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  • richardmitnick 11:26 am on May 17, 2017 Permalink | Reply
    Tags: , , , , , , , Maura McLaughlin, NANOGrave, , ,   

    From Physics: Women in STEM – “Q and A: Catching a Gravitational Wave with a Pulsar’s Beam” Maura McLaughlin 

    Physics LogoAbout Physics

    Physics Logo 2


    May 12, 2017
    Katherine Wright

    Maura McLaughlin explains how the electromagnetic signals from fast-spinning neutron stars could be used to detect gravitational waves.

    Maura McLaughlin. Greg Ellis/West Virginia University

    Pulsars captivate Maura McLaughlin, a professor at West Virginia University. These highly magnetized neutron stars flash beams of electromagnetic radiation as they spin. And with masses equivalent to that of the Sun, but diameters seventy thousand times smaller, they are—besides black holes—the densest objects in the Universe. Astrophysicists still have many questions about pulsars, ranging from how they emit electromagnetic radiation to why they are so incredibly dense. But it’s exploiting the highly stable, periodic electromagnetic signals of pulsars to study gravitational waves that currently has McLaughlin hooked. In an interview with Physics, she explained where her fascination with pulsars came from, what gravitational-wave sources she hopes to detect, and why she recently visited Washington, D.C., to talk with members of Congress.

    With the 2015 detection of gravitational waves, it’s obviously an exciting time to work in astrophysics. But what initially drew you to the field and to pulsars?

    The astrophysicist Alex Wolszczan. I met him in the early 90s while I was an undergrad at Penn State, and just after he had discovered the first extrasolar planets. These planets were orbiting a pulsar—lots of people don’t know that. I found this pulsar system fascinating and ended up working with Wolszczan one summer as a research assistant. I got to go to Puerto Rico to observe pulsars at the Arecibo Observatory, which is the biggest telescope in the world. The experience was really cool.
    How do researchers detect gravitational waves with pulsars?

    The collaboration that I’m part of—NANOGrav—is searching for changes in the travel time of the pulsar’s radio emission due to the passing of gravitational waves.


    NANOGrave Gravitational waves JPL-Caltech David Champion

    When a gravitational wave passes between us and the pulsar, it stretches and squeezes spacetime, causing the pulse to arrive a bit earlier or later than it would in the absence of the wave. We time the arrival of pulsar signals for years to try to detect these small changes.
    What gravitational-wave-producing events do you expect to detect with pulsars? Could you see the same events as LIGO did?

    LIGO is sensitive to very short time-scale gravitational waves, on the order of milliseconds to seconds, while our experiment is sensitive to very long time-scale gravitational waves, on the order of years. We could never detect gravitational waves from two stellar-mass black holes merging—the time scale of the event is just too short. But we will be able to detect waves from black hole binaries in their inspiralling stage, when they’re still orbiting each other with periods of years. Also, our approach can only detect black holes that are much more massive that those LIGO observed. Our primary targets are supermassive black holes, even more massive than the one at the core of the Milky Way.

    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 is basically probing the evolution and end products of stars, whereas our experiment is probing the evolution of galaxies and the cosmos. We’ll be able to look way back in time at the processes by which galaxies formed through mergers.
    The first detection of gravitational waves was front-page news. What impact has it had on your research?

    I, and others in NANOGrav, got lots of condolences after LIGO’s detection, like “oh we’re sorry you weren’t first.” But it’s been good for us. It has really spurred us on to make a detection. And it has made us more optimistic—if it worked for LIGO it should work for us, as our methods are rooted in the same principles. None of us doubted gravitational waves existed, but as far as funding agencies and the public go, LIGO’s detection makes a big difference. Now people can’t say, “Who knows if these things exist?” or “Who knows if these methods work?” LIGO’s detection has shown they do exist and the methods do work.

    Apart from doubters, what other challenges do you face with your pulsar experiment?

    Right now, our most significant challenge is that our radio telescopes are in danger of being shut down. Both Arecibo and the Green Bank Telescope (GBT) in West Virginia are suffering significant funding cuts.

    NAIC/Arecibo Observatory, Puerto Rico, USA

    GBO radio telescope, Green Bank, West Virginia, USA

    Many of our NANOGrav discussions lately are about what we can do to retain access to these telescopes. Losing one of these telescopes would reduce our experiment’s sensitivity by roughly half and increase the time to detection by at least several years. If we lose both, our project is dead in the water. Arecibo and GBT are currently the two most sensitive radio telescopes in the world . I think its crazy that they are possibly being shut down.

    [Do not forget FAST-China]

    FAST radio telescope, now operating, located in the Dawodang depression in Pingtang county Guizhou Province, South China

    What are you doing to address the problem?

    I recently spent two days on Capitol Hill in Washington, D.C., talking to senators and House representatives trying to make the case to keep GBT open. Most of the politicians actually agreed it should stay open; it’s just a matter of funding. Science in general just doesn’t have enough funding.

    How do you frame the issues when talking to politicians about science?

    I try really hard to stress the opportunities for training students, the infrastructure, and the number of people who work at these telescopes. The technologies developed at the facilities are cutting edge and can be used for more than studying space. The science is incredibly interesting, but that in itself doesn’t always appeal to everybody.

    With the current administration, arguments of US prominence are also really valuable. China [has built ans is operating] a bigger telescope than Arecibo, and soon we won’t have the largest radio telescope in the world. Right now we are world leaders, but if the US wants to keeps its dominance then these telescopes have to remain open.

    With the challenges you face, what would you say to someone thinking of joining this field?

    Despite uncertainties with the telescopes, the future is bright. Now is a really good time to join the field: we’re going to make a detection any day now.

    See the full article here .

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  • richardmitnick 6:12 pm on March 7, 2017 Permalink | Reply
    Tags: , , , , NANOGrave,   

    From APS: “Gravitational Waves: Hints, Allegations, and Things Left Unsaid” 


    American Physical Society

    APS April Meeting 2017

    If the APS April Meeting 2016 was a champagne-soaked celebration for gravitational wave scientists, the 2017 meeting was more like spring training — there was lots of potential, but the real action is yet to come.

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

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

    The Laser Interferometer Gravitational-Wave Observatory, or LIGO, launched the era of gravitational wave astronomy in February 2016 with the announcement of a collision between two black holes observed in September 2015. “I’m contractually obligated to show the slide [of the original detection] at any LIGO talk for at least another year,” joked Jocelyn Read, a physicist at California State University, Fullerton, during her presentation at this year’s meeting.

    The scientific collaboration that operates the two LIGO detectors netted a second merger between slightly smaller black holes on December 26, 2015. (A third “trigger” showed up in LIGO data on October 12, 2015, but ultimately did not meet the stringent “five-sigma” statistical significance standard that physicists generally insist on.)

    The detectors then went offline in January 2016 for repairs and upgrades. The second observing run began on November 30, but due to weather-related shutdowns and other logistical hurdles, the two detectors had operated simultaneously on only 12 days as of this year’s meeting, which limited the experiment’s statistical power. Collaboration members said they had no new detections to announce.

    Instead, scientists focused on sharpening theoretical estimates of how often various events occur. In particular, they are eager to see collisions involving neutron stars, which lack sufficient mass to collapse all the way to a black hole. Neutron star collisions are thought to be plentiful, but would emit weaker gravitational waves than do mergers of more massive black holes, so the volume of space the LIGO detectors can scan for such events is smaller.

    Even with recent upgrades, failure to detect a neutron star merger during the current observing run would not rule out existing models, said Read. But she added that with future improvements and the long-anticipated addition of Virgo, a LIGO-like detector based in Cascina, Italy, neutron stars should soon come out of hiding.

    VIRGO Gravitational Wave interferometer, near Pisa, Italy [Not yet operational]

    “We’re expecting that with a little more volume and a little more time, we’re going to be starting to make some astrophysically interesting statements.”

    LIGO scientists are also looking for signals from individual pulsars — rapidly rotating neutron stars that are observed on earth as pulses of radio waves. A bump on a pulsar’s surface should produce gravitational waves, but so far, no waves with the right shape have been picked up. This absence puts a limit on the size of any irregularities and on the emission power of gravitational waves from nearby pulsars such as the Crab and Vela pulsars, said Michael Landry, head of the Hanford LIGO observatory, and could soon start putting limits on more distant ones.

    Presenters dropped a few hints of possible excitement to come. LIGO data taken through the end of January produced two short signals that were unusual enough to exceed the experiment’s “false alarm” threshold — signals with shapes and strengths expected to show up once a month or less by chance alone. Both LIGO collaboration members and astronomers at conventional telescopes are investigating the data to determine whether they represent real events.

    For now, potential events will continue to be scrutinized by collaboration members, and released to the public via announcements coming months after initial detection. But LIGO leaders expect to shorten the lag time as detections become more frequent, perhaps eventually putting out monthly updates. “We hope to make it quicker,” said LIGO collaboration spokesperson Gabriela González, a physicist at Louisiana State University in Baton Rouge.

    LIGO is not the only means by which scientists are searching for gravitational waves. Some scientists are using powerful radio telescopes to track signals emanating from dozens of extremely fast-rotating pulsars. A specific pattern of correlations between tiny hiccups in the arrival times of these pulses would be a signature of long-wavelength gravitational waves expected from mergers of distant supermassive black holes.

    Teams in the U.S., Europe, and Australia have monitored pulsars for more than a decade, so far without positive results. But in an invited talk, Laura Sampson of Northwestern University in Evanston, Illinois, coyly announced “hints of some interesting signals.” With 11 years of timing data from 18 pulsars tracked by the Green Bank Telescope in West Virginia and the Arecibo Telescope in Puerto Rico, Sampson and other scientists affiliated with a collaboration called NANOGrav have eked out a result with a statistical significance of around 1.5 to 2 sigma.

    GBO radio telescope, Green Bank, West Virginia, USA

    NAIC/Arecibo Observatory, Puerto Rico, USA

    Data from the Green Bank Telescope in West Virginia and Arecibo Telescope in Puerto Rico help researchers use pulsars to study gravitational waves.

    “It’s the first hint we’ve ever had that there might be a signal in the data,” Sampson said. “Everything we’ve done before was straight-up limits.”

    As NANOGrav continues to gather data, their signal could grow toward the 5-sigma gold standard, or it could vanish. Sampson and her colleagues hope to have an answer in the next year or two. “This is of course very exciting news,” said Gonzalez.

    See the full article here .

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    Physicists are drowning in a flood of research papers in their own fields and coping with an even larger deluge in other areas of physics. How can an active researcher stay informed about the most important developments in physics? Physics highlights a selection of papers from the Physical Review journals. In consultation with expert scientists, the editors choose these papers for their importance and/or intrinsic interest. To highlight these papers, Physics features three kinds of articles: Viewpoints are commentaries written by active researchers, who are asked to explain the results to physicists in other subfields. Focus stories are written by professional science writers in a journalistic style and are intended to be accessible to students and non-experts. Synopses are brief editor-written summaries.

  • richardmitnick 8:06 am on July 21, 2016 Permalink | Reply
    Tags: , , European Pulsar Timing Array, , International Pulsar Timing Array, NANOGrave   

    From Nautilus: “The Hidden Science of the Missing Gravitational Waves” 



    July 21, 2016
    By Sarah Scoles

    Illustration by Francesco Izzo

    A relatively unknown experiment is already drawing conclusions from the sound of silence.

    Space should be churned up like a speedboat-filled lake, crisscrossed by gravitational waves rushing at the speed of light in every direction. That’s because any kind of acceleration, of any kind of mass, will produce a gravitational wave. When you whoosh your arm through the air, you are launching a gravitational wave that will travel forever. The Earth produces gravitational waves as it orbits the sun. So do black holes that twirl around or crash into each other.

    Every accelerating mass produces a signal, and all those signals should add together into a detectable background.

    So where is it? Scientists have been trying to tune in to the staticky drone of gravitational wave background noise for years. An experiment that uses the timing of distant pulsars has been running for over a decade, searching for the portion of the background due to pairs of supermassive black holes. But they haven’t heard a peep.

    The Telescope Range: Austie Helm musters a flock of sheep under the Parkes Radio Telescope in New South Wales. The land for the telescope was bought from Helm. David Moore / CSIRO Archives

    Then, early this year, the Laser Interferometer Gravitational-Wave Observatory (LIGO) achieved a positive detection of a single gravitational wave event, resulting from the merger of lighter, stellar-mass black holes.

    LSC LIGO Scientific Collaboration
    Caltech/MIT Advanced aLigo Hanford, WA, USA installation
    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

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

    The more subtle mission of the pulsar timing experiments and their search for background seemed to get drowned out. They have, after all, produced a null result.

    But sometimes silence speaks volumes.

    Gravitational waves come in different frequencies, just like light waves. Their frequency is based on their motion—objects in a year-long orbit, no matter their mass, will make waves with the same frequency (though lighter objects will produce a lower-amplitude wave).

    Some gravitational-wave sources are strong and close enough that scientists can pick up individual events, like the 200-hertz-frequency “chirp” they detected at LIGO this February, which happened when two black holes around 30 times the mass of the sun merged into one. Others are distant and hard to resolve individually—like close-orbiting, destined-to-merge pairs of supermassive black holes, which can be billions of times bigger than the sun and are often billions of light-years away. These latter, in aggregate, should create a constant background at a much lower frequency than what LIGO can pick up.

    It was in the summer of 1967 that astronomer Jocelyn Bell first saw the signal that would give scientists the tools they needed to listen in on this background. She had been hunting for distant galaxies with a radio telescope, when a spike rose above the baseline noise in her data, a pulse of radio waves that reappeared every 1.3 seconds. It looked like a steady heartbeat on an EKG. She was mystified by the regular blip-blip-blip of it. The only objects she knew that could produce such fast, reliable signals were synthetic. She and her advisor, Anthony Hewish, half-jokingly suggested they were looking at a message from aliens, and dubbed the source of the radio waves LGM-1 for “Little Green Man 1.”

    Soon, though, astronomers discovered that the signal was coming from something almost as bizarre as aliens—a neutron star, a city-sized star made mostly of crushed-close neutrons that is the remnant left behind after a supernova. Around the time that Bell found her strange signal, two astronomers—Franco Pacini and Thomas Gold—noted that a spinning neutron star surrounded by a magnetic field could emit radiation (although, to this day, scientists cannot explain all the details of why). Gold connected this to Bell’s discovery, explaining how the spin could periodically point a beam of radiation at Earth, making a pulse blip across our telescopes.

    Neutron stars can spin around hundreds of times per second, sweeping their beams across space as they do. If these beams happen to be aligned with the Earth, they would briefly illuminate our planet like a distant lighthouse. When Hewish found a second pulsing source in 1968, the connection was confirmed: It was located in the middle of the Crab Nebula, which is gas left over from a supernova explosion.

    Pulsar clocks are extremely reliable. Because they are so dense, so spherical, and have so much spin momentum, almost nothing can change their rotation rate. The timing of their lighthouse sweep is remarkably constant, earning them the moniker “nature’s best clocks.” The most precise ones—which are also the fastest, called millisecond pulsars—slow their spins by just a few picoseconds per year. By comparison, the most precise atomic clock ever created loses about 66 picoseconds a year.

    By 1979, astronomers had realized that they—or, really, someone else in the future with better telescopes—could use these strange, ultra-precise clocks to detect gravitational waves. Steven Detweiler of the University of Florida in Gainesville and Mikhail Vasilievich Sazhin of Moscow State University independently discovered that if a gravitational wave passed over a pulsar, or the Earth, the time at which the pulsar’s emissions arrived at the Earth would change. Astronomers wouldn’t get the tick-tick-tick at the hyper-regular intervals they expected.

    “If a gravitational wave passes through the pulsar, it changes the effective distance to that pulsar, rocking it back and forth,” says Maura McLaughlin of West Virginia University in Morgantown, and the former chair of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). That changes how far the emissions have to travel and when they arrive at our planet. The same thing happens if a wave passes through the Earth.

    For a tens of billions of solar masses pair of supermassive black holes hundreds of millions of light-years away, a millisecond pulsar’s pulse arrival time would change by microseconds. But most such binaries are expected to be farther away and less massive, and the skew would be just tens of nanoseconds or smaller. In Detweiler and Sahzin’s time, telescope instruments could not take and dump data that fast; computers could not store and process the terabyte-level output; and no one had yet discovered any millisecond pulsars. They needed something else.

    Sentinels: The Hellings-Down Curve is the characteristic pattern expected from two distant pulsars in the presence of a stochastic gravitational wave background.Reproduced from Am. J. Phys. 83, 635 (2015), with the permission of the American Association of Physics Teachers.

    In 1982, Ronald Hellings of the Jet Propulsion Laboratory and George Downs of the California Institute of Technology, both in Pasadena, made a breakthrough: They suggested scientists look at lots of pulsars at once, and use their collective late-and-early arrivals to detect the whole noisy gravitational-wave background at once—not individual disturbances. They modeled how that staticky background, buzzing across the universe, would show up in the blips of a bunch of pulsars, which scientists later called a “pulsar timing array.”

    Try picturing it, suggests Chiara Mingarelli of the California Institute of Technology in Pasadena. “You can imagine a gravitational-wave background as being like the surface of the ocean,” she says. “And we’re on the Earth on a boat, and we’re bobbing up and down in this gravitational-wave sea.”

    So are the pulsars, but their bobbing in the sea looks like pure noise, says McLaughlin, “because they are all happening at different times and are hence uncorrelated.”

    But the bobbing from Earth, while it’s noisy, has some structure. That structure is what Hellings and Downs mapped out. When gravitational waves make the Earth bob, they change the arrivals of flashes from all pulsars at the same time. Gravitational waves squeeze in one direction, compressing spacetime, while stretching in the other, expanding it. Imagine that along a north-south line, space condenses. At the same time, east-west expands. Two pulsars in the northern direction of our sky would show similar speedups in the timing of their blips, and two pulsars in an eastern direction would have similar slowdowns.

    Hellings and Downs laid out how these late and early arrivals should match up with pulsars spread across the sky. Using their predicted signature and a passel of pulsars, the scientists were able to gain sensitivity over looking at single pulsars. The Hellings-Downs Curve, as the signature signal is now called, is still what astronomers look for today. At the time that Hellings and Downs did their work, though, the technology wasn’t good enough, and astronomers had not discovered any ultra-precise millisecond pulsars. “There was no way,” says McLaughlin. They would need to bury their technique into a time capsule for the future to find.

    But they also realized the potential for new science. No one was close to a direct detection of gravitational waves, and LIGO wouldn’t receive its first funding for 12 more years. Pulsar astronomers had a shot at being the first to prove beyond doubt that gravitational waves exist. And on top of that, they could use those gravitational waves to learn about how the universe came to be the way it is. They knew how to be sensitive to the signal, and they knew computers would catch up to the processing speeds the project needed.

    Throughout the ’80s and ’90s, people continued work on the gravitational-wave background—in the background. “But they hadn’t really been giving it all they had because we weren’t at the level where we could really expect to make a detection,” says McLaughlin.

    But as the years passed, telescope instruments gained more processing power. New pulsars piled up. While astronomers knew of just four millisecond pulsars in the 1980s, they found 31 more in the 1990s, and 65 more between 2000 and 2010. They have discovered 150 since then, bringing the total to 250.

    In 2005, Dick Manchester of Australia Telescope National Facility decided it was time to act. He and his colleagues founded the first pulsar search for background gravitational waves: the Parkes Pulsar Timing Array. Using the pastorally located 209-foot Parkes Telescope in New South Wales, which often has sheep meandering beneath its dish, the team began its search. They collected blip after blip from 20 of the most precise pulsars, watching them like airport departure/arrival screens, searching for the Hellings-Downs Curve.

    Farther north, astronomers formed the European Pulsar Timing Array later the same year, catching pulsar radio waves with five different telescopes in Effelsberg, Germany; Cheshire, England; Nançay, France; Pranu Sanguni, Italy; and Westerbork, the Netherlands. Each measures 210 to 330 feet across, and they are still running today, keeping time with 18 high-precision pulsars. Because only 24 hours exist in a day, and most telescopes aren’t all-pulsars-all-the-time, having more telescopes involved allows astronomers to spread more observations across instruments.


    MPIFR/Effelsberg Radio Telescope, Germany
    MPIFR/Effelsberg Radio Telescope, Germany

    Nançay  decametric radio telescope Nançay France
    Nançay decametric radio telescope Nançay France

    Westerbork Synthesis Radio Telescope, Netherlands
    Westerbork Synthesis Radio Telescope, Netherlands

    In the United States, pulsar astronomers were behind, but they had a secret weapon. For telescopes, bigger is better. And like American sodas, American telescopes outweighed the competition. U.S. astronomers had access to the Arecibo Telescope in Puerto Rico, which measures 1,000 feet across, and the Green Bank Telescope [GBT]in West Virginia, which is 328 feet wide, compared to Europe’s 330-footers and Australia’s single 209-foot dish.

    NAIC/Arecibo Observatory, Puerto Rico, USA
    NAIC/Arecibo Observatory, Puerto Rico, USA

    NRAO/GBT radio telescope, West Virginia, USA
    GBT radio telescope, West Virginia, USA

    Fred Lo, the director of the National Radio Astronomy Observatory, which operates the Green Bank Telescope, wanted to take advantage of that size difference. In 2008, he called together a group of prominent pulsar scientists who worked at or used his observatory, like McLaughlin, Duncan Lorimer of West Virginia University, and observatory scientist Scott Ransom. Each scientist was working on his or her individual projects, chipping away on their own favorite pulsars. He connected them, telling them to get their act together and start collaborating, and join the hunt for the gravitational-wave background.

    “At that time we picked an acronym,” McLaughlin continues. “The most important part, of course.” They called themselves NANOGrav, for the North American Nanohertz Observatory for Gravitational Waves.


    NANOGrave Gravitational waves JPL-Caltech  David Champion
    NANOGrave Gravitational waves JPL-Caltech David Champion

    Each of the three teams collected and analyzed data from the telescopes they were most familiar with, by virtue of their geographical proximity and federal funding sources. But they all knew that if they combined their work, they would have a better shot at sensing the waves sooner. All three groups linked up in 2009 to form a network of networks: the International Pulsar Timing Array (IPTA).


    Using a list of 39 of the best pulsars, they got to work. Today, that list has grown to roughly 100. And while some competition exists among pulsar-precisionist groups, the scientific benefits of sharing data outweigh the costs. “There are people who really want to be the ones to do it and to get the glory, but I think that is a small group of people,” says McLaughlin. “Nearly everyone has accepted that the first detection will come from IPTA data.”

    In a sense, though, NANOGrav has already produced new science, even without recording a single bit of signal.

    What’s not widely appreciated is that the silence from pulsar timing array experiments is some of the first science—beyond “we found them!” or “we didn’t find them!”—to come out of decades of experimental gravitational-wave work. That’s why McLaughlin gets upset when the LIGO discovery looms so large that no other research seems important. “I’ve had several people say, ‘So are you guys just going to give up now?’ ” she says. “I’m like, ‘Noooo, that’s not the point.’ ”

    Because the gravitational background noise that NANOGrav is searching for would come from a whole population of supermassive black holes, it would describe not just individual objects—like the LIGO detection did—but also the formations and evolutions of entire galaxy populations. As a result, the size of the signal reflects some of the basic features of our universe.

    To estimate the size of that signal, scientists used models of how many double supermassive black holes the universe holds, how big they are, how fast they whip around each other, and where they are. These estimates reflected the state of the art understanding about how galaxies form, how they change over time, and how they get bigger. The conclusion was that, if they monitored around 20 pulsars for five to 10 years, their sensitivity should be sufficient to hear the nanohertz gravitational background drone. When, 11 years after array initiation, they still had found nothing, they effectively learned that some of those initial assumptions were wrong. All three teams estimated in 2015 that the actual noise amplitude had to be at least 10 times lower than their initial estimates.

    This lowering of expected signal strength was a kind of anti-news, the opposite of LIGO’s historic detection. But challenging scientists to reconsider their notions of galaxy formation and evolution could lead to interesting new science. Perhaps fewer galaxies host big black holes in their centers than scientists thought—and right now scientists think that almost all substantial (non-dwarf) galaxies do. Maybe galaxy mergers are less frequent than was estimated. (Right now, says Mingarelli, they are trying to figure out what “fewer” actually means.) Or maybe the time between the first encounter between two black holes and their coalescence doesn’t quite follow the equation theorists have developed. It could also be that most black hole mergers stall out somehow before the holes are close enough to emit swelling (detectable) gravitational waves, and that the pair just keep orbiting each other endlessly and never merge. Or maybe scientists have been sizing supermassive black holes all wrong, and they are smaller than once thought, so that their waves are smaller. Right now, all of these scenarios are in play as possibilities.

    Of course, the goal remains to make an actual detection. Based on new calculations from their nine-year dataset, NANOGrav estimates that they will reach the sensitivity necessary to finally hear the static in another five to 10 years. In their latest paper, their sensitivity estimates include adding four new hyperstable pulsars each year, taking them from 54 to around 100. “I think pulsar-timing is ready in terms of people, techniques, and analysis,” says Michele Vallisneri, a member of the LIGO collaboration, a visiting associate at the California Institute of Technology, and a research scientist at the Jet Propulsion Laboratory. But, he cautions, it is also possible that “nature may have put our goal farther than we think it is.”

    Time to detection also depends on something more down-to-Earth: funding. “[If] we lose access to either the Green Bank Telescope or Arecibo, the time to detection is pushed back several years … and possibly forever if we lose both,” says McLaughlin. The National Science Foundation will stop funding Green Bank in 2017 or 2018, and the observatory is pursuing private partnerships. At Arecibo, threats of closure have popped up for years—including this summer, as one also did for Parkes—but both telescopes remain open. Those in Europe are, so far, safe.

    Whatever happens, NANOGrav is one example of what will become many categories of instruments to complement LIGO’s initial discovery, says Vallisneri. As he puts it, “astronomers didn’t stop looking after Galileo first saw the satellites of Jupiter and the phases of Venus.”

    See the full article here .

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  • richardmitnick 2:02 pm on March 30, 2015 Permalink | Reply
    Tags: , , , , , NANOGrave,   

    From Caltech: “New NSF-Funded Physics Frontiers Center Expands Hunt for Gravitational Waves” 

    Caltech Logo

    Kathy Svitil

    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


    See the full article here.

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