoretical explanation for a number of mysteries in Standard Model physics, such as the mass of the Higgs boson and the existence of dark matter. Some of the most complex and expensive experiments in the world like the Large Hadron Collider particle accelerator were created in an effort to discover these supersymmetric particles, but so far there’s been no experimental evidence that these particles actually exist.

    LHC

    CERN map


    CERN LHC Tunnel

    CERN LHC particles

    Many of the lightest particles theorized in the supersymmetric model are WIMPs and go by names like the gravitino, sneutrino and neutralino. The latter is still considered to be the leading candidate for dark matter by many physicists and is thought to have formed in abundance in the early universe. Detecting evidence of this ancient theoretical particle is the goal of many dark matter experiments, including the one D’Angelo works on at Gran Sasso.

    D’Angelo told me he became interested in dark matter a few years after joining the Gran Sasso laboratory and began contributing to the laboratory’s DarkSide experiment, which seemed like a natural extension of his work on solar neutrinos. DarkSide is essentially a large tank filled with liquid argon and equipped with incredibly sensitive sensors. If WIMPs exist, physicists expect to detect them from the ionization produced through their collision with the argon nuclei.

    Dark Side-50 Dark Matter Experiment at Gran Sasso

    The set up of the SABRE experiment is deliberately similar to another experiment that has been running at Gran Sasso since 1995 called DAMA. In 2003, the DAMA experiment began looking for seasonal fluctuations in dark matter particles that was predicted in the 1980s as a consequence of the relative motion of the sun and Earth to the rest of the galaxy. The theory posited that the relative speed of any dark matter particles detected on Earth should peak in June and bottom out in December.

    The DarkSide experiment has been running at Gran Sasso since 2013 and D’Angelo said it is expected to continue for several more years. These days, however, he’s found himself involved with a different dark matter experiment at Gran Sasso called SABRE [above], which will also look for direct evidence of dark matter particles based on the light produced when energy is released through their collision with Sodium-Iodide crystals.

    Over the course of nearly 15 years, DAMA did in fact register seasonal fluctuations in its detectors that were in accordance with this theory and the expected signature of a dark matter particle. In short, it seemed as if DAMA was the first experiment in the world to detect a dark matter particle. The problem, however, was that DAMA couldn’t completely rule out the possibility that the signature it had detected was in fact due to some other seasonal variation on Earth, rather than the ebb and flow of dark matter as the Earth revolved around the Sun.

    SABRE aims to remove the ambiguities in DAMA’s data. After all the kinks are worked out in the testing equipment, the Gran Sasso experiment will become one half of SABRE. The other half will be located in Australia in a converted gold mine. By having a laboratory in the northern hemisphere and another in the southern hemisphere, this should help eliminate any false positives that result from normal seasonal fluctuations. At the moment, the SABRE detector is still in a proof of principle phase and is expected to begin observations in both hemispheres within the next few years.

    When it comes to SABRE, it’s possible that the experiment may disprove the best evidence physicists have found so far for a dark matter particle. But as D’Angelo pointed out, this type of disappointment is a fundamental part of science.

    “Of course I am afraid that there might not be any dark matter there and we are hunting ghosts, but science is like this,” D’Angelo said. “Sometimes you spend several years looking for something and in the end it’s not there so you have to change the way you were thinking about things.”

    For D’Angelo, probing the subatomic world with neutrino and dark matter research from a cave in Italy is his way of connecting to the universe writ large.

    “The tiniest elements of nature are bonded to the most macroscopic phenomena, like the expansion of the universe,” D’Angelo said. “The infinitely small touches the infinitely big in this sense, and I find that fascinating. The physics I do, it’s goal is to push over the boundary of human knowledge.”

    See the full article here .

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

    INFN Gran Sasso National Laboratory (LNGS) is the largest underground laboratory in the world devoted to neutrino and astroparticle physics, a worldwide research facility for scientists working in this field of research, where particle physics, cosmology and astrophysics meet. It is unequalled anywhere else, as it offers the most advanced underground infrastructures in terms of dimensions, complexity and completeness.

    LNGS is funded by the National Institute for Nuclear Physics (INFN), the Italian Institution in charge to coordinate and support research in elementary particles physics, nuclear and sub nuclear physics

    Located between L’Aquila and Teramo, at about 120 kilometres from Rome, the underground structures are on one side of the 10-kilometre long highway tunnel which crosses the Gran Sasso massif (towards Rome); the underground complex consists of three huge experimental halls (each 100-metre long, 20-metre large and 18-metre high) and bypass tunnels, for a total volume of about 180.000 m3.

    Access to experimental halls is horizontal and it is made easier by the highway tunnel. Halls are equipped with all technical and safety equipment and plants necessary for the experimental activities and to ensure proper working conditions for people involved.

    The 1400 metre-rock thickness above the Laboratory represents a natural coverage that provides a cosmic ray flux reduction by one million times; moreover, the flux of neutrons in the underground halls is about thousand times less than on the surface due to the very small amount of uranium and thorium of the Dolomite calcareous rock of the mountain.

    The permeability of cosmic radiation provided by the rock coverage together with the huge dimensions and the impressive basic infrastructure, make the Laboratory unmatched in the detection of weak or rare signals, which are relevant for astroparticle, sub nuclear and nuclear physics.

    Outside, immersed in a National Park of exceptional environmental and naturalistic interest on the slopes of the Gran Sasso mountain chain, an area of more than 23 acres hosts laboratories and workshops, the Computing Centre, the Directorate and several other Offices.

    Currently 1100 scientists from 29 different Countries are taking part in the experimental activities of LNGS.
    LNGS research activities range from neutrino physics to dark matter search, to nuclear astrophysics, and also to earth physics, biology and fundamental physics.

     
    • Marco Pereira 2:43 pm on September 1, 2018 Permalink | Reply

      I created a theory called the Hypergeometrical Universe Theory (HU). This theory uses three hypotheses:
      a) The Universe is a lightspeed expanding hyperspherical hypersurface. This was later proven correct by observations by the Sloan Digital Sky Survey
      https://hypergeometricaluniverse.quora.com/Proof-of-an-Extra-Spatial-Dimension
      b) Matter is made directly and simply from coherences between stationary states of deformation of the local metric called Fundamental Dilator or FD.
      https://hypergeometricaluniverse.quora.com/The-Fundamental-Dilator
      c) FDs obey the Quantum Lagrangian Principle (QLP). Yves Couder had a physical implementation (approximation) of the Fundamental Dilator and was perplexed that it would behave Quantum Mechanically. FDs and the QLP are the reason for Quantum Mechanics. QLP replaces Newtonian Dynamics and allows for the derivation of Quantum Gravity or Gravity as applied to Black Holes.

      HU derives a new law of Gravitation that is epoch-dependent. That makes Type 1a Supernovae to be epoch-dependent (within the context of the theory). HU then derives the Absolute Luminosity of SN1a as a function of G and showed that Absolute Luminosity scales with G^{-3}.
      Once corrected the Photometrically Determined SN1a distances, HU CORRECTLY PREDICTS all SN1a distances given their redshifts z.

      The extra dimension refutes all 4D spacetime theories, including General Relativity and L-CDM. HU also falsifies all Dark Matter evidence:
      https://www.quora.com/Are-dark-matter-and-dark-energy-falsifiable/answer/Marco-Pereira-1
      including the Spiral Galaxy Conundrum and the Coma Cluster Conundrum.

      Somehow, my theory is still been censored by the community as a whole (either directly or by omission).

      I hope this posting will help correct this situation.

      Like

  • richardmitnick 4:40 pm on May 6, 2018 Permalink | Reply
    Tags: , , , , , , Vera Rubin,   

    From Symmetry: “The origins of dark matter” 

    Symmetry Mag
    From Symmetry

    11/08/16 [Just brought forward in social media]
    Matthew R. Francis

    1
    Artwork by Sandbox Studio, Chicago with Corinne Mucha

    [Because this article is well over a year old, I have updated it with Dark Matter experiments and also included a section on the origins of Dark Matter research by Vera Rubin and Fritz Zicky.]

    Dark Matter Research

    Caterpillar Project A Milky-Way-size dark-matter halo and its subhalos circled, an enormous suite of simulations . Griffen et al. 2016

    Milky Way Dark Matter Halo Credit ESO L. Calçada


    Dark matter halo. Image credit: Virgo consortium / A. Amblard / ESA

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

    Scientists studying the cosmic microwave background hope to learn about more than just how the universe grew—it could also offer insight into dark matter, dark energy and the mass of the neutrino.

    Dark matter cosmic web and the large-scale structure it forms The Millenium Simulation, V. Springel et al

    Dark Matter Particle Explorer China

    DEAP Dark Matter detector, The DEAP-3600, suspended in the SNOLAB deep in Sudbury’s Creighton Mine

    LUX/Dark matter experiment at SURF

    Edelweiss Dark Matter Experiment, located at the Modane Underground Laboratory in France

    Transitions are everywhere we look. Water freezes, melts, or boils; chemical bonds break and form to make new substances out of different arrangements of atoms. The universe itself went through major transitions in early times. New particles were created and destroyed continually until things cooled enough to let them survive. Those particles include ones we know about, such as the Higgs boson or the top quark. But they could also include dark matter, invisible particles which we presently know only because of their gravitational effects. In cosmic terms, dark matter particles could be a “thermal relic,” forged in the hot early universe and then left behind during the transitions to more moderate later eras. One of these transitions, known as “freeze-out,” changed the nature of the whole universe.

    The hot cosmic freezer

    On average, today’s universe is a pretty boring place. If you pick a random spot in the cosmos, it’s far more likely to be in intergalactic space than, say, the heart of a star or even inside an alien solar system. That spot is probably cold, dark and quiet. The same wasn’t true for a random spot shortly after the Big Bang. “The universe was so hot that particles were being produced from photons smashing into other photons, of photons hitting electrons, and electrons hitting positrons and producing these very heavy particles,” says Matthew Buckley of Rutgers University. The entire cosmos was a particle-smashing party, but parties aren’t meant to last. This one lasted only a trillionth of a second. After that came the cosmic freeze-out. During the freeze-out, the universe expanded and cooled enough for particles to collide far less frequently and catastrophically. “One of these massive particles floating through the universe is finding fewer and fewer antimatter versions of itself to collide with and annihilate,” Buckley says. “Eventually the universe would get large enough and cold enough that the rate of production and the rate of annihilation basically goes to zero, and you just a relic abundance, these few particles that are floating out there lonely in space.” Many physicists think dark matter is a thermal relic, created in huge numbers in before the cosmos was a half-second old and lingering today because it barely interacts with any other particle.

    A WIMPy miracle

    One reason to think of dark matter as a thermal relic is an interesting coincidence known as the “WIMP miracle.” WIMP stands for “weakly-interacting massive particle,” and WIMPs are the most widely accepted candidates for dark matter. Theory says WIMPs are likely heavier than protons and interact via the weak force, or at least interactions related to the weak force. The last bit is important, because freeze-out for a specific particle depends on what forces affect it and the mass of the particle. Thermal relics made by the weak force were born early in the universe’s history because particles need to be jammed in tight for the weak force, which only works across short distances, to be a factor.

    “If dark matter is a thermal relic, you can calculate how big the interaction [between dark matter particles] needs to be,” Buckley says. Both the primordial light known as the cosmic microwave background [CMB] and the behavior of galaxies tell us that most dark matter must be slow-moving (“cold” in the language of physics).

    COBE CMB


    NASA/COBE 1989 to 1993.


    Cosmic Microwave Background NASA/WMAP


    NASA/WMAP 2001 to 2010


    CMB per ESA/Planck


    ESA/Planck 2009 to 2013

    That means interactions between dark matter particles must be low in strength. “Through what is perhaps a very deep fact about the universe,” Buckley says, “that interaction turns out to be the strength of what we know as the weak nuclear force.” That’s the WIMP miracle: The numbers are perfect to make just the right amount of WIMPy matter. The big catch, though, is that experiments haven’t found any WIMPs yet.

    It’s too soon to say WIMPs don’t exist, but it does rule out some of the simpler theoretical predictions about them.

    Ultimately, the WIMP miracle could just be a coincidence. Instead of the weak force, dark matter could involve a new force of nature that doesn’t affect ordinary matter strongly enough to detect. In that scenario, says Jessie Shelton of the University of Illinois at Urbana-Champaign, “you could have thermal freeze-out, but the freeze-out is of dark matter to some other dark field instead of [something in] the Standard Model.” In that scenario, dark matter would still be a thermal relic but not a WIMP. For Shelton, Buckley, and many other physicists, the dark matter search is still full of possibilities. “We have really compelling reasons to look for thermal WIMPs,” Shelton says. “It’s worth remembering that this is only one tiny corner of a much broader space of possibilities.”

    Well, what about AXIONS?

    CERN CAST Axion Solar Telescope


    Inside the ADMX experiment hall at the University of Washington Credit Mark Stone U. of Washington

    Origins of Dark Matter Research

    Vera Rubin measuring spectra (Emilio Segre Visual Archives AIP SPL)

    Vera Florence Cooper Rubin was an American astronomer who pioneered work on galaxy rotation rates. She uncovered the discrepancy between the predicted angular motion of galaxies and the observed motion, by studying galactic rotation curves. This phenomenon became known as the galaxy rotation problem, and was evidence of the existence of dark matter. Although initially met with skepticism, Rubin’s results were confirmed over subsequent decades. Her legacy was described by The New York Times as “ushering in a Copernican-scale change” in cosmological theory.

    Fritz Zwicky, the Father of Dark Matter research.No image credit after long search

    Fritz Zwicky, a Swiss astronomer. He worked most of his life at the California Institute of Technology in the United States of America, where he made many important contributions in theoretical and observational astronomy. In 1933, Zwicky was the first to use the virial theorem to infer the existence of unseen dark matter, describing it as “dunkle Materie

    There was no Nobel award for either Rubin or Zwicky.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 8:57 am on October 18, 2017 Permalink | Reply
    Tags: , , , DAMA LIBRA Dark Matter Experiment, , , , , NIST PROSPECT detector, , , Vera Rubin,   

    From COSMOS: “Closing in on dark matter” 

    Cosmos Magazine bloc

    COSMOS Magazine

    18 October 2017
    Cathal O’Connell

    1
    Dark matter can’t be detected but it glues galaxies together. It outweighs ordinary matter by five to one. Maltaguy1/Getty Images

    One Saturday I hired a metal detector and drove four hours to the historic gold-rush town of Bright in Victoria, Australia, where my wedding ring lies lost, somewhere on the bed of the Ovens River. I spent the evening wading through the icy waters in gumboots, uncovering such treasures as a bottle cap, a fisher’s lead weight and a bracelet caked in rust. I did not uncover the ring. But that doesn’t mean the ring is not there.

    Like me, physicists around the world are in the midst of an important search that has so far proven fruitless. Their quarry is nothing less than most of the matter in the universe, so-called “dark matter”.

    So far their most sensitive detectors have found – to be pithy – nada. Despite the lack of results, scientists aren’t giving up. “The frequency with which articles show up in the popular press saying ‘maybe dark matter isn’t real’ massively exceeds the frequency with which physicists or astronomers find any reason to re-examine that question,” says Katie Mack, a theoretical astrophysicist at the University of Melbourne.

    In many respects, the quest for dark matter has only just begun. We can expect quite a few more null results before the real treasure turns up. So here is where we stand, and what we can expect from the next few years.

    Imagine a toddler sitting on one end of a seesaw and launching her father, at the other end, high into the air. It’s a weird and unsettling image, yet we regularly observe this kind of ‘impossible’ behaviour in the universe at large. Like the little girl on the seesaw, galaxies behave as if they have four or five times the mass we can see.

    Our first inkling of this discrepancy came in the 1930s, when the Swiss astronomer Fritz Zwicky noticed odd movements among the Coma cluster of galaxies.

    2
    Fritz Zwicky: The Father of Dark Matter. https://www.youtube.com/watch?v=TV0c1EFIKy4

    Zwicky’s anomaly was largely ignored until the 1970s, when astrophysicist Vera Rubin, based at the Carnegie Institute in Washington, noticed that the way galaxies spin did not tally with the laws of physics.

    3
    Astronomer Vera Rubin in 1974, with her “measuring engine” used to examine photographic plates. Credit: Courtesy of Carnegie Institution of Washington

    The meticulous observations by Rubin (who passed away in December 2016) convinced most of the astronomical community something was amiss. There were two possible answers to the problem: either galaxies were a lot heavier than they appeared, or our theory of gravity was kaput when it came to galaxy-scale movements.

    From the outset, astronomers preferred the first explanation. At first they thought the missing matter was probably nothing too weird – just regular astronomical objects (like planets, black holes and stars) too dim for us to see. But as we surveyed the sky with ever bigger telescopes, these so-called ‘massive compact halo objects’ (or MACHOs) never turned up in the numbers needed to explain all the extra mass.

    Other astrophysicists, such as the Mordehai Milgrom at Israel’s Weizmann Institute, explored models where gravity behaved differently at cosmic scales. [See https://sciencesprings.wordpress.com/2017/05/18/from-nautilus-the-physicist-who-denies-dark-matter/%5D

    5
    Mordehai Milgrom. Cosmos on Nautilus

    They were not successful.

    Slowly astronomers realised they had something radically different on their hands – a new kind of stuff they called ‘dark matter’, which must outweigh the universe’s regular matter by about five to one. “Certainly, when all the evidence is taken together,” Mack says, “there’s no competing idea right now that comes anywhere close to explaining it as well.”

    We know four main facts about dark matter. First, it has gravity. Second, it doesn’t emit, absorb or reflect light. Third, it moves slowly. Fourth, it doesn’t seem to interact with anything, even itself.

    Like detectives in a TV murder mystery, physicists have compiled a list of suspects. Topping the list are three hypothetical particles already wanted on other charges: axions, sterile neutrinos and WIMPs. Besides nailing dark matter, each would help explain a grand mystery of their own.

    The axion is a particle proposed by Roberto Peccei and Helen Quinn back in 1977 to explain a quirk of the strong force (namely, why it can’t distinguish left from right, the way the weak force does). Thirty years on, axions are still our best explanation for that puzzle.

    Axions could have any mass, but if – and it is a big ‘if’ – they have a mass about 100 billion times lighter than an electron, theorists have calculated they would have been created in the Big Bang in such vast numbers that they could account for the universe’s dark matter. Like detectives with a dragnet, physicists are searching through different possible masses in an attempt to close in from both ends and corner the axion.

    The Axion Dark Matter eXperiment (ADMX), based at the University of Washington, is dragging the lightest end of the range.

    U Washington ADMX


    U Washington ADMX Axion Dark Matter Experiment

    Since 2010 the project has been trying to catch axions by turning them into photons using strong magnetic fields. So far ADMX has ruled out the featherweight mass range between 150 to 270 billion times lighter than the electron.

    The CERN Axion Solar Telescope (CAST) is dragging the heavyweight end of the range looking for axions that are a few tens of millions to about a million times lighter than the electron.

    CERN CAST Axion Solar Telescope

    The theorised source of these hefty axions is the Sun, where they might be created by X-rays in the presence of strong electric fields. In an example of recycling at its big-science best, CAST was assembled from a piece of the Large Hadron Collider -– a giant test magnet. It aims to detect solar axions by turning them back into X-rays. It has been running since 2003. The search goes on.

    4
    Hypothetical particles known as axions could explain dark matter. Physicists at CERN have taken a giant magnet from the Large Hadron Collider and turned it into an axion detector, the CERN Axion Solar Telescope. Howard Cunningham/Getty Images

    Sterile neutrinos are the hypothetical heavier, lazier brothers of neutrinos – the ghostly, fast-moving particles created in nuclear reactions and in the centre of the Sun. They are called ‘sterile’ or ‘inactive’ because they only interact via gravity.

    Besides being a dark-matter candidate, sterile neutrinos would plug a number of holes in the Standard Model,

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    which, like a subatomic version of the periodic table, has had great success in predicting the properties of the fundamental building blocks of the universe. For instance, sterile neutrinos could explain why neutrinos are so light, and why every neutrino we’ve ever seen has a ‘left-handed’ spin; sterile neutrinos would be the missing ‘right-handed’ partners.

    Physicists are trying to detect sterile neutrinos in different ways, including searching deep space for the X-rays emitted when they decay. NASA’s Chandra X-ray telescope has picked up an excess of X-rays from the Perseus cluster of galaxies, which is so far unexplained.

    NASA/Chandra Telescope

    6
    Perseus cluster. NASA

    Meanwhile, regular neutrino detectors based at nuclear reactors, such as Daya Bay in China, have noticed anomalies that might be explained by sterile neutrinos.

    Daya Bay, approximately 52 kilometers northeast of Hong Kong and 45 kilometers east of Shenzhen, China

    “Like Elvis, people see hints of the sterile neutrino everywhere,” quipped Francis Halzen in August 2016, when he and his colleagues at the IceCube Neutrino Observatory announced the disappointing results of their own search.


    U Wisconsin ICECUBE neutrino detector at the South Pole

    Their detector, buried up to 2.5 km deep in ice near the South Pole, found no evidence of the elusive sterile neutrino – a result that seems to rule out the Daya Bay reactor sightings. For a conclusive answer, we’ll need to wait for the next neutrino searches, such as the Precision Reactor Antineutrino Oscillation and Spectrum Measurement (PROSPECT) under construction at the US National Institute of Standards and Technology (NIST) in Maryland.

    8
    The PROSPECT detector will consist of an 11 x 14 array of long skinny cells filled with liquid scintillator, which is designed to sense antineutrinos emanating from the reactor core. If a sterile neutrino flavor exists, then PROSPECT will see waves of antineutrinos that appear and disappear with a period determined by their energy. Composition not drawn to scale. NIST.

    The third and most popular suspect is WIMPs – weakly interacting massive particles. The name covers a broad range of hypothetical particles that would interact via the weak force. They pop naturally out of the ideas of supersymmetry, an extension proposed to tidy up the loose ends of the Standard Model.

    Physicists calculate that the simplest possible WIMP, with a mass of about 100 billion electron volts, would have been created in the Big Bang at just the right numbers to explain dark matter: the so-called ‘WIMP miracle’.

    WIMP detectors are typically deep underground, watching for a telltale flash given out when a particle of dark matter bumps into an atomic nucleus.

    The most sensitive WIMP experiment yet is LUX, a bathtub-sized vat holding 370 kg of liquid xenon at the Sanford Underground Research Facility [SURF] in South Dakota. In 2016, the LUX team announced it had discovered no dark matter signals during its first 20-month-long search. Undeterred, the LUX team plan to upgrade to a 7,000-kg vat, LUX-ZEPLIN, by 2020.

    LBNL Lux Zeplin project at SURF

    The most intriguing dark matter result so far comes from the DAMA/LIBRA experiment in Italy. Using a detector made of highly purified sodium-iodide crystals, 1.5 km beneath Italy’s Gran Sasso mountain, scientists believe they have seen evidence of dark matter every year for the past 14 years (see Cosmos 65, p60). Their evidence comes in an annual rise and fall in background detections. Such a pattern might reflect the Earth’s relative speed through the dark-matter cloud that surrounds the Milky Way; while our planet moves around the Sun at 30 km/s, the Solar System as a whole is travelling at 230 km/s around the centre of the Milky Way.

    DAMA LIBRA Dark Matter Experiment, 1.5 km beneath Italy’s Gran Sasso mountain

    Gran Sasso LABORATORI NAZIONALI del GRAN SASSO, located in L’Aquila, Italy

    For half of the year the Earth’s orbital speed would add to the speed of the Solar System, increasing the rate of dark-matter interactions. For the other half, the speeds would subtract and the rate of interactions decrease. The problem is that lots of other things change with the seasons too, such as the thickness of the atmosphere. To rule out terrestrial effects, astronomers are setting up two identical detectors, called SABRE, in opposite hemispheres – so that one is collecting data in winter and the other in summer.

    One detector will be based at Gran Sasso, the other in Australia, in an abandoned gold mine near Stawell, Victoria. Each detector will be made of 50 kg of sodium iodide, and have noise levels 10 times lower than DAMA/LIBRA. Construction on each is under way, and could be finished this year.

    Rather than detecting dark matter, others are trying to make it. The closest we can get to the conditions of the Big Bang – where dark matter was presumably created – is in the collision chambers of the Large Hadron Collider, CERN’s 27-km long particle smasher. These chambers are ringed by sensors that can pick up the energies of millions of particles generated in each smash-up, and tally this against the known collision energy. If some energy is missing, it might indicate the creation of a particle that could not be detected by any sensors: dark matter.

    So far, notwithstanding a brief, hallucinatory blip in late 2015, the LHC has not discovered anything that might constitute a dark matter particle such as a WIMP. But the LHC has only collected about 1% of the data it is due to produce before it is retired in 2025. So it is too early to throw in the towel on producing dark matter yet. Plans are afoot for the LHC’s successor, which will be able to probe far higher energies.

    Snowmelt from the Alpine ranges had swelled the Ovens River. I had to hug the shore with my metal detector, where the water was shallow and easy to sweep. I searched those parts that I could search as thoroughly as possible. If I did not find my prize, I wanted to at least be able to point to the map and say with confidence where the ring was not.

    The map that physicists search has coordinates of energy levels and interaction strengths. Each new search sweeps out a new territory, so even a null result is valuable information. So far, in our search for the three primary candidates – axions, sterile neutrinos and WIMPs – we have only probed the most shallow, accessible waters. “There’s nothing really that says they have to be easy to detect,” Mack says. “It may just be that their interactions with our detectors are smaller than expected.”

    It took almost 50 years for the Higgs boson to be discovered. Gravitational waves took almost a century. Let’s not give up on dark matter just yet.

    I certainly won’t be giving up my own search. Next summer, when the Ovens dries, I will return to Bright and sweep the next unprobed area of the riverbed. I’d say wish me luck, but the point is to be so rigorous that luck has nothing to do with it.

    See the full article here .

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  • richardmitnick 5:00 pm on June 13, 2017 Permalink | Reply
    Tags: A different kind of dark matter could help to resolve an old celestial conundrum, , , , , , , Dark matter superfluid, Dark matter vortices, , Kent Ford, , Vera Rubin,   

    From Quanta: “Dark Matter Recipe Calls for One Part Superfluid” 

    Quanta Magazine
    Quanta Magazine

    June 13, 2017
    Jennifer Ouellette

    A different kind of dark matter could help to resolve an old celestial conundrum.

    1
    Markos Kay for Quanta Magazine

    For years, dark matter has been behaving badly. The term was first invoked nearly 80 years ago by the astronomer Fritz Zwicky, who realized that some unseen gravitational force was needed to stop individual galaxies from escaping giant galaxy clusters. Later, Vera Rubin and Kent Ford used unseen dark matter to explain why galaxies themselves don’t fly apart.

    Yet even though we use the term “dark matter” to describe these two situations, it’s not clear that the same kind of stuff is at work. The simplest and most popular model holds that dark matter is made of weakly interacting particles that move about slowly under the force of gravity. This so-called “cold” dark matter accurately describes large-scale structures like galaxy clusters. However, it doesn’t do a great job at predicting the rotation curves of individual galaxies. Dark matter seems to act differently at this scale.

    In the latest effort to resolve this conundrum, two physicists have proposed that dark matter is capable of changing phases at different size scales. Justin Khoury, a physicist at the University of Pennsylvania, and his former postdoc Lasha Berezhiani, who is now at Princeton University, say that in the cold, dense environment of the galactic halo, dark matter condenses into a superfluid — an exotic quantum state of matter that has zero viscosity. If dark matter forms a superfluid at the galactic scale, it could give rise to a new force that would account for the observations that don’t fit the cold dark matter model. Yet at the scale of galaxy clusters, the special conditions required for a superfluid state to form don’t exist; here, dark matter behaves like conventional cold dark matter.

    “It’s a neat idea,” said Tim Tait, a particle physicist at the University of California, Irvine. “You get to have two different kinds of dark matter described by one thing.” And that neat idea may soon be testable. Although other physicists have toyed with similar ideas, Khoury and Berezhiani are nearing the point where they can extract testable predictions that would allow astronomers to explore whether our galaxy is swimming in a superfluid sea.

    Impossible Superfluids

    Here on Earth, superfluids aren’t exactly commonplace. But physicists have been cooking them up in their labs since 1938. Cool down particles to sufficiently low temperatures and their quantum nature will start to emerge. Their matter waves will spread out and overlap with one other, eventually coordinating themselves to behave as if they were one big “superatom.” They will become coherent, much like the light particles in a laser all have the same energy and vibrate as one. These days even undergraduates create so-called Bose-Einstein condensates (BECs) in the lab, many of which can be classified as superfluids.

    Superfluids don’t exist in the everyday world — it’s too warm for the necessary quantum effects to hold sway. Because of that, “probably ten years ago, people would have balked at this idea and just said ‘this is impossible,’” said Tait. But recently, more physicists have warmed to the possibility of superfluid phases forming naturally in the extreme conditions of space. Superfluids may exist inside neutron stars, and some researchers have speculated that space-time itself may be a superfluid. So why shouldn’t dark matter have a superfluid phase, too?

    To make a superfluid out of a collection of particles, you need to do two things: Pack the particles together at very high densities and cool them down to extremely low temperatures. In the lab, physicists (or undergraduates) confine the particles in an electromagnetic trap, then zap them with lasers to remove the kinetic energy and lower the temperature to just above absolute zero.

    2
    Lucy Reading-Ikkanda/Quanta Magazine

    The dark matter particles that would make Khoury and Berezhiani’s idea work are emphatically not WIMP-like. WIMPs should be pretty massive as fundamental particles go — about as massive as 100 protons, give or take. For Khoury’s scenario to work, the dark matter particle would have to be a billion times less massive. Consequently, there should be billions of times as many of them zipping through the universe — enough to account for the observed effects of dark matter and to achieve the dense packing required for a superfluid to form. In addition, ordinary WIMPs don’t interact with one another. Dark matter superfluid particles would require strongly interacting particles.

    The closest candidate is the axion, a hypothetical ultralight particle with a mass that could be 10,000 trillion trillion times as small as the mass of the electron. According to Chanda Prescod-Weinstein, a theoretical physicist at the University of Washington, axions could theoretically condense into something like a Bose-Einstein condensate.

    But the standard axion doesn’t quite fit Khoury and Berezhiani’s needs. In their model, particles would need to experience a strong, repulsive interaction with one another. Typical axion models have interactions that are both weak and attractive. That said, “I think everyone thinks that dark matter probably does interact with itself at some level,” said Tait. It’s just a matter of determining whether that interaction is weak or strong.

    Cosmic Superfluid Searches

    The next step for Khoury and Berezhiani is to figure out how to test their model — to find a telltale signature that could distinguish this superfluid concept from ordinary cold dark matter. One possibility: dark matter vortices. In the lab, rotating superfluids give rise to swirling vortices that keep going without ever losing energy. Superfluid dark matter halos in a galaxy should rotate sufficiently fast to also produce arrays of vortices. If the vortices were massive enough, it would be possible to detect them directly.

    Inside galaxies, the role of the electromagnetic trap would be played by the galaxy’s gravitational pull, which could squeeze dark matter together enough to satisfy the density requirement. The temperature requirement is easier: Space, after all, is naturally cold.

    Outside of the “halos” found in the immediate vicinity of galaxies, the pull of gravity is weaker, and dark matter wouldn’t be packed together tightly enough to go into its superfluid state. It would act as dark matter ordinarily does, explaining what astronomers see at larger scales.

    But what’s so special about having dark matter be a superfluid? How can this special state change the way that dark matter appears to behave? A number of researchers over the years have played with similar ideas. But Khoury’s approach is unique because it shows how the superfluid could give rise to an extra force.

    In physics, if you disturb a field, you’ll often create a wave. Shake some electrons — for instance, in an antenna — and you’ll disturb an electric field and get radio waves. Wiggle the gravitational field with two colliding black holes and you’ll create gravitational waves. Likewise, if you poke a superfluid, you’ll produce phonons — sound waves in the superfluid itself. These phonons give rise to an extra force in addition to gravity, one that’s analogous to the electrostatic force between charged particles. “It’s nice because you have an additional force on top of gravity, but it really is intrinsically linked to dark matter,” said Khoury. “It’s a property of the dark matter medium that gives rise to this force.” The extra force would be enough to explain the puzzling behavior of dark matter inside galactic halos.

    A Different Dark Matter Particle

    Dark matter hunters have been at work for a long time. Their efforts have focused on so-called weakly interacting massive particles, or WIMPs. WIMPs have been popular because not only would the particles account for the majority of astrophysical observations, they pop out naturally from hypothesized extensions of the Standard Model of particle physics.

    Yet no one has ever seen a WIMP, and those hypothesized extensions of the Standard Model haven’t shown up in experiments either, much to physicists’ disappointment.

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    With each new null result, the prospects dim even more, and physicists are increasingly considering other dark matter candidates. “At what point do we decide that we’ve been barking up the wrong tree?” said Stacy McGaugh, an astronomer at Case Western Reserve University.

    Unfortunately, this is unlikely to be the case: Khoury’s most recent computer simulations suggest that vortices in the dark matter superfluid would be “pretty flimsy,” he said, and unlikely to offer researchers clear-cut evidence that they exist. He speculates it might be possible to exploit the phenomenon of gravitational lensing to see if there are any scattering effects, similar to how a crystal will scatter X-ray light that passes through it.

    Gravitational Lensing NASA/ESA

    Astronomers could also search for indirect evidence that dark matter behaves like a superfluid. Here, they’d look to galactic mergers.

    The rate that galaxies collide with one another is influenced by something called dynamical friction. Imagine a massive body passing through a sea of particles. Many of the small particles will get pulled along by the massive body. And since the total momentum of the system can’t change, the massive body must slow down a bit to compensate.

    That’s what happens when two galaxies start to merge. If they get sufficiently close, their dark matter halos will start to pass through each other, and the rearrangement of the independently moving particles will give rise to dynamical friction, pulling the halos even closer. The effect helps galaxies to merge, and works to increase the rate of galactic mergers across the universe.

    But if the dark matter halo is in a superfluid phase, the particles move in sync. There would be no friction pulling the galaxies together, so it would be more difficult for them to merge. This should leave behind a telltale pattern: rippling interference patterns in how matter is distributed in the galaxies.

    Perfectly Reasonable Miracles

    While McGaugh is mostly positive about the notion of superfluid dark matter, he confesses to a niggling worry that in trying so hard to combine the best of both worlds, physicists might be creating what he terms a “Tycho Brahe solution.” The 16th-century Danish astronomer invented a hybrid cosmology in which the Earth was at the center of the universe but all the other planets orbited the sun. It attempted to split the difference between the ancient Ptolemaic system and the Copernican cosmology that would eventually replace it. “I worry a little that these kinds of efforts are in that vein, that maybe we’re missing something more fundamental,” said McGaugh. “But I still think we have to explore these ideas.”

    Tait admires this new superfluid model intellectually, but he would like to see the theory fleshed out more at the microscopic level, to a point where “we can really calculate everything and show why it all works out the way it’s supposed to. At some level, what we’re doing now is invoking a few miracles” in order to get everything to fit into place, he said. “Maybe they’re perfectly reasonable miracles, but I’m not fully convinced yet.”

    One potential sticking point is that Khoury and Berezhiani’s concept requires a very specific kind of particle that acts like a superfluid in just the right regime, because the kind of extra force produced in their model depends upon the specific properties of the superfluid. They are on the hunt for an existing superfluid — one created in the lab — with those desired properties. “If you could find such a system in nature, it would be amazing,” said Khoury, since this would essentially provide a useful analog for further exploration. “You could in principle simulate the properties of galaxies using cold atoms in the lab to mimic how superfluid dark matter behaves.”

    While researchers have been playing with superfluids for many decades, particle physicists are only just beginning to appreciate the usefulness of some of the ideas coming from subjects like condensed matter physics. Combining tools from those disciplines and applying it to gravitational physics might just resolve the longstanding dispute on dark matter — and who knows what other breakthroughs might await?

    “Do I need superfluid models? Physics isn’t really about what I need,” said Prescod-Weinstein. “It’s about what the universe may be doing. It may be naturally forming Bose-Einstein condensates, just like masers naturally form in the Orion nebula. Do I need lasers in space? No, but they’re pretty cool.”

    See the full article here .

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    Formerly known as Simons Science News, Quanta Magazine is an editorially independent online publication launched by the Simons Foundation to enhance public understanding of science. Why Quanta? Albert Einstein called photons “quanta of light.” Our goal is to “illuminate science.” At Quanta Magazine, scientific accuracy is every bit as important as telling a good story. All of our articles are meticulously researched, reported, edited, copy-edited and fact-checked.

     
  • richardmitnick 11:15 am on October 4, 2016 Permalink | Reply
    Tags: , , , , Vera Rubin,   

    From Astronomy: Women in STEM – “How Vera Rubin discovered dark matter” 

    Astronomy magazine

    astronomy.com

    October 04, 2016
    Sarah Scoles

    1
    A young Vera Rubin was already observing the stars when she was an undergraduate at Vassar College, where she earned her bachelor’s degree in astronomy in 1948. Archives & Special Collections, Vassar College Library

    In the late 1970s, Vera Rubin and Kent Ford of the Carnegie Institution of Washington stared, confused, at the punch-card readouts from their observations of the Andromeda Galaxy.

    Andromeda Galaxy Adam Evans
    Andromeda Galaxy, Adam Evans”

    The vast spiral seemed to be rotating all wrong. The stuff at the edges was moving just as fast as the stuff near the center, apparently violating Newton’s Laws of Motion (which also govern how the planets move around our Sun). While the explanation for that strange behavior didn’t become clear to Rubin until two years later, these printouts represented the first direct evidence of dark matter.

    Scientists now know that dark matter comprises some 84 percent of the universe’s material. Its invisible particles swarm and stream and slam through the whole cosmos. It affects how stars move within galaxies, how galaxies tug on each other, and how all that matter clumped together in the first place. It is to the cosmos like air is to humans: ubiquitous, necessary, unseen but felt. The discovery of this strange substance deserves a Nobel Prize. But, for Rubin, none has come, although she has long been a “people’s choice” and predicted winner.

    In the past few years, scientists have gotten that free trip to Sweden for demonstrating that neutrinos have mass, for inventing blue LEDs, for isolating graphene’s single carbon layer, and for discovering dark energy. All of these experiments and ideas are worthy of praise, and some, like dark energy, even tilted the axis of our understanding of the universe. But the graphene work began in 2004; dark energy observations happened in the late ’90s; scientists weighed neutrinos around the same time; and blue LEDs burst onto the scene a few years before that. Rubin’s work on dark matter, on the other hand, took place in the 1970s. It’s like the committee cannot see her, although nearly all of astrophysics feels her influence.

    Rubin is now 87. She is too infirm for interviews. And because the Nobel can only be awarded to the living, time is running out for her.

    Emily Levesque, an astronomer at the University of Washington in Seattle who has spoken out about Rubin’s notable lack of a Nobel, says, “The existence of dark matter has utterly revolutionized our concept of the universe and our entire field; the ongoing effort to understand the role of dark matter has basically spawned entire subfields within astrophysics and particle physics at this point. Alfred Nobel’s will describes the physics prize as recognizing ‘the most important discovery’ within the field of physics. If dark matter doesn’t fit that description, I don’t know what does.”

    There’s no way to prove why Rubin remains prize-less. But a webpage showing images of past winners looks like a 50th-reunion publication from a boys’ prep school. No woman has received the Nobel Prize in physics since 1963, when Maria Goeppert Mayer shared it with Eugene Wigner and J. Hans Jensen for their work on atomic structure and theory. And the only woman other than Mayer ever to win was Marie Curie. With statistics like that, it’s hard to believe gender has nothing to do with the decision.

    Some, like Chanda Prescod-Weinstein of the Massachusetts Institute of Technology, have called for no men to accept the prize until Rubin receives it. But given the human ego and nearly million-dollar prize amount, that’s likely to remain an Internet-only call to action.

    No room for women

    Rubin isn’t unfamiliar with discrimination more outright than the Nobel committee’s. Former colleague Neta Bahcall of Princeton University tells a story about a trip Rubin took to Palomar Observatory outside of San Diego early in her career. For many years, the observatory was a researcher’s man cave. Rubin was one of the first women to gain access to its gilt-edged, carved-pillar grandeur. But while she was allowed to be present, the building had no women’s restroom, just urinal-studded water closets.

    “She went to her room, she cut up paper into a skirt image, and she stuck it on the little person image on the door of the bathroom,” says Bahcall. “She said, ‘There you go; now you have a ladies’ room.’ That’s the type of person Vera is.”

    Rubin has continued to champion women’s rights to — and rights within — astronomy. “She frequently would see the list of speakers [at a conference],” says Bahcall, “and if there were very few or no women speakers, she would contact [the organizers] and tell them they have a problem and need to fix it.”

    But, as Rubin told science writer Ann Finkbeiner for Astronomy in 2000, she is “getting fed up. . . . What’s wrong with this story is that nothing’s changing, or it’s changing so slowly.”

    An early start

    Rubin, born in 1928, first found her interest in astronomy when her family moved to Washington, D.C. Windows lined the wall next to her bed. She watched the stars move, distant and unreachable. “What fascinated me was that if I opened my eyes during the night, they had all rotated around the pole,” she told David DeVorkin in 1995 as part of the American Institute of Physics oral history interview series. “And I found that inconceivable. I just was captured.”

    She started watching meteor showers and drew maps of the streaks, which striped the sky for a second and then were gone. She built a telescope and chose astronomical topics for English papers, using every subject as an opportunity to peer deeper into the universe. “How could you possibly live on this Earth and not want to study these things?” she wondered, retelling the story to DeVorkin.

    While her parents supported her, it was a different story at school. When she told her physics teacher, for instance, that she had received a scholarship to Vassar College, he said, “As long as you stay away from science, you should do OK.”

    She didn’t.

    2
    Rubin and Kent for (white hat) check on their equipment at Lowell Observatory in 1965 during one of their first observing runs together. Carnegie Institution, Department of Terrestrial Magnetism

    Rotation of the universe

    After receiving her bachelor’s degree from Vassar, Rubin enrolled in graduate school in astronomy at Cornell University in Ithaca, New York. Ensconced in Ithaca’s gorges and working with astronomer Martha Stahr Carpenter, Rubin began to hunt around for a master’s thesis idea. Carpenter was obsessed with galaxies and how their innards moved. “Her course in galaxy dynamics really set me off on a direction that I followed almost my entire career,” said Rubin.

    One day, her new husband, Robert Rubin, brought her a journal article by astronomer George Gamow. In it, Gamow wondered, “What if we took the way solar systems rotate and applied it to how galaxies move in the universe?”

    Rubin wondered, “What if, indeed?” and took that wonder a step further. She began to measure how galaxies moved. Did some cluster together in their travel through space — perhaps rotating around a pole, like the planets rotate around the common Sun? Was it random?

    While gathering data, she found a plane that was denser with galaxies than other regions. She didn’t know it at the time, and no one else would discover it for years, but she had identified the “supergalactic plane,” the equator of our home supercluster of galaxies.

    When she presented her thesis, William Shaw, one of her advisers, told her just two things: One, the word data is plural. Two, her work was sloppy. But, he continued, she should consider presenting it at the American Astronomical Society (AAS) meeting. Or, rather, she should consider having it presented for her. Because she was pregnant with her first child — due just a month before the meeting — and not a member of the society, he graciously volunteered to give a talk on her results. “In his name,” she clarified to DeVorkin. “Not in my name. I said to him, ‘Oh, I can go.’ ”

    She called her talk “Rotation of the Universe,” ascribing the ambitious title to “the enthusiasm of youth,” as she recalled. At the AAS meeting, she didn’t know anyone, and she thought of herself as a different category of human. “I put these people in a very special class. They were professional astronomers, and I was not,” she said, showcasing a classic case of impostor syndrome, a psychological phenomenon in which people don’t feel they deserve their accomplishments and status and will inevitably be exposed as frauds. “One of the biggest problems in my life [during] those years was really attempting to answer the question to myself, ‘Will I ever really be an astronomer?’ ”

    The “real astronomers” pounced on her result (except, notably, Martin Schwarzschild, who defined how big black holes are). “My paper was followed by a rather acrimonious discussion,” she told DeVorkin. “I didn’t know anyone, so I didn’t know who these people were that were getting up and saying the things they said. As I recall, all the comments were negative.”

    Her paper was never published.

    Back into the field

    For six months after her first child was born, Rubin stayed home. But while she loved having a child, staying at home emptied her. She cried every time The Astrophysical Journal arrived at the house. “I realized that as much as we both adored this child, there was nothing in my background that had led me to expect that [my husband] would go off to work each day doing what he loved to do, and I would stay home with this lovely child,” she said to DeVorkin. “I really found it very, very hard. And it was he who insisted that I go back to school.”

    She was accepted into a Ph.D. program at Georgetown University in Washington, D.C., and she discovered that galaxies did clump together, like iron filings, and weren’t randomly strewn. The work, though now part of mainstream astronomy, was largely ignored for decades; that lack of reinforcement perhaps contributed to her lingering, false feeling that she wasn’t a real astronomer. As she described it, “My husband heard my question often, ‘Will I ever really be an astronomer?’ First I thought when I’d have a Ph.D., I would. Then even after I had my Ph.D., I wondered if I would.”

    3
    Rubin operates the 2.1-meter telescope at Kitt Peak National Observatory. Kent Ford’s spectograph is attached so they can measure the speed of matter at different distances from galaxies’ centers. NOAO/AURA/NSF

    Mysteriously flat

    In 1965, after a stint as a professor at Georgetown, Rubin began her work at the Carnegie Institution’s Department of Terrestrial Magnetism in Washington, D.C., where she met astronomer Kent Ford and his spectacular spectrometer, which was more sensitive than any other at the time.

    A spectrometer takes light and splits it up into its constituent wavelengths. Instead of just showing that a fluorescent bulb glows white, for instance, it would show how much of that light is blue and how much yellow, and which specific wavelengths of blue and yellow. Ford’s spectrometer stood out from others at the time because it employed state-of-the-art photomultipliers that let researchers study small regions of galaxies, and not simply the entire objects.

    With this device, Ford and Rubin decided to look at quasars — distant galaxies with dynamic, supermassive black holes at their centers. But this was competitive work: Quasars had just been discovered in 1963, and their identity was in those days a mystery that everyone wanted to solve. Rubin and Ford didn’t have their own telescope and had to request time on the world-class instruments that astronomers who worked directly for the observatories could access all the time. Rubin didn’t like the competition.

    “After about a year or two, it was very, very clear to me that that was not the way I wanted to work,” she told Alan Lightman in another American Institute of Physics oral history interview. “I decided to pick a problem that I could go observing and make headway on, hopefully a problem that people would be interested in, but not so interested [in] that anyone would bother me before I was done.”

    Rubin and Ford chose to focus on the nearby Andromeda Galaxy (M31). It represented a return to Rubin’s interest in galaxy dynamics. “People had inferred what galaxy rotations must be like,” said Rubin, “but no one had really made a detailed study to show that that was so.” Now, because of Ford’s out-of-this-world spectrograph, they could turn the inferences into observations.

    When they pointed the telescope at M31, they expected to see it rotate like the solar system does: Objects closer to the center move faster than ones toward the edge. Mass causes gravity, which determines the speed of rotation. Since most of the stars, dust, and gas — and therefore gravity — is clustered in the middle of galaxies, the stuff on the periphery shouldn’t feel much pull. They concentrated their observations on Hydrogen-II (HII) regions — areas of ionized hydrogen gas where stars have recently formed — at different distances from the galaxy’s center. But no matter how far out they looked, the HII regions seemed to be moving at the same speed. They weren’t slowing down.

    “We kept going farther and farther out and had some disappointment that we never saw anything,” says Ford. “I do remember my puzzling at the end of the first couple of nights that the spectra were all so straight,” said Rubin, referring to the unchanging speed of the various HII regions.

    They didn’t know what, if anything, it meant yet.

    The project took years and involved treks westward to telescopes. Ford recalls flying to Flagstaff, Arizona, dragging the spectrograph from the closet, working for a few nights at Lowell, and then throwing the instrument into a Suburban so they could drive it to Kitt Peak. “We both thought we were better at guiding the telescope,” he says. They raced each other to be first to the eyepiece.

    The data came out on punch cards, which Rubin spent hours analyzing in a cubbyhole beneath a set of stairs. They all showed the same thing.

    Rubin and Ford moved on from M31 to test other galaxies and their rotation curves. Like an obsessive artist, each painted the same picture. Although the result contradicted theory, and although they didn’t understand what it meant, no one doubted their data. “All you had to do was show them a picture of the spectrum,” Rubin told Lightman. “It just piled up too fast. Soon there were 20, then 40, then 60 rotation curves, and they were all flat.”

    A dark answer

    Dark matter existed as a concept, first proposed by astronomers like Jan Oort in 1932 and Fritz Zwicky in 1933, who also noticed discrepancies in how much mass astronomers could see and how much physics implied should be present. But few paid their work any attention, writing their research off as little more than cosmological oddities. And no one had bagged such solid evidence of it before. And because no one had predicted what dark matter’s existence might mean for galaxy dynamics, Rubin and Ford initially didn’t recognize the meaning of their flat rotation curves.

    “Months were taken up in trying to understand what I was looking at,” Rubin told journalist Maria Popova. “One day I just decided that I had to understand what this complexity was that I was looking at, and I made sketches on a piece of paper, and suddenly I understood it all.”

    If a halo of dark matter graced each galaxy, she realized, the mass would be spread throughout the galaxy, rather than concentrating in the center. The gravitational force — and the orbital speed — would be similar throughout.

    Rubin and Ford had discovered the unseeable stuff that influences not only how galaxies move, but how the universe came to be and what it will become. “My entire education highlighted how fundamental dark matter is to our current understanding of astrophysics,” says Levesque, “and it’s hard for me to imagine the field or the universe without it.”

    Within a few years of the M31 observations, physicists like Jeremiah Ostriker and James Peebles provided the theoretical framework to support what Rubin and Ford had already shown, and dark matter settled firmly into its celebrated place in the universe.

    In more recent years, the Planck satellite measured the dark matter content of the universe by looking at the cosmic microwave background, the radiation left over from the Big Bang. The clumps of matter in this baby picture of the universe evolved into the galaxy superclusters we see today, and it was dark matter that clumped first and drew the regular matter together.

    Data from galaxy clusters now also confirms dark matter and helps scientists measure how much of it exists within a given group — a modern echo of Zwicky’s almost forgotten work. When light from more distant sources passes near a cluster, the gravity — from the cluster’s huge mass — bends the light like a lens.

    The amount of bending can reveal the amount of dark matter.

    No matter which way or where scientists measure Rubin’s discovery, it’s huge.

    And while no one knows what all the dark matter is, scientists have discovered that some small fraction of it is made of neutrinos — tiny, fast-moving particles that don’t really interact with normal matter. Measurements from the cosmic microwave background, like those being taken by experiments called POLARBEAR in Chile and BICEP2 and BICEP3 in Antarctica, will help pin down how many neutrinos are streaming through the universe and how much of the dark matter they make up.

    Some setups, like the Gran Sasso National Laboratory in Italy and the Deep Underground Science and Engineering Laboratory in South Dakota, are trying to detect dark matter particles directly, when they crash into atoms in cryogenically cooled tanks filled with liquefied noble gases. So far, they haven’t managed to capture a dark matter particle in action. But researchers are taking dark matter — whatever it is — into account when they think about how the universe evolves.

    The Nobel committee may overlook Rubin, passing by her as if they can’t see what all of astrophysics feels. But that won’t hurt her legacy, says Levesque: It will hurt the legacy of the Nobel itself. “It would then permanently lack any recognition of such groundbreaking work,” Levesque says.

    Rubin herself has never spoken about how she deserves a Nobel Prize. She simply continued her scientific work until recently, all the while influencing the origins, evolutions, and fates of other scientists. “If they didn’t get a job or they didn’t get a paper published, she would cheer people up,” says Bahcall. “She kept telling her story about how there are ups and downs and you stick with it and keep doing what you love doing.”

    Rubin, herself, loves trying to understand the universe, and in doing so, she has changed everyone’s understanding of it. That carries more weight than some medal from Sweden. But let Sweden recognize that for what it is: worthy of a prize.

    See the full article here .

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