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  • richardmitnick 9:21 pm on October 16, 2018 Permalink | Reply
    Tags: "We have a case of cosmic look-alikes " said co-author Geoffrey Ryan of UMCP-so the simplest explanation is that they are from the same family of objects.", , , , , Caltech/MIT Advanced aLigo, , GW170817 and GRB 150101B, ,   

    From NASA Chandra: All in the Family: Kin of Gravitational-Wave Source Discovered 

    NASA Chandra Banner

    NASA/Chandra Telescope

    From NASA Chandra

    October 16, 2018
    Media contacts:
    Megan Watzke
    Chandra X-ray Center, Cambridge, Mass.

    Credit: X-ray: NASA/CXC/GSFC/UMC/E. Troja et al.; Optical and infrared: NASA/STScI

    NASA/ESA Hubble Telescope

    A source with remarkable similarities to GW170817, the first source identified to emit gravitational waves and light, has been discovered.

    This new object, called GRB 150101B, was first seen as a gamma-ray burst in January 2015.

    Follow-up observations with Chandra and several other telescopes at different wavelengths uncovered common traits between the two objects.

    Chandra images showed how GRB 150101B faded with time, a key piece of information.

    About a year ago, astronomers excitedly reported the first detection of electromagnetic waves, or light, from a gravitational wave source. Now, a year later, researchers are announcing the existence of a cosmic relative to that historic event.

    The discovery was made using data from telescopes including NASA’s Chandra X-ray Observatory, Fermi Gamma-ray Space Telescope, Neil Gehrels Swift Observatory, the NASA Hubble Space Telescope (HST), and the Discovery Channel Telescope (DCT).

    NASA/Fermi LAT

    NASA/Fermi Gamma Ray Space Telescope

    NASA Neil Gehrels Swift Observatory

    Discovery Channel Telescope at Lowell Observatory, Happy Jack AZ, USA, Altitude 2,360 m (7,740 ft)

    The object of the new study, called GRB 150101B, was first reported as a gamma-ray burst detected by Fermi in January 2015. This detection and follow-up observations at other wavelengths show GRB 150101B shares remarkable similarities to the neutron star merger and gravitational wave source discovered by Advanced Laser Interferometer Gravitational Wave Observatory (LIGO) and its European counterpart Virgo in 2017 known as GW170817. The latest study concludes that these two separate objects may, in fact, be related.

    “It’s a big step to go from one detected object to two,” said Eleonora Troja, lead author of the study from NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and the University of Maryland at College Park (UMCP). “Our discovery tells us that events like GW170817 and GRB 150101B could represent a whole new class of erupting objects that turn on and off in X-rays and might actually be relatively common.”

    Troja and her colleagues think both GRB 150101B and GW170817 were most likely produced by the same type of event: the merger of two neutron stars, a catastrophic coalescence that generated a narrow jet, or beam, of high-energy particles. The jet produced a short, intense burst of gamma rays (known as a short GRB), a high-energy flash that can last only seconds. GW170817 proved that these events may also create ripples in space-time itself called gravitational waves.

    The apparent match between GRB 150101B and GW170817 is striking: both produced an unusually faint and short-lived gamma ray burst, and both were a source of bright, blue optical light lasting a few days, and X-ray emission lasted much longer. The host galaxies are also remarkably similar, based on Hubble Space Telescope and DCT observations. Both are bright elliptical galaxies with a population of stars a few billion years old and displaying no evidence for new stars forming.

    “We have a case of cosmic look-alikes,” said co-author Geoffrey Ryan of UMCP. “They look the same, act the same and come from similar neighborhoods, so the simplest explanation is that they are from the same family of objects.”

    In the cases of both GRB 150101B and GW170817, the slow rise in the X-ray emission compared to most GRBs implies that the explosion was likely viewed “off-axis,” that is, with the jet not pointing directly towards the Earth. The discovery of GRB150101 represents only the second time astronomers have ever detected an off-axis short GRB.

    While there are many commonalities between GRB 150101B and GW170817, there are two very important differences. One is their location. GW170817 is about 130 million light years from Earth, while GRB 150101B lies about 1.7 billion light years away. Even if Advanced LIGO had been operating in early 2015, it would very likely not have detected gravitational waves from GRB 150101B because of its greater distance.

    “The beauty of GW170817 is that it gave us a set of characteristics, kind of like genetic markers, to identify new family members of explosive objects at even greater distances than LIGO can currently reach,” said co-author Luigi Piro of National Institute for Astrophysics in Rome.

    The optical emission from GB150101B is largely in the blue portion of the spectrum, providing an important clue that this event involved a so-called kilonova, as seen in GW170817. A kilonova is an extremely powerful explosion that not only releases a large amount energy, but may also produce important elements like gold, platinum, and uranium that other stellar explosions do not.

    It is possible that a few mergers like the ones seen in GW170817 and GRB 150101B had been detected as short GRBs before but had not been identified with other telescopes. Without detections at longer wavelengths like X-rays or optical light, GRB positions are not accurate enough to determine what galaxy they are located in.

    In the case of GRB 150101B, astronomers thought at first that the counterpart was an X-ray source detected by Swift in the center of the galaxy, likely from material falling into a supermassive black hole. However, follow-up observations with Chandra detected the true counterpart away from the center of the host galaxy.

    The other important difference between GW170817 and GRB 150101B is that without gravitational wave detection, the team does not know the masses of the two objects that merged. It is possible that the merger was between a black hole and a neutron star, rather than two neutron stars.

    “We need more cases like GW170817 that combine gravitational wave and electromagnetic data to find an example between a neutron star and black hole. Such a detection would be the first of its kind,” said co-author Hendrik Van Eerten of the University of Bath in the United Kingdom. “Our results are encouraging for finding more mergers and making such a detection.”

    A paper describing these results appears in the journal Nature Communications today.

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    NASA’s Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA’s Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra’s science and flight operations from Cambridge, Mass.

  • richardmitnick 10:35 pm on October 12, 2018 Permalink | Reply
    Tags: , , , , Caltech/MIT Advanced aLigo, , , GRB 150101B, GRB 170817A, GRB's-Gamma ray bursts,   

    From AAS NOVA: ” Two Explosions with Similar Quirks” 


    From AAS NOVA

    12 October 2018
    Susanna Kohler

    Artist’s by now iconic illustration of the merger of two neutron stars, producing a short gamma-ray burst. [NSF/LIGO/Sonoma State University/A. Simonnet]

    High-energy radiation released during the merger of two neutron stars last year has left astronomers puzzled. Could a burst of gamma rays from 2015 help us to piece together a coherent picture of both explosions?

    A Burst Alone?

    When two neutron stars collided last August, forming a distinctive gravitational-wave signal and a burst of radiation detected by telescopes around the world, scientists knew that these observations would change our understanding of short gamma-ray bursts (GRBs).Though we’d previously observed thousands of GRBs, GRB 170817A was the first to have such a broad range of complementary observations — both in gravitational waves and across the electromagnetic spectrum — providing insight into its origin.

    Total isotropic-equivalent energies for Fermi-detected gamma-ray bursts with known redshifts. GRB 170817A (pink star) is a factor of ~1,000 dimmer than typical short GRBs (orange points). GRB 170817A and GRB 150101B (green star) are two of the closest detected short GRBs. [Adapted from Burns et al. 2018]

    But it quickly became evident that GRB 170817A was not your typical GRB. For starters, this burst was unusually weak, appearing 1,000 times less luminous than a typical short GRB. Additionally, the behavior of this burst was unusual: instead of having only a single component, the ~2-second explosion exhibited two distinct components — first a short, hard (higher-energy) spike, and then a longer, soft (lower-energy) tail.

    The peculiarities of GRB 170817A prompted a slew of models explaining its unusual appearance. Ultimately, the question is: can our interpretations of GRB 170817A safely be applied to the general population of gamma-ray bursts? Or must we assume that GRB 170817A is a unique event, not representative of the general population?

    New analysis of a GRB from 2015 — presented in a recent study led by Eric Burns (NASA Goddard SFC) — may help to answer this question.

    A Matter of Angles

    What does a burst from 2015 have to do with the curious case of GRB 170817A? Burns and collaborators have demonstrated that this 2015 burst, GRB 150101B, exhibited the same strange behavior as GRB 170817A: its emission can be broken down into two components consisting of a short, hard spike, followed by a long, soft tail. Unlike GRB 170817A, however, GRB 150101B is not underluminous — and it lasted less than a tenth of the time.

    Fermi count rates in different energy ranges showing the short hard spike and the longer soft tail in GRB 150101B. The short hard spike is visible above 50 keV (top and middle panels). The soft tail is visible in the 10–50 keV channel (bottom panel). [Burns et al. 2018]

    Intriguingly, these similarities and differences can all be explained by a single model. Burns and collaborators propose that GRB 150101B and GRB 170817A exhibit the exact same two-component behavior, and their differences in luminosity and duration can be explained by quirks of special relativity.

    High-speed outflows such as these will have different apparent luminosities and durations depending on whether we view them along their axis or slightly from the side. Burns and collaborators demonstrate that these the two bursts could easily have the same profile — but GRB 150101B was viewed nearly on-axis, whereas GRB 170817A was viewed from an angle.

    If this is true, then perhaps more GRBs have hard spikes and soft tails similar to these two; the tails may just be difficult to detect in more distant bursts. While more work remains to be done, the recognition that GRB 170817A may not be unique is an important one for understanding both its behavior and that of other short GRBs.


    “Fermi GBM Observations of GRB 150101B: A Second Nearby Event with a Short Hard Spike and a Soft Tail,” E. Burns et al 2018 ApJL 863 L34.

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

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

    ESA/eLISA the future of gravitational wave research

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

    NASA/Fermi LAT

    NASA/Fermi Gamma Ray Space Telescope

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition


    AAS Mission and Vision Statement

    The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

    The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
    The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
    The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
    The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
    The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

    Adopted June 7, 2009

  • richardmitnick 8:37 am on October 4, 2018 Permalink | Reply
    Tags: , Blue Waters supercomputer at the University of Illinois at Urbana-Champaign, Caltech/MIT Advanced aLigo, , ,   

    From NASA Goddard Space Flight Center via Manu Garcia of IAC: “New Simulation Sheds Light on Spiraling Supermassive Black Holes” 

    From Manu Garcia, a friend from IAC.

    The universe around us.
    Astronomy, everything you wanted to know about our local universe and never dared to ask.

    NASA Goddard Banner
    From NASA Goddard Space Flight Center

    Oct. 2, 2018
    Jeanette Kazmierczak
    NASA’s Goddard Space Flight Center, Greenbelt, Md.

    This animation rotates 360 degrees around a frozen version of the simulation in the plane of the disk. Credit: NASA’s Goddard Space Flight Center

    A new model is bringing scientists a step closer to understanding the kinds of light signals produced when two supermassive black holes, which are millions to billions of times the mass of the Sun, spiral toward a collision. For the first time, a new computer simulation that fully incorporates the physical effects of Einstein’s general theory of relativity shows that gas in such systems will glow predominantly in ultraviolet and X-ray light.

    Just about every galaxy the size of our own Milky Way or larger contains a monster black hole at its center. Observations show galaxy mergers occur frequently in the universe, but so far no one has seen a merger of these giant black holes.

    “We know galaxies with central supermassive black holes combine all the time in the universe, yet we only see a small fraction of galaxies with two of them near their centers,” said Scott Noble, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “The pairs we do see aren’t emitting strong gravitational-wave signals because they’re too far away from each other. Our goal is to identify — with light alone — even closer pairs from which gravitational-wave signals may be detected in the future.”

    A paper describing the team’s analysis of the new simulation was published Tuesday, Oct. 2, in The Astrophysical Journal.

    Gas glows brightly in this computer simulation of supermassive black holes only 40 orbits from merging. Models like this may eventually help scientists pinpoint real examples of these powerful binary systems. Credits: NASA’s Goddard Space Flight Center

    Scientists have detected merging stellar-mass black holes — which range from around three to several dozen solar masses — using the National Science Foundation’s Laser Interferometer Gravitational-Wave Observatory (LIGO).

    Gravitational waves are space-time ripples traveling at the speed of light. They are created when massive orbiting objects like black holes and neutron stars spiral together and merge.

    Black holes heading toward a merger. Precise laser interferometry can detect the ripples in space-time generated when two black holes collide. LIGO-Caltech-MIT-Sonoma State Aurore Simonn

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Supermassive mergers will be much more difficult to find than their stellar-mass cousins. One reason ground-based observatories can’t detect gravitational waves from these events is because Earth itself is too noisy, shaking from seismic vibrations and gravitational changes from atmospheric disturbances. The detectors must be in space, like the Laser Interferometer Space Antenna (LISA) led by ESA (the European Space Agency) and planned for launch in the 2030s.

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

    Observatories monitoring sets of rapidly spinning, superdense stars called pulsars may detect gravitational waves from monster mergers. Like lighthouses, pulsars emit regularly timed beams of light that flash in and out of view as they rotate. Gravitational waves could cause slight changes in the timing of those flashes, but so far studies haven’t yielded any detections.

    But supermassive binaries nearing collision may have one thing stellar-mass binaries lack — a gas-rich environment. Scientists suspect the supernova explosion that creates a stellar black hole also blows away most of the surrounding gas. The black hole consumes what little remains so quickly there isn’t much left to glow when the merger happens.

    Supermassive binaries, on the other hand, result from galaxy mergers. Each supersized black hole brings along an entourage of gas and dust clouds, stars and planets. Scientists think a galaxy collision propels much of this material toward the central black holes, which consume it on a time scale similar to that needed for the binary to merge. As the black holes near, magnetic and gravitational forces heat the remaining gas, producing light astronomers should be able to see.

    “It’s very important to proceed on two tracks,” said co-author Manuela Campanelli, director of the Center for Computational Relativity and Gravitation at the Rochester Institute of Technology in New York, who initiated this project nine years ago. “Modeling these events requires sophisticated computational tools that include all the physical effects produced by two supermassive black holes orbiting each other at a fraction of the speed of light. Knowing what light signals to expect from these events will help modern observations identify them. Modeling and observations will then feed into each other, helping us better understand what is happening at the hearts of most galaxies.”

    The new simulation shows three orbits of a pair of supermassive black holes only 40 orbits from merging. The models reveal the light emitted at this stage of the process may be dominated by UV light with some high-energy X-rays, similar to what’s seen in any galaxy with a well-fed supermassive black hole.

    Three regions of light-emitting gas glow as the black holes merge, all connected by streams of hot gas: a large ring encircling the entire system, called the circumbinary disk, and two smaller ones around each black hole, called mini disks. All these objects emit predominantly UV light. When gas flows into a mini disk at a high rate, the disk’s UV light interacts with each black hole’s corona, a region of high-energy subatomic particles above and below the disk. This interaction produces X-rays. When the accretion rate is lower, UV light dims relative to the X-rays.

    Based on the simulation, the researchers expect X-rays emitted by a near-merger will be brighter and more variable than X-rays seen from single supermassive black holes. The pace of the changes links to both the orbital speed of gas located at the inner edge of the circumbinary disk as well as that of the merging black holes.

    This 360-degree video places the viewer in the middle of two circling supermassive black holes around 18.6 million miles (30 million kilometers) apart with an orbital period of 46 minutes. The simulation shows how the black holes distort the starry background and capture light, producing black hole silhouettes. A distinctive feature called a photon ring outlines the black holes. The entire system would have around 1 million times the Sun’s mass. Credits: NASA’s Goddard Space Flight Center; background, ESA/Gaia/DPAC

    “The way both black holes deflect light gives rise to complex lensing effects, as seen in the movie when one black hole passes in front of the other,” said Stéphane d’Ascoli, a doctoral student at École Normale Supérieure in Paris and lead author of the paper. “Some exotic features came as a surprise, such as the eyebrow-shaped shadows one black hole occasionally creates near the horizon of the other.”

    The simulation ran on the National Center for Supercomputing Applications’ Blue Waters supercomputer at the University of Illinois at Urbana-Champaign.

    U Illinois Urbana-Champaign Blue Waters Cray Linux XE/XK hybrid machine supercomputer

    Modeling three orbits of the system took 46 days on 9,600 computing cores. Campanelli said the collaboration was recently awarded additional time on Blue Waters to continue developing their models.

    The original simulation estimated gas temperatures. The team plans to refine their code to model how changing parameters of the system, like temperature, distance, total mass and accretion rate, will affect the emitted light. They’re interested in seeing what happens to gas traveling between the two black holes as well as modeling longer time spans.

    “We need to find signals in the light from supermassive black hole binaries distinctive enough that astronomers can find these rare systems among the throng of bright single supermassive black holes,” said co-author Julian Krolik, an astrophysicist at Johns Hopkins University in Baltimore. “If we can do that, we might be able to discover merging supermassive black holes before they’re seen by a space-based gravitational-wave observatory.”

    See the full article here.


    Please help promote STEM in your local schools.

    Stem Education Coalition

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

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

    NASA/Goddard Campus

  • richardmitnick 2:02 pm on September 25, 2018 Permalink | Reply
    Tags: , Caltech/MIT Advanced aLigo, , , , , , LSND, , , ,   

    From Symmetry: “How not to be fooled in physics” 

    Symmetry Mag
    From Symmetry

    Laura Dattaro

    Illustration by Sandbox Studio, Chicago with Ana Kova

    Particle physicists and astrophysicists employ a variety of tools to avoid erroneous results.

    In the 1990s, an experiment conducted in Los Alamos, about 35 miles northwest of the capital of New Mexico, appeared to find something odd.

    Scientists designed the Liquid Scintillator Neutrino Detector experiment at the US Department of Energy’s Los Alamos National Laboratory to count neutrinos, ghostly particles that come in three types and rarely interact with other matter.

    LSND experiment at Los Alamos National Laboratory and Virginia Tech

    LSND was looking for evidence of neutrino oscillation, or neutrinos changing from one type to another.

    Several previous experiments had seen indications of such oscillations, which show that neutrinos have small masses not incorporated into the Standard Model, the ruling theory of particle physics. LSND scientists wanted to double-check these earlier measurements.

    By studying a nearly pure source of one type of neutrinos—muon neutrinos—LSND did find evidence of oscillation to a different type of neutrinos, electron neutrinos. However, they found many more electron neutrinos in their detector than predicted, creating a new puzzle.

    This excess could have been a sign that neutrinos oscillate between not three but four different types, suggesting the existence of a possible new type of neutrino, called a sterile neutrino, which theorists had suggested as a possible way to incorporate tiny neutrino masses into the Standard Model.

    Or there could be another explanation. The question is: What? And how can scientists guard against being fooled in physics?

    Brand new thing

    Many physicists are looking for results that go beyond the Standard Model. They come up with experiments to test its predictions; if what they find doesn’t match up, they have potentially discovered something new.

    “Do we see what we expected from the calculations if all we have there is the Standard Model?” says Paris Sphicas, a researcher at CERN.

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

    Standard Model of Particle Physics from Symmetry Magazine

    “If the answer is yes, then it means we have nothing new. If the answer is no, then you have the next question, which is, ‘Is this within the uncertainties of our estimates? Could this be a result of a mistake in our estimates?’ And so on and so on.”

    A long list of possible factors can trick scientists into thinking they’ve made a discovery. A big part of scientific research is identifying them and finding ways to test what’s really going on.

    “The community standard for discovery is a high bar, and it ought to be,” says Yale University neutrino physicist Bonnie Fleming. “It takes time to really convince ourselves we’ve really found something.”

    In the case of the LSND anomaly, scientists wonder whether unaccounted-for background events tipped the scales or if some sort of mechanical problem caused an error in the measurement.

    Scientists have designed follow-up experiments to see if they can reproduce the result. An experiment called MiniBooNE, hosted by Fermi National Accelerator Laboratory, recently reported seeing signs of a similar excess. Other experiments, such as the MINOS experiment, also at Fermilab, have not seen it, complicating the search.


    FNAL Minos map


    FNAL MINOS Far Detector in the Soudan Mine in northern Minnesota

    “[LSND and MiniBooNE] are clearly measuring an excess of events over what they expect,” says MINOS co-spokesperson Jenny Thomas, a physicist at University College London. “Are those important signal events, or are they a background they haven’t estimated properly? That’s what they are up against.”

    Managing expectations

    Much of the work in understanding a signal involves preparatory work before one is even seen.

    In designing an experiment, researchers need to understand what physics processes can produce or mimic the signal being sought, events that are often referred to as “background.”

    Physicists can predict backgrounds through simulations of experiments. Some types of detector backgrounds can be identified through “null tests,” such as pointing a telescope at a blank wall. Other backgrounds can be identified through tests with the data itself, such as so-called “jack-knife tests,” which involve splitting data into subsets—say, data from Monday and data from Tuesday—which by design must produce the same results. Any inconsistencies would warn scientists about a signal that appears in just one subset.

    Researchers looking at a specific signal work to develop a deep understanding of what other physics processes could produce the same signature in their detector. MiniBooNE, for example, studies a beam primarily made of muon neutrinos to measure how often those neutrinos oscillate to other flavors. But it will occasionally pick up stray electron neutrinos, which look like muon neutrinos that have transformed. Beyond that, other physics processes can mimic the signal of an electron neutrino event.

    “We know we’re going to be faked by those, so we have to do the best job to estimate how many of them there are,” Fleming says. “Whatever excess we find has to be in addition to those.”

    Even more variable than a particle beam: human beings. While science strives to be an objective measurement of facts, the process itself is conducted by a collection of people whose actions can be colored by biases, personal stories and emotion. A preconceived notion that an experiment will (or won’t) produce a certain result, for example, could influence a researcher’s work in subtle ways.

    “I think there’s a stereotype that scientists are somehow dispassionate, cold, calculating observers of reality,” says Brian Keating, an astrophysicist at University of California San Diego and author of the book Losing the Nobel Prize, which chronicles how the desire to make a prize-winning discovery can steer a scientist away from best practices. “In reality, the truth is we actually participate in it, and there are sociological elements at work that influence a human being. Scientists, despite the stereotypes, are very much human beings.”

    Staying cognizant of this fact and incorporating methods for removing bias are especially important if a particular claim upends long-standing knowledge—such as, for example, our understanding of neutrinos. In these cases, scientists know to adhere to the adage: Extraordinary claims require extraordinary evidence.

    “If you’re walking outside your house and you see a car, you probably think, ‘That’s a car,’” says Jonah Kanner, a research scientist at Caltech. “But if you see a dragon, you might think, ‘Is that really a dragon? Am I sure that’s a dragon?’ You’d want a higher level of evidence.”

    Dragon or discovery?

    Physicists have been burned by dragons before. In 1969, for example, a scientist named Joe Weber announced that he had detected gravitational waves: ripples in the fabric of space-time first predicted by Albert Einstein in 1916. Such a detection, which many had thought was impossible to make, would have proved a key tenet of relativity. Weber rocketed to momentary fame, until other physicists found they could not replicate his results.

    The false discovery rocked the gravitational wave community, which, over the decades, became increasingly cautious about making such announcements.

    So in 2009, as the Laser Interferometer Gravitational Wave Observatory, or LIGO, came online for its next science run, the scientific collaboration came up with a way to make sure collaboration members stayed skeptical of their results. They developed a method of adding a false or simulated signal into the detector data stream without alerting the majority of the 800 or so researchers on the team. They called it a blind injection. The rest of the members knew an injection was possible, but not guaranteed.

    “We’d been not detecting signals for 30 years,” Kanner, a member of the LIGO collaboration, says. “How clear or obvious would the signature have to be for everyone to believe it?… It forced us to push our algorithms and our statistics and our procedures, but also to test the sociology and see if we could get a group of people to agree on this.”

    In late 2010, the team got the alert they had been waiting for: The computers detected a signal. For six months, hundreds of scientists analyzed the results, eventually concluding that the signal looked like gravitational waves. They wrote a paper detailing the evidence, and more than 400 team members voted on its approval. Then a senior member told them it had all been faked.

    Picking out and spending so much time examining such an artificial signal may seem like a waste of time, but the test worked just as intended. The exercise forced the scientists to work through all of the ways they would need to scrutinize a real result before one ever came through. It forced the collaboration to develop new tests and approaches to demonstrating the consistency of a possible signal in advance of a real event.

    “It was designed to keep us honest in a sense,” Kanner says. “Everyone to some extent goes in with some guess or expectation about what’s going to come out of that experiment. Part of the idea of the blind injection was to try and tip the scales on that bias, where our beliefs about whether we thought nature should produce an event would be less important.”

    All of the hard work paid off: In September 2015, when an authentic signal hit the LIGO detectors, scientists knew what to do. In 2016, the collaboration announced the first confirmed direct detection of gravitational waves. One year later, the discovery won the Nobel Prize.

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

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

    ESA/eLISA the future of gravitational wave research

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

    No easy answers

    While blind injections worked for the gravitational waves community, each area of physics presents its own unique challenges.

    Neutrino physicists have an extremely small sample size with which to work, because their particles interact so rarely. That’s why experiments such as the NOvA experiment and the upcoming Deep Underground Neutrino experiment use such enormous detectors.

    FNAL/NOvA experiment map

    FNAL NOvA detector in northern Minnesota

    FNAL NOvA Near Detector

    Astronomers have even fewer samples: They have just one universe to study, and no way to conduct controlled experiments. That’s why they conduct decades-long surveys, to collect as much data as possible.

    Researchers working at the Large Hadron Collider have no shortage of interactions to study—an estimated 600 million events are detected every second.


    CERN map

    CERN LHC Tunnel

    CERN LHC particles

    But due to the enormous size, cost and complexity of the technology, scientists have built only one LHC. That’s why inside the collider sit multiple different detectors, which can check one another’s work by measuring the same things in a variety of ways with detectors of different designs.


    CERN/CMS Detector

    CERN ALICE detector

    CERN LHCb chamber, LHC

    While there are many central tenets to checking a result—knowing your experiment and background well, running simulations and checking that they agree with your data, testing alternative explanations of a suspected result—there’s no comprehensive checklist that every physicist performs. Strategies vary from experiment to experiment, among fields and over time.

    Scientists must do everything they can to test a result, because in the end, it will need to stand up to the scrutiny of their peers. Fellow physicists will question the new result, subject it to their own analyses, try out alternative interpretations, and, ultimately, try to repeat the measurement in a different way. Especially if they’re dealing with dragons.

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 7:42 pm on September 11, 2018 Permalink | Reply
    Tags: A cool fact about this accelerator? It’s 60 years old and includes a Van de Graaff accelerator that was repurposed for use with CASPAR, , , “We are made of stardust.” Carl Sagan, , Caltech/MIT Advanced aLigo, , , , LUNA at Gran Sasso, Stellar burning and evolutionary phases in stars,   

    From Sanford Underground Research Facility: “CASPAR” 

    SURF logo
    Sanford Underground levels

    From Sanford Underground Research Facility

    Constance Walter
    Photos by Matt Kapust

    CASPAR is a low-energy particle accelerator that allows researchers to study processes that take place inside collapsing stars.

    “We are made of stardust.”

    While that statement may sound like a song title from the 1960s, it was actually made by astrophysicist and science fiction author Carl Sagan.

    Carl Sagan NASA/JPL

    And he was right. The nuclear burning inside collapsing stars produces the elements that make up and sustain life on Earth: carbon, nitrogen, iron and calcium, to name a few. Even lead, gold and the rock beneath our feet come from stars.

    The Compact Accelerator System for Performing Astrophysical Research (CASPAR) collaboration uses a low-energy accelerator to better understand how elements are produced in the Universe and at what rate and how much energy is produced during the process.

    “Unlike other underground experiments, we look at many different interactions and are not focused on discovering just one event,” said Dan Robertson, research associate professor at the University of Notre Dame. “All of these details give us a better understanding of the life of a star and what material is kicked out into the Universe during explosive stellar events.”


    Studying the stars from underground

    Although it may seem counter-intuitive, going nearly a mile underground at Sanford Lab gives the CASPAR team a perfect place to study those stellar environments. CASPAR is one of just two underground accelerators in the world studying stellar environments. The other is the Laboratory for Underground Nuclear Astrophysics (LUNA), which is located at Gran Sasso National Laboratory in Italy and has been in existence for 25 years. Frank Strieder, principal investigator for the project and an associate professor of physics at South Dakota School of Mines & Technology (SD Mines), worked on that experiment for 22 years.

    LUNA-Laboratory for Underground Nuclear Astrophysics , which is located at Gran Sasso National Laboratory in Italy

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

    “Both experiments are studying stellar burning and evolutionary phases in stars, but the work is different,” Strieder said. “And with our accelerator, we can cover a larger energy range than previous underground experiments.”

    The accelerator

    The most famous particle accelerator in the world is the 17-mile long Large Hadron Collider, located in Switzerland and France, which generates up to 7 trillion volts as it hurls particles toward each other at nearly the speed of light.


    CERN map

    CERN LHC Tunnel

    CERN LHC particles

    CASPAR, on the other hand, is a 50-foot long system that includes a Van de Graaff accelerator that uses radio-frequency energy to accelerate a beam of protons or alpha particles toward a target of up to 1.1 million volts.

    Robertson compares the accelerator to a tabletop version of the Van de Graaff used in high school or at a science museum—touch the polished metal dome and your hair stands on end. “Think of the accelerator as generating and storing a large voltage which then repels ionized particles (which we create at its heart) away from it.”

    A cool fact about this accelerator? It’s 60 years old and was repurposed for use with CASPAR.

    The target

    Every reaction the CASPAR team investigates, requires two elements to interact—a projectile and a target. The target material varies according to the interaction they want to study and could include anything from nitrogen and carbon up to magnesium. These elements are usually stored on a heavier backing material for stability, which are kept extremely cold.

    The team bombards the target with either a proton beam or alpha beam generated in the accelerator. The power the beam dissipates in the target is up to 100 watts, “which is the same power as a good light bulb,” Strieder said.

    What’s LIGO got to do with it?

    In late 2017, the Laser-Interferometer Gravitational Wave Observatory (LIGO), recorded a violent collision of two neutron stars—this was on top of two previous observations of black hole mergers that emitted gravitational waves. Observations made after the collision reinforce the need for measurements like those CASPAR hopes to take, explained Strieder.

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

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

    ESA/eLISA the future of gravitational wave research

    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)
    See also https://sciencesprings.wordpress.com/2017/10/16/from-ucsc-a-uc-santa-cruz-special-report-neutron-stars-gravitational-waves-and-all-the-gold-in-the-universe/

    “The basic point is that from the information we learned from this cataclysmic event, we can calculate the amount of heavy element material produced.” Strieder said. “And then compare it with the heavy elements found in our planetary system.”

    Volts of energy generated by CASPAR

    Volts of energy generated by LHC

    Collecting data

    In July 2017, CASPAR achieved first beam and began full operations earlier this year. The accelerator runs for several days at a time, collecting data using a germanium detector.

    “We are recording the number of reactions that occur per time period, and in what conditions,” Roberson said. “For example, what energy did the interacting particle have prior to striking the target? The measurement of radiation and particles emitted during the interaction helps us backtrack what happened in the target material and at what rate. This can then be extrapolated to events in a star and scaled up for the star’s massive size.”

    A lofty goal

    The end goal for the field of nuclear astrophysics is to complete the puzzle of how everything is made in the Universe and the locations and processes that govern such production. The experiments studying stellar processes are looking at singular puzzle pieces without knowing what the complete picture is.

    “Only as we understand how these pieces fit can we begin to put the whole puzzle together,” Robertson said. “CASPAR’s unique location deep underground means it is able to more clearly investigate the images previously obscured by cosmic interference.”

    See the full article here .

    Please help promote STEM in your local schools.

    Stem Education Coalition

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

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

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

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

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

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

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

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

    Fermilab LBNE

  • richardmitnick 1:13 pm on September 7, 2018 Permalink | Reply
    Tags: , , , , Black Hole Mergers Through Cosmic Time, Caltech/MIT Advanced aLigo, ,   

    From AAS NOVA: “Black Hole Mergers Through Cosmic Time” 


    From AAS NOVA

    7 September 2018
    Kerry Hensley

    This artist’s conception shows a pair of black holes heading toward a merger. Precise laser interferometry can detect the ripples in space-time generated when two black holes collide. [LIGO/Caltech/MIT/Sonoma State (Aurore Simonnet)]

    The advent of gravitational-wave astrophysics has made possible the study of elusive cosmic phenomena — like the mysterious merging of stellar-mass black holes.

    When Black Holes Meet

    Physical Review Letters Black Hole Disks in Galactic Nuclei

    As of November 15, 2017, six black-hole mergers have been discovered via gravitational waves. [LSC/LIGO/Caltech/Sonoma State (Aurore Simonnet)]

    The cataclysmic inspiraling of a pair of black holes doomed to merge sends ripples through space-time. Thanks to the Laser Interferometer Gravitational-Wave Observatory (LIGO), we have now detected a handful of instances of these ripples — enough to take a closer look at the broader population of binary black-hole mergers.

    Beyond just collecting individual merger events, we can now explore whether or not the rate at which black hole mergers occur has evolved over the course of cosmic time. The merger rate reflects the underlying star formation rate as well as the particulars of stellar evolution. Ultimately, understanding how the merger rate has changed can help us learn how black-hole binaries form.

    How can we tell whether or not the rate of binary black-hole mergers has evolved with redshift? A team led by Maya Fishbach (University of Chicago) aimed to extract this information from the first six binary black-hole detections from LIGO/Virgo.

    The cumulative probability distribution of detected black-hole binaries depends on black hole mass, detector sensitivity (with the dashed lines indicating a more sensitive detector), and the underlying redshift distribution. Evolution of the merger rate with redshift would shift these curves — which demonstrate the case of a uniform redshift distribution — to the left or right. [Fishbach et al. 2018]

    LIGO Provides a Listening Ear

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

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

    ESA/eLISA the future of gravitational wave research

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

    One challenge is that the redshift distribution of black-hole binaries that we observe from LIGO/Virgo isn’t just a function of the underlying redshift distribution — it’s also a function of the mass distribution. Since mergers of more massive black holes generate “louder” signals and are more likely to be detected, a binary black-hole population with more massive members will generate more detections at high redshift than a population with fewer massive members.

    To remedy this, Fishbach and collaborators used models of realistic redshift distributions to fit the redshift and the two component masses simultaneously. Based on the six available binary black-hole detections, Fishbach and collaborators find that the observations are consistent with a merger rate that is constant in redshift.

    There does appear to be a slight decrease in the merger rate density with increasing redshift, but the authors caution that this could arise if the detections of the “quieter” mergers are published later; an artificially large proportion of “louder” events could skew the redshift distribution toward low-redshift events.

    Looking Ahead to Future Detections

    Merger rate density as a function of redshift for two redshift parameterizations. Both redshift models are consistent with a constant merger rate, which is indicated by the dotted line. Click to enlarge. [Fishbach et al. 2018]

    What does the future hold for estimating the black hole merger rate as a function of redshift? To explore this question, Fishbach and collaborators generated synthetic black hole populations and modeled the likely detections by LIGO/Virgo.

    They find that with a few hundred binary black-hole detections per year — an estimate based off of the expected improvements to LIGO/Virgo sensitivity — any deviations from a constant merger rate should be detectable within a few years. Exciting developments to come!


    Maya Fishbach et al 2018 ApJL 863 L41.http://iopscience.iop.org/article/10.3847/2041-8213/aad800/meta

    Related journal articles
    See the full article for further references with links.

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition


    AAS Mission and Vision Statement

    The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

    The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
    The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
    The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
    The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
    The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

    Adopted June 7, 2009

  • richardmitnick 1:03 pm on September 5, 2018 Permalink | Reply
    Tags: , , , , Caltech/MIT Advanced aLigo, , , ,   

    From Caltech: “Superfast Jet Observed Streaming Away from Stellar Collision” 

    Caltech Logo

    From Caltech

    Elise Cutts

    An artist’s impression of the jet (pictured as a ball of fire), produced in the neutron star merger first detected on August 17, 2017 by telescopes around the world, as well as LIGO, which detects gravitational waves (green ripples). Credit: James Josephides (Swinburne University of Technology, Australia)

    Using a collection of National Science Foundation radio telescopes, researchers have confirmed that a narrow jet of material was ejected at near light speeds from a neutron star collision. The collision, which was observed August 17, 2017 and occurred 130 million miles from Earth, initially produced gravitational waves that were observed by the Laser Interferometry Gravitational-wave Observatory (LIGO), alongside a flood of light in the form of gamma rays, X-rays, visible light, and radio waves. It was the first cosmic event to be observed in both gravitational waves and light waves.

    Confirmation that a superfast jet had been produced by the neutron star collision came after radio astronomers discovered that a region of radio emission created by the merger had moved in a seemingly impossible way that only a jet could explain. The radio observations were made using the Very Long Baseline Array (VLBA), the Robert C. Byrd Green Bank Telescope (GBT), and the Very Large Array (VLA). The VLA is operated by the National Radio Astronomy Observatory (NRAO), which is closely associated with the other two telescopes involved in the discovery.


    GBO radio telescope, Green Bank, West Virginia, USA

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

    “We measured an apparent motion that is four times faster than light. That illusion, called superluminal motion, results when the jet is pointed nearly toward Earth and the material in the jet is moving close to the speed of light,” says Kunal Mooley, a Caltech postdoctoral scholar with a joint appointment at the NRAO and lead author of a new study about the jet appearing online September 5 in the journal Nature. Mooley and Assistant Professor of Astronomy Gregg Hallinan were part of an international collaboration that observed and interpreted the movement of the radio emission.

    “We were lucky to be able to observe this event, because if the jet had been pointed too much farther away from Earth, the radio emission would have been too faint for us to detect,” says Hallinan.

    Superfast jets are known to give rise to intense, short-duration gamma-ray bursts or sGRBs, predicted by theorists to be associated with neutron star collisions. The observation of a jet associated with this collision is therefore an important confirmation of theoretical expectations.

    Superfast jets are known to give rise to intense, short-duration gamma-ray bursts or sGRBs, predicted by theorists to be associated with neutron star collisions. The observation of a jet associated with this collision is therefore an important confirmation of theoretical expectations.

    The aftermath of the merger is now also better understood: the jet likely interacted with surrounding debris, forming a broad “cocoon” of material that expanded outward and accounted for the majority of the radio signal observed soon after the collision. Later on, the observed radio emission came mainly from the jet.

    Read the full story from NRAO at https://public.nrao.edu/news/superfast-jet-neutron-star-merger/.

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

    Please help promote STEM in your local schools.

    Stem Education Coalition

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

    Caltech campus

  • richardmitnick 12:02 pm on September 3, 2018 Permalink | Reply
    Tags: A new line of technical equipment in order to dramatically improve gravitational wave detectors, A small glass cell containing a cloud of 100 million caesium atoms, Boosting gravitational wave detectors with quantum tricks, Caltech/MIT Advanced aLigo, Gravitational wave detectors, ,   

    From Niels Bohr Institute: “Boosting gravitational wave detectors with quantum tricks” 

    University of Copenhagen

    Niels Bohr Institute bloc

    From Niels Bohr Institute

    03 September 2018
    Eugene Polzik, professor and head of the Center for Quantum Optics, Quantop at the Niels Bohr Institute, University of Copenhagen
    Phone: +45 2338 2045
    Email: polzik@nbi.dk

    Gravitational wave detectors: Niels Bohr Institute scientists are convinced they can expand space surveillance using a small glass cell filled with caesium atoms.

    Eugene Polzik and Farid Khalili from LIGO collaboration and Moscow State University, have recently published in the scientific journal Physical Review Letters how they can improve gravitational wave detectors. Photo: Ola J. Joensen

    A group of scientists from the Niels Bohr Institute (NBI) at the University of Copenhagen will soon start developing a new line of technical equipment in order to dramatically improve gravitational wave detectors.

    Gravitational wave detectors are extremely sensitive and can e.g. register colliding neutron stars in space. Yet even higher sensitivity is sought for in order to expand our knowledge about the Universe, and the NBI-scientists are convinced that their equipment can improve the detectors, says Professor Eugene Polzik: “And we should be able to show proof of concept within approximately three years”.

    If the NBI-scientists are able to improve the gravitational wave detectors as much as they “realistically expect can be done”, the detectors will be able to monitor and carry out measurements in an eight times bigger volume of space than what is currently possible, explains Eugene Polzik: “This will represent a truly significant extension”.

    Polzik is head of Quantum Optics (Quantop) at NBI and he will spearhead the development of the tailor made equipment for gravitational wave detectors. The research – which is supported by the EU, the Eureka Network Projects and the US-based John Templeton Foundation with grants totaling DKK 10 million – will be carried out in Eugene Polzik’s lab at NBI.

    A collision well noticed

    News media all over the world shifted into overdrive in October of 2017 when it was confirmed that a large international team of scientists had indeed measured the collision of two neutron stars; an event which took place 140 million light years from Earth and resulted in the formation of a kilonova.

    The international team of scientists – which also included experts from NBI – was able to confirm the collision by measuring gravitational waves from space – waves in the fabric of spacetime itself, moving at the speed of light. The waves were registered by three gravitational wave detectors: the two US-based LIGO-detectors and the European Virgo-detector in Italy.

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

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

    ESA/eLISA the future of gravitational wave research

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

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

    Caesium atoms contained in a spin-protecting cell are expected to enhance the sensitivity of Gravitational Waves Detectors. Photo: Ola J. Joensen

    “These gravitational wave detectors represent by far the most sensitive measuring equipment man has yet manufactured – still the detectors are not as accurate as they could possibly be. And this is what we intend to improve”, says Professor Eugene Polzik.

    How this can be done is outlined in an article which Eugene Polzik and a colleague, Farid Khalili from LIGO collaboration and Moscow State University, have recently published in the scientific journal Physical Review Letters. And this is not merely a theoretical proposal, says Eugene Polzik:

    “We are convinced this will work as intended. Our calculations show that we ought to be able to improve the precision of measurements carried out by the gravitational wave detectors by a factor of two. And if we succeed, this will result in an increase by a factor of eight of the volume in space which gravitational wave detectors are able to examine at present”.

    A small glass cell

    In July of last year Eugene Polzik and his team at Quantop published a highly noticed article in Nature – and this work is actually the very foundation of their upcoming attempt to improve the gravitational wave detectors.

    If laser light used to measure motion of a vibrating membrane (left) is first transmitted through an atom cloud (center) the measurement sensitivity can be better than standard quantum limits envisioned by Bohr and Heisenberg. Photo: Bastian Leonhardt Strube and Mads Vadsholt

    The article in Nature centered on ‘fooling’ Heisenberg’s Uncertainty Principle, which basically says that you cannot simultaneously know the exact position and the exact speed of an object.

    This has to do with the fact that observations conducted by shining light on an object inevitably will lead to the object being ‘kicked’ in random directions by photons, particles of light. This phenomenon is known as Quantum Back Action (QBA) and these random movements put a limit to the accuracy with which measurements can be carried out at the quantum level.

    The article in Nature in the summer of 2017 made headlines because Eugene Polzik and his team were able to show that it is – to a large extent – actually possible to neutralize QBA.

    And QBA is the very reason why gravitational wave detectors – that also operate with light, namely laser light – “are not as accurate as they could possibly be”, as professor Polzik says.

    Put simply, it is possible to neutralize QBA if the light used to observe an object is initially sent through a ‘filter’. This was what the article in Nature described – and the ‘filter’ which the NBI-scientists at Quantop had developed and described consisted of a cloud of 100 million caesium atoms locked-up in a hermetically closed glass cell just one centimeter long, 1/3 of a millimeter high and 1/3 of a millimeter wide.

    The principle behind this ‘filter’ is exactly what Polzik and his team are aiming to incorporate in gravitational wave detectors.

    PhD student Tulio Brasil, postdoctoral fellow Michael Zugenmaier and Professor Eugene Polzik in front of the future site of the experiment. Foto: Ola J. Joensen

    In theory one can optimize measurements of gravitational waves by switching to stronger laser light than the detectors in both Europe and USA are operating with. However, according to quantum mechanics, that is not an option, says Eugene Polzik:

    “Switching to stronger laser light will just make a set of mirrors in the detectors shake more because Quantum Back Action will be caused by more photons. These mirrors are absolutely crucial, and if they start shaking, it will in fact increase inaccuracy”.

    Instead, the NBI-scientists have come up with a plan based on the atomic ‘filter’ which they demonstrated in the Nature article: They will send the laser light by which the gravitational wave detectors operate through a tailor made version of the cell with the locked-up atoms, says Eugene Polzik: “And we hope that it will do the job”.

    See the full article here .


    Stem Education Coalition

    Niels Bohr Institute Campus

    The Niels Bohr Institute (Danish: Niels Bohr Institutet) is a research institute of the University of Copenhagen. The research of the institute spans astronomy, geophysics, nanotechnology, particle physics, quantum mechanics and biophysics.

    The Institute was founded in 1921, as the Institute for Theoretical Physics of the University of Copenhagen, by the Danish theoretical physicist Niels Bohr, who had been on the staff of the University of Copenhagen since 1914, and who had been lobbying for its creation since his appointment as professor in 1916. On the 80th anniversary of Niels Bohr’s birth – October 7, 1965 – the Institute officially became The Niels Bohr Institute.[1] Much of its original funding came from the charitable foundation of the Carlsberg brewery, and later from the Rockefeller Foundation.[2]

    During the 1920s, and 1930s, the Institute was the center of the developing disciplines of atomic physics and quantum physics. Physicists from across Europe (and sometimes further abroad) often visited the Institute to confer with Bohr on new theories and discoveries. The Copenhagen interpretation of quantum mechanics is named after work done at the Institute during this time.

    On January 1, 1993 the institute was fused with the Astronomic Observatory, the Ørsted Laboratory and the Geophysical Institute. The new resulting institute retained the name Niels Bohr Institute.

    The University of Copenhagen (UCPH) (Danish: Københavns Universitet) is the oldest university and research institution in Denmark. Founded in 1479 as a studium generale, it is the second oldest institution for higher education in Scandinavia after Uppsala University (1477). The university has 23,473 undergraduate students, 17,398 postgraduate students, 2,968 doctoral students and over 9,000 employees. The university has four campuses located in and around Copenhagen, with the headquarters located in central Copenhagen. Most courses are taught in Danish; however, many courses are also offered in English and a few in German. The university has several thousands of foreign students, about half of whom come from Nordic countries.

    The university is a member of the International Alliance of Research Universities (IARU), along with University of Cambridge, Yale University, The Australian National University, and UC Berkeley, amongst others. The 2016 Academic Ranking of World Universities ranks the University of Copenhagen as the best university in Scandinavia and 30th in the world, the 2016-2017 Times Higher Education World University Rankings as 120th in the world, and the 2016-2017 QS World University Rankings as 68th in the world. The university has had 9 alumni become Nobel laureates and has produced one Turing Award recipient

  • richardmitnick 3:20 pm on May 10, 2018 Permalink | Reply
    Tags: , , , Caltech/MIT Advanced aLigo, , Gravitational Waves Shed Light on Neutron Star Interiors,   

    From Sky & Telescope: “Gravitational Waves Shed Light on Neutron Star Interiors” 

    SKY&Telescope bloc

    From Sky & Telescope

    May 9, 2018
    Elizabeth Howell

    The gravitational-wave detection last year of a neutron star merger has revealed details on neutron star structure, ruling out exotic quark matter in the objects’ cores.

    Artist’s illustration of the final stages of a neutron-star merger. NASA / Goddard Space Flight Center

    A pair of independent studies gives new constraints on the size of neutron stars, suggesting that they are no more than 14 kilometers (8.6 miles) in radius. That’s about twice the length of the Las Vegas strip. This size limit is slightly larger than previous estimates, suggesting that neutron stars might be less exotic than previously thought.

    Neutron stars are the dense stellar remnants of supernova explosions. Within a tiny radius, they contain a mass of about 1.4 times that of the sun. The extreme densities and pressures smush electrons into the atomic nuclei their orbit — protons and electrons combine into neutrons, so that neutron stars are made mostly of neutrons. But there’s a possibility that the density at their cores might become so high, it breaks matter down into even smaller particles, such as quarks.

    As astrophysicist Feryal Özel (University of Arizona) explained in the July 2017 issue of Sky & Telescope, for neutron stars size really does matter — the smaller the star, the higher its core density. Previous measurements have pointed to a maximum neutron star radius between 10 and 11 km. That may not sound very different from 14 km, but it would be enough to raise the central density by more than a factor of two. “This is enough to have a profound effect on the amount of repulsion the particles experience,” Özel wrote, which would introduce the possibility of a quark-filled core.

    The new neutron star sizes, published in two papers appearing in April 25th Physical Review Letters, are based on the August 17, 2017, LIGO/Virgo detection of gravitational waves from a pair of neutron stars merging 130 million light-years away.

    UC Santa Cruz

    UC Santa Cruz


    A UC Santa Cruz special report

    Tim Stephens

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

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

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

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

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

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


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

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

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

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

    ESA/eLISA the future of gravitational wave research

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

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

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

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

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


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

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

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

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

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


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

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

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

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

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

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


    Neutron stars
    A team from UC Santa Cruz was the first to observe the light from a neutron star merger that took place on August 17, 2017 and was detected by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO)

    Graduate students and post-doctoral scholars at UC Santa Cruz played key roles in the dramatic discovery and analysis of colliding neutron stars.Astronomer Ryan Foley leads a team of young graduate students and postdoctoral scholars who have pulled off an extraordinary coup. Following up on the detection of gravitational waves from the violent merger of two neutron stars, Foley’s team was the first to find the source with a telescope and take images of the light from this cataclysmic event. In so doing, they beat much larger and more senior teams with much more powerful telescopes at their disposal.

    “We’re sort of the scrappy young upstarts who worked hard and got the job done,” said Foley, an untenured assistant professor of astronomy and astrophysics at UC Santa Cruz.

    David Coulter, graduate student

    The discovery on August 17, 2017, has been a scientific bonanza, yielding over 100 scientific papers from numerous teams investigating the new observations. Foley’s team is publishing seven papers, each of which has a graduate student or postdoc as the first author.

    “I think it speaks to Ryan’s generosity and how seriously he takes his role as a mentor that he is not putting himself front and center, but has gone out of his way to highlight the roles played by his students and postdocs,” said Enrico Ramirez-Ruiz, professor and chair of astronomy and astrophysics at UC Santa Cruz and the most senior member of Foley’s team.

    “Our team is by far the youngest and most diverse of all of the teams involved in the follow-up observations of this neutron star merger,” Ramirez-Ruiz added.

    Charles Kilpatrick, postdoctoral scholar

    Charles Kilpatrick, a 29-year-old postdoctoral scholar, was the first person in the world to see an image of the light from colliding neutron stars. He was sitting in an office at UC Santa Cruz, working with first-year graduate student Cesar Rojas-Bravo to process image data as it came in from the Swope Telescope in Chile. To see if the Swope images showed anything new, he had also downloaded “template” images taken in the past of the same galaxies the team was searching.

    Ariadna Murguia-Berthier, graduate student

    “In one image I saw something there that was not in the template image,” Kilpatrick said. “It took me a while to realize the ramifications of what I was seeing. This opens up so much new science, it really marks the beginning of something that will continue to be studied for years down the road.”

    At the time, Foley and most of the others in his team were at a meeting in Copenhagen. When they found out about the gravitational wave detection, they quickly got together to plan their search strategy. From Copenhagen, the team sent instructions to the telescope operators in Chile telling them where to point the telescope. Graduate student David Coulter played a key role in prioritizing the galaxies they would search to find the source, and he is the first author of the discovery paper published in Science.

    Matthew Siebert, graduate student

    “It’s still a little unreal when I think about what we’ve accomplished,” Coulter said. “For me, despite the euphoria of recognizing what we were seeing at the moment, we were all incredibly focused on the task at hand. Only afterward did the significance really sink in.”

    Just as Coulter finished writing his paper about the discovery, his wife went into labor, giving birth to a baby girl on September 30. “I was doing revisions to the paper at the hospital,” he said.

    It’s been a wild ride for the whole team, first in the rush to find the source, and then under pressure to quickly analyze the data and write up their findings for publication. “It was really an all-hands-on-deck moment when we all had to pull together and work quickly to exploit this opportunity,” said Kilpatrick, who is first author of a paper comparing the observations with theoretical models.

    César Rojas Bravo, graduate student

    Graduate student Matthew Siebert led a paper analyzing the unusual properties of the light emitted by the merger. Astronomers have observed thousands of supernovae (exploding stars) and other “transients” that appear suddenly in the sky and then fade away, but never before have they observed anything that looks like this neutron star merger. Siebert’s paper concluded that there is only a one in 100,000 chance that the transient they observed is not related to the gravitational waves.

    Ariadna Murguia-Berthier, a graduate student working with Ramirez-Ruiz, is first author of a paper synthesizing data from a range of sources to provide a coherent theoretical framework for understanding the observations.

    Another aspect of the discovery of great interest to astronomers is the nature of the galaxy and the galactic environment in which the merger occurred. Postdoctoral scholar Yen-Chen Pan led a paper analyzing the properties of the host galaxy. Enia Xhakaj, a new graduate student who had just joined the group in August, got the opportunity to help with the analysis and be a coauthor on the paper.

    Yen-Chen Pan, postdoctoral scholar

    “There are so many interesting things to learn from this,” Foley said. “It’s a great experience for all of us to be part of such an important discovery.”

    Enia Xhakaj, graduate student


    Scientific Papers from the 1M2H Collaboration

    Coulter et al., Science, Swope Supernova Survey 2017a (SSS17a), the Optical Counterpart to a Gravitational Wave Source

    Drout et al., Science, Light Curves of the Neutron Star Merger GW170817/SSS17a: Implications for R-Process Nucleosynthesis

    Shappee et al., Science, Early Spectra of the Gravitational Wave Source GW170817: Evolution of a Neutron Star Merger

    Kilpatrick et al., Science, Electromagnetic Evidence that SSS17a is the Result of a Binary Neutron Star Merger

    Siebert et al., ApJL, The Unprecedented Properties of the First Electromagnetic Counterpart to a Gravitational-wave Source

    Pan et al., ApJL, The Old Host-galaxy Environment of SSS17a, the First Electromagnetic Counterpart to a Gravitational-wave Source

    Murguia-Berthier et al., ApJL, A Neutron Star Binary Merger Model for GW170817/GRB170817a/SSS17a

    Kasen et al., Nature, Origin of the heavy elements in binary neutron star mergers from a gravitational wave event

    Abbott et al., Nature, A gravitational-wave standard siren measurement of the Hubble constant (The LIGO Scientific Collaboration and The Virgo Collaboration, The 1M2H Collaboration, The Dark Energy Camera GW-EM Collaboration and the DES Collaboration, The DLT40 Collaboration, The Las Cumbres Observatory Collaboration, The VINROUGE Collaboration & The MASTER Collaboration)

    Abbott et al., ApJL, Multi-messenger Observations of a Binary Neutron Star Merger


    Watch Ryan Foley tell the story of how his team found the neutron star merger in the video below. 2.5 HOURS.

    Press releases:

    UC Santa Cruz Press Release

    UC Berkeley Press Release

    Carnegie Institution of Science Press Release

    LIGO Collaboration Press Release

    National Science Foundation Press Release

    Media coverage:

    The Atlantic – The Slack Chat That Changed Astronomy

    Washington Post – Scientists detect gravitational waves from a new kind of nova, sparking a new era in astronomy

    New York Times – LIGO Detects Fierce Collision of Neutron Stars for the First Time

    Science – Merging neutron stars generate gravitational waves and a celestial light show

    CBS News – Gravitational waves – and light – seen in neutron star collision

    CBC News – Astronomers see source of gravitational waves for 1st time

    San Jose Mercury News – A bright light seen across the universe, proving Einstein right

    Popular Science – Gravitational waves just showed us something even cooler than black holes

    Scientific American – Gravitational Wave Astronomers Hit Mother Lode

    Nature – Colliding stars spark rush to solve cosmic mysteries

    National Geographic – In a First, Gravitational Waves Linked to Neutron Star Crash

    Associated Press – Astronomers witness huge cosmic crash, find origins of gold

    Science News – Neutron star collision showers the universe with a wealth of discoveries

    UCSC press release
    First observations of merging neutron stars mark a new era in astronomy


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

    Dark Energy Survey

    Dark Energy Camera [DECam], built at FNAL

    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet

    Gemini South telescope, Cerro Tololo Inter-American Observatory (CTIO) campus near La Serena, Chile, at an altitude of 7200 feet

    Noted in the video but not in the article:

    NASA/Chandra Telescope

    NASA/SWIFT Telescope

    NRAO/Karl V Jansky VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA

    Prompt telescope CTIO Chile

    NASA NuSTAR X-ray telescope

    See the full article here

    Massive objects, such as black holes and neutron stars, emit these ripples in spacetime as they move through space. The gravitational waves observed from the neutron star collision served as a probe of the objects’ structure. Even though the two papers used different approaches, they calculated roughly the same maximum size for neutron stars: Eemeli Annala (University of Helsinki, Finland) led a study that limited it to 13.6 km [Physical Review Letters], while Farrukh J. Fattoyev (Indiana University) and colleagues limited it to 13.76 km [Physical Review Letters]

    Neutron Stars in the Lab

    Neutron star. Casey Reed / Penn State University

    Given their extremely high density, astronomers aren’t certain what neutron stars look like on the inside. Some of their ideas are based on nuclear physics, while the concept of quark matter in particular is based on the physics of high-energy particles. The various approaches can give different predictions about neutron stars’ internal structure.

    Experiments at the Large Hadron Collider (LHC) at CERN and the Relativistic Heavy Ion Collider at Brookhaven National Laboratory give a sense of what a neutron star might look like in its core. Researchers at these institutions smash lead ions together at close to the speed of light to produce the high temperatures that break down protons and neutrons into a quark-gluon plasma.


    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    BNL RHIC Campus

    BNL/RHIC Star Detector


    “These collisions create ion-sized droplets of matter so dense that the structure of the protons and neutrons melts, and we are left with a small droplet of quark matter for a very brief moment,” says theoretical physicist Aleksi Kurkela (CERN), Annala’s coauthor. “We think that this hot quark-gluon plasma is closely related to the ‘cool’ quark matter that we may find in the cores of neutron stars. By studying the properties of the quark-gluon plasma, we try to learn and infer what is happening in the cores of neutron stars.”

    If neutron stars produce quarks in their centers, they might undergo a phase change. “We could potentially observe . . . neutron stars with similar masses but with quite different radii,” Kurkela explains. “Then the interpretation would be that the one with larger radius would be made of stiffer material, supposedly neutron matter. The smaller one would be made of, or at least would have a core made of, softer material which could be quark matter.”

    “While our current theories provide a very good description of dense matter at nuclear densities, their predictions significantly deviate when extrapolated to super-nuclear densities,” adds Fattoyev (Indiana University).

    Indeed, some of LIGO’s observations aren’t matching up with what scientists previously theorized, specifically with regards to the types of matter found inside of neutron stars, Kurkela says.

    From Shape to Size

    This artist’s conception portrays two neutron stars at the moment of collision.
    Dana Berry / SkyWorks Digital, Inc.

    As two neutron stars circle each other, their respective gravitational fields create tidal forces in their partner: Gravity pulls more strongly on the side of the star closer to its companion compared to its far side. As a result, both neutron stars stretch, tidally deforming into a shape resembling a rugby ball, Kurkela explains.

    The neutron stars’ shapes show what they are made of. If the matter inside of neutron stars were soft, that is, containing quarks in addition to neutrons, LIGO would see the neutron stars deform. But LIGO’s observations don’t fit those theories Instead, Kurkela explains, LIGO’s work showed that the neutron stars were like hard, unsquishable balls, even as they merged into each other, which means they contain only neutrons in their cores. The results allowed investigators to rule out the existence of quarks inside of neutron stars.

    Scientists will need more gravitational-wave observations to confirm what LIGO saw. Moreover, since neutron star collisions generate light in addition to gravitational waves, scientists hope to get more information on composition through follow-up X-ray observations, such as from the Neutron star Interior Composition Explorer (NICER) perched on the International Space Station.

    See the full article here .

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    Sky & Telescope magazine, founded in 1941 by Charles A. Federer Jr. and Helen Spence Federer, has the largest, most experienced staff of any astronomy magazine in the world. Its editors are virtually all amateur or professional astronomers, and every one has built a telescope, written a book, done original research, developed a new product, or otherwise distinguished him or herself.

    Sky & Telescope magazine, now in its eighth decade, came about because of some happy accidents. Its earliest known ancestor was a four-page bulletin called The Amateur Astronomer, which was begun in 1929 by the Amateur Astronomers Association in New York City. Then, in 1935, the American Museum of Natural History opened its Hayden Planetarium and began to issue a monthly bulletin that became a full-size magazine called The Sky within a year. Under the editorship of Hans Christian Adamson, The Sky featured large illustrations and articles from astronomers all over the globe. It immediately absorbed The Amateur Astronomer.

    Despite initial success, by 1939 the planetarium found itself unable to continue financial support of The Sky. Charles A. Federer, who would become the dominant force behind Sky & Telescope, was then working as a lecturer at the planetarium. He was asked to take over publishing The Sky. Federer agreed and started an independent publishing corporation in New York.

    “Our first issue came out in January 1940,” he noted. “We dropped from 32 to 24 pages, used cheaper quality paper…but editorially we further defined the departments and tried to squeeze as much information as possible between the covers.” Federer was The Sky’s editor, and his wife, Helen, served as managing editor. In that January 1940 issue, they stated their goal: “We shall try to make the magazine meet the needs of amateur astronomy, so that amateur astronomers will come to regard it as essential to their pursuit, and professionals to consider it a worthwhile medium in which to bring their work before the public.”

  • richardmitnick 11:58 am on April 27, 2018 Permalink | Reply
    Tags: 000 Black Hole Mergers A Year..., , , , Caltech/MIT Advanced aLigo, , , , LIGO Misses 100   

    From Ethan Siegel: “LIGO Misses 100,000 Black Hole Mergers A Year…” 

    Ethan Siegel
    Apr 26, 2018

    …but if a radical new idea comes to fruition, maybe we can find them after all.

    The General Relativity picture of curved spacetime, where matter and energy determine how these systems evolve over time, has made successful predictions that no other theory can match, including for the existence and properties of gravitational waves: ripples in spacetime. (LIGO)

    After decades of planning, building, prototyping, upgrading, and calibrating, the Laser Interferometer Gravitational-wave Observatory (LIGO) finally achieved it’s ultimate goal just a little over two years ago: the first direct detection of gravitational waves.

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

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

    ESA/eLISA the future of gravitational wave research

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

    Since 2015, LIGO has seen the ripples in spacetime or gravitational waves from no fewer than six separate events. Five (and possibly more) black hole-black hole pairs and one neutron star-neutron star inspiral-and-merger had their unique, unmistakable signatures detected by multiple gravitational wave detectors simultaneously, enabling us to confirm a key prediction of Einstein’s General Relativity that had eluded experimentalists for a century. But in theory, black hole-black hole mergers should occur every few minutes somewhere in the Universe; LIGO is missing more than 100,000 of these annually. For the first time, a team of scientists may just have figured out how to detect all the mergers that LIGO is currently missing.

    When two black holes orbit one another, they’re both radiating energy away, and doing so constantly. According to Einstein’s General Relativity, any time a mass moves and accelerates through a changing gravitational field, itself changing its momentum, it has to emit radiation inherent to space itself: gravitational radiation. Each of the two masses in their gravitational dance emits them, and part of the theoretical work behind LIGO was calculating in excruciating detail what the magnitude, duration, amplitude, and frequencies of gravitational waves would be emitted for any two arbitrary black hole masses and orientations.

    The gravitational wave signal from the first pair of detected, merging black holes from the LIGO collaboration. Although a large amount of information can be extracted, no images or the presence/absence of an event horizon can be gleaned. (B. P. Abbott et al., (LIGO Scientific Collaboration and Virgo Collaboration), Physical Review Letters 116, 061102 (2016))

    It was only from that sort of template creation and matching that we were able to detect these events at all. It was incredibly successful as well; the confirmations, when they occurred, were spectacular in their agreement with the predictions. But LIGO is only sensitive to those final few moments of a merger, where the amplitude of these gravitational waves is sufficient to contract-and-expand these enormous arms by a tiny fraction of a wavelength of light, enough so that after a thousand reflections, the light shifts by a barely-perceptible amount.

    The masses of stellar remnants are measured in many different ways. This graphic shows the masses for black holes detected through electromagnetic observations (purple); the black holes measured by gravitational-wave observations (blue); neutron stars measured with electromagnetic observations (yellow); and the masses of the neutron stars that merged in an event called GW170817, which were detected in gravitational waves (orange).(LIGO-Virgo/Frank Elavsky/Northwestern)

    Over the time that LIGO’s been operational, it has seen six robust events: about 0.001% of the total number of mergers expected in the Universe. Sure, most of them are anticipated to be far away, oriented non-optimally, or to occur between low-mass, low-amplitude black holes. There’s a good reason LIGO hasn’t seen them; the current generation of ground-based gravitational wave detectors are severely limited in sensitivity and range.

    Illustrated here is the range of Advanced LIGO and its capability of detecting merging black holes. Merging neutron stars may have only one-tenth the range and 0.1% the volume, but if neutron stars are abundant enough, LIGO may have a chance at those, too. (LIGO Collaboration / Amber Stuver / Richard Powell / Atlas of the Universe)

    But with 100,000 black hole-black hole mergers occurring annually in the observable Universe, these gravitational wave signals are constantly passing through Earth and our detectors. They’re simply below the detectable threshold, meaning that they have an impact on an apparatus like LIGO or Virgo, but not one we can pull out and identify as a unique, unambiguous gravitational wave event. You may not be able to detect them individually, but with so many of them occurring, it may be possible to extract an aggregate signal. Rather than an individual chirp, these combined mergers should produce a gravitational wave background hum. These mergers are quick and shouldn’t overlap with one another, meaning that the background should look like a series of disconnected signals that are too faint to detect.

    The noise (top), the strain (middle), and the reconstructed signal (bottom) in a bona fide gravitational wave event seen in all three detectors. For most of the mergers, they’re simply too far away for their amplitude in order for LIGO/Virgo to detect them. (The LIGO Scientific Collaboration and The Virgo Collaboration)

    That is, they’re too faint to detect individually! But if you know what your signal looks like and you both build up enough statistics and apply enough computational power, you just might be able to tease it out of the noise. It won’t tell you how many individual events you have, but it can tell you how many total events there are over the time you observe it. In other words, rather than say, “we expect 100,000 of these a year,” we can actually observe the overall black hole-black hole merger rate in the Universe. More importantly, we can learn, for the first time, what the total number-and-mass density of black holes in the Universe actually is.

    A map of the 7 million second exposure of the Chandra Deep Field-South. This region shows hundreds of supermassive black holes, each one in a galaxy far beyond our own. There should be hundreds of thousands of times as many stellar-mass black holes; we’re just waiting for the capability of detecting them. (NASA/CXC/B. Luo et al., 2017, ApJS, 228, 2)

    NASA/Chandra X-ray Telescope

    In a new paper entitled Optimal Search for an Astrophysical Gravitational-Wave Background [PHYSICAL REVIEW X], scientists Rory Smith and Eric Thrane propose to do exactly that. For every problem like this, there’s a computationally optimal way to approach it, and Smith and Thrane worked hard to come up with the answer. There are a number of interesting things the authors deduce they can learn from this computational exercise:

    You can derive the most sensitive possible search for this background of unresolved black holes.
    You can learn about the populations of black holes at earlier times in the Universe compared to the modern, nearby Universe.
    You can combine the results of this search with both confirmed detections and marginal, candidate detections to remove the bias inherent in seeing the largest-amplitude signals the most easily.
    If it’s successful, this method can be generalized to neutron stars, non-merging masses, and even potentially the gravitational wave background left over from the Universe’s birth.

    The final prediction of cosmic inflation is the existence of primordial gravitational waves. It is the only one of inflation’s predictions to not be verified by observation… yet. (National Science Foundation (NASA, JPL, Keck Foundation, Moore Foundation, related) — Funded BICEP2 Program; modifications by E. Siegel)

    Best of all, their conclusions are incredibly optimistic for what the future holds for applying this supercomputer-based technique to the LIGO and Virgo data sets. Writing in the journal Physical Review X, they state:

    “…Preliminary estimates suggest that advanced detectors, operating at design sensitivity, can detect a stochastic background from binary black holes in about 1 day. These estimates rely on extrapolation using Gaussian mixture modeling of our Bayesian evidence distributions. The next step is to carry out a mock data challenge in which we demonstrate the safety and efficacy of the search using ≈1 day of design sensitivity Monte Carlo data. Such a demonstration would allow us to verify the extrapolations made here with a modest computational cost ≈500 000 core hours….”

    In other words, they plan to demonstrate that this signal can be extracted from a noisy background by simulating it, blinding the computer, and then proving that the supercomputer, alone, can identify it.

    By simulating both data sets with (left) and without (right) a signal, the researchers anticipate that a realistic astrophysical background should be detected with a supercomputer time of approximately 20 hours, compared to more than year using existing methods. (R. Smith and E. Thrane, Phys. Rev. X 8, 021019 (2018)[link is above])

    The era of gravitational wave astronomy is now upon us. Owing to the incredible capabilities of ground-based detectors like LIGO and Virgo, we have now detected six robust events over the past 2+ years, from black holes to merging neutron stars. But huge questions surrounding the black holes in the Universe, such as how many there are, what their masses are early on compared to today, and what percent of the Universe is made of black holes, still remain to be answered. The direct efforts have gotten us a very long way, but the indirect signals matter, too, and can potentially teach us even more if we’re willing to make inferences that follow the physics and math. LIGO may be missing upwards of 100,000 black hole-black hole mergers a year. But with this new proposed technique, we might finally learn what else is out there, with the potential to apply this to neutron stars, non-merging black holes, and even the leftover ripples from our cosmic birth. It’s an incredible time to be alive.

    See the full article here .

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    Stem Education Coalition

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

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