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  • richardmitnick 3:45 pm on December 5, 2019 Permalink | Reply
    Tags: , , , , , , LIGO, , , Quantum vacuum squeezer   

    From MIT News: “New instrument extends LIGO’s reach” 

    MIT News

    From MIT News

    December 5, 2019
    Jennifer Chu

    1
    Researchers install a new quantum squeezing device into one of LIGO’s gravitational wave detectors. Image: Lisa Barsotti

    2
    A close-up of the quantum squeezer which has expanded LIGO’s expected detection range by 50 percent. Image: Maggie Tse

    Just a year ago, the National Science Foundation-funded Laser Interferometer Gravitational-wave Observatory, or LIGO, was picking up whispers of gravitational waves every month or so. Now, a new addition to the system is enabling the instruments to detect these ripples in space-time nearly every week.

    Since the start of LIGO’s third operating run in April, a new instrument known as a quantum vacuum squeezer has helped scientists pick out dozens of gravitational wave signals, including one that appears to have been generated by a binary neutron star — the explosive merging of two neutron stars.

    The squeezer, as scientists call it, was designed, built, and integrated with LIGO’s detectors by MIT researchers, along with collaborators from Caltech and the Australian National University, who detail its workings in a paper published today in the journal Physical Review Letters.

    What the instrument “squeezes” is quantum noise — infinitesimally small fluctuations in the vacuum of space that make it into the detectors. The signals that LIGO detects are so tiny that these quantum, otherwise minor fluctuations can have a contaminating effect, potentially muddying or completely masking incoming signals of gravitational waves.

    “Where quantum mechanics comes in relates to the fact that LIGO’s laser is made of photons,” explains lead author Maggie Tse, a graduate student at MIT. “Instead of a continuous stream of laser light, if you look close enough it’s actually a noisy parade of individual photons, each under the influence of vacuum fluctuations. Whereas a continuous stream of light would create a constant hum in the detector, the individual photons each arrive at the detector with a little ‘pop.’”

    “This quantum noise is like a popcorn crackle in the background that creeps into our interferometer, and is very difficult to measure,” adds Nergis Mavalvala, the Marble Professor of Astrophysics and associate head of the Department of Physics at MIT.

    With the new squeezer technology, LIGO has shaved down this confounding quantum crackle, extending the detectors’ range by 15 percent. Combined with an increase in LIGO’s laser power, this means the detectors can pick out a gravitational wave generated by a source in the universe out to about 140 megaparsecs, or more than 400 million light years away. This extended range has enabled LIGO to detect gravitational waves on an almost weekly basis.

    “When the rate of detection goes up, not only do we understand more about the sources we know, because we have more to study, but our potential for discovering unknown things comes in,” says Mavalvala, a longtime member of the LIGO scientific team. “We’re casting a broader net.”

    The new paper’s lead authors are graduate students Maggie Tse and Haocun Yu, and Lisa Barsotti, a principal research scientist at MIT’s Kavli Institute for Astrophysics and Space Research, along with others in the LIGO Scientific Collaboration.

    Quantum limit

    LIGO comprises two identical detectors, one located at Hanford, Washington, and the other at Livingston, Louisiana. Each detector consists of two 4-kilometer-long tunnels, or arms, each extending out from the other in the shape of an “L.”

    MIT /Caltech Advanced aLigo

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

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

    To detect a gravitational wave, scientists send a laser beam from the corner of the L-shaped detector, down each arm, at the end of which is suspended a mirror. Each laser bounces off its respective mirror and travels back down each arm to where it started. If a gravitational wave passes through the detector, it should shift one or both of the mirrors’ position, which would in turn affect the timing of each laser’s arrival back at its origin. This timing is something scientists can measure to identify a gravitational wave signal.

    The main source of uncertainty in LIGO’s measurements comes from quantum noise in a laser’s surrounding vacuum. While a vacuum is typically thought of as a nothingness, or emptiness in space, physicists understand it as a state in which subatomic particles (in this case, photons) are being constantly created and destroyed, appearing then disappearing so quickly they are extremely difficult to detect. Both the time of arrival (phase) and number (amplitude) of these photons are equally unknown, and equally uncertain, making it difficult for scientists to pick out gravitational-wave signals from the resulting background of quantum noise.

    And yet, this quantum crackle is constant, and as LIGO seeks to detect farther, fainter signals, this quantum noise has become more of a limiting factor.

    “The measurement we’re making is so sensitive that the quantum vacuum matters,” Barsotti notes.

    Putting the squeeze on “spooky” noise

    The research team at MIT began over 15 years ago to design a device to squeeze down the uncertainty in quantum noise, to reveal fainter and more distant gravitational wave signals that would otherwise be buried the quantum noise.

    Quantum squeezing was a theory that was first proposed in the 1980s, the general idea being that quantum vacuum noise can be represented as a sphere of uncertainty along two main axes: phase and amplitude. If this sphere were squeezed, like a stress ball, in a way that constricted the sphere along the amplitude axis, this would in effect shrink the uncertainty in the amplitude state of a vacuum (the squeezed part of the stress ball), while increasing the uncertainty in the phase state (stress ball’s displaced, distended portion). Since it is predominantly the phase uncertainty that contributes noise to LIGO, shrinking it could make the detector more sensitive to astrophysical signals.

    When the theory was first proposed nearly 40 years ago, a handful of research groups tried to build quantum squeezing instruments in the lab.

    “After these first demonstrations, it went quiet,” Mavalvala says.

    “The challenge with building squeezers is that the squeezed vacuum state is very fragile and delicate,” Tse adds. “Getting the squeezed ball, in one piece, from where it is generated to where it is measured is surprisingly hard. Any misstep, and the ball can bounce right back to its unsqueezed state.”

    Then, around 2002, just as LIGO’s detectors first started searching for gravitational waves, researchers at MIT began thinking about quantum squeezing as a way to reduce the noise that could possibly mask an incredibly faint gravitational wave signal. They developed a preliminary design for a vacuum squeezer, which they tested in 2010 at LIGO’s Hanford site. The result was encouraging: The instrument managed to boost LIGO’s signal-to-noise ratio — the strength of a promising signal versus the background noise.

    Since then, the team, led by Tse and Barsotti, has refined its design, and built and integrated squeezers into both LIGO detectors. The heart of the squeezer is an optical parametric oscillator, or OPO — a bowtie-shaped device that holds a small crystal within a configuration of mirrors. When the researchers direct a laser beam to the crystal, the crystal’s atoms facilitate interactions between the laser and the quantum vacuum in a way that rearranges their properties of phase versus amplitude, creating a new, “squeezed” vacuum that then continues down each of the detector’s arm as it normally would. This squeezed vacuum has smaller phase fluctuations than an ordinary vacuum, allowing scientists to better detect gravitational waves.

    In addition to increasing LIGO’s ability to detect gravitational waves, the new quantum squeezer may also help scientists better extract information about the sources that produce these waves.

    “We have this spooky quantum vacuum that we can manipulate without actually violating the laws of nature, and we can then make an improved measurement,” Mavalvala says. “It tells us that we can do an end-run around nature sometimes. Not always, but sometimes.”

    This research was supported, in part, by the National Science Foundation. LIGO was constructed by Caltech and MIT.

    See the full article here .


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  • richardmitnick 2:07 pm on June 27, 2017 Permalink | Reply
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    From Symmetry: “The rise of LIGO’s space-studying super-team” 

    Symmetry Mag

    Symmetry

    06/27/17
    Troy Rummler

    The era of multi-messenger astronomy promises rich rewards—and a steep learning curve.

    NASA/Fermi LAT

    Sometimes you need more than one perspective to get the full story.

    Scientists including astronomers working with the Fermi Large Area Telescope have recorded brief bursts of high-energy photons called gamma rays coming from distant reaches of space. They suspect such eruptions result from the merging of two neutron stars—the collapsed cores of dying stars—or from the collision of a neutron star and a black hole.

    But gamma rays alone can’t tell them that. The story of the dense, crashing cores would be more convincing if astronomers saw a second signal coming from the same event—for example, the release of ripples in space-time called gravitational waves.

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

    “The Fermi Large Area Telescope detects a few short gamma ray bursts per year already, but detecting one in correspondence to a gravitational-wave event would be the first direct confirmation of this scenario,” says postdoctoral researcher Giacomo Vianello of the Kavli Institute for Particle Astrophysics and Cosmology, a joint institution of SLAC National Accelerator Laboratory and Stanford University.

    Scientists discovered gravitational waves in 2015 (announced in 2016). Using the Laser Interferometer Gravitational-Wave Observatory, or LIGO, they detected the coalescence of two massive black holes.


    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

    LIGO scientists are now sharing their data with a network of fellow space watchers to see if any of their signals match up. Combining multiple signals to create a more complete picture of astronomical events is called multi-messenger astronomy.​

    Looking for a match

    “We had this dream of finding astronomical events to match up with our gravitational wave triggers,” says LIGO scientist Peter Shawhan of the University of Maryland. ​

    But LIGO can only narrow down the source of its signals to a region large enough to contain roughly 100,000 galaxies.

    Searching for contemporaneous signals within that gigantic volume of space is extremely challenging, especially since most telescopes only view a small part of the sky at a time. So Shawhan and his colleagues developed a plan to send out an automatic alert to other observatories whenever LIGO detected an interesting signal of its own. The alert would contain preliminary calculations and the estimated location of the source of the potential gravitational waves.

    “Our early efforts were pretty crude and only involved a small number of partners with telescopes, but it kind of got this idea started,” Shawhan says. The LIGO Collaboration and the Virgo Collaboration, its European partner, revamped and expanded the program while upgrading their detectors. Since 2014, 92 groups have signed up to receive alerts from LIGO, and the number is growing.

    LIGO is not alone in latching onto the promise of multi-messenger astronomy. The Supernova Early Warning System (SNEWS) also unites multiple experiments to look at the same event in different ways.

    Neutral, rarely interacting particles called neutrinos escape more quickly from collapsing stars than optical light, so a network of neutrino experiments is prepared to alert optical observatories as soon as they get the first warning of a nearby supernova in the form of a burst of neutrinos.

    National Science Foundation Director France Córdova has lauded multi-messenger astronomy, calling it in 2016 a bold research idea that would lead to transformative discoveries.​

    The learning curve

    Catching gamma ray bursts alongside gravitational waves is no simple feat.

    The Fermi Large Area Telescope orbits the earth as the primary instrument on the Fermi Gamma-ray Space Telescope.

    NASA/Fermi Telescope

    The telescope is constantly in motion and has a large field of view that surveys the entire sky multiple times per day.

    But a gamma-ray burst lasts just a few seconds, and it takes about three hours for LAT to complete its sweep. So even if an event that releases gravitational waves also produces a gamma-ray burst, LAT might not be looking in the right direction at the right time. It would need to catch the afterglow of the event.

    Fermi LAT scientist Nicola Omodei of Stanford University acknowledges another challenge: The window to see the burst alongside gravitational waves might not line up with the theoretical predictions. It’s never been done before, so the signal could look different or come at a different time than expected.

    That doesn’t stop him and his colleagues from trying, though. “We want to cover all bases, and we adopt different strategies,” he says. “To make sure we are not missing any preceding or delayed signal, we also look on much longer time scales, analyzing the days before and after the trigger.”

    Scientists using the second instrument on the Fermi Gamma-ray Space Telescope have already found an unconfirmed signal that aligned with the first gravitational waves LIGO detected, says scientist Valerie Connaughton of the Universities Space Research Association, who works on the Gamma-Ray Burst Monitor. “We were surprised to find a transient event 0.4 seconds after the first GW seen by LIGO.”

    While the event is theoretically unlikely to be connected to the gravitational wave, she says the timing and location “are enough for us to be interested and to challenge the theorists to explain how something that was not expected to produce gamma rays might have done so.”

    From the ground up

    It’s not just space-based experiments looking for signals that align with LIGO alerts. A working group called DESgw, members of the Dark Energy Survey with independent collaborators, have found a way to use the Dark Energy Camera, a 570-Megapixel digital camera mounted on a telescope in the Chilean Andes, to follow up on gravitational wave detections.​


    Dark Energy Camera [DECam], built at FNAL


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam

    “We have developed a rapid response system to interrupt the planned observations when a trigger occurs,” says DES scientist Marcelle Soares-Santos of Fermi National Accelerator Laboratory. “The DES is a cosmological survey; following up gravitational wave sources was not originally part of the DES scientific program.”

    Once they receive a signal, the DESgw collaborators meet to evaluate the alert and weigh the cost of changing the planned telescope observations against what scientific data they could expect to see—most often how much of the LIGO source location could be covered by DECam observations.

    “We could, in principle, put the telescope onto the sky for every event as soon as night falls,” says DES scientist Jim Annis, also of Fermilab. “In practice, our telescope is large and the demand for its time is high, so we wait for the right events in the right part of the sky before we open up and start imaging.”

    At an even lower elevation, scientists at the IceCube neutrino experiment—made up of detectors drilled down into Antarctic ice—are following LIGO’s exploits as well.

    U Wisconsin ICECUBE neutrino detector at the South Pole

    Lunar Icecube

    IceCube DeepCore

    IceCube PINGU

    DM-Ice II at IceCube

    “The neutrinos IceCube is looking for originate from the most extreme environment in the cosmos,” says IceCube scientist Imre Bartos of Columbia University. “We don’t know what these environments are for sure, but we strongly suspect that they are related to black holes.”

    LIGO and IceCube are natural partners. Both gravitational waves and neutrinos travel for the most part unimpeded through space. Thus, they carry pure information about where they originate, and the two signals can be monitored together nearly in real time to help refine the calculated location of the source.

    The ability to do this is new, Bartos says. Neither gravitational waves nor high-energy neutrinos had been detected from the cosmos when he started working on IceCube in 2008. “During the past few years, both of them were discovered, putting the field on a whole new footing.”

    Shawhan and the LIGO collaboration are similarly optimistic about the future of their program and multi-messenger astronomy. More gravitational wave detectors are planned or under construction, including an upgrade to the European detector Virgo, the KAGRA detector in Japan, and a third LIGO detector in India, and that means scientists will home in closer and closer on their targets.​


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

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

    IndIGO LIGO in India

    IndIGO in India

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 8:50 am on April 4, 2017 Permalink | Reply
    Tags: , , , , , LIGO   

    From astrobites: “Observing across the gravitational wave spectrum” 

    Astrobites bloc

    Astrobites

    Apr 4, 2017
    Maria Charisi

    Title: The promise of multi-band gravitational wave astronomy after GW150914
    Author: Alberto Sesana
    First author’s institution: University of Birmingham, UK
    1
    Status: Published in Physical Review Letters (2016) [open access]

    A hundred years ago, Einstein published a new theory of gravity, the General Theory of Relativity. Massive objects, like the Sun, curve the geometry of the spacetime around them. The curvature of the spacetime then dictates the motion of other objects around them, e.g., the orbit of the Earth around the Sun. The theory predicts that when massive objects, like black holes (BHs) accelerate, they perturb the spacetime and produce gravitational waves, tiny ripples in spacetime that propagate outwards with the speed of light.

    However, it wasn’t until only a year ago that this prediction was directly confirmed. On September 14, 2015, the Laser Interferometer Gravitational-Wave Observatory (LIGO) detected gravitational waves (GWs) from two colliding black holes (also see Abbott et al. 2016 for the discovery paper).

    2
    Figure 1: The gravitational waveform as seen by the LIGO detector in Hanford, WA (red) and in Livingston, LA (blue). The illustration on the top shows the stages of the binary merger that correspond to the different parts of the waveform.



    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

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

    From the waveform shown in Figure 1, we can infer that the binary that produced GW150914 initially consisted of two black holes with masses about 36 and 29 times the mass of the sun, which merged to form a new black hole of 52 solar masses, releasing the remaining 3 solar masses in gravitational radiation. The masses of the black holes were surprisingly high, compared to most astronomers’ expectations (from observations of other BH systems in the galaxy, we expected binaries with BHs of about 10 solar masses), challenging our understanding of binary formation.

    This paper points out that massive binaries, like GW150914, produce strong gravitational radiation at earlier stages of their evolution, e.g., years before the merger, when the binary is at larger separations, orbiting at lower frequencies. They found that the low-frequency GWs could be detectable by the Laser Interferometer Space Antenna (LISA). LISA will be a space-based GW observatory sensitive in the milli-Hertz frequencies, which cannot be detected from the ground.

    3
    Figure 2: The gravitational wave amplitude for a distribution of binaries with masses similar to GW150914. Each line represents the final years of the evolution of each binary. The purple and orange line show the sensitivity of LISA and LIGO, respectively.

    ESA/eLISA

    If we could detect binary black holes long before they merge, we could learn a lot more about the merger and the sources themselves. First, the binary evolves in the LISA band for several years, as opposed to a few seconds in the LIGO band. This will allow us to constrain the parameters of the binary (e.g., the BH masses, distance, etc) to very high precision. Additionally, we will be able to predict the exact time of the merger within seconds and the location of the merger within about a square degree in the sky (for comparison GW150914 was localized within 100 deg^2). This huge improvement in localization, combined with the ability to predict the exact time of the merger, will greatly facilitate the searches for electromagnetic counterparts, i.e. electromagnetic radiation produced during the merger. The detection of light associated with GWs (or even the lack of counterparts to deep limits) will help us understand the environments, in which BH mergers occur. Last but not least, since LISA is still in the design phase, studies like this will inform the decisions on the technical characteristics of the instrument.

    This feat of science and engineering, decades in the making, opened a new window to observe the universe and signifies the beginning of a new exciting era in modern astronomy!

    See the full article here .

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    What do we do?

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

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

     
  • richardmitnick 7:34 am on May 20, 2015 Permalink | Reply
    Tags: , , , LIGO   

    From ANU: “New era of astronomy as gravitational wave hunt begins” 

    ANU Australian National University Bloc

    Australian National University

    19 May 2015
    Dr Phil Dooley

    1
    The ANU system is installed at LIGO. Image: LIGO

    Australian scientists are in the hunt for the last missing piece of Einstein’s General Theory of Relativity, gravitational waves, as the Advanced LIGO Project in the United States comes on line.

    LIGO
    LIGO

    LIGO (the Laser Interferometer Gravitational-wave Observatories) aims to find gravitational waves, ripples in the fabric of space and time caused by the most violent events in the universe such as supernovae or collisions between black holes.

    “We’ll find things we can’t imagine – gravitational waves are a completely different messenger from light,” said Professor David McClelland from The Australian National University (ANU), who leads the Australian LIGO team.

    “It’s like the moment when Galileo first turned a telescope towards the skies and started a new epoch of astronomy. Here we shall begin a whole new and fundamentally different way of observing the Universe.”

    Australia is a partner in Advanced LIGO with research groups from ANU and the University of Adelaide, supported by the Australian Research Council, directly contributing to its construction and commissioning.

    LIGO will ultimately be joined by detectors in Europe, Japan and India seeking evidence for gravitational waves, in the form of movements a fraction of the radius of a proton.

    “Advanced LIGO is easily the most sensitive detector ever created, at the limits of the Heisenberg Uncertainty Principle,” said Professor Jesper Munch, leader of the University of Adelaide research group.

    In his 1915 General Theory of Relativity, Einstein proposed that large masses such as stars cause curvature in space and time, which leads to gravity and also bends light.

    A number of observations in the past 100 years have confirmed other consequences of Einstein’s theory, but only in regions of weak gravity, said LIGO team member Professor Daniel Shaddock, from ANU Research School of Physics and Engineering (RSPE).

    “Gravitational waves are produced when massive objects accelerate or collide,” he said.

    “Finding gravitational waves would test our theories in a completely different scenario, where huge gravitational forces are at play. It is the ultimate test for General Relativity.”

    Gravitational waves have been proven to exist indirectly through the decay of the orbit of two neutron stars rotating around each other. However, Professor McClelland says direct detection of them is within our grasp.

    “By the end of the year there’s a chance that the 100-year search will be over,” he said.

    “Or, if we don’t see something in the next 12 to 24 months then we may have found either a problem with Einstein’s General Relativity or some new insight about the Universe,” he said.

    LIGO is an identical pair of laboratories in opposite corners of the United States. Each laboratory consists of two four-kilometre-long vacuum-pipes at right angles to each other, with mirrors suspended at either end. A laser beam is sent back and forth between the mirrors to form an interferometer.

    They were built by Caltech and MIT in the 1990s. However, they have only now the sensitivity levels required to detect gravitational waves with a tenfold improvement following a complete redesign and replacement of the detectors.

    A gravitational wave passing through the interferometer should momentarily move the mirrors at a frequency of about a kilohertz somewhere in the region of 10-19 of a meter (one ten-thousandth of the radius of a proton), which will be picked up by the laser system.

    The team at ANU have developed a system which locks the laser beam to the 40 kilogram mirrors to ensure that infinitesimal movements caused by a passing gravitational wave are identified, while other small movements are nullified.

    The University of Adelaide group has developed a system to correct for any deformation of the mirrors due to heat, a crucial factor with the stored laser power of the system approaching half a megawatt.

    “The technology required pushes the limit of all the components, including low noise detectors, high power lasers, quantum effects and technology such as optical polishing, coatings and vacuum systems,” said Professor Munch.

    “It is a crowning achievement in optical sensing as the world celebrates the International Year of Light in 2015.”

    See the full article here.

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    ANU is a world-leading university in Australia’s capital city, Canberra. Our location points to our unique history, ties to the Australian Government and special standing as a resource for the Australian people.

    Our focus on research as an asset, and an approach to education, ensures our graduates are in demand the world-over for their abilities to understand, and apply vision and creativity to addressing complex contemporary challenges.

     
  • richardmitnick 2:02 pm on March 30, 2015 Permalink | Reply
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    From Caltech: “New NSF-Funded Physics Frontiers Center Expands Hunt for Gravitational Waves” 

    Caltech Logo
    Caltech

    03/30/2015
    Kathy Svitil

    1
    Gravitational waves are ripples in space-time (represented by the green grid) produced by interacting supermassive black holes in distant galaxies. As these waves wash over the Milky Way, they cause minute yet measurable changes in the arrival times at Earth of the radio signals from pulsars, the Universe’s most stable natural clocks. These telltale changes can be detected by sensitive radio telescopes, like the Arecibo Observatory in Puerto Rico and the Green Bank Telescope in West Virginia. Credit: David Champion

    The search for gravitational waves—elusive ripples in the fabric of space-time predicted to arise from extremely energetic and large-scale cosmic events such as the collisions of neutron stars and black holes—has expanded, thanks to a $14.5-million, five-year award from the National Science Foundation for the creation and operation of a multi-institution Physics Frontiers Center (PFC) called the North American Nanohertz Observatory for Gravitational Waves (NANOGrav).

    The NANOGrav PFC will be directed by Xavier Siemens, a physicist at the University of Wisconsin–Milwaukee and the principal investigator for the project, and will fund the NANOGrav research activities of 55 scientists and students distributed across the 15-institution collaboration, including the work of four Caltech/JPL scientists—Senior Faculty Associate Curt Cutler; Visiting Associates Joseph Lazio and Michele Vallisneri; and Walid Majid, a visiting associate at Caltech and a JPL research scientist—as well as two new postdoctoral fellows at Caltech to be supported by the PFC funds. JPL is managed by Caltech for NASA.

    “Caltech has a long tradition of leadership in both the theoretical prediction of sources of gravitational waves and experimental searches for them,” says Sterl Phinney, professor of theoretical astrophysics and executive officer for astronomy in the Division of Physics, Mathematics and Astronomy. “This ranges from waves created during the inflation of the early universe, which have periods of billions of years; to waves from supermassive black hole binaries in the nuclei of galaxies, with periods of years; to a multitude of sources with periods of minutes to hours; to the final inspiraling of neutron stars and stellar mass black holes, which create gravitational waves with periods less than a tenth of a second.”

    The detection of the high-frequency gravitational waves created in this last set of events is a central goal of Advanced LIGO (the next-generation Laser Interferometry Gravitational-Wave Observatory), scheduled to begin operation later in 2015. LIGO and Advanced LIGO, funded by NSF, are comanaged by Caltech and MIT.

    “This new Physics Frontier Center is a significant boost to what has long been the dark horse in the exploration of the spectrum of gravitational waves: low-frequency gravitational waves,” Phinney says. These gravitational waves are predicted to have such a long wavelength—significantly larger than our solar system—that we cannot build a detector large enough to observe them. Fortunately, the universe itself has created its own detection tool, millisecond pulsars—the rapidly spinning, superdense remains of massive stars that have exploded as supernovas. These ultrastable stars appear to “tick” every time their beamed emissions sweep past Earth like a lighthouse beacon. Gravitational waves may be detected in the small but perceptible fluctuations—a few tens of nanoseconds over five or more years—they cause in the measured arrival times at Earth of radio pulses from these millisecond pulsars.

    NANOGrav makes use of the Arecibo Observatory in Puerto Rico and the National Radio Astronomy Observatory’s Green Bank Telescope (GBT), and will obtain other data from telescopes in Europe, Australia, and Canada. The team of researchers at Caltech will lead NANOGrav’s efforts to develop the approaches and algorithms for extracting the weak gravitational-wave signals from the minute changes in the arrival times of pulses from radio pulsars that are observed regularly by these instruments.

    Arecibo Observatory
    Arecibo Radio Observatory Telescope

    NRAO GBT
    NRAO/GBT

    See the full article here.

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  • richardmitnick 5:04 am on March 4, 2015 Permalink | Reply
    Tags: , , , LIGO,   

    From AAAS: “Physicists gear up to catch a gravitational wave” 

    AAAS

    AAAS

    3 March 2015
    Adrian Cho

    1
    The twin 4-kilometer arms of LIGO Livingston embrace a working forest, where logging generates vibrations that the instrument must damp out.

    This patch of woodland just north of Livingston, Louisiana, population 1893, isn’t the first place you’d go looking for a breakthrough in physics. Standing on a small overpass that crosses an odd arching tunnel, Joseph Giaime, a physicist at Louisiana State University (LSU), 55 kilometers west in Baton Rouge, gestures toward an expanse of spindly loblolly pine, parts of it freshly reduced to stumps and mud. “It’s a working forest,” he says, “so they come in here to harvest the logs.” On a quiet late fall morning, it seems like only a logger or perhaps a hunter would ever come here.

    Yet it is here that physicists may fulfill perhaps the most spectacular prediction of Albert Einstein’s theory of gravity, or general relativity. The tunnel runs east to west for 4 kilometers and meets a similar one running north to south in a nearby warehouselike building. The structures house the Laser Interferometer Gravitational-Wave Observatory (LIGO), an ultrasensitive instrument that may soon detect ripples in space and time set off when neutron stars or black holes merge.

    Einstein himself predicted the existence of such gravitational waves nearly a century ago. But only now is the quest to detect them coming to a culmination. The device in Livingston and its twin in Hanford, Washington, ran from 2002 to 2010 and saw nothing. But those Initial LIGO instruments aimed only to prove that the experiment was technologically feasible, physicists say. Now, they’re finishing a $205 million rebuild of the detectors, known as Advanced LIGO, which should make them 10 times more sensitive and, they say, virtually ensure a detection. “It’s as close to a guarantee as one gets in life,” says Peter Saulson, a physicist at Syracuse University in New York, who works on LIGO.

    Detecting those ripples would open a new window on the cosmos. But it won’t come easy. Each tunnel contains a pair of mirrors that form an “optical cavity,” within which infrared light bounces back and forth. To look for the stretching of space, physicists will compare the cavities’ lengths. But they’ll have to sense that motion through the din of other vibrations. Glancing at the pavement on the overpass, Giaime says that the ground constantly jiggles by about a millionth of a meter, shaken by seismic waves, the rumble of nearby trains, and other things. LIGO physicists have to shield the mirrors from such vibrations so that they can see the cavities stretch or shorten by distances 10 trillion times smaller—just a billionth the width of an atom.

    IN 1915, Einstein explained that gravity arises when mass and energy warp space and time, or spacetime. A year later, he predicted that massive objects undergoing the right kind of oscillating motion should emit ripples in spacetime—gravitational waves that zip along at light speed.

    For decades that prediction remained controversial, in part because the mathematics of general relativity is so complicated. Einstein himself at first made a technical error, says Rainer Weiss, a physicist at the Massachusetts Institute of Technology (MIT) in Cambridge. “Einstein had it right,” he says, “but then he [messed] up.” Some theorists argued that the waves were a mathematical artifact and shouldn’t actually exist. In 1936, Einstein himself briefly took that mistaken position.

    2
    Rainer Weiss of the Massachusetts Institute of Technology laid out the basic plan for LIGO 43 years ago. © MATT WEBER

    Even if the waves were real, detecting them seemed impossible, Weiss says. At a time when scientists knew nothing of the cosmos’s gravitational powerhouses—neutron stars and black holes—the only obvious source of waves was a pair of stars orbiting each other. Calculations showed that they would produce a signal too faint to be detected.

    By the 1950s, theorists were speculating about neutron stars and black holes, and they finally agreed that the waves should exist. In 1969, Joseph Weber, a physicist at the University of Maryland, College Park, even claimed to have discovered them. His setup included two massive aluminum cylinders 1.5 meters long and 0.6 meters wide, one of them in Illinois. A gravitational wave would stretch a bar and cause it to vibrate like a tuning fork, and electrical sensors would then detect the stretching. Weber saw signs of waves pinging the bars together. But other experimenters couldn’t reproduce Weber’s published results, and theorists argued that his claimed signals were implausibly strong.

    Still, Weber’s efforts triggered the development of LIGO. In 1969, Weiss, a laser expert, had been assigned to teach general relativity. “I knew bugger all about it,” he says. In particular, he couldn’t understand Weber’s method. So he devised his own optical method, identifying the relevant sources of noise. “I worked it out for myself, and I gave it to the students as a homework problem,” he says.

    Weiss’s idea, which he published in 1972 in an internal MIT publication, was slow to catch on. “It was obvious to me that this was pie in the sky and it would never work,” recalls Kip Thorne, a theorist at the California Institute of Technology (Caltech) in Pasadena, California. Thorne recorded his skepticism in Gravitation, the massive textbook that he co-wrote and published in 1973. “I had an exercise that said ‘Show that this technology will never work to detect gravitational waves,’ ” Thorne says.

    But by 1978 Thorne had warmed to the idea, and he persuaded Caltech to put up $2 million to build a 40-meter prototype interferometer. “It wasn’t a hard sell at all,” Thorne says, “which was a contrast to the situation at MIT.” Weiss says that Thorne played a vital role in winning support for a full-scale detector from the National Science Foundation in 1990. Construction in Livingston and Hanford finally began in 1994.

    Now, many physicists say Advanced LIGO is all but a sure winner. On a bright Monday morning in December, researchers at Livingston are embarking on a 10-day stint that will mark their first attempt to run as if making observations. LIGO Livingston has the feel of an outpost. Roughly 30 physicists, engineers, technicians, and operators gather in the large room that serves as the facility’s foyer, auditorium, and—with a table-tennis table in one corner—rec room. “Engineering run 6 began 8 minutes ago,” announces Janeen Romie, an engineer from Caltech. It seems odd that so few people can run such a big rig.

    But in principle, LIGO is simple. Within the interferometer’s sewer pipe–like vacuum chamber, at the elbow of the device, a laser beam shines on a beam splitter, which sends half the light down each of the interferometer’s arms. Within each arm, the light builds up as it bounces between the mirrors at either end. Some of the light leaks through the mirrors at the near ends of the arms and shines back on the beam splitter. If the two arms are exactly the same length, the merging waves will overlap and interfere with each other in a way that directs the light back toward the laser.

    The ultimate motion sensor

    3
    In a LIGO interferometer, light waves leaking out of the two storage arms ordinarily interfere to send light back to the laser. By stretching the two arms by different amounts, a gravitational wave would alter the interference and send light toward a photodetector. G. GRULLÓN/SCIENCE

    But if the lengths are slightly different, then the recombining waves will be out of sync and light will emerge from the beam splitter perpendicular to the original beam. From that “dark port” output, physicists can measure any difference in the arms’ lengths to an iota of the light’s wavelength. Because a gravitational wave sweeping across the apparatus would generally stretch one arm more than the other, it would cause light to warble out of the dark port at the frequency at which the wave ripples. That light would be the signal of the gravitational wave.

    In practice, LIGO is a monumental challenge in sifting an infinitesimal signal from a mountain of vibrational noise. Sources of gravitational waves should “sing” at frequencies ranging from 10 to 1000 cycles per second, or hertz. But at frequencies of hundreds or thousands of hertz the individual photons in the laser beam produce noise as they jostle the mirrors. To smooth out such noise, researchers crank up the amount of light and deploy massive mirrors. At frequencies of tens of hertz and lower, seismic vibrations dominate, so researchers dangle the mirrors from elaborate suspension systems and actively counteract that motion. Still, a large earthquake anywhere in the world or even the surf pounding the distant coast can knock the interferometer off line.

    To boost the Hanford and Livingston detectors’ sensitivity 10-fold, to a ten-billionth of a nanometer, physicists have completely rebuilt the devices. Each of the original 22-kilogram mirrors hung like a pendulum from a single steel fiber; the new 40-kilogram mirrors hang on silica fibers at the end of a four-pendulum chain. Instead of LIGO’s original 10 kilowatts of light power, researchers aim to circulate 750 kilowatts. They will collect 100,000 channels of data to monitor the interferometer. Comparing the new and old LIGO is “like comparing a car to a wheel,” says Frederick Raab, a Caltech physicist who leads the Hanford site.

    The new Livingston machine has already doubled Initial LIGO’s sensitivity. “In 6 months they’ve made equivalent progress to what Initial LIGO made in 3 or 4 years,” says Raab, who adds that the Hanford site is about 6 months behind. But Valery Frolov, a Caltech physicist in charge of commissioning the Livingston detector, cautions that machine isn’t running anywhere close to specs. The seismic isolation was supposed to be better, he says, and researchers haven’t been able to keep the interferometer “locked” and running for long periods. As for reaching design sensitivity, “I don’t know whether it will take 1 year or whether it will take 5 years like Initial LIGO did,” he warns.

    Still, LIGO researchers plan to make a first observing run this year and hope to reach design sensitivity next year. “We will have detections that we will be able to stand up and defend, if not in 2016, then in 2017 or 2018,” says Gabriela González, a physicist at LSU and spokesperson for the more than 900-member LIGO Science Collaboration.

    That forecast is based on the statistics of the stars. LIGO’s prime target is the waves generated by a pair of neutron stars—the cores of exploded stars that weigh more than the sun but measure tens of kilometers across—whirling into each other in a death spiral lasting several minutes. Initial LIGO could sense such a pair up to 50 million light-years way. Given the rarity of neutron-star pairs, that search volume was too small to guarantee seeing one. Advanced LIGO should see 10 times as far and probe 1000 times as much space, enough to contain about 10 sources per year, González says. However, Clifford Will, a theorist at the University of Florida in Gainesville, notes that the number of sources is the most uncertain part of the experiment. “If it’s less than one per year, that’s not going to be too good,” he says.

    Enlarging the search

    4
    Compared with Initial LIGO, Advanced LIGO will be able to detect gravitational wave sources up to 10 times as far away, probing 1000 times as much space. Such a volume will likely yield multiple sources. ADAPTED FROM NSF BY G. GRULLÓN/SCIENCE

    The hunt will be global. As well as combining data from the two LIGO detectors, researchers will share data with their peers working on the VIRGO detector, an interferometer with 3-kilometer arms near Pisa, Italy, that is undergoing upgrades, and on GEO600, one with 600-meter arms near Hannover, Germany.

    VIRGO interferometer EGO
    VIRGO interferometer EGO Campus
    VIRGO

    GEO600
    GEO600

    By comparing data, collaborators can better sift signals from noise and can pinpoint sources on the sky. Japanese researchers are also building a detector, and LIGO leaders hope to add a third detector, in India.

    FOR THEORISTS—if not for the rest of the world—seeing gravitational waves for the first time will be something of an anti-climax. “We are so confident that gravitational waves exist that we don’t actually need to see one,” says Marc Kamionkowski, a theorist at Johns Hopkins University in Baltimore, Maryland. That’s because in 1974 American astrophysicists Russell Hulse and Joseph Taylor Jr. found indirect but convincing evidence of the waves. They spotted two pulsars—neutron stars that emit radio signals with clockwork regularity—orbiting each other. From the timing of the radio pulses, Hulse and Taylor could monitor the pulsars’ orbit. They found it is decaying at exactly the rate expected if the pulsars were radiating energy in the form of gravitational waves.

    LIGO’s real payoff will come in opening a new frontier in astronomy, says Robert Wald, a gravitational theorist at the University of Chicago in Illinois. “It’s kind of like after being able to see for a while, being able to hear, too,” Wald says. For example, if a black hole tears apart a neutron star, then details of the gravitational waves may reveal the properties of matter in neutron stars.

    All told, detecting gravitational waves would merit science’s highest accolade, physicists say. “As soon as they detect a gravitational wave, it’s a Nobel Prize,” Kamionkowski predicts. “It’s such an extraordinary experimental accomplishment.” But the prize can be shared by at most three people, so the question is who should get it.

    Weiss is a shoo-in, many say, but he demurs. “I don’t want to deny that there was some innovation [in my work], but it didn’t come out of the blue,” he says. “The lone crazy man working in a box, that just doesn’t hold true.” In 1962 two Russian physicists published a paper on detecting gravitational waves with an interferometer, as Weiss says he learned long after his 1972 work. In the 1970s, Robert Forward of the Hughes Aircraft Company in Malibu, California, ran a small interferometer. Key design elements of LIGO came from Ronald Drever, project director at Caltech from 1979 to 1987, who, Thorne says, “has to be recognized as one of the fathers of the LIGO idea.”

    But to make that prize-winning discovery, physicists must get Advanced LIGO up and running. At 8 a.m. on Tuesday morning, LIGO operator Gary Traylor comes off the night shift. “Last night was a total washout,” he says in his soft Southern accent, swiveling in a chair in the brightly lit control room. “There’s a low pressure area moving over the Atlantic that’s causing 20-foot waves to crash into the coast,” Traylor says, and that distant drumming overwhelmed the detector. So in the small hours, LIGO did sense waves. But not the ones everybody is hoping to see.

    See the full article here.

    The American Association for the Advancement of Science is an international non-profit organization dedicated to advancing science for the benefit of all people.

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  • richardmitnick 1:38 pm on October 3, 2014 Permalink | Reply
    Tags: , , , , LIGO, ,   

    From Symmetry: “To catch a gravitational wave” 

    Symmetry

    October 03, 2014
    Jessica Orwig

    Advanced LIGO, designed to detect gravitational waves, will eventually be 1000 times more powerful than its predecessor.

    Thirty years ago, a professor and a student with access to a radiotelescope in Puerto Rico made the first discovery of a binary pulsar: a cosmic dance between a pair of small, dense, rapidly rotating neutron stars, called pulsars, in orbit around one another.

    Scientists noticed that their do-si-do was gradually speeding up, which served as indirect evidence for a phenomenon predicted by Albert Einstein called gravitational waves.

    Today in Livingston, Louisiana, and Hanford, Washington, scientists are preparing the next stage of a pair of experiments that they hope will detect gravitational waves directly within the next five years. They’re called the Laser Interferometer Gravitational-Wave Observatory, or LIGO.

    Distorting the fabric of spacetime

    Gravitational waves are faint ripples in the fabric of spacetime thought to propagate throughout the universe. According to the theory of general relativity, objects with mass—and therefore gravitational pull—should emit these waves whenever they accelerate. Scientists think the stars in the binary pulsar that Russell Hulse and Joseph Taylor discovered in 1974 are being pulled closer and closer together because they are losing miniscule amounts of energy each year through the emission of gravitational waves.

    If a gravitational wave from a binary pulsar passes through Livingston or Hanford, the LIGO experiments will be waiting. In summer 2015, scientists will begin collecting data with Advanced LIGO, the next stage of LIGO, with more powerful lasers and attuned sensors. Advanced LIGO will by 2020 become 1000 times more likely than its predecessor to detect gravitational waves.

    “We’ll be able to see well beyond the local group, up to 300 megaparsecs away, which includes thousands of galaxies,” says Mario Diaz, a professor at the University of Texas at Brownsville and director of the Center for Gravitational Wave Astronomy. ”That’s the reason why pretty much everyone agrees if gravitational waves exist then Advanced LIGO has to see them.”

    Eventually joining LIGO in its attempt to catch a gravitational wave will be the VIRGO Interferometer at the European Gravitational Observatory in Italy and the Kamioka Gravitational Wave Detector at the Kamioka Mine in Japan. VIRGO started its search in 2007 and is currently undergoing upgrades. KAGRA is expected to begin operations in 2018. By the time KAGRA comes online, all three instruments should have similar levels of sensitivity.

    Advanced LIGO

    LIGO is made up of two identical laser interferometers, one in Louisiana and the other in Washington.

    ligo
    Courtesy of LIGO Laboratory

    At a laser interferometer, scientists take a single, powerful laser beam and split it in two. The two beams then travel down two equally long tunnels. At the end of each tunnel, each beam hits a mirror and reflects back.

    The tunnels are perpendicular to one another, creating a giant “L.” Because of this, the reflected beams return to the same spot and cancel each other out. That is, unless a gravitational wave intervenes.

    inter
    The light path through a Michelson interferometer. The two light rays with a common source combine at the half-silvered mirror to reach the detector. They may either interfere constructively (strengthening in intensity) if their light waves arrive in phase, or interfere destructively (weakening in intensity) if they arrive out of phase, depending on the exact distances between the three mirrors.

    If a gravitational wave passes through, it will distort the fabric of spacetime in which the observatory sits. This will warp the physical distance between the mirrors, giving one of the laser beams the advantage in reaching its final destination first. Because the beams will not cancel one another out, they will produce a signal in the detector.

    Advanced LIGO isn’t any bigger than LIGO, says Fred Raab of Caltech, head of the LIGO Hanford Observatory. Scientists are transforming the experiment from the inside. “That was part of the strategy for building LIGO… it’s the upgrades to technology that really counts.”

    The impressive part, says Gabriela Gonzalez, LIGO spokesperson and professor at Louisiana State University, is the miniscule size of the change in distance and the technology’s capability to detect it.

    “The [tunnels] are 4 kilometers long, and we have sensitivities to about 10-18 meters,” Gonzalez says. “We can tell how 4 kilometers one way differs from 4 kilometers the other way by a change that is a thousandth the size of a proton diameter.”

    Scientists built two identical machines 1865 miles apart because the wavelength of the gravitational waves they’re looking for should be about that long; if they measure the same signal in both detectors simultaneously, it will be a good indication that the signature is genuine.

    One of the new features of Advanced LIGO will be an additional mirror that will enable scientists to enhance sensitivity to different frequencies of gravitational waves. With different frequencies come different levels of spacetime distortion and hence different changes in the distance between the two mirrors. The different signals will tell scientists something about the properties of gravitational waves and their sources.

    “The extra mirror allows us to apply a boost in sensitivity to a smaller range of frequencies in the search band,” Raab says. “It works kind of like the treble/bass adjustment in your car stereo. You still hear the music, but with different frequencies enhanced.”

    Straight to the source

    Scientists at Advanced LIGO would like to identify the sources of gravitational waves.

    They most likely come from binary neutron stars like the one Hulse and Taylor discovered. But they could also originate in systems that right now exist only in theory, such as black hole binaries and neutron star-black hole binary systems.

    Christopher Berry, a research fellow at the University of Birmingham, is part of a team that is designing a way to quickly estimate where in the sky the source of a gravitational wave might originate in order to share that information with astronomers around the world, who could take a closer look.

    “You can analyze the data to determine quantities like mass, orientation and location,” he says. “One of the things we want to do with parameter estimation is quickly estimate where in the sky a source came from and then tell people with telescopes to point there.”

    Gravitational waves could also come from the same systems that produce gamma-ray bursts, the brightest known electromagnetic events in the universe. Scientists think that gamma-ray bursts may come from merging binary neutron stars, a hypothesis LIGO could investigate.

    Determining a link between gamma-ray bursts and binary neutron stars would be one outstanding achievement for Advanced LIGO, but the future observatory has potential for more, Berry says.

    “We can see inside the sun using neutrinos, and gravitational waves are yet another way to look at the universe,” he says. “We can make discoveries we weren’t expecting.”

    See the full article here.

    Symmetry is a joint Fermilab/SLAC publication.


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