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  • richardmitnick 10:32 am on February 16, 2018 Permalink | Reply
    Tags: , , , , Gravitational waves, ,   

    From Science Magazine: “Gravitational waves help reveal the weight limit for neutron stars, the densest objects in the cosmos” 

    AAAS
    Science Magazine

    Feb. 15, 2018
    Adrian Cho

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    To derive the new mass limit, astrophysicists teased out the evolution of the famed merger of two neutron stars, spotted on 17 August 2017 and shown in this artist’s conception. University of Warwick/Mark Garlick/Wikimedia Commons (CC BY 4.0)

    How heavy can neutron stars get? Astrophysicists have long wondered how massive these stellar corpses could be without collapsing under their own gravity to form a black hole. Last year’s blockbuster observations of two neutron stars merging revealed a collapse as it happened, enabling four different groups to converge on the maximum mass—about 2.2 times that of the sun.


    “I’m encouraged that they all agree,” says James Lattimer, a nuclear astrophysicist at the State University of New York in Stony Brook. A solid mass limit for neutron stars will help theorists understand these mysterious objects. “Of all the characteristics of a neutron star, the two most important are the maximum mass and the radius,” Lattimer says.

    A dying star can have one of three afterlives. A lightweight star shrinks into a white dwarf, an Earth-size sphere of carbon. A heavy star explodes when its massive core collapses to an infinitesimal point: a black hole. A star in the middle range—8 to 25 solar masses—also explodes, but leaves behind a fantastically dense sphere of nearly pure neutrons measuring a couple of dozen kilometers across: a neutron star.

    As the neutron stars spiraled into each other, gravitational-wave detectors in the United States and Italy sensed ripples in space generated by the whirling bodies. The waves allowed physicists to peg their combined mass at 2.73 solar masses. Two seconds after the gravitational waves, orbiting telescopes detected a powerful, short gamma ray burst. Telescopes on Earth spotted the event’s afterglow, which faded over several days from bright blue to dimmer red.

    Together, the clues suggest the merger first produced a spinning, overweight neutron star momentarily propped up by centrifugal force. The afterglow shows that the merger spewed between 0.1 and 0.2 solar masses of newly formed radioactive elements into space, more than could have escaped from a black hole. The ejected material’s initial blue tint shows that at first, it lacked heavy elements called lanthanides. A flux of particles called neutrinos presumably slowed those elements’ formation, and a neutron star radiates copious neutrinos. The short gamma ray burst, the supposed birth cry of a black hole, indicates that the merged neutron star collapsed in seconds.

    To derive their mass limits, the teams dove into the details of the spinning neutron star. They generally argue that at first the outer layers of the merged neutron star likely spun faster than its center. Then it flung off material and slowed to form a rigid spinning body whose mass researchers could calculate from the masses of the original neutron stars minus the ejected material. The fact that this spinning neutron star survived only momentarily suggests that its mass was close to the limit for such a spinner.

    That last inference is essential, Rezzolla says. Theory suggests that the mass of a rigidly spinning neutron star can exceed that of a stationary one by up to 18%, he says. That scaling allows researchers to infer the maximum mass of a stationary, stable neutron star. The whole argument works because the initial neutron stars weren’t so massive that they immediately produced a black hole or so light that they produced a spinning neutron star that lingered longer, Shibata says. “This was a very lucky event,” he says.

    The analyses are persuasive, Lattimer says, although he quibbles with the precision implied in numbers such as 2.17 solar masses. “If you say 2.2 plus or minus a 10th, I would think it gets the same message across.”

    See the full article here .

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  • richardmitnick 2:51 pm on February 6, 2018 Permalink | Reply
    Tags: , , , BurstCube, , , , , Gravitational waves,   

    From Goddard: “NASA Technology to Help Locate Electromagnetic Counterparts of Gravitational Waves” 

    NASA Goddard Banner
    NASA Goddard Space Flight Center

    Feb. 6, 2018
    By Lori Keesey
    NASA’s Goddard Space Flight Center

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    Principal Investigator Jeremy Perkins and his co-investigator, Georgia de Nolfo, recently won funding to build a new CubeSat mission, called BurstCube. Respectively, Perkins and de Nolfo hold a crystal, or scintillator, and silicon photomultiplier array technology that will be used to detect and localize gamma-ray bursts for gravitational-wave science. The photomultiplier array shown here specifically was developed for another CubeSat mission called TRYAD, which will investigate gamma-ray bursts in high-altitude lightning clouds.
    Credits: NASA/W. Hrybyk

    A compact detector technology applicable to all types of cross-disciplinary scientific investigations has found a home on a new CubeSat mission designed to find the electromagnetic counterparts of events that generate gravitational waves.

    NASA scientist Georgia de Nolfo and her collaborator, astrophysicist Jeremy Perkins, recently received funding from the agency’s Astrophysics Research and Analysis Program to develop a CubeSat mission called BurstCube. This mission, which will carry the compact sensor technology that de Nolfo developed, will detect and localize gamma-ray bursts caused by the collapse of massive stars and mergers of orbiting neutron stars. It also will detect solar flares and other high-energy transients once it’s deployed into low-Earth orbit in the early 2020s.

    The cataclysmic deaths of massive stars and mergers of neutron stars are of special interest to scientists because they produce gravitational waves — literally, ripples in the fabric of space-time that radiate out in all directions, much like what happens when a stone is thrown into a pond.

    Since the Laser Interferometer Gravitational Wave Observatory, or LIGO, confirmed their existence a couple years ago, LIGO and the European Virgo detectors have detected other events, including the first-ever detection of gravitational waves from the merger of two neutron stars announced in October 2017.

    Less than two seconds after LIGO detected the waves washing over Earth’s space-time, NASA’s Fermi Gamma-ray Space Telescope detected a weak burst of high-energy light — the first burst to be unambiguously connected to a gravitational-wave source.

    These detections have opened a new window on the universe, giving scientists a more complete view of these events that complements knowledge obtained through traditional observational techniques, which rely on detecting electromagnetic radiation — light — in all its forms.

    Complementary Capability

    Perkins and de Nolfo, both scientists at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, see BurstCube as a companion to Fermi in this search for gravitational-wave sources. Though not as capable as the much larger Gamma-ray Burst Monitor, or GBM, on Fermi, BurstCube will increase coverage of the sky. Fermi-GBM observes the entire sky not blocked by the Earth. “But what happens if an event occurs and Fermi is on the other side of Earth, which is blocking its view,” Perkins said. “Fermi won’t see the burst.”

    BurstCube, which is expected to launch around the time additional ground-based LIGO-type observatories begin operations, will assist in detecting these fleeting, hard-to-capture high-energy photons and help determine where they originated. In addition to quickly reporting their locations to the ground so that other telescopes can find the event in other wavelengths and home in on its host galaxy, BurstCube’s other job is to study the sources themselves.

    Miniaturized Technology

    BurstCube will use the same detector technology as Fermi’s GBM; however, with important differences.

    Under the concept de Nolfo has advanced through Goddard’s Internal Research and Development program funding, the team will position four blocks of cesium-iodide crystals, operating as scintillators, in different orientations within the spacecraft. When an incoming gamma ray strikes one of the crystals, it will absorb the energy and luminesce, converting that energy into optical light.

    Four arrays of silicon photomultipliers and their associated read-out devices each sit behind the four crystals. The photomultipliers convert the light into an electrical pulse and then amplify this signal by creating an avalanche of electrons. This multiplying effect makes the detector far more sensitive to this faint and fleeting gamma rays.

    Unlike the photomultipliers on Fermi’s GBM, which are bulky and resemble old-fashioned television tubes, de Nolfo’s devices are made of silicon, a semiconductor material. “Compared with more conventional photomultiplier tubes, silicon photomultipliers significantly reduce mass, volume, power and cost,” Perkins said. “The combination of the crystals and new readout devices makes it possible to consider a compact, low-power instrument that is readily deployable on a CubeSat platform.”

    In another success for Goddard technology, the BurstCube team also has baselined the Dellingr 6U CubeSat bus that a small team of center scientists and engineers developed to show that CubeSat platforms could be more reliable and capable of gathering highly robust scientific data.

    “This is high-demand technology,” de Nolfo said. “There are applications everywhere.”

    For other Goddard technology news, go to https://www.nasa.gov/sites/default/files/atoms/files/winter_2018_final_lowrez.pdf

    See the full article here.

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    NASA’s Goddard Space Flight Center is home to the nation’s largest organization of combined scientists, engineers and technologists that build spacecraft, instruments and new technology to study the Earth, the sun, our solar system, and the universe.

    Named for American rocketry pioneer Dr. Robert H. Goddard, the center was established in 1959 as NASA’s first space flight complex. Goddard and its several facilities are critical in carrying out NASA’s missions of space exploration and scientific discovery.


    NASA/Goddard Campus

     
  • richardmitnick 4:00 pm on December 20, 2017 Permalink | Reply
    Tags: , , , Gravitational waves, Update on Neutron Star Smash-Up: Jet Hits a Roadblock   

    From Caltech: “Update on Neutron Star Smash-Up: Jet Hits a Roadblock” 

    Caltech Logo

    Caltech

    12/20/2017

    Whitney Clavin
    (626) 395-1856
    wclavin@caltech.edu

    1
    On August 17, 2017, observatories around the world witnessed the collision of two neutron stars. At first, many scientists thought a narrow high-speed jet, directed away from our line of sight, or off-axis, was produced (diagram at left). But observations made at radio wavelengths now indicate the jet hit surrounding material, producing a slower-moving, wide-angle outflow, dubbed a cocoon (pink structure at right). Credit: NRAO/AUI/NSF/D. Berry

    Radio observations are illuminating what happened during recent gravitational-wave event.

    Millions of years ago, a pair of extremely dense stars, called neutron stars, collided in a violent smash-up that shook space and time. On August 17, 2017, both gravitational waves—ripples in space and time—and light waves emitted during that neutron star merger finally reached Earth. The gravitational waves came first and were detected by the twin detectors of the National Science Foundation (NSF)-funded Laser Interferometry Gravitational-wave Observatory (LIGO), aided by the European Virgo observatory.


    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-Zib

    ESA/eLISA the future of gravitational wave research

    1
    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)

    The light waves were observed seconds, days, and months later by dozens of telescopes on the ground and in space.

    Now, scientists from Caltech and several other institutions are reporting that light with radio wavelengths continues to brighten more than 100 days after the August 17 event. These radio observations indicate that a jet, launched from the two neutron stars as they collided, is slamming into surrounding material and creating a slower-moving, billowy cocoon.

    “We think the jet is dumping its energy into the cocoon,” says Gregg Hallinan, an assistant professor of astronomy at Caltech. “At first, people thought the material from the collision was coming out in a jet like a firehose, but we are finding that that the flow of material is slower and wider, expanding outward like a bubble.”

    The findings, made with the Karl G. Jansky Very Large Array in New Mexico, the Australia Telescope Compact Array, and the Giant Metrewave Radio Telescope in India, are reported in a new paper in the December 20 online issue of the journal Nature. The lead author is Kunal Mooley (PhD ’15), formerly of the University of Oxford and now a Jansky Fellow at Caltech.

    NRAO/Karl V Jansky VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA, at an elevation of 6970 ft (2124 m)

    CSIRO ATCA at the Paul Wild Observatory, about 25 km west of the town of Narrabri in rural NSW about 500 km north-west of Sydney, AU

    GMRT Radio Telescope, located near Pune, India

    The new data argue against a popular theory describing the aftermath of the neutron star merger—a theory that proposes the event created a fast-moving and beam-like jet thought to be associated with extreme blasts of energy called gamma-ray bursts, and in particular with short gamma-ray bursts, or sGRBs. Scientists think that sGRBs, which pop up every few weeks in our skies, arise from the merger of a pair of neutron stars or the merger of a neutron star with a black hole (an event that has yet to be detected by LIGO). An sGRB is seen when the jet points exactly in the direction of Earth.


    A hydrodynamical simulation shows a cocoon breaking out of the neutron star merger. This model explains the gamma-ray, X-ray, ultraviolet, optical, infrared, and radio data gathered by the GROWTH team from 18 telescopes around the world. Credit: Ehud Nakar (Tel Aviv), Ore Gottlieb (Tel Aviv), Leo Singer (NASA), Mansi Kasliwal (Caltech), and the GROWTH collaboration.

    On August 17, NASA’s Fermi Gamma-ray Space Telescope and the European INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) missions detected gamma rays just seconds after the neutron stars merged.

    NASA/Fermi LAT


    NASA/Fermi Telescope

    ESA/Integral

    The gamma rays were much weaker than what is expected for sGRBS, so the researchers reasoned that a fast and narrowly focused jet was produced but must have been pointed slightly askew from the direction of Earth, or off-axis.

    The radio emission—originally detected 16 days after the August 17 event and still measurable and increasing in strength as of December 2—tells a different story. If the jet had been fast and beam-like, the radio light would have weakened with time as the jet lost energy. The fact that the brightness of the radio light is increasing instead suggests the presence of a cocoon that is choking the jet. The reason for this is complex, but it has to do with the fact that the slower-moving, wider-angle material of the cocoon gives off more radio light than the faster-moving, sharply focused jet material.

    “It’s like the jet was fogged out,” says Mooley. “The jet may be off-axis, but it is not a simple pointed beam or as fast as some people thought. It may be blocked off by material thrown off during the merger, giving rise to a cocoon and emitting light in many different directions.”

    This means that the August 17 event was not a typical sGRB as originally proposed.

    “Standard sGRBs are 10,000 times brighter than we saw for this event,” says Hallinan. “Many people thought this was because the gamma-ray emission was off-axis and thus much weaker. But it turns out that the gamma rays are coming from the cocoon rather than the jet. It is possible that the jet managed to eventually break out through the cocoon, but we haven’t seen any evidence for this yet. It is more likely that it got trapped and snuffed out by the cocoon.”

    The possibility that a cocoon was involved in the August 17 event was originally proposed in a study led by Caltech’s Mansi Kasliwal (MS ’07, PhD ’11), assistant professor of astronomy, and colleagues. She and her team from the NSF-funded Global Relay of Observatories Watching Transients Happen (GROWTH) project observed the event at multiple wavelengths using many different telescopes.

    “The cocoon model explains puzzling features we have observed in the neutron star merger,” says Kasliwal. “It fits observations across the electromagnetic spectrum, from the early blue light we witnessed to the radio waves and X-rays that turned on later. The cocoon model had predicted that the radio emission would continue to increase in brightness, and that’s exactly what we see.”

    The researchers say that future observations with LIGO, Virgo, and other telescopes will help further clarify the origins and mechanisms of these extreme events. The observatories should be able to detect additional neutron star mergers—and perhaps eventually, mergers of neutron stars and black holes.

    Work at Caltech on this study was funded by the NSF, the Sloan Research Foundation, and Research Corporation for Science Advancement. Other Caltech authors are Kishalay De, a graduate student, and Shri Kulkarni, George Ellery Hale Professor of Astronomy and Planetary Science.

    See the full article here .

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    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”

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  • richardmitnick 1:51 pm on December 11, 2017 Permalink | Reply
    Tags: , , , Binary neutron stars, , , Gravitational waves, ,   

    From DES: “What the galaxy that hosted the gravitational wave event GW170817 can teach us about binary neutron stars” 

    Dark Energy Icon

    The Dark Energy Survey

    November 22, 2017 [Just now in social media.]
    Antonella Palmese
    Sunayana Bhargava

    Astronomers know many facts about galaxies. For example, we know that their colours tell us about the stars inside them and how old they are. We also know that their shapes can tell us about how they formed. Past and current large-scale surveys such as the Dark Energy Survey (DES) observe millions of galaxies at different distances, and therefore at different stages of their evolution. These galaxies can be catalogued and characterized in a number of different ways. However, one type of star system we know little about are binary neutron stars (BNS). The handful of confirmed binary neutron stars found have all been within our own galaxy.

    The optical counterpart to GW170817 was observed by the Dark Energy Camera (DECam) and other instruments to have come from a galaxy named NGC 4993, which is 130 million light years away from us. This event was likely produced by a binary neutron star merger. Antonella Palmese, together with other galaxy evolution and gravitational wave experts (Will Hartley, Marcelle Soares-Santos, Jim Annis, Huan Lin, Christopher Conselice, Federica Tarsitano and more) asked the question: what can we learn about the stars in NGC 4993? How did this binary system emerge in the overall history of the galaxy? Although we only have one snapshot of this galaxy, which is precisely 130 million years old, we can make use of other properties to infer how this galaxy evolved over cosmic time.

    At first glance, NGC 4993 looks like a normal, old massive elliptical galaxy (left panel in Figure 1), known by astronomers as an “early type galaxy”. But if we examine it more closely, we see that it contains shell structures: arcs of brighter stellar densities around the center of the galaxy. If we consider the profile of a typical, early type galaxy (see middle panel in Figure 1) and subtract it from the profile of NGC 4993, we notice key differences that help us characterize the kind of environment needed for binary neutron stars to form.

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    Figure 1. Left panel: DECam image of NCG 4993. Shell structures indicative of a recent galaxy merger are clearly visible. Middle panel: r-band residuals after subtraction of a Sérsic light profile. Right panel: F606W-band HST ACS image with a 3 component galaxy model subtracted. Dust lanes crossing the centre of the galaxy are evident after this subtraction. The green lines show the position of the transient.

    A number of papers starting from the 1980s have supported, with simulations and observations, the idea that these kind of shell structures are the debris of a recent merger between two galaxies (see a simulation example: http://hubblesite.org/video/558/news/4-galaxies ). During the merger, the stars from the smaller galaxy that passed close to NGC4993 millions of years ago were stripped away. As a result, many stars are concentrated in these arc-like regions. From the innermost shell position and the velocity of stars, we estimate that the shells in this galaxy should be visible for ~200 million years before dispersing. This means, if we still see them, the galaxy merger must have happened up to 200 million years before the BNS coalescence (see Figure 2 for a timeline). Could the dynamics of this galaxy merger be involved in the formation of the GW progenitor?

    3
    Figure 2. Timeline of NGC 4993

    DES only observes in optical photometric bands so we added information from infrared and spectroscopic surveys to study this galaxy in greater detail. We find more evidence for a recent galaxy merger (e.g. dust lanes, right panel of Figure 1, and two different stellar populations). We also find that the age of most of the stars in this galaxy is ~11 billion years old – only a few billion years younger than the Universe! This means that during its ‘recent’ stages, this galaxy has not been forming stars.

    Most of the current models for the formation of BNS suggest that they begin as a binary of two massive stars from a star formation event. During the evolution of the massive star binary, both stars will become supernova. If the gravitational force between the stars is strong enough to keep them bound against the force of the supernovae explosions, they become neutron stars in orbit until they coalesce. Simulations show us that neutron stars usually orbit around each other for ~500 million years before they merge, but it can take up to some billion years. Their lifetime before becoming neutron stars is much shorter than that.

    So if there was no recent star formation in NGC 4993, where did these massive stars, which go on to become neutron stars, come from? If they formed 11 billion years ago with other stars in the galaxy, why did they only merge now? Our work shows that it is unlikely that the BNS was formed ordinarily. We do not expect this BNS to be so old given the current knowledge of their expected lifetime from simulations. We instead suggest that the formation of the BNS was not through traditional channels. Instead, dynamical interactions between stars due to the galaxy merger might have caused the two neutron stars to form a binary or to coalesce. The plan for the future is to discover many more of these BNS systems inside their galactic hosts. With more data, it will be possible to determine how galaxies are able to produce the right conditions for this energetic dance of dense bodies to occur, creating ripples of energy (gravitational waves) that teach us about the Universe.

    See the full article here .

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    DECam, built at FNAL
    DECam, built at FNAL
    CTIO Victor M Blanco 4m Telescope
    CTIO Victor M Blanco 4m Telescope interior
    CTIO Victor M Blanco Telescope at Cerro Tololo which houses the DECAm

    The Dark Energy Survey (DES) is designed to probe the origin of the accelerating universe and help uncover the nature of dark energy by measuring the 14-billion-year history of cosmic expansion with high precision. More than 120 scientists from 23 institutions in the United States, Spain, the United Kingdom, Brazil, and Germany are working on the project. This collaboration [has built] an extremely sensitive 570-Megapixel digital camera, DECam, and [has mounted] it on the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory high in the Chilean Andes. Started in Sept. 2012 and continuing for five years, DES will survey a large swath of the southern sky out to vast distances in order to provide new clues to this most fundamental of questions.

     
  • richardmitnick 3:11 pm on November 14, 2017 Permalink | Reply
    Tags: , , , Gravitational waves,   

    From Symmetry: “Q&A with Nobel laureate Barry Barish” 

    Symmetry Mag
    Symmetry

    11/14/17
    Leah Hesla

    1
    Illustration by Ana Kova

    These days the LIGO experiment seems almost unstoppable.


    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-Zib

    ESA/eLISA the future of gravitational wave research

    1
    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)

    In September 2015, LIGO detected gravitational waves directly for the first time in history. Afterward, they spotted them three times more, definitively blowing open the doors on the new field of gravitational-wave astronomy.

    On October 3, the Nobel Committee awarded their 2017 prize in physics to some of the main engines behind the experiment. Just two weeks after that, LIGO scientists revealed that they’d seen, for the first time, gravitational waves from the collision of neutron stars, an event confirmed by optical telescopes—yet another first.

    These recent achievements weren’t inevitable. It took LIGO scientists decades to get to this point.

    LIGO leader Barry Barish, one of the three recipients of the 2017 Nobel, recently sat down with Symmetry writer Leah Hesla to give a behind-the-scenes look at his 22 years on the experiment.

    2
    Barry Barish, who obtained his B.S. and Ph.D from UC Berkeley in 1957 and 1962, respectively, shared the 2017 Nobel Prize in Physics for the discovery of gravitational waves. Barish is the Ronald and Maxine Linde Professor of Physics, Emeritus, at Caltech. (Caltech photo)

    What has been your role at LIGO?

    I started in 1994 and came on board at a time when we didn’t have the money. I had to get the money and have a strategy that [the National Science Foundation] would buy into, and I had to have a plan that they would keep supporting for 22 years. My main mission was to build this instrument—which we didn’t know how to make—well enough to do what it did.

    So we had to build enough trust and success without discovering gravitational waves so that NSF would keep supporting us. And we had to have the flexibility to evolve LIGO’s design, without costing an arm and a leg, to make the improvements that would eventually make it sensitive enough to succeed.

    We started running in about 2000 and took data and improved the experiment over 10 years. But we just weren’t sensitive enough. We managed to get a major improvement program to what’s called Advanced LIGO from the National Science Foundation. After a year and a half or so of making it work, we turned on the device in September of 2015 and, within days, we’d made the detection.

    What steps did LIGO take to be as sensitive as possible?

    We were limited very much by the shaking of the Earth—at the low frequencies, the Earth just shakes too much. We also couldn’t get rid of the background noise at high frequencies—we can’t sample fast enough.

    In the initial LIGO, we reduced the shaking by something like 100 million. We had the fanciest set of shock absorbers possible. The shock absorbers in your car take a bump that you go over, which is high-frequency, and transfer it softly to low-frequency. You get just a little up and down; you don’t feel very much when you go over a bump. You can’t get rid of the bump—that’s energy—but you can transfer it out of the frequencies where it bothers you.

    So we do the same thing. We have a set of springs that are fancier but are basically like shock absorbers in your car. That gave us a factor of 100 million reduction in the shaking of the Earth.

    But that wasn’t good enough [for initial LIGO].

    What did you do to increase sensitivity for Advanced LIGO?

    After 15 years of not being able to detect gravitational waves, we implemented what we call active seismic isolation, in addition to passive springs. It’s very much equivalent to what happens when you get on an airplane and you put those [noise cancellation] earphones on. All of a sudden the airplane is less noisy. That works by detecting the ambient noise—not the noise by the attendant dropping a glass or something. That’s a sharp noise, and you’d still hear that, or somebody talking to you, which is a loud independent noise. But the ambient noise of the motors and the shaking of the airplane itself are more or less the same now as they were a second ago, so if you measure the frequency of the ambient noise, you can cancel it.

    In Advanced LIGO, we do the same thing. We measure the shaking of the Earth, and then we cancel it with active sensors. The only difference is that our problem is much harder. We have to do this directionally. The Earth shakes in a particular direction—it might be up and down, it might be sideways or at an angle. It took us years to develop this active seismic isolation.

    The idea was there 15 years ago, but we had to do a lot of work to develop very, very sensitive active seismic isolation. The technology didn’t exist—we developed all that technology. It reduced the shaking of the Earth by another factor of 100 [over LIGO’s initial 100 million], so we reduced it by a factor of 10 billion.

    So we could see a factor of 100 further out in the universe than we could have otherwise. And each factor of 10 gets cubed because we’re looking at stars and galaxies [in three dimensions]. So when we improved [initial LIGO’s sensitivity] by a factor of 100 beyond this already phenomenal number of 100 million, it improved our sensitivity immediately, and our rate of seeing these kinds of events, by a factor of a hundred cubed—by a million.

    That’s why, after a few days of running, we saw something. We couldn’t have seen this in all the years that we ran at lower sensitivity.

    What key steps did you take when you came on board in 1994?

    First we had to build a kind of technical group that had the experience and abilities to take on a $100 million project. So I hired a lot of people. It was a good time to do that because it was soon after the closure of the Superconducting Super Collider in Texas. I knew some of the most talented people who were involved in that, so I brought them into LIGO, including the person who would be the project manager.

    Second, I made sure the infrastructure was scaled to a stage where we were doing it not the cheapest we could, but rather the most flexible.

    The third thing was to convince NSF that doing this construction project wasn’t the end of what we had to do in terms of development. So we put together a vigorous R&D program, which NSF supported, to develop the technology that would follow similar ones that we used.

    And then there were some technical changes—to become as forward-looking as possible in terms of what we might need later.

    What were the technical changes?

    The first was to change from what was the most popularly used laser in the 1990s, which was a gas laser, to a solid-state laser, which was new at that time. The solid-state laser had the difficulty that the light was no longer in the visible range. It was in the infrared, and people weren’t used to interferometers like that. They like to have light bouncing around that they can see, but you can’t see the solid-state laser light with your naked eye. That’s like particle physics. You can’t see the particles in the accelerator either. We use sensors to do that. So we made that kind of change, going from analog controls to digital controls, which are computer-based.

    We also inherited the kind of control programs that had been developed for accelerators and used at the Superconducting Super Collider, and we brought the SSC controls people into LIGO. These changes didn’t pay off immediately, but paved the road toward making a device that could be modern and not outdated as we moved through the 20 years. It wasn’t so much fixing things as making LIGO much more forward-looking—to make it more and more sensitive, which is the key thing for us.

    Did you draw on past experience?

    I think my history in particle physics was crucial in many ways, for example, in technical ways—things like digital controls, how we monitored beam. We don’t use the same technology, but the idea that you don’t have to see it physically to monitor it—those kinds of things carried over.

    The organization, how we have scientific collaborations, was again something that I created here at LIGO, which was modeled after high-energy physics collaborations. Some of it has to be modified for this different kind of project—this is not an accelerator—but it has a lot of similarities because of the way you approach a large scientific project.

    Were you concerned the experiment wouldn’t happen? If not, what did concern you?

    As long as we kept making technical progress, I didn’t have that concern. My only real concern was nature. Would we be fortunate enough to see gravitational waves at the sensitivities we could get to? It wasn’t predicted totally. There were optimistic predictions—that we could have detected things earlier — but there are also predictions we haven’t gotten to. So my main concern was nature.

    When did you hear about the first detection of gravitational waves?

    If you see gravitational waves from some spectacular thing, you’d also like to be able to see something in telescopes and electromagnetic astronomy that’s correlated. So because of that, LIGO has an early alarm system that alerts you that there might be a gravitational wave event. We more or less have the ability to see spectacular things early. But if you want people to turn their telescopes or other devices to point at something in the sky, you have to tell them something in time scales of minutes or hours, not weeks or months.

    The day we saw this, which we saw early in its running, it happened at 4:50 in the morning in Louisiana, 2:50 in the morning in California, so I found out about it at breakfast time for me, which was about four hours later. When we alert the astronomers, we alert key people from LIGO as well. We get things like that all the time, but this looked a little more serious than others. After a few more hours that day, it became clear that this was nothing like anything we’d seen before, and in fact looked a lot like what we were looking for, and so I would say some people became convinced within hours.

    I wasn’t, but that’s my own conservatism: What’s either fooling us or how are we fooling ourselves? There were two main issues. One is the possibility that maybe somebody was inserting a rogue event in our data, some malicious way to try to fool us. We had to make sure we could trace the history of the events from the apparatus itself and make sure there was no possibility that somebody could do this. That took about a month of work. The second was that LIGO was a brand new, upgraded version, so I wasn’t sure that there weren’t new ways to generate things that would fool us. Although we had a lot of experience over a lot of years, it wasn’t really with this version of LIGO. This version was only a few days old. So it took us another month or so to convince us that it was real. It was obvious that there was going to be a classic discovery if it held up.

    What does it feel like to win the Nobel Prize?

    It happened at 3 in the morning here [in California]. [The night before], I had a nice dinner with my wife, and we went to bed early. I set the alarm for 2:40. They were supposed to announce the result at 2:45. I don’t know why I set it for 2:40, but I did. I moved the house phone into our bedroom.

    The alarm did go off at 2:40. There was no call, obviously—I hadn’t been awakened, so I assumed, kind of in my groggy state, that we must have been passed over. I started going to my laptop to see who was going to get it. Then my cell phone started ringing. My wife heard it. My cell phone number is not given out, generally. There are tens of people who have it, but how [the Nobel Foundation] got it, I’m not sure. Some colleague, I suppose. It was a surprise to me that it came on the cell phone.

    The president of the Nobel Foundation told me who he was, said he had good news and told me I won. And then we chatted for a few minutes, and he asked me how I felt. And I spontaneously said that I felt “thrilled and humbled at the same time.” There’s no word for that, exactly, but that mixture of feeling is what I had and still have.

    Do you have advice for others organizing big science projects?

    We have an opportunity. As I grew into this and as science grew big, we always had to push and push and push on technology, and we’ve certainly done that on LIGO. We do that in particle physics, we do that in accelerators.

    I think the table has turned somewhat and that the technology has grown so fast in the recent decades that there’s incredible opportunities to do new science. The development of new technologies gives us so much ability to ask difficult scientific questions. We’re in an era that I think is going to propagate fantastically into the future.

    Just in the new millennium, maybe the three most important discoveries in physics have all been done with, I would say, high-tech, modern, large-scale devices: the neutrino experiments at SNO and Kamiokande doing the neutrino oscillations, which won a Nobel Prize in 2013; the Higgs boson—no device is more complicated or bigger or more technically advanced than the CERN LHC experiments; and then ours, which is not quite the scale of the LHC, but it’s the same scale as these experiments—the billion dollar scale—and it’s very high-tech.

    Einstein thought that gravitational waves could never be detected, but he didn’t know about lasers, digital controls and active seismic isolation and all things that we developed, all the high-tech things that are coming from industry and our pushing them a little bit harder.

    The fact is, technology is changing so fast. Most of us can’t live without GPS, and 10 or 15 years ago, we didn’t have GPS. GPS exists because of general relativity, which is what I do. The inner silicon microstrip detectors in the CERN experiment were developed originally for particle physics. They developed rapidly. But now, they’re way behind what’s being done in industry in the same area. Our challenge is to learn how to grab what is being developed, because technology is becoming great.

    I think we need to become really aware and understand the developments of technology and how to apply those to the most basic physics questions that we have and do it in a forward-looking way.

    What are your hopes for the future of LIGO?

    It’s fantastic. For LIGO itself, we’re not limited by anything in nature. We’re limited by ourselves in terms of improving it over the next 15 years, just like we improved in going from initial LIGO to Advanced LIGO. We’re not at the limit.

    So we can look forward to certainly a factor of 2 to 3 improvement, which we’ve already been funded for and are ready for, and that will happen over the next few years. And that factor of 2 or 3 gets cubed in our case.

    This represents a completely new way to look at the universe. Everything we look at was with electromagnetic radiation, and a little bit with neutrinos, until we came along. We know that only a few percent of what’s out there is luminous, and so we are opening a new age of astronomy, really. At the same time, we’re able to test Einstein’s theories of general relativity in its most important way, which is by looking where the fields are the strongest, around black holes.

    That’s the opportunity that exists over a long time scale with gravitational waves. The fact that they’re a totally different way of looking at the sky means that in the long term it will develop into an important part of how we understand our universe and where we came from. Gravitational waves are the best way possible, in theory—we can’t do it now—of going back to the very beginning, the Big Bang, because they weren’t absorbed. What we know now comes from photons, but they can go back to only 300,000 years from the Big Bang because they’re absorbed.

    We can go back to the beginning. We don’t know how to do it yet, but that is the potential.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 3:16 pm on November 13, 2017 Permalink | Reply
    Tags: , , , , , Gravitational waves, , Observing low-frequency gravitational waves would be akin to being able to hear bass singers not just sopranos. To explore this uncharted area of gravitational wave science researchers look not to hum, The new Nature Astronomy study concerns supermassive black hole binaries   

    From JPL-Caltech: “Listening for Gravitational Waves Using Pulsars” 

    NASA JPL Banner

    JPL-Caltech

    November 13, 2017
    Elizabeth Landau
    Jet Propulsion Laboratory, Pasadena, Calif.
    (818) 354-6425
    Elizabeth.Landau@jpl.nasa.gov

    1
    This computer simulation shows the collision of two black holes, which produces gravitational waves. Credit: Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project.

    One of the most spectacular achievements in physics so far this century has been the observation of gravitational waves, ripples in space-time that result from masses accelerating in space. So far, there have been five detections of gravitational waves, thanks to the Laser Interferometer Gravitational-Wave Observatory (LIGO) and, more recently, the European Virgo gravitational-wave detector.


    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-Zib

    ESA/eLISA the future of gravitational wave research

    1
    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)

    Using these facilities, scientists have been able to pin down the extremely subtle signals from relatively small black holes and, as of October, neutron stars.

    UC Santa Cruz

    UC Santa Cruz

    14

    A UC Santa Cruz special report

    Tim Stephens

    Astronomer Ryan Foley says “observing the explosion of two colliding neutron stars” [see https://sciencesprings.wordpress.com/2017/10/17/from-ucsc-first-observations-of-merging-neutron-stars-mark-a-new-era-in-astronomy ]–the first visible event ever linked to gravitational waves–is probably the biggest discovery he’ll make in his lifetime. That’s saying a lot for a young assistant professor who presumably has a long career still ahead of him.

    2
    The first optical image of a gravitational wave source was taken by a team led by Ryan Foley of UC Santa Cruz using the Swope Telescope at the Carnegie Institution’s Las Campanas Observatory in Chile. This image of Swope Supernova Survey 2017a (SSS17a, indicated by arrow) shows the light emitted from the cataclysmic merger of two neutron stars. (Image credit: 1M2H Team/UC Santa Cruz & Carnegie Observatories/Ryan Foley)

    Carnegie Institution Swope telescope at Las Campanas, Chile, 100 kilometres (62 mi) northeast of the city of La Serena. near the north end of a 7 km (4.3 mi) long mountain ridge. Cerro Las Campanas, near the southern end and over 2,500 m (8,200 ft) high, at Las Campanas, Chile

    A neutron star forms when a massive star runs out of fuel and explodes as a supernova, throwing off its outer layers and leaving behind a collapsed core composed almost entirely of neutrons. Neutrons are the uncharged particles in the nucleus of an atom, where they are bound together with positively charged protons. In a neutron star, they are packed together just as densely as in the nucleus of an atom, resulting in an object with one to three times the mass of our sun but only about 12 miles wide.

    “Basically, a neutron star is a gigantic atom with the mass of the sun and the size of a city like San Francisco or Manhattan,” said Foley, an assistant professor of astronomy and astrophysics at UC Santa Cruz.

    These objects are so dense, a cup of neutron star material would weigh as much as Mount Everest, and a teaspoon would weigh a billion tons. It’s as dense as matter can get without collapsing into a black hole.

    THE MERGER

    Like other stars, neutron stars sometimes occur in pairs, orbiting each other and gradually spiraling inward. Eventually, they come together in a catastrophic merger that distorts space and time (creating gravitational waves) and emits a brilliant flare of electromagnetic radiation, including visible, infrared, and ultraviolet light, x-rays, gamma rays, and radio waves. Merging black holes also create gravitational waves, but there’s nothing to be seen because no light can escape from a black hole.

    Foley’s team was the first to observe the light from a neutron star merger that took place on August 17, 2017, and was detected by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO).

    But there are merging objects far larger whose gravitational wave signals have not yet been detected: supermassive black holes, more than 100 million times more massive than our Sun. Most large galaxies have a central supermassive black hole. When galaxies collide, their central black holes tend to spiral toward each other, releasing gravitational waves in their cosmic dance. Much as a large animal like a lion produces a deeper roar than a tiny mouse’s squeak, merging supermassive black holes create lower-frequency gravitational waves than the relatively small black holes LIGO and similar ground-based experiments can detect.

    “Observing low-frequency gravitational waves would be akin to being able to hear bass singers, not just sopranos,” said Joseph Lazio, chief scientist for NASA’s Deep Space Network, based at NASA’s Jet Propulsion Laboratory, Pasadena, California, and co-author of a new study in Nature Astronomy.

    To explore this uncharted area of gravitational wave science, researchers look not to human-made machines, but to a natural experiment in the sky called a pulsar timing array. Pulsars are dense remnants of dead stars that regularly emit beams of radio waves, which is why some call them “cosmic lighthouses.” Because their rapid pulse of radio emission is so predictable, a large array of well-understood pulsars can be used to measure extremely subtle abnormalities, such as gravitational waves. The North American Nanohertz Observatory for Gravitational Waves (NANOGrav), a Physics Frontier Center of the National Science Foundation, is one of the leading groups of researchers using pulsars to search for gravitational waves.

    The new Nature Astronomy study concerns supermassive black hole binaries — systems of two of these cosmic monsters. For the first time, researchers surveyed the local universe for galaxies likely to host these binaries, then predicted which black hole pairs are the likeliest to merge and be detected while doing so. The study also estimates how long it will take to detect one of these mergers.

    “By expanding our pulsar timing array over the next 10 years or so, there is a high likelihood of detecting gravitational waves from at least one supermassive black hole binary,” said Chiara Mingarelli, lead study author, who worked on this research as a Marie Curie postdoctoral fellow at Caltech and JPL, and is now at the Flatiron Institute in New York.

    Mingarelli and colleagues used data from the 2 Micron All-Sky Survey (2MASS), which surveyed the sky from 1997 to 2001, and galaxy merger rates from the Illustris simulation project, an endeavor to make large-scale cosmological simulations. In their sample of about 5,000 galaxies, scientists found that about 90 would have supermassive black holes most likely to merge with another black hole.

    While LIGO and similar experiments detect objects in the final seconds before they merge, pulsar timing arrays are sensitive to gravitational wave signals from supermassive black holes that are spiraling toward each other and will not combine for millions of years. That’s because galaxies merge hundreds of millions of years before the central black holes they host combine to make one giant supermassive black hole.

    Researchers also found that while bigger galaxies have bigger black holes and produce stronger gravitational waves when they combine, these mergers also happen fast, shortening the time period for detection. For example, black holes merging in the large galaxy M87 would have a 4-million-year window of detection. By contrast, in the smaller Sombrero Galaxy, black holes mergers typically take about 160 million years, offering more opportunities for pulsar timing arrays to detect gravitational waves from them.

    Black hole mergers generate gravitational waves because, as they orbit each other, their gravity distorts the fabric of space-time, sending ripples outward in all directions at the speed of light. These distortions actually shift the position of Earth and the pulsars ever so slightly, resulting in a characteristic and detectable signal from the array of celestial lighthouses.

    “A difference between when the pulsar signals should arrive, and when they do arrive, can signal a gravitational wave,”Mingarelli said. “And since the pulsars we study are about 3,000 light-years away, they act as a galactic-scale gravitational-wave detector.”

    Because all supermassive black holes are so distant, gravitational waves, which travel at the speed of light, take a long time to arrive at Earth. This study looked at supermassive black holes within about 700 million light-years, meaning waves from a merger between any two of them would take up to that long to be detected here by scientists. By comparison, about 650 million years ago, algae flourished and spread rapidly in Earth’s oceans — an event important to the evolution of more complex life.

    Many open questions remain about how galaxies merge and what will happen when the Milky Way approaches Andromeda, the nearby galaxy that will collide with ours in about 4 billion years.

    “Detecting gravitational waves from billion-solar-mass black hole mergers will help unlock some of the most persistent puzzles in galaxy formation,” said Leonidas Moustakas, a JPL research scientist who wrote an accompanying “News and Views” article in the journal.

    2MASS was funded by NASA’s Office of Space Science, the National Science Foundation, the U.S. Naval Observatory and the University of Massachusetts. JPL managed the program for NASA’s Office of Space Science, Washington. Data was processed at IPAC at Caltech in Pasadena, California.

    See the full article here .

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    NASA JPL Campus

    Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. Although the facility has a Pasadena postal address, it is actually headquartered in the city of La Cañada Flintridge [1], on the northwest border of Pasadena. JPL is managed by the nearby California Institute of Technology (Caltech) for the National Aeronautics and Space Administration. The Laboratory’s primary function is the construction and operation of robotic planetary spacecraft, though it also conducts Earth-orbit and astronomy missions. It is also responsible for operating NASA’s Deep Space Network.

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  • richardmitnick 5:36 pm on October 16, 2017 Permalink | Reply
    Tags: , , , , , , , Gravitational waves, ,   

    From UCSC: “A UC Santa Cruz special report: Neutron stars, gravitational waves, and all the gold in the universe” 

    UC Santa Cruz

    UC Santa Cruz

    10.16.17
    Tim Stephens

    2

    Astronomer Ryan Foley says observing the explosion of two colliding neutron stars–the first visible event ever linked to gravitational waves–is probably the biggest discovery he’ll make in his lifetime. That’s saying a lot for a young assistant professor who presumably has a long career still ahead of him.

    1

    So what makes this strange cataclysm in another galaxy so exciting to astronomers? And what the heck is a neutron star, anyway?

    A neutron star forms when a massive star runs out of fuel and explodes as a supernova, throwing off its outer layers and leaving behind a collapsed core composed almost entirely of neutrons. Neutrons are the uncharged particles in the nucleus of an atom, where they are bound together with positively charged protons. In a neutron star, they are packed together just as densely as in the nucleus of an atom, resulting in an object with one to three times the mass of our sun but only about 12 miles wide.

    “Basically, a neutron star is a gigantic atom with the mass of the sun and the size of a city like San Francisco or Manhattan,” said Foley, an assistant professor of astronomy and astrophysics at UC Santa Cruz.

    These objects are so dense, a cup of neutron star material would weigh as much as Mount Everest, and a teaspoon would weigh a billion tons. It’s as dense as matter can get without collapsing into a black hole.

    THE MERGER

    Like other stars, neutron stars sometimes occur in pairs, orbiting each other and gradually spiraling inward. Eventually, they come together in a catastrophic merger that distorts space and time (creating gravitational waves) and emits a brilliant flare of electromagnetic radiation, including visible, infrared, and ultraviolet light, x-rays, gamma rays, and radio waves. Merging black holes also create gravitational waves, but there’s nothing to be seen because no light can escape from a black hole.

    Foley’s team was the first to observe the light from a neutron star merger that took place on August 17, 2017, and was detected by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO).


    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-Zib

    ESA/eLISA the future of gravitational wave research

    1
    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)

    Now, for the first time, scientists can study both the gravitational waves (ripples in the fabric of space-time), and the radiation emitted from the violent merger of the densest objects in the universe.

    3
    The UC Santa Cruz team found SSS17a by comparing a new image of the galaxy N4993 (right) with images taken four months earlier by the Hubble Space Telescope (left). The arrows indicate where SSS17a was absent from the Hubble image and visible in the new image from the Swope Telescope. (Image credits: Left, Hubble/STScI; Right, 1M2H Team/UC Santa Cruz & Carnegie Observatories/Ryan Foley)


    Carnegie Institution Swope telescope at Las Campanas, Chile

    It’s that combination of data, and all that can be learned from it, that has astronomers and physicists so excited. The observations of this one event are keeping hundreds of scientists busy exploring its implications for everything from fundamental physics and cosmology to the origins of gold and other heavy elements.


    A small team of UC Santa Cruz astronomers were the first team to observe light from two neutron stars merging in August. The implications are huge.

    All THE GOLD IN THE UNIVERSE

    It turns out that the origins of the heaviest elements, such as gold, platinum, uranium—pretty much everything heavier than iron—has been an enduring conundrum. All the lighter elements have well-explained origins in the nuclear fusion reactions that make stars shine or in the explosions of stars (supernovae). Initially, astrophysicists thought supernovae could account for the heavy elements, too, but there have always been problems with that theory, says Enrico Ramirez-Ruiz, professor and chair of astronomy and astrophysics at UC Santa Cruz.

    5
    The violent merger of two neutron stars is thought to involve three main energy-transfer processes, shown in this diagram, that give rise to the different types of radiation seen by astronomers, including a gamma-ray burst and a kilonova explosion seen in visible light. (Image credit: Murguia-Berthier et al., Science)

    A theoretical astrophysicist, Ramirez-Ruiz has been a leading proponent of the idea that neutron star mergers are the source of the heavy elements. Building a heavy atomic nucleus means adding a lot of neutrons to it. This process is called rapid neutron capture, or the r-process, and it requires some of the most extreme conditions in the universe: extreme temperatures, extreme densities, and a massive flow of neutrons. A neutron star merger fits the bill.

    Ramirez-Ruiz and other theoretical astrophysicists use supercomputers to simulate the physics of extreme events like supernovae and neutron star mergers. This work always goes hand in hand with observational astronomy. Theoretical predictions tell observers what signatures to look for to identify these events, and observations tell theorists if they got the physics right or if they need to tweak their models. The observations by Foley and others of the neutron star merger now known as SSS17a are giving theorists, for the first time, a full set of observational data to compare with their theoretical models.

    According to Ramirez-Ruiz, the observations support the theory that neutron star mergers can account for all the gold in the universe, as well as about half of all the other elements heavier than iron.

    RIPPLES IN THE FABRIC OF SPACE-TIME

    Einstein predicted the existence of gravitational waves in 1916 in his general theory of relativity, but until recently they were impossible to observe. LIGO’s extraordinarily sensitive detectors achieved the first direct detection of gravitational waves, from the collision of two black holes, in 2015. Gravitational waves are created by any massive accelerating object, but the strongest waves (and the only ones we have any chance of detecting) are produced by the most extreme phenomena.

    Two massive compact objects—such as black holes, neutron stars, or white dwarfs—orbiting around each other faster and faster as they draw closer together are just the kind of system that should radiate strong gravitational waves. Like ripples spreading in a pond, the waves get smaller as they spread outward from the source. By the time they reached Earth, the ripples detected by LIGO caused distortions of space-time thousands of times smaller than the nucleus of an atom.

    The rarefied signals recorded by LIGO’s detectors not only prove the existence of gravitational waves, they also provide crucial information about the events that produced them. Combined with the telescope observations of the neutron star merger, it’s an incredibly rich set of data.

    LIGO can tell scientists the masses of the merging objects and the mass of the new object created in the merger, which reveals whether the merger produced another neutron star or a more massive object that collapsed into a black hole. To calculate how much mass was ejected in the explosion, and how much mass was converted to energy, scientists also need the optical observations from telescopes. That’s especially important for quantifying the nucleosynthesis of heavy elements during the merger.

    LIGO can also provide a measure of the distance to the merging neutron stars, which can now be compared with the distance measurement based on the light from the merger. That’s important to cosmologists studying the expansion of the universe, because the two measurements are based on different fundamental forces (gravity and electromagnetism), giving completely independent results.

    “This is a huge step forward in astronomy,” Foley said. “Having done it once, we now know we can do it again, and it opens up a whole new world of what we call ‘multi-messenger’ astronomy, viewing the universe through different fundamental forces.”

    LIGO can tell scientists the masses of the merging objects and the mass of the new object created in the merger, which reveals whether the merger produced another neutron star or a more massive object that collapsed into a black hole. To calculate how much mass was ejected in the explosion, and how much mass was converted to energy, scientists also need the optical observations from telescopes. That’s especially important for quantifying the nucleosynthesis of heavy elements during the merger.

    Published research

    Credits

    Writing: Tim Stephens
    Header image: Illustration by Robin Dienel courtesy of the Carnegie Institution for Science
    Design and development: Rob Knight
    Project managers: Sherry Main, Scott Hernandez-Jason, Tim Stephens

    See the full article here .

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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.

    5
    UCSC alumna Shelley Wright, now an assistant professor of physics at UC San Diego, discusses the dichroic filter of the NIROSETI instrument. (Photo by Laurie Hatch)

    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.

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  • richardmitnick 1:05 pm on October 9, 2017 Permalink | Reply
    Tags: , , , , , Gravitational waves, Unsung heroes of LIGO and Virgo   

    From Nature: “LIGO’s unsung heroes” 

    Nature Mag
    Nature

    09 October 2017
    Davide Castelvecchi

    1
    LIGO hunts gravitational waves with the help of two laser interferometers — and hundreds of people. Joe McNally/Getty

    Every October, the announcements of the Nobel Prizes bring with them some controversy. This year’s physics prize — in recognition of the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the United States — was less debated than most. The three winners — Kip Thorne and Barry Barish, both at the California Institute of Technology (Caltech) in Pasadena, and Rainer Weiss at the Massachusetts Institute of Technology (MIT) in Cambridge — had attracted near-universal praise for their roles in the project’s success.

    But the award has still put into stark relief the difficulty of singling out just a few individuals from the large collaborations of today’s ‘Big Science’. The LIGO collaboration uses two giant laser interferometers to listen for deformations in space-time caused by some of the Universe’s most cataclysmic events. Physicists detected their first gravitational waves — interpreted as being produced by the collision of two black holes more than a billion years ago — in September 2015. The resulting paper, published in February 20161, has a mind-boggling 1,004 authors.

    Some of those are members of the LIGO Laboratory, the Caltech–MIT consortium that manages LIGO’s two interferometers in Louisiana and Washington State. But the list also includes the larger LIGO Scientific Collaboration: researchers from 18 countries, some of which — such as Germany and the United Kingdom — have made crucial contributions to the detectors.

    Yet more authors are from LIGO’s sister Virgo Collaboration, led by France and Italy, which built the Virgo interferometer near Pisa, Italy. The two experiments pool their data and analyse them together. Countless other people not named on the paper have also been involved in LIGO’s design, development, construction and operation since Weiss first detailed how to build a laser interferometer in 1972.

    To honour the many unsung heroes of gravitational waves, Nature collected testimonials about just a few of them. Like the Nobel Prize, this list is inevitably very incomplete.

    1. The pioneer: Joseph Weber

    Researchers using two detectors in the United States shook the world when they announced their discovery of gravitational waves. The year was 1969, and the detectors were not LIGO but tonne-sized cylinders of aluminium built by Joseph Weber, a physicist at the University of Maryland in College Park. His claim was later found to be invalid, but many physicists still credit Weber for having founded the field. “Joe Weber indeed started thinking about how to detect gravitational waves in about 1957,” Virginia Trimble, an astrophysicist and Weber’s widow, told Nature in an e-mail. At that time, many researchers were not even sure that gravitational waves existed. In the 1960s, Weber was also one of the first researchers to consider the possibility of using interferometers to detect them.

    2. The German connection: Heinz Billing

    The founder of Germany’s side of LIGO, Heinz Billing, a physicist at the Max Planck Institute for Astrophysics near Munich, first heard of Weiss’s pioneering interferometer designs in 1975, when he was asked to review Weiss’s request to the National Science Foundation to fund a prototype at MIT. Billing and his team liked it so much that they started building one themselves. “The Munich group quickly invented some of the most important ingredients that made the detectors possible,” says Karsten Danzmann, a director at the Max Planck Institute for Gravitational Physics in Hanover, Germany. Billing, in particular, came up with an idea to stabilize the laser that was later used in the UK–German GEO600 interferometer based near Hanover — and in LIGO itself. GEO600 is still a crucial testing and development centre for technologies introduced in the successive rounds of LIGO upgrades. “There is an awful lot of GEO in LIGO,” says Danzmann. Billing, who died on 4 January at the age of 102, was also a pioneer in magnetic data storage.

    3. The laser expert: Alain Brillet

    The 1980s were years of intense research and development for gravitational-wave detectors. Alain Brillet, an optical physicist with extensive experience in interferometers, then at the University of Paris-Sud in Orsay, France, saw an opportunity to contribute. “I decided to start with the optical part, the lasers and optics, because that was my specialty,” he says. Brillet went on to co-found Virgo. But many of his ideas — in particular, the type of laser that would give the most stable signal — were implemented in LIGO and other interferometers as well, says MIT physicist David Shoemaker, who studied with Brillet in Orsay and is now LIGO’s spokesperson.

    4. The facilitator: Richard Isaacson

    Gravitational theorist Richard Isaacson went to Washington DC to work at the National Science Foundation (NSF) in 1973 for what he thought would be a brief stint as one of the programme directors. During the handover, his predecessor advised him to pay attention to an “interesting guy” called Rainer Weiss. Isaacson secured Weiss a small grant for his 1975 prototype, and later became LIGO’s chief advocate inside government. He was instrumental in the project’s winning hundreds of millions of dollars in funding, despite the uncertain prospect of success. It was the first time that the NSF had managed a large project: US facilities such as particle accelerators were traditionally the remit of the Department of Energy, which had field offices staffed with dozens of experts. Isaacson did it by himself for more than ten years, and by the early 1990s he had paid a high personal cost. “Eventually, my health broke and my marriage went bad,” says Isaacson. By the time he retired in 2001, the construction of LIGO had been completed.

    5. The first director: Rochus ‘Robbie’ Vogt

    Before Barry Barish took the reins of LIGO, another director had left his mark on the collaboration: Rochus Vogt. The Caltech physicist, a veteran of the NASA Voyager mission, was put in charge in 1987. Until then, the project had been led by the ‘troika’ of visionary founders — Thorne, Weiss, and the physicist Ronald Drever, who started UK research on gravitational waves at the University of Glasgow before moving to Caltech — but managing large organizations was not their strength. “Thank God that was done,” Weiss recalled in a talk at NSF headquarters last year. “You don’t manage it with three guys who are sort of a little bit flaky.” Vogt, who was once described as a taller and leaner Henry Kissinger, had a booming voice and forceful style that did not please everyone. But he was able to put together the first major request for NSF funding and, Thorne recalled in a 5 October press conference, “laid the foundations for moving LIGO forward to our construction”.

    6. The theorist: Alessandra Buonanno

    As Thorne realized early on, in the future field of gravitational-wave astronomy, it would not be enough to collect data; researchers would also need to know what signals to look for. But it is notoriously difficult to extract quantitative predictions from the equations of Einstein’s general relativity. Theoretical physicist Alessandra Buonanno had devised formulae for calculating the approximate orbits of spiralling objects and the gravitational waves they would generate in work she had done, in part with her PhD adviser Thibault Damour, at the Institute of Advanced Scientific Studies near Paris. The LIGO and Virgo collaborations use a database of hundreds of thousands of these waveforms for spotting gravitational waves in their data in real time. Buonanno is now a director at the Max Planck Institute for Gravitational Physics in Potsdam and a senior member of the LIGO Scientific Collaboration.


    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-Zib

    ESA/eLISA the future of gravitational wave research

    1
    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)

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Nature is a weekly international journal publishing the finest peer-reviewed research in all fields of science and technology on the basis of its originality, importance, interdisciplinary interest, timeliness, accessibility, elegance and surprising conclusions. Nature also provides rapid, authoritative, insightful and arresting news and interpretation of topical and coming trends affecting science, scientists and the wider public.

     
  • richardmitnick 2:20 pm on October 8, 2017 Permalink | Reply
    Tags: , , , , , , Gravitational waves, , , , ,   

    From Quanta: Women in STEM: “Mining Black Hole Collisions for New Physics” Asimina Arvanitaki 

    Quanta Magazine
    Quanta Magazine

    July 21, 2016
    Joshua Sokol

    The physicist Asimina Arvanitaki is thinking up ways to search gravitational wave data for evidence of dark matter particles orbiting black holes.

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    Asimina Arvanitaki during a July visit to the CERN particle physics laboratory in Geneva, Switzerland.
    Samuel Rubio for Quanta Magazine

    When physicists announced in February that they had detected gravitational waves firsthand, the foundations of physics scarcely rattled.


    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-Zib

    ESA/eLISA the future of gravitational wave research

    1
    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)

    The signal exactly matched the expectations physicists had arrived at after a century of tinkering with Einstein’s theory of general relativity. “There is a question: Can you do fundamental physics with it? Can you do things beyond the standard model with it?” said Savas Dimopoulos, a theoretical physicist at Stanford University. “And most people think the answer to that is no.”

    Asimina Arvanitaki is not one of those people. A theoretical physicist at Ontario’s Perimeter Institute of Theoretical Physics,


    Perimeter Institute in Waterloo, Canada

    Arvanitaki has been dreaming up ways to use black holes to explore nature’s fundamental particles and forces since 2010, when she published a paper with Dimopoulos, her mentor from graduate school, and others. Together, they sketched out a “string axiverse,” a pantheon of as yet undiscovered, weakly interacting particles. Axions such as these have long been a favored candidate to explain dark matter and other mysteries.

    In the intervening years, Arvanitaki and her colleagues have developed the idea through successive papers. But February’s announcement marked a turning point, where it all started to seem possible to test these ideas. Studying gravitational waves from the newfound population of merging black holes would allow physicists to search for those axions, since the axions would bind to black holes in what Arvanitaki describes as a “black hole atom.”

    “When it came up, we were like, ‘Oh my god, we’re going to do it now, we’re going to look for this,’” she said. “It’s a whole different ball game if you actually have data.”

    That’s Arvanitaki’s knack: matching what she calls “well-motivated,” field-hopping theoretical ideas with the precise experiment that could probe them. “By thinking away from what people are used to thinking about, you see that there is low-hanging fruit that lie in the interfaces,” she said. At the end of April, she was named the Stavros Niarchos Foundation’s Aristarchus Chair at the Perimeter Institute, the first woman to hold a research chair there.

    It’s a long way to come for someone raised in the small Grecian village of Koklas, where the graduating class at her high school — at which both of her parents taught — consisted of nine students. Quanta Magazine spoke with Arvanitaki about her plan to use black holes as particle detectors. An edited and condensed version of those discussions follows.

    QUANTA MAGZINE: When did you start to think that black holes might be good places to look for axions?

    ASIMINA ARVANITAKI: When we were writing the axiverse paper, Nemanja Kaloper, a physicist who is very good in general relativity, came and told us, “Hey, did you know there is this effect in general relativity called superradiance?” And we’re like, “No, this cannot be, I don’t think this happens. This cannot happen for a realistic system. You must be wrong.” And then he eventually convinced us that this could be possible, and then we spent like a year figuring out the dynamics.
    What is superradiance, and how does it work?

    An astrophysical black hole can rotate. There is a region around it called the “ergo region” where even light has to rotate. Imagine I take a piece of matter and throw it in a trajectory that goes through the ergo region. Now imagine you have some explosives in the matter, and it breaks apart into pieces. Part of it falls into the black hole and part escapes into infinity. The piece that is coming out has more total energy than the piece that went in the black hole.

    You can perform the same experiment by scattering radiation from a black hole. Take an electromagnetic wave pulse, scatter it from the black hole, and you see that the pulse you got back has a higher amplitude.

    So you can send a pulse of light near a black hole in such a way that it would take some energy and angular momentum from the black hole’s spin?

    This is old news, by the way, this is very old news. In ’72 Press and Teukolsky wrote a Nature paper that suggested the following cute thing. Let’s imagine you performed the same experiment as the light, but now imagine that you have the black hole surrounded by a giant mirror. What will happen in that case is the light will bounce on the mirror many times, the amplitude [of the light] grows exponentially, and the mirror eventually explodes due to radiation pressure. They called it the black hole bomb.

    The property that allows light to do this is that light is made of photons, and photons are bosons — particles that can sit in the same space at the same time with the same wave function. Now imagine that you have another boson that has a mass. It can [orbit] the black hole. The particle’s mass acts like a mirror, because it confines the particle in the vicinity of the black hole.

    In this way, axions might get stuck around a black hole?

    This process requires that the size of the particle is comparable to the black hole size. Turns out that [axion] mass can be anywhere from Hubble scale — with a quantum wavelength as big as the universe — or you could have a particle that’s tiny in size.

    So if they exist, axions can bind to black holes with a similar size and mass. What’s next?

    What happens is the number of particles in this bound orbit starts growing exponentially. At the same time the black hole spins down. If you solve for the wave functions of the bound orbits, what you find is that they look like hydrogen wave functions. Instead of electromagnetism binding your atom, what’s binding it is gravity. There are three quantum numbers you can describe, just the same. You can use the exact terminology that you can use in the hydrogen atom.

    How could we check to see if any of the black holes LIGO finds have axion clouds orbiting around black hole nuclei?

    This is a process that extracts energy and angular momentum from the black hole. If you were to measure spin versus mass of black holes, you should see that in a certain mass range for black holes you see no quickly rotating black holes.

    This is where Advanced LIGO comes in. You saw the event they saw. [Their measurements] allowed them to measure the masses of the merging objects, the mass of the final object, the spin of the final object, and to have some information about the spins of the initial objects.

    If I were to take the spins of the black holes before they merged, they could have been affected by superradiance. Now imagine a graph of black hole spin versus mass. Advanced LIGO could maybe get, if the things that we hear are correct, a thousand events per year. Now you have a thousand data points on this plot. So you may trace out the region that is affected by this particle just by those measurements.

    That would be supercool.

    That’s of course indirect. So the other cool thing is that it turns out there are signatures that have to do with the cloud of particles themselves. And essentially what they do is turn the black hole into a gravitational wave laser.

    Awesome. OK, what does that mean?

    2
    Samuel Rubio for Quanta Magazine

    Yeah, what that means is important. Just like you have transitions of electrons in an excited atom, you can have transitions of particles in the gravitational wave atom. The rate of emission of gravitational waves from these transitions is enhanced by the 1080 particles that you have. It would look like a very monochromatic line. It wouldn’t look like a transient. Imagine something now that emits a signal at a very fixed frequency.

    Where could LIGO expect to see signals like this?

    In Advanced LIGO, you actually see the birth of a black hole. You know when and where a black hole was born with a certain mass and a certain spin. So if you know the particle masses that you’re looking for, you can predict when the black hole will start growing the [axion] cloud around it. It could be that you see a merger in that day, and one or 10 years down the line, they go back to the same position and they see this laser turning on, they see this monochromatic line coming out from the cloud.

    You can also do a blind search. Because you have black holes that are roaming the universe by themselves, and they could still have some leftover cloud around them, you can do a blind search for monochromatic gravitational waves.

    Were you surprised to find out that axions and black holes could combine to produce such a dramatic effect?

    Oh my god yes. What are you talking about? We had panic attacks. You know how many panic attacks we had saying that this effect, no, this cannot be true, this is too good to be true? So yes, it was a surprise.

    The experiments you suggest draw from a lot of different theoretical ideas — like how we could look for high-frequency gravitational waves with tabletop sensors, or test whether dark matter oscillates using atomic clocks. When you’re thinking about making risky bets on physics beyond the standard model, what sorts of theories seem worth the effort?

    What is well motivated? Things that are not: “What if you had this?” People imagine: “What if dark matter was this thing? What if dark matter was the other thing?” For example, supersymmetry makes predictions about what types of dark matter should be there. String theory makes predictions about what types of particles you should have. There is always an underlying reason why these particles are there; it’s not just the endless theoretical possibilities that we have.

    And axions fit that definition?

    This is a particle that was proposed 30 years ago to explain the smallness of the observed electric dipole moment of the neutron. There are several experiments around the world looking for it already, at different wavelengths. So this particle, we’ve been looking for it for 30 years. This can be the dark matter. That particle solves an outstanding problem of the standard model, so that makes it a good particle to look for.

    Now, whether or not the particle is there I cannot answer for nature. Nature will have to answer.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    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 6:56 am on October 3, 2017 Permalink | Reply
    Tags: , Gravitational waves, , ,   

    From Symmetry: “Nobel recognizes gravitational wave discovery” 

    Symmetry Mag

    Symmetry

    10/03/17
    Kathryn Jepsen

    1
    Sandbox Studio

    Scientists Rainer Weiss, Kip Thorne and Barry Barish won the 2017 Nobel Prize in Physics for their roles in creating the LIGO experiment.


    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-Zib

    ESA/eLISA the future of gravitational wave research

    1
    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)

    After being passed up for the honor last year, three scientists who made essential contributions to the LIGO collaboration have been awarded the 2017 Nobel Prize in Physics.

    Rainer Weiss will share the prize with Kip Thorne and Barry Barish for their roles in the discovery of gravitational waves, ripples in space-time predicted by Albert Einstein. Weiss and Thorne conceived of the experiment, and project manager Barish is credited with reviving the struggling experiment and making it happen.

    “I view this more as a thing that recognizes the work of about 1000 people,” Weiss said during a Q&A after the announcement this morning. “It’s really a dedicated effort that has been going on, I hate to tell you, for as long as 40 years, people trying to make a detection in the early days and then slowly but surely getting the technology together to do it.”

    A third founder of LIGO, scientist Ronald Drever, died in March. Nobel Prizes are not awarded posthumously.

    According to Einstein’s general theory of relativity, powerful cosmic events release energy in the form of waves traveling through the fabric of existence at the speed of light. LIGO detects these disturbances when they disrupt the symmetry between the passages of identical laser beams traveling identical distances.

    The setup for the LIGO experiment looks like a giant L, with each side stretching about 2.5 miles long. Scientists split a laser beam and shine the two halves down the two sides of the L. When each half of the beam reaches the end, it reflects off a mirror and heads back to the place where its journey began.

    Normally, the two halves of the beam return at the same time. When there’s a mismatch, scientists know something is going on. Gravitational waves compress space-time in one direction and stretch it in another, giving one half of the beam a shortcut and sending the other on a longer trip. LIGO is sensitive enough to notice a difference between the arms as small as 1000th the diameter of an atomic nucleus.

    Scientists on LIGO and their partner collaboration, called Virgo, reported the first detection of gravitational waves in February 2016. The waves were generated in the collision of two black holes with 29 and 36 times the mass of the sun 1.3 billion years ago. They reached the LIGO experiment as scientists were conducting an engineering test.

    “It took us a long time, something like two months, to convince ourselves that we had seen something from outside that was truly a gravitational wave,” Weiss said.

    LIGO, which stands for Laser Interferometer Gravitational-Wave Observatory, consists of two of these pieces of equipment, one located in Louisiana and another in Washington state.

    The experiment is operated jointly by MIT, Weiss’s home institution, and Caltech, Barish and Thorne’s home institution. The experiment has collaborators from more than 80 institutions from more than 20 countries. A third interferometer, operated by the Virgo collaboration, recently joined LIGO to make the first joint observation of gravitational waves.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.


     
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