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  • richardmitnick 1:32 pm on February 2, 2019 Permalink | Reply
    Tags: , , , Big Bang Observer, , , , , , Gravity is talking. Lisa will listen, Multimessinger Astonomy   

    From Ethan Siegel: “Ask Ethan: How Can LISA, Without Fixed-Length Arms, Ever Detect Gravitational Waves?” 

    From Ethan Siegel

    LIGO, here on Earth, has exquisitely-precise distances its lasers travel. With three spacecrafts in motion, how could LISA work?

    Since it began operating in 2015, advanced LIGO has ushered in an era of a new type of astronomy: using gravitational wave signals. The way we do it, however, is through a very special technique known as laser interferometry. By splitting a laser and sending each half of the beam down a perpendicular path, reflecting them back, and recombining them, we can create an interference pattern. If the lengths of those paths change, the interference pattern changes, enabling us to detect those waves. And that leads to the best question I got about science during my recent Astrotour in Iceland, courtesy of Ben Turner, who asked:

    LIGO works by having these exquisitely precise lasers, reflected down perfectly length-calibrated paths, to detect these tiny changes in distance (less than the width of a proton) induced by a passing gravitational wave. With LISA, we plan on having three independent, untethered spacecrafts freely-floating in space. They’ll be affected by all sorts of phenomena, from gravity to radiation to the solar wind. How can we possibly get a gravitational wave signal out of this?

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

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

    Gravity is talking. Lisa will listen. Dialogos of Eide

    ESA/eLISA the future of gravitational wave research

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

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

    It’s a great question, and the toughest one posed to me all year thus far. Let’s explore the answer.

    3D rendering of the gravitational waves emitted from a binary neutron star system at merger. The central region (in density) is stretched by a factor of ~5 for better visibility. The orientation of the merger itself determines how the signal will be polarized. (AEI POTSDAM-GOLM)

    Since the dawn of time, humanity has been practicing astronomy with light, which has progressed from naked-eye viewing to the use of telescopes, cameras, and wavelengths that go far beyond the limits of human vision. We’ve detected cosmic particles from space in a wide variety of flavors: electrons, protons, atomic nuclei, antimatter, and even neutrinos.

    But gravitational waves are an entirely new way for humanity to view the Universe. Instead of some detectable, discrete quantum particle that interacts with another, leading to a detectable signal in some sort of electronic device, gravitational waves act as ripples in the fabric of space itself. With a certain set of properties, including:

    propagation speed,
    frequency, and

    they affect everything occupying the space that they pass through.

    Gravitational waves propagate in one direction, alternately expanding and compressing space in mutually perpendicular directions, defined by the gravitational wave’s polarization. Gravitational waves themselves, in a quantum theory of gravity, should be made of individual quanta of the gravitational field: gravitons. (M. PÖSSEL/EINSTEIN ONLINE)

    When one of these gravitational waves passes through a LIGO-like detector, it does exactly what you might suspect. The gravitational wave, along the direction it propagates at the speed of gravity (which equals the speed of light), doesn’t affect space at all. Along the plane perpendicular to its propagation, however, it alternately causes space to expand and contract in mutually perpendicular directions. There are multiple types of polarization that are possible:

    “plus” (+) polarization, where the up-down and left-right directions expand and contract,
    “cross” (×) polarization, where the left-diagonal and right-diagonal directions expand and contract,
    or “circularly” polarized waves, similar to way light can be circularly polarized; this is a different parameterization of plus and cross polarizations.

    Whatever the physical case, the polarization is determined by the nature of the source.

    When a wave enters a detector, any two perpendicular directions will be compelled to contract and expand, alternately and in-phase, relative to one another. The amount that they contract or expand is related to the amplitude of the wave. The period of the expansion and contraction is determined by the frequency of the wave, which a detector of a specific arm length (or effective arm length, where there are multiple reflections down the arms, as in the case of LIGO) will be sensitive to.

    With multiple such detectors in a variety of orientations to one another in three-dimensional space, the location, orientation, and even polarization of the original source can be reconstructed. By using the predictive power of Einstein’s General Relativity and the effects of gravitational waves on the matter-and-energy occupying the space they pass through, we can learn about events happening all across the Universe.

    LIGO and Virgo have discovered a new population of black holes with masses that are larger than what had been seen before with X-ray studies alone (purple). This plot shows the masses of all ten confident binary black hole mergers detected by LIGO/Virgo (blue), along with the one neutron star-neutron star merger seen (orange). LIGO/Virgo, with the upgrade in sensitivity, should detect multiple mergers every week. (LIGO/VIRGO/NORTHWESTERN UNIV./FRANK ELAVSKY)

    But it’s only due to the extraordinary technical achievement of these interferometers that we can actually make these measurements. In a terrestrial, LIGO-like detector, the distances of the two perpendicular arms are fixed. Laser light, even if reflected back-and-forth along the arms thousands of times, will eventually see the two beams come back together and construct a very specific interference pattern.

    If the noise can be minimized below a certain level, the pattern will hold absolutely steady, so long as no gravitational waves are present.

    If, then, a gravitational wave passes through, and one arm contracts while the other expands, the pattern will shift.

    When the two arms are of exactly equal length and there is no gravitational wave passing through, the signal is null and the interference pattern is constant. As the arm lengths change, the signal is real and oscillatory, and the interference pattern changes with time in a predictable fashion. (NASA’S SPACE PLACE)

    By measuring the amplitude and frequency at which the pattern shifts, the properties of a gravitational wave can be reconstructed. By measuring a coincident signal in multiple such gravitational wave detectors, the source properties and location can be reconstructed as well. The more detectors with differing orientations and locations are present, the better-constrained the properties of the gravitational wave source will be.

    This is why adding the Virgo detector to the twin LIGO detectors in Livingston and Hanford enabled a far superior reconstruction of the location of gravitational wave sources. In the future, additional LIGO-like detectors in Japan and India will allow scientists to pinpoint gravitational waves in an even superior fashion.

    But there’s a limit to what we can do with detectors like this. Seismic noise from being located on the Earth itself limits how sensitive a ground-based detector can be. Signals below a certain amplitude can never be detected. Additionally, when light signals are reflected between mirrors, the noise generated by the Earth accumulates cumulatively.

    The fact that the Earth itself exists in the Solar System, even if there were no plate tectonics, ensures that the most common type of gravitational wave events — binary stars, supermassive black holes, and other low-frequency sources (taking 100 seconds or more to oscillate) — cannot be seen from the ground. Earth’s gravitational field, human activity, and natural geological processes means that these low-frequency signals cannot be practically seen from Earth. For that, we need to go to space.

    And that’s where LISA comes in.

    The sensitivities of a variety of gravitational wave detectors, old, new, and proposed. Note, in particular, Advanced LIGO (in orange), LISA (in dark blue), and BBO (in light blue). LIGO can only detect low-mass and short-period events; longer-baseline, lower-noise observatories are needed for more massive black holes. (MINGLEI TONG, CLASS.QUANT.GRAV. 29 (2012) 155006)

    LISA is the Laser Interferometer Space Antenna. In its current design, it consists of three dual-purpose spacecrafts, separated in an equilateral triangle configuration by roughly 5,000,000 kilometers along each laser arm.

    Inside each spacecraft, there are two free-floating cubes that are shielded by the spacecraft itself from the effects of interplanetary space. They will remain at a constant temperature, pressure, and will be unaffected by the solar wind, radiation pressure, or the bombardment of micrometeorites.

    By carefully measuring the distances between pairs of cubes on different spacecrafts, using the same laser interferometry technique, scientists can do everything that multiple LIGO detectors do, except for these long-period gravitational waves that only LISA is sensitive to. Without the Earth to create noise, it seems like an ideal setup.

    The primary scientific goal of the Laser Interferometer Space Antenna (LISA) mission is to detect and observe gravitational waves from massive black holes and galactic binaries with periods in the range of a tens of seconds to a few hours. This low-frequency range is inaccessible to ground-based interferometers because of the unshieldable background of local gravitational noise arising from atmospheric effects and seismic activity. (ESA-C. VIJOUX)

    But even without the terrestrial effects of human activity, seismic noise, and being deep within Earth’s gravitational field, there are still sources of noise that LISA must contend with. The solar wind will strike the detectors, and the LISA spacecrafts must be able to compensate for that. The gravitational influence of other planets and solar radiation pressure will induce tiny orbital changes relative to one another. Quite simply, there is no way to hold the spacecract at a fixed, constant distance of exactly 5 million km, relative to one another, in space. No amount of rocket fuel or electric thrusters will be able to maintain that exactly.

    Remember: the goal is to detect gravitational waves — themselves a tiny, minuscule signal — over and above the background of all this noise.

    The three LISA spacecraft will be placed in orbits that form a triangular formation with center 20° behind the Earth and side length 5 million km. This figure is not to scale. (NASA)

    So how does LISA plan to do it?

    The secret is in these gold-platinum alloy cubes. In the center of each optical system, a solid cube that’s 4 centimeters (about 1.6″) on each side floats freely in the weightless conditions of space. While external sensors monitor the solar wind and solar radiation pressure, with electronic sensors compensating for those extraneous forces, the gravitational forces from all the known bodies in the Solar System can be calculated and anticipated.

    As the spacecrafts, and the cubes, move relative to one another, the lasers adjust in a predictable, well-known fashion. So long as they continue to reflect off of the cubes, the distances between them can be measured.

    The gold-platinum alloy cubes, of central importance to the upcoming LISA mission, have already been built and tested in the proof-of-concept LISA Pathfinder mission

    ESA/LISA Pathfinder

    It’s not a matter of keeping the distances fixed and measuring a tiny change due to a passing wave; it’s a matter of understanding exactly how the distances will behave over time, accounting for them, and then looking for the periodic departures from those measurements to a high-enough precision. LISA won’t hold the three spacecrafts in a fixed position, but will allow them to adjust freely as Einstein’s laws dictate. It’s only because gravity is so well-understood that the additional signal of the gravitational waves, assuming the wind and radiation from the Sun is sufficiently compensated for, can be teased out.

    The proposed ‘Big Bang Observer’ would take the design of LISA, the Laser Interferometer Space Antenna, and create a large equilateral triangle around Earth’s orbit to get the longest-baseline gravitational wave observatory ever. (GREGORY HARRY, MIT, FROM THE LIGO WORKSHOP OF 2009, LIGO-G0900426)

    If we want to go even farther, we have dreams of putting three LISA-like detectors in an equilateral triangle around different points in Earth’s orbit: a proposed mission called Big Bang Observer (BBO). While LISA can detect binary systems with periods ranging from minutes to hours, BBO will be able to detect the grandest behemonths of all: supermassive binary black holes anywhere in the Universe, with periods of years.

    If we’re willing to invest in it, space-based gravitational wave observatories could allow us to map out all of the most massive, densest objects located throughout the entire Universe. The key isn’t holding your laser arms fixed, but simply in knowing exactly how, in the absence of gravitational waves, they’d move relative to one another. The rest is simply a matter of extracting the signal of each gravitational wave out. Without the Earth’s noise to slow us down, the entire cosmos is within our reach.

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

  • richardmitnick 12:15 pm on January 20, 2019 Permalink | Reply
    Tags: , , , , , , , KAGRA, Multimessinger Astonomy   

    From Science News: “A new gravitational wave detector is almost ready to join the search” 

    From Science News

    January 18, 2019
    Emily Conover

    Japan’s KAGRA experiment tests new techniques for spotting ripples in spacetime.

    KAGRA gravitational wave detector, Kamioka mine in Kamioka-cho, Hida-city, Gifu-prefecture, Japan

    KAGRA tunnel

    In the quest for better gravitational wave detectors, scientists are going cold.

    An up-and-coming detector called KAGRA aims to spot spacetime ripples by harnessing advanced technological twists: chilling key components to temperatures hovering just above absolute zero, and placing the ultrasensitive setup in an enormous underground cavern.

    Scientists with KAGRA, located in Kamioka, Japan, now have results from their first ultrafrigid tests. Those experiments suggest that the detector should be ready to start searching for gravitational waves later in 2019, the team reports January 14 at arXiv.org.

    The new detector will join similar observatories in the search for the minute cosmic undulations, which are stirred up by violent events like collisions of black holes. The Laser Interferometer Gravitational-Wave Observatory, LIGO, has two detectors located in Hanford, Wash., and Livingston, La. Another observatory, Virgo, is located near Pisa, Italy.

    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

    ESA/eLISA the future of gravitational wave research

    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)

    Those detectors sit above ground, and don’t use the cooling technique, making KAGRA the first of its kind.

    KAGRA consists of two 3-kilometer-long arms, arranged in an “L” shape. Within each arm, laser light bounces back and forth between two mirrors located at both ends. The light acts like a giant measuring stick, capturing tiny changes in the length of each arm, which can be caused by a passing gravitational wave stretching and squeezing spacetime.

    FREEZE UP KAGRA’s mirrors (one shown) are cooled to very low temperatures to prevent jiggling that could hamper the search for gravitational waves.

    Because gravitational wave detectors measure length changes tinier than the diameter of a proton, minuscule effects like the jiggling of molecules on the mirrors’ surfaces can interfere with the measurements. Cooling the mirrors to about 20 kelvins (–253° Celsius) limits that jiggling.

    In the new tests, performed in spring 2018, researchers cooled only one of KAGRA’s four mirrors, says KAGRA leader Takaaki Kajita of the University of Tokyo. When the detector starts up for real, the others will be chilled too.

    Having the detector underground also helps keep the mirrors from vibrating due to activity on Earth’s surface. LIGO is so sensitive that it can be affected by rumbling trucks, a stiff breeze or even mischievous wildlife (SN Online: 4/18/18). KAGRA’s underground lair should be significantly quieter.

    Building underground and going cold required years of effort from KAGRA’s researchers. “They’ve taken on these two great challenges, which are both important to the long-term future of the field,” says LIGO spokesperson David Shoemaker of MIT. In the future, even more advanced gravitational wave detectors could build on KAGRA’s techniques.

    For now, adding KAGRA to the existing observatories should help scientists improve their studies of where gravitational wiggles come from. Once scientists detect a gravitational wave signal, they alert astronomers, who search for light from the cataclysm that generated the waves in the hope of better understanding the event (SN: 11/11/17, p. 6). Having an additional gravitational wave detector in a different part of the world will help better triangulate wave sources. “This feature is very important,” Kajita says, “because telescopes can only see a small part of the sky at a time.”

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

  • richardmitnick 2:59 pm on December 3, 2018 Permalink | Reply
    Tags: , , LIGO and Virgo Announce Four New Detections, Multimessinger Astonomy   

    From MIT Caltech Advanced aLIGO: “LIGO and Virgo Announce Four New Detections” 

    From MIT Caltech Advanced aLIGO

    Valerio Boschi
Virgo-EGO Communication Office
    +39 050 752 463

    Antonella Varaschin
INFN Communications Office
    +39 06 68400360

    Kimberly Allen

    Director of Media Relations and Deputy Director, MIT News Office
    +1 617-253-2702

    Whitney Clavin

    Senior Content and Media Strategist
    Caltech Communications
    +1 626-395-1856

    John Toon

    Institute Research and Economic Development Communications
    Georgia Institute of Technology

    +1 404-894-6986

    Amanda Hallberg Greenwell
Head, Office of Legislative and Public Affairs
    National Science Foundation
    +1 703-292-8070

    LIGO-Virgo/Frank Elavsky/Northwestern

    The observatories are also releasing their first catalog of gravitational-wave events.

    On Saturday, December 1, scientists attending the Gravitational Wave Physics and Astronomy Workshop in College Park, Maryland, presented new results from the National Science Foundation’s LIGO (Laser Interferometer Gravitational-Wave Observatory) and the European- based VIRGO gravitational-wave detector regarding their searches for coalescing cosmic objects, such as pairs of black holes and pairs of neutron stars. The LIGO and Virgo collaborations have now confidently detected gravitational waves from a total of 10 stellar-mass binary black hole mergers and one merger of neutron stars, which are the dense, spherical remains of stellar explosions. Six of the black hole merger events had been reported before, while four are newly announced.

    From September 12, 2015, to January 19, 2016, during the first LIGO observing run since undergoing upgrades in a program called Advanced LIGO, gravitational waves from three binary black hole mergers were detected. The second observing run, which lasted from November 30, 2016, to August 25, 2017, yielded one binary neutron star merger and seven additional binary black hole mergers, including the four new gravitational-wave events being reported now. The new events are known as GW170729, GW170809, GW170818, and GW170823, in reference to the dates they were detected.

    All of the events are included in a new catalog, also released Saturday, with some of the events breaking records. For instance, the new event GW170729, detected in the second observing run on July 29, 2017, is the most massive and distant gravitational-wave source ever observed. In this coalescence, which happened roughly 5 billion years ago, an equivalent energy of almost five solar masses was converted into gravitational radiation.

    GW170814 was the first binary black hole merger measured by the three-detector network, and allowed for the first tests of gravitational-wave polarization (analogous to light polarization).

    The event GW170817, detected three days after GW170814, represented the first time that gravitational waves were ever observed from the merger of a binary neutron star system. What’s more, this collision was seen in gravitational waves and light, marking an exciting new chapter in multi-messenger astronomy, in which cosmic objects are observed simultaneously in different forms of radiation.

    One of the new events, GW170818, which was detected by the global network formed by the LIGO and Virgo observatories, was very precisely pinpointed in the sky. The position of the binary black holes, located 2.5 billion light-years from Earth, was identified in the sky with a precision of 39 square degrees. That makes it the next best localized gravitational-wave source after the GW170817 neutron star merger.

    Caltech’s Albert Lazzarini, Deputy Director of the LIGO Laboratory, says “The release of four additional binary black hole mergers further informs us of the nature of the population of these binary systems in the universe and better constrains the event rate for these types of events.”

    “In just one year, LIGO and VIRGO working together have dramatically advanced gravitational- wave science, and the rate of discovery suggests the most spectacular findings are yet to come,” says Denise Caldwell, Director of NSF’s Division of Physics. “The accomplishments of NSF’s LIGO and its international partners are a source of pride for the agency, and we expect even greater advances as LIGO’s sensitivity becomes better and better in the coming year.”

    “The next observing run, starting in Spring 2019, should yield many more gravitational-wave candidates, and the science the community can accomplish will grow accordingly,” says David Shoemaker, spokesperson for the LIGO Scientific Collaboration and senior research scientist in MIT’s Kavli Institute for Astrophysics and Space Research. “It’s an incredibly exciting time.”

    “It is gratifying to see the new capabilities that become available through the addition of Advanced Virgo to the global network,” says Jo van den Brand of Nikhef (the Dutch National Institute for Subatomic Physics) and VU University Amsterdam, who is the spokesperson for the Virgo Collaboration. “Our greatly improved pointing precision will allow astronomers to rapidly find any other cosmic messengers emitted by the gravitational-wave sources.” The enhanced pointing capability of the LIGO-Virgo network is made possible by exploiting the time delays of the signal arrival at the different sites and the so-called antenna patterns of the interferometers.

    “The new catalog is another proof of the exemplary international collaboration of the gravitational wave community and an asset for the forthcoming runs and upgrades”, adds EGO Director Stavros Katsanevas.

    The scientific papers describing these new findings, which are being initially published on the arXiv repository of electronic preprints, present detailed information in the form of a catalog of all the gravitational wave detections and candidate events of the two observing runs as well as describing the characteristics of the merging black hole population. Most notably, we find that almost all black holes formed from stars are lighter than 45 times the mass of the Sun. Thanks to more advanced data processing and better calibration of the instruments, the accuracy of the astrophysical parameters of the previously announced events increased considerably.

    Laura Cadonati, Deputy Spokesperson for the LIGO Scientific Collaboration, says “These new discoveries were only made possible through the tireless and carefully coordinated work of the detector commissioners at all three observatories, and the scientists around the world responsible for data quality and cleaning, searching for buried signals, and parameter estimation for each candidate — each a scientific specialty requiring enormous expertise and experience.”

    Related Links

    Paper: “GWTC-1: A Gravitational-Wave Transient Catalog of Compact Binary Mergers Observed by LIGO and Virgo during the First and Second Observing Runs

    Paper: “Binary Black Hole Population Properties Inferred from the First and Second Observing Runs of Advanced LIGO and Advanced Virgo

    The Collaborations

    LIGO is funded by NSF and operated by Caltech and MIT, which conceived of LIGO and led the Initial and Advanced LIGO projects. Financial support for the Advanced LIGO project was led by the NSF with Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council) and Australia (Australian Research Council-OzGrav) making significant commitments and contributions to the project. More than 1,200 scientists from around the world participate in the effort through the LIGO Scientific Collaboration, which includes the GEO Collaboration. A list of additional partners is available at https://my.ligo.org/census.php.

    The Virgo collaboration consists of more than 300 physicists and engineers belonging to 28 different European research groups: six from Centre National de la Recherche Scientifique (CNRS) in France; 11 from the Istituto Nazionale di Fisica Nucleare (INFN) in Italy; two in the Netherlands with Nikhef; the MTA Wigner RCP in Hungary; the POLGRAW group in Poland; Spain with IFAE and the Universities of Valencia and Barcelona; two in Belgium with the Universities of Liege and Louvain; Jena University in Germany; and the European Gravitational Observatory (EGO), the laboratory hosting the Virgo detector near Pisa in Italy, funded by CNRS, INFN, and Nikhef. A list of the Virgo Collaboration can be found at http://public.virgo-gw.eu/the-virgo-collaboration/. More information is available on the Virgo website at http://www.virgo-gw.eu.

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    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

    ESA/eLISA the future of gravitational wave research

    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)

  • richardmitnick 6:19 am on August 24, 2018 Permalink | Reply
    Tags: , , , , , Multimessinger Astonomy,   

    From The Conversation: “We’re going to get a better detector: time for upgrades in the search for gravitational waves” 

    From The Conversation

    August 16, 2018
    Robert Ward

    It’s been a year since ripples in space-time from a colliding pair of dead stars tickled the gravitational wave detectors of the Advanced LIGO and Advanced Virgo facilities.

    Soon after, astronomers around the world began a campaign to observe the afterglow of the collision of a binary neutron star merger in radio waves, microwaves, visible light, x-rays and more.

    See https://sciencesprings.wordpress.com/2017/10/16/from-ucsc-a-uc-santa-cruz-special-report-neutron-stars-gravitational-waves-and-all-the-gold-in-the-universe/

    This was the dawn of multi-messenger astronomy: a new era in astronomy, where events in the universe are observed with more than just a single type of radiation. In this case, the messengers were gravitational waves and electromagnetic radiation.

    What we’ve learned (so far)

    From this single event, we learned an incredible amount. Last October, on the day the detection was made public, 84 scientific papers were published (or the preprints made available).

    We learned that gravity and light travel at the same speed, neutron star mergers are a source of short gamma-ray bursts, and that kilonovae – the explosion from a neutron star merger – are where our gold comes from.

    This rich science came from the fact that we were able to combine our observatories to witness this single event from multiple astronomical “windows”. The gravitational waves arrived first, followed 1.7 seconds later by gamma-rays. That is a pretty small delay, considering the waves had been travelling for 130 million years.

    Over the next few weeks, visible light and radio waves began to be observed and then slowly faded.

    It seemed like the news about gravitational waves was coming fast and furious, with the first detection announced in 2016, a Nobel prize in 2017, and the announcement of the binary neutron star merger just weeks after the Nobel prize.

    Time for upgrades

    On this first anniversary of the neutron star merger, the gravitational wave detectors are offline for upgrades. They actually went offline shortly after the detection and will come back online some time early in 2019.

    The work of making gravitational wave detectors function requires extraordinary patience and dedication. These are exquisite experiments – it took more than 40 years of technological development by a community of more than a thousand scientists to get to the point of detecting the first signal.

    Naturally, improving on this work is not easy. So what does it actually take?

    We really do listen to gravitational waves, and our detectors act more like microphones than telescopes or cameras.

    Quiet please!

    To detect gravitational waves, we need to do more than just turn off the dishwasher. We need to build the quietest, best-isolated thing on Earth.

    Unfortunately, the laws of quantum mechanics and thermodynamics both prevent us from eliminating the noise entirely. Nonetheless, we strive to do the best that these fundamental limits permit. This involves, among many other extraordinary things, hanging our mirrors on glass threads .

    Before sealing up the chamber and pumping the vacuum system down, a LIGO optics technician inspects one of LIGO’s core optics (mirrors) by illuminating its surface with light at a glancing angle. Matt Heintze/Caltech/MIT/LIGO Lab

    Our mirrors weight 40kg each and are suspended from four of these glass threads, which are less than a half-millimetre in diameter and exquisitely crafted.

    The threads are under enormous stress, and the slightest imperfection (or the slightest touch) can cause them to explode.

    Just such an explosion happened earlier this year while installing a new mirror. Fortunately, the precious mirror fell into a cradle designed for just such a possibility, and was not damaged.

    Nonetheless, the delicate, intricate work of creating the glass threads, attaching them to the mirror, hanging the mirror and then installing it all needed to be redone.

    Improvements to the detector

    This was a heartbreaking setback for the team, but the added delay was not entirely in vain. In parallel with remaking the glass threads and rehanging the new mirror, we made some other improvements to the detector, for which we otherwise would not have had enough time.

    One of the goals of this upgrade period is to install something called a quantum squeezed light source into the gravitational wave detectors.

    As mentioned earlier, quantum mechanics mandates a certain minimum amount of noise in any measurement. We can’t arbitrarily reduce this quantum noise, but we can move it around and change its shape by squeezing it.

    This is a bit like sweeping dust under the rug. It’s not really gone, but it might not bother you so much anymore. The quantum squeezed light source does just this.

    Australian National University scientists Nutsinee Kijbunchoo and Terry McCrae build components for a quantum squeezed light source at LIGO Hanford Observatory in Washington, US. Nutsinee Kijbunchoo

    A gravitational wave detector is already a very complex system, and a squeezed light source is another complex system, so putting them together can be a challenge.

    Despite the complexity of this challenge, when the squeezed light source was activated for the first time at the LIGO detector in Livingston, Louisiana, US, in February this year there was an immediate improvement in the quantum noise: the gravitational wave detector output got just a bit quieter.

    ESA/NASA eLISA space based, the future of gravitational wave research

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    The Conversation US launched as a pilot project in October 2014. It is an independent source of news and views from the academic and research community, delivered direct to the public.
    Our team of professional editors work with university and research institute experts to unlock their knowledge for use by the wider public.
    Access to independent, high quality, authenticated, explanatory journalism underpins a functioning democracy. Our aim is to promote better understanding of current affairs and complex issues. And hopefully allow for a better quality of public discourse and conversation.

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