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  • richardmitnick 9:05 am on February 27, 2020 Permalink | Reply
    Tags: , , , , , Multi-messenger astrophysics,   

    From ARC Centres of Excellence for Gravitational Wave Discovery via phys.org: “Future space detector LISA could reveal the secret life and death of stars” 


    From ARC Centres of Excellence for Gravitational Wave Discovery



    Artist’s illustration of an ‘isolated neutron star’—one without associated supernova remnants, binary companions or radio pulsations. Credit: Casey Reed – Penn State University

    A team of astrophysicists led by Ph.D. student Mike Lau, from the ARC Centre of Excellence in Gravitational Wave Discovery (OzGrav), recently predicted that gravitational waves of double neutron stars may be detected by the future space satellite LISA. The results were presented at the 14th annual Australian National Institute for Theoretical Astrophysics (ANITA) science workshop 2020. These measurements may help decipher the life and death of stars.

    Lau, first author of the paper, compares his team to astro-paleontologists: “Like learning about a dinosaur from its fossil, we piece together the life of a binary star from their double neutron star fossils.”

    A neutron star is the remaining ‘corpse’ of a huge star after the supernova explosion that occurs at the end of its life. A double neutron star, a system of two neutron stars orbiting each other, produces periodic disturbances in the surrounding space-time, much like ripples spreading on a pond surface. These ‘ripples’ are called gravitational waves, and made headlines when the LIGO/Virgo Collaboration detected them for the first time in 2015. These gravitational waves formed when a pair of black holes spiraled too close together and merged.

    However, scientists still haven’t found a way to measure the gravitational waves given off when two neutron stars or black holes are still far apart in their orbit. These weaker waves hold valuable information about the lives of stars and could reveal the existence of entirely new object populations in our Galaxy.

    The recent study [below] shows that the Laser Interferometer Space Antenna (LISA) could potentially detect these gravitational waves from double neutron stars.


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

    LISA is a space-borne gravitational-wave detector that is scheduled for launch in 2034, as part of a mission led by the European Space Agency. It’s made of three satellites linked by laser beams, forming a triangle that will orbit the Sun. Passing gravitational waves will stretch and squeeze the 40 million-kilometer laser arms of this triangle. The highly sensitive detector will pick up the slowly-oscillating waves—these are currently undetectable by LIGO and Virgo.

    MIT /Caltech Advanced aLigo

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Using computer simulations to model a population of double neutron stars, the team predicts that in four years of operation, LISA will have measured the gravitational waves emitted by dozens of double neutron stars as they orbit each other. Their results were published in the Monthly Notices of the Royal Astronomical Society.

    A supernova explosion kicks the neutron star it forms and makes the initial circular orbit oval-shaped. Usually, gravitational wave emission rounds off the orbit—that is the case for double neutron stars detected by LIGO and Virgo. But LISA will be able to detect double neutron stars when they’re still far apart, so it may be possible to catch a glimpse of the oval orbit.

    How oval the orbit is, described as the eccentricity of the orbit, can tell astronomers a lot about what the two stars looked like before they became double neutron stars. For example, their separation and how strongly they were ‘kicked’ by the supernova.

    The understanding of binary stars—stars that are born as a pair—is plagued with many uncertainties. Scientists hope that by the 2030s, LISA’s detection of double neutron stars will shed some light on their secret lives.

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    About Science X in 100 words
    Science X™ is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004 (Physorg.com), Science X’s readership has grown steadily to include 5 million scientists, researchers, and engineers every month. Science X publishes approximately 200 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Science X community members enjoy access to many personalized features such as social networking, a personal home page set-up, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.
    Mission 12 reasons for reading daily news on Science X Organization Key editors and writersinclude 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.


    A new window of discovery.
    A new age of gravitational wave astronomy.
    One hundred years ago, Albert Einstein produced one of the greatest intellectual achievements in physics, the theory of general relativity. In general relativity, spacetime is dynamic. It can be warped into a black hole. Accelerating masses create ripples in spacetime known as gravitational waves (GWs) that carry energy away from the source. Recent advances in detector sensitivity led to the first direct detection of gravitational waves in 2015. This was a landmark achievement in human discovery and heralded the birth of the new field of gravitational wave astronomy. This was followed in 2017 by the first observations of the collision of two neutron-stars. The accompanying explosion was subsequently seen in follow-up observations by telescopes across the globe, and ushered in a new era of multi-messenger astronomy.

    The mission of the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) is to capitalise on the historic first detections of gravitational waves to understand the extreme physics of black holes and warped spacetime, and to inspire the next generation of Australian scientists and engineers through this new window on the Universe.

    OzGrav is funded by the Australian Government through the Australian Research Council Centres of Excellence funding scheme, and is a partnership between Swinburne University (host of OzGrav headquarters), the Australian National University, Monash University, University of Adelaide, University of Melbourne, and University of Western Australia, along with other collaborating organisations in Australia and overseas.


    The objectives for the ARC Centres of Excellence are to to:

    undertake highly innovative and potentially transformational research that aims to achieve international standing in the fields of research envisaged and leads to a significant advancement of capabilities and knowledge
    link existing Australian research strengths and build critical mass with new capacity for interdisciplinary, collaborative approaches to address the most challenging and significant research problems
    develope relationships and build new networks with major national and international centres and research programs to help strengthen research, achieve global competitiveness and gain recognition for Australian research
    build Australia’s human capacity in a range of research areas by attracting and retaining, from within Australia and abroad, researchers of high international standing as well as the most promising research students
    provide high-quality postgraduate and postdoctoral training environments for the next generation of researchers
    offer Australian researchers opportunities to work on large-scale problems over long periods of time
    establish Centres that have an impact on the wider community through interaction with higher education institutes, governments, industry and the private and non-profit sector.

  • richardmitnick 1:52 pm on February 22, 2020 Permalink | Reply
    Tags: , , , , Black Hole convergence, , , LIGO/VIRO, Multi-messenger astrophysics   

    From AAS NOVA: “Gravitational Waves After Galaxy Collisions” 


    From AAS NOVA

    21 February 2020
    Susanna Kohler

    A new study explores whether the collision of very small galaxies could lead to the merging black holes detected in gravitational waves. [NASA/ESA]

    Thanks to the Laser Interferometer Gravitational-wave Observatory (LIGO), we now know that black holes in our distant universe sometimes find each other in a dramatic inspiral and collision, releasing a burst of gravitational-wave emission that we can detect here on Earth.

    But what happened earlier in these black holes’ lives to bring them to this point? A new study explores the possibility that LIGO’s black holes once lay at the centers of very small galaxies — until those galaxies collided.

    Simulated iconic image of two merging black holes, viewed face-on. LIGO has announced the detection of ten of these events so far. [SXS Lensing]

    Central Lurkers

    Since we discovered the first wiggles in spacetime signifying the distant merger of two black holes, LIGO has announced around ten confident detections of gravitational waves from black hole–black hole collisions — with the prospect of many more discoveries in the future.

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

    But how did these black holes find each other? A team of scientists led by Christopher Conselice (University of Nottingham, UK) has proposed a picture that hinges on the central black holes we believe lie at the heart of most, if not all, galaxies.

    The team proposes that very low-mass dwarf galaxies contain central black holes of less than 100 solar masses. The mergers of pairs of these tiny galaxies ultimately lead to the inspirals and mergers of their central black holes — possibly accounting for the majority of LIGO’s detections of black hole–black hole collisions.

    Testing Feasibility

    Conselice and collaborators test this scenario by breaking it down into multiple steps.

    The relationship between black hole mass and host galaxy stellar mass (black solid line; blue dashed lines show uncertainties), extrapolated down to low masses. Red lines indicate the masses of LIGO-detected black holes. [Conselice et al. 2020]

    1.Can you get central black holes of the right mass?
    We’ve observed a relationship between galaxy mass and central black hole mass. By extrapolating this relationship to low masses, we find that ultradwarf galaxies can have central black holes of less than 100 solar masses — consistent with the LIGO-observed black holes of 10–70 solar masses.
    2. Will these ultradwarf galaxies merge frequently enough?
    Mergers of galaxies occurred more frequently in the early universe than they do today. Cosmological models indicate that galaxies don’t merge frequently enough today to reproduce LIGO’s observations — but at a redshift of z ~ 1.5 or higher, ultradwarf galaxies could merge often enough to match LIGO-measured gravitational-wave event rates.
    3.Will the black holes collide fast enough after the galaxies merge?
    If the galaxies merged at a redshift of z > 1.5, the central black holes would have to sink to the middle of the merger, inspiral, and collide on timescales of 6–8 billion years to match LIGO observations. This is feasible if the black holes are embedded in a massive star cluster at the galaxy center.

    A Future Hunt for Hosts

    Conselice and collaborators’ calculations show that merging ultradwarf galaxies in the distant universe could, conceivably, account for LIGO’s black hole–black hole merger detections.

    An example of a dwarf spheroidal galaxy. The smallest dwarfs are far too faint to detect at high redshifts with current technology. [ESO/Digitized Sky Survey 2]

    In the future, we can hope to test this theory by better pinpointing the hosts of gravitational-wave events. If we find that the black-hole collisions all originate from bright, massive galaxies, then the ultradwarf-merger theory is out. But if we can’t spot the hosts, this might be because they’re ultradwarfs that are too small and faint to detect.

    The field of gravitational-wave astronomy is still only just coming of age, and theoretical work like this study shows how just how much we can hope to learn in the future!


    “LIGO/Virgo Sources from Merging Black Holes in Ultradwarf Galaxies,” Christopher J. Conselice et al 2020 ApJ 890 8.

    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.

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  • richardmitnick 7:40 am on January 20, 2020 Permalink | Reply
    Tags: "Astronomers Detect a Burst of Gravitational Waves From The Direction of Betelgeuse", , , , , , Gravitation Wave Astronomy, Multi-messenger astrophysics   

    From MIT Caltech Advanced aLIGO via Science Alert: “Astronomers Detect a Burst of Gravitational Waves From The Direction of Betelgeuse” 

    MIT Caltech Caltech Advanced aLigo new bloc

    From MIT Caltech Advanced aLIGO



    Science Alert

    Betelgeuse captured in 2010. (Rogelio Bernal Andreo/Wikimedia Commons/CC BY-SA 3.0)

    20 JAN 2020

    Gravitational waves [below] are caused by calamitous events in the Universe. Neutron stars that finally merge after circling each other for a long time can create them, and so can two black holes that collide with each other. But sometimes there’s a burst of gravitational waves that doesn’t have a clear cause.

    One such burst was detected by LIGO/VIRGO on January 14, and it came from the same region of sky that hosts the star Betelgeuse. Yeah, Betelgeuse, aka Alpha Orionis. The star that has been exhibiting some dimming behaviour recently, and is expected to go supernova at some point in the future.

    Might the two be connected?

    Betelgeuse is a red supergiant star in the constellation Orion. It left the main sequence about one million years ago and has been a red supergiant for about 40,000 years. Eventually, Betelgeuse will have burned enough of its hydrogen that its core will collapse, and it will explode as a supernova.

    Recently, Betelgeuse dimmed. That set off all kinds of speculation that it might be getting ready to go supernova. Astrophysicists quickly poured water on that idea. There’s no exact number, but it’s estimated that Betelgeuse won’t go supernova for another 100,000 years. But when a star dims, there’s clearly something going on.

    Is this new burst of gravitational waves connected to Betelgeuse’s recent dimming? To its future supernova explosion?

    Astronomers understand that Betelgeuse is a variable star, and its brightness can fluctuate. Stars like Betelgeuse aren’t just static entities. It’s a semi-regular variable star that shows both periodic and non-periodic changes in its brightness.

    The kind of gravitational waves that LIGO detected are called burst waves. It’s possible that a supernova could produce them, but Betelgeuse hasn’t gone supernova and won’t for a long time.

    Some think that the detection of gravitational waves in Betelgeuse’s direction is unrelated to the star itself. In fact, the detection of the burst waves may not have even been real.

    Christopher Berry is an astrophysicist studying gravitational waves at Northwestern University’s Center for Interdisciplinary Exploration and Research in Astrophysics.

    On Twitter he spoke up about the gravitational burst waves.

    Andy Howell from Las Cumbres Observatory studies supernova and dark energy. He had something to say on Twitter too, and appeared to be having fun with the whole thing. He even walked outside to check up on Betelgeuse after the detection of the burst gravitational waves.


    So there you have it. No supernova for now, anyway. The burst gravitational waves may just be a glitch, and Betelgeuse’s dimming is well-understood and not a threat.

    One day Betelgeuse will explode, and our night sky will change forever. But for us here on Earth, that supernova poses no problem.

    An exploding star is an awesome event. And it produces a cataclysm of deadly radiation. X-rays, ultraviolet radiation, and even stellar material are ejected with great force. The deadliest radiation is gamma rays, and Betelgeuse likely won’t even produce any of those when it blows.

    But in any case, we’re about 700 light years away from Betelgeuse, and that’s way too much distance for us to worry.

    The biggest fallout is that the Orion constellation will change forever. And there’ll be a new object to study in the sky: a supernova remnant.


    Please help promote STEM in your local schools.

    Stem Education Coalition

    See the full article here .

    The Collaborations

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

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

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

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

    ESA/eLISA the future of gravitational wave research

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

  • richardmitnick 2:12 pm on January 7, 2020 Permalink | Reply
    Tags: "LIGO-Virgo Network Catches Another Neutron Star Collision", , , , , , , , Multi-messenger astrophysics   

    From MIT Caltech Advanced aLIGO and Advanced Virgo: “LIGO-Virgo Network Catches Another Neutron Star Collision” 

    MIT /Caltech Advanced aLigo

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    From MIT Caltech Advanced aLIGO and Advanced Virgo

    January 6, 2020

    Whitney Clavin

    Abigail Abazorius

    Livia Conti

    Josh Chamot

    Artist’s rendition of two colliding neutron stars. Credit: National Science Foundation/LIGO/Sonoma State University/A. Simonnet

    On April 25, 2019, the LIGO Livingston Observatory picked up what appeared to be gravitational ripples from a collision of two neutron stars. LIGO Livingston is part of a gravitational-wave network that includes LIGO (the Laser Interferometer Gravitational-wave Observatory), funded by the National Science Foundation (NSF), and the European Virgo detector. Now, a new study confirms that this event was indeed likely the result of a merger of two neutron stars. This would be only the second time this type of event has ever been observed in gravitational waves.

    The first such observation, which took place in August of 2017, made history for being the first time that both gravitational waves and light were detected from the same cosmic event. The April 25 merger, by contrast, did not result in any light being detected. However, through an analysis of the gravitational-wave data alone, researchers have learned that the collision produced an object with an unusually high mass.

    “From conventional observations with light, we already knew of 17 binary neutron star systems in our own galaxy and we have estimated the masses of these stars,” says Ben Farr, a LIGO team member based at the University of Oregon. “What’s surprising is that the combined mass of this binary is much higher than what was expected.”

    “We have detected a second event consistent with a binary neutron star system and this is an important confirmation of the August 2017 event that marked an exciting new beginning for multi-messenger astronomy two years ago,” says Jo van den Brand, Virgo Spokesperson and professor at Maastricht University, and Nikhef and VU University Amsterdam in the Netherlands. Multi-messenger astronomy occurs when different types of signals are witnessed simultaneously, such as those based on gravitational waves and light.

    The study, submitted to The Astrophysical Journal Letters, is authored by an international team comprised of the LIGO Scientific Collaboration and the Virgo Collaboration, the latter of which is associated with the Virgo gravitational-wave detector in Italy. The results were presented at a press briefing today, January 6, at the 235th meeting of the American Astronomical Society in Honolulu, Hawaii.

    One of two science papers:

    On January 6, 2020, the LIGO Scientific Collaboration and the Virgo Collaboration announced the discovery of a second binary neutron star merger, labeled GW190425. This is the first confirmed gravitational-wave detection based on data from a single observatory. No electromagnetic counterpart was found. This system is notable for having a total mass that exceeds that of known galactic neutron star binaries.
    Publications & Documents

    Publication: GW190425: Observation of a compact binary coalescence with total mass ∼3.4 Msun

    The other paper hasn’t been accepted or published yet and may be a while.

    Neutron stars are the remnants of dying stars that undergo catastrophic explosions as they collapse at the end of their lives. When two neutron stars spiral together, they undergo a violent merger that sends gravitational shudders through the fabric of space and time.

    LIGO became the first observatory to directly detect gravitational waves in 2015; in that instance, the waves were generated by the fierce collision of two black holes. Since then, LIGO and Virgo have registered dozens of additional candidate black hole mergers.

    The August 2017 neutron star merger was witnessed by both LIGO detectors, one in Livingston, Louisiana, and one in Hanford, Washington, together with a host of light-based telescopes around the world (neutron star collisions produce light, while black hole collisions are generally thought not to do so). This merger was not clearly visible in the Virgo data, but that fact provided key information that ultimately pinpointed the event’s location in the sky.

    The April 2019 event was first identified in data from the LIGO Livingston detector alone. The LIGO Hanford detector was temporarily offline at the time, and, at a distance of more than 500 million light-years, the event was too faint to be visible in Virgo’s data. Using the Livingston data, combined with information derived from Virgo’s data, the team narrowed the location of the event to a patch of sky more than 8,200 square degrees in size, or about 20 percent of the sky. For comparison, the August 2017 event was narrowed to a region of just 16 square degrees, or 0.04 percent of the sky.

    “This is our first published event for a single-observatory detection,” says Caltech’s Anamaria Effler, a scientist who works at LIGO Livingston. “But Virgo made a valuable contribution. We used information about its non-detection to tell us roughly where the signal must have originated from.”

    The LIGO data reveal that the combined mass of the merged bodies is about 3.4 times the mass of our sun. In our galaxy, known binary neutron star systems have combined masses up to only 2.9 times that of sun. One possibility for the unusually high mass is that the collision took place not between two neutron stars, but a neutron star and a black hole, since black holes are heavier than neutron stars. But if this were the case, the black hole would have to be exceptionally small for its class. Instead, the scientists believe it is much more likely that LIGO witnessed a shattering of two neutron stars.

    “What we know from the data are the masses, and the individual masses most likely correspond to neutron stars. However, as a binary neutron star system, the total mass is much higher than any of the other known galactic neutron star binaries,” says Surabhi Sachdev, a LIGO team member based at Penn State. “And this could have interesting implications for how the pair originally formed.”

    Neutron star pairs are thought to form in two possible ways. They might form from binary systems of massive stars that each end their lives as neutron stars, or they might arise when two separately formed neutron stars come together within a dense stellar environment. The LIGO data for the April 25 event do not indicate which of these scenarios is more likely, but they do suggest that more data and new models are needed to explain the merger’s unexpectedly high mass.


    Please help promote STEM in your local schools.

    Stem Education Coalition

    See the full article here .

    The Collaborations

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

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

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

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

    ESA/eLISA the future of gravitational wave research

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

  • richardmitnick 10:17 am on December 29, 2019 Permalink | Reply
    Tags: , , , , , , Multi-messenger astrophysics, ,   

    From particlebites: “Dark Photons in Light Places” 

    particlebites bloc

    From particlebites

    December 29, 2019
    Amara McCune

    Title: “Searching for dark photon dark matter in LIGO O1 data”

    Author: Huai-Ke Guo, Keith Riles, Feng-Wei Yang, & Yue Zhao

    Reference: https://www.nature.com/articles/s42005-019-0255-0

    There is very little we know about dark matter save for its existence.

    Fritz Zwicky discovered Dark Matter when observing the movement of the Coma Cluster., Vera Rubin a Woman in STEM denied the Nobel, did most of the work on Dark Matter.

    Fritz Zwicky from http:// palomarskies.blogspot.com

    Coma cluster via NASA/ESA Hubble

    Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science)

    Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL)

    Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu

    The LSST, or Large Synoptic Survey Telescope is to be named the Vera C. Rubin Observatory by an act of the U.S. Congress.

    LSST telescope, The Vera Rubin Survey Telescope currently under construction on the El Peñón peak at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.

    Dark Matter Research

    Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey

    Scientists studying the cosmic microwave background [CMB] hope to learn about more than just how the universe grew—it could also offer insight into dark matter, dark energy and the mass of the neutrino.

    CMB per ESA/Planck

    Dark matter cosmic web and the large-scale structure it forms The Millenium Simulation, V. Springel et al

    Dark Matter Particle Explorer China

    DEAP Dark Matter detector, The DEAP-3600, suspended in the SNOLAB deep in Sudbury’s Creighton Mine

    LBNL LZ Dark Matter project at SURF, Lead, SD, USA

    Inside the ADMX experiment hall at the University of Washington Credit Mark Stone U. of Washington. Axion Dark Matter Experiment

    Its mass(es), its interactions, even the proposition that it consists of particles at all is mostly up to the creativity of the theorist. For those who don’t turn to modified theories of gravity to explain the gravitational effects on galaxy rotation and clustering that suggest a massive concentration of unseen matter in the universe (among other compelling evidence), there are a few more widely accepted explanations for what dark matter might be. These include weakly-interacting massive particles (WIMPS), primordial black holes, or new particles altogether, such as axions or dark photons.

    In particle physics, this latter category is what’s known as the “hidden sector,” a hypothetical collection of quantum fields and their corresponding particles that are utilized in theorists’ toolboxes to help explain phenomena such as dark matter. In order to test the validity of the hidden sector, several experimental techniques have been concocted to narrow down the vast parameter space of possibilities, which generally consist of three strategies:

    1.Direct detection: Detector experiments look for low-energy recoils of dark matter particle collisions with nuclei, often involving emitted light or phonons.
    2.Indirect detection: These searches focus on potential decay products of dark matter particles, which depends on the theory in question.
    3.Collider production: As the name implies, colliders seek to produce dark matter in order to study its properties. This is reliant on the other two methods for verification.

    The first detection of gravitational waves from a black hole merger in 2015 ushered in a new era of physics, in which the cosmological range of theory-testing is no longer limited to the electromagnetic spectrum.

    MIT /Caltech Advanced aLigo

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

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

    Caltech/MIT Advanced aLigo detector installation Hanford, WA, USA

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Gravity is talking. Lisa will listen. Dialogos of Eide

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

    Bringing LIGO (the Laser Interferometer Gravitational-Wave Observatory) to the table, proposals for the indirect detection of dark matter via gravitational waves began to spring up in the literature, with implications for primordial black hole detection or dark matter ensconced in neutron stars. Yet a new proposal, in a paper by Guo et. al., [Scientific Reports-Communication Physics] suggests that direct dark matter detection with gravitational waves may be possible, specifically in the case of dark photons.

    Dark photons are hidden sector particles in the ultralight regime of dark matter candidates. Theorized as the gauge boson of a U(1) gauge group, meaning the particle is a force-carrier akin to the photon of quantum electrodynamics, dark photons either do not couple or very weakly couple to Standard Model particles in various formulations. Unlike a regular photon, dark photons can acquire a mass via the Higgs mechanism. Since dark photons need to be non-relativistic in order to meet cosmological dark matter constraints, we can model them as a coherently oscillating background field: a plane wave with amplitude determined by dark matter energy density and oscillation frequency determined by mass. In the case that dark photons weakly interact with ordinary matter, this means an oscillating force is imparted. This sets LIGO up as a means of direct detection due to the mirror displacement dark photons could induce in LIGO detectors.

    Figure 1: The experimental setup of the Advanced LIGO interferometer. We can see that light leaves the laser and is reflected between a few power recycling mirrors (PR), split by a beam splitter (BS), and bounced between input and end test masses (ITM and ETM). The entire system is mounted on seismically-isolated platforms to reduce noise as much as possible. Source: https://arxiv.org/pdf/1411.4547.pdf

    LIGO consists of a Michelson interferometer, in which a laser shines upon a beam splitter which in turn creates two perpendicular beams. The light from each beam then hits a mirror, is reflected back, and the two beams combine, producing an interference pattern. In the actual LIGO detectors, the beams are reflected back some 280 times (down a 4 km arm length) and are split to be initially out of phase so that the photodiode detector should not detect any light in the absence of a gravitational wave. A key feature of gravitational waves is their polarization, which stretches spacetime in one direction and compresses it in the perpendicular direction in an alternating fashion. This means that when a gravitational wave passes through the detector, the effective length of one of the interferometer arms is reduced while the other is increased, and the photodiode will detect an interference pattern as a result.

    LIGO has been able to reach an incredible sensitivity of one part in 10^{23} in its detectors over a 100 Hz bandwidth, meaning that its instruments can detect mirror displacements up to 1/10,000th the size of a proton. Taking advantage of this number, Guo et. al. demonstrated that the differential strain (the ratio of the relative displacement of the mirrors to the interferometer’s arm length, or h = \Delta L/L) is also sensitive to ultralight dark matter via the modeling process described above. The acceleration induced by the dark photon dark matter on the LIGO mirrors is ultimately proportional to the dark electric field and charge-to-mass ratio of the mirrors themselves.

    Once this signal is approximated, next comes the task of estimating the background. Since the coherence length is of order 10^9 m for a dark photon field oscillating at order 100 Hz, a distance much larger than the separation between the LIGO detectors at Hanford and Livingston (in Washington and Louisiana, respectively), the signals from dark photons at both detectors should be highly correlated. This has the effect of reducing the noise in the overall signal, since the noise in each of the detectors should be statistically independent. The signal-to-noise ratio can then be computed directly using discrete Fourier transforms from segments of data along the total observation time. However, this process of breaking up the data, known as “binning,” means that some signal power is lost and must be corrected for.

    Figure 2: The end result of the Guo et. al. analysis of dark photon-induced mirror displacement in LIGO. Above we can see a plot of the coupling of dark photons to baryons as a function of the dark photon oscillation frequency. We can see that over further Advanced LIGO runs, up to O4-O5, these limits are expected to improve by several orders of magnitude. Source: https://www.nature.com/articles/s42005-019-0255-0

    In applying this analysis to the strain data from the first run of Advanced LIGO, Guo et. al. generated a plot which sets new limits for the coupling of dark photons to baryons as a function of the dark photon oscillation frequency. There are a few key subtleties in this analysis, primarily that there are many potential dark photon models which rely on different gauge groups, yet this framework allows for similar analysis of other dark photon models. With plans for future iterations of gravitational wave detectors, further improved sensitivities, and many more data runs, there seems to be great potential to apply LIGO to direct dark matter detection. It’s exciting to see these instruments in action for discoveries that were not in mind when LIGO was first designed, and I’m looking forward to seeing what we can come up with next!

    Learn More:

    An overview of gravitational waves and dark matter: https://www.symmetrymagazine.org/article/what-gravitational-waves-can-say-about-dark-matter
    A summary of dark photon experiments and results: https://physics.aps.org/articles/v7/115
    Details on the hardware of Advanced LIGO: https://arxiv.org/pdf/1411.4547.pdf
    A similar analysis done by Pierce et. al.: https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.121.061102

    See the full article here .


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    What is ParticleBites?

    ParticleBites is an online particle physics journal club written by graduate students and postdocs. Each post presents an interesting paper in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.

    The papers are accessible on the arXiv preprint server. Most of our posts are based on papers from hep-ph (high energy phenomenology) and hep-ex (high energy experiment).

    Why read ParticleBites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.

    Our goal is to solve this problem, one paper at a time. With each brief ParticleBite, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in particle physics.

    Who writes ParticleBites?

    ParticleBites is written and edited by graduate students and postdocs working in high energy physics. Feel free to contact us if you’re interested in applying to write for ParticleBites.

    ParticleBites was founded in 2013 by Flip Tanedo following the Communicating Science (ComSciCon) 2013 workshop.

    Flip Tanedo UCI Chancellor’s ADVANCE postdoctoral scholar in theoretical physics. As of July 2016, I will be an assistant professor of physics at the University of California, Riverside

    It is now organized and directed by Flip and Julia Gonski, with ongoing guidance from Nathan Sanders.

  • richardmitnick 7:37 am on October 30, 2019 Permalink | Reply
    Tags: "NSF invests in cyberinfrastructure institute to harness cosmic data", Cyberinfrastructure, Multi-messenger astrophysics, SCIMMA-Scalable Cyberinfrastructure Institute for Multi-Messenger Astrophysics, ,   

    From University of Washington: “NSF invests in cyberinfrastructure institute to harness cosmic data” 

    U Washington

    From University of Washington

    The National Science Foundation awarded the University of Wisconsin-Milwaukee and nine collaborating organizations, including the University of Washington, $2.8 million for a two-year “conceptualization phase” of the Scalable Cyberinfrastructure Institute for Multi-Messenger Astrophysics.

    The night sky at Palouse Falls in southeastern Washington.Mark Stone/University of Washington

    SCIMMA’s goal is to develop algorithms, databases and computing and networking cyberinfrastructure to help scientists interpret multi-messenger observations. Multi-messenger astrophysics combines observations of light, gravitational waves and particles to understand some of the most extreme events in the universe. For example, the observation of both gravitational waves and light from the collision of two neutron stars in 2017 helped explain the origin of heavy elements, allowed an independent measurement of the expansion of the universe and confirmed the association between neutron-star mergers and gamma-ray bursts.

    The institute would facilitate global collaborations, thus transcending the capabilities of any single existing institution or team. It is directed by Patrick Brady, a professor of physics at the University of Wisconsin-Milwaukee and director of the Center for Gravitation, Cosmology and Astrophysics. One of three co-principal investigators on the project is Mario Jurić, a UW associate professor of astronomy and senior data science fellow at the UW eScience Institute.

    As part of SCIMMA, UW researchers will work to develop a “transient alert” system that will alert researchers around the world about cosmic events picked up, for example, by astronomical observatories.

    “These events could include phenomena like collisions between black holes and neutron stars detected via gravitational waves, exploding supernovae detected by neutrino emissions, and other energetic phenomena detected in visible wavelengths of light,” said Jurić, who is also a faculty member with the UW DIRAC Institute. “UW researchers have demonstrated these technologies as part of the Zwicky Transient Facility project, where the UW-built ZTF Alert Distribution System transmitted more than 100 million alerts over the past two years.”

    Zwicky Transient Facility (ZTF) instrument installed on the 1.2m diameter Samuel Oschin Telescope at Palomar Observatory in California. Courtesy Caltech Optical Observatories

    Caltech Palomar Samuel Oschin 48 inch Telescope, located in San Diego County, California, United States, altitude 1,712 m (5,617 ft)

    W researchers will also help develop a prototype remote analysis platform, which will allow scientists to analyze archived multi-messenger astrophysics using future resources provided by SCIMMA, said Jurić.

    SCIMMA’s two-year conceptualization phase began Sept. 1. Among its goals are enabling seamless co-analysis of disparate datasets by supporting the interoperability of software and data services. In addition, over the next two years SCIMMA will develop education and training curricula designed to enhance the STEM workforce, according to an announcement by the NSF.

    “Multi-messenger astrophysics is a data-intensive science in its infancy that is already transforming our understanding of the universe,” said Brady. “The promise of multi-messenger astrophysics, however, can be realized only if sufficient cyberinfrastructure is available to rapidly handle, combine and analyze the very large-scale distributed data from all types of astronomical measurements. The conceptualization phase of SCIMMA will balance rapid prototyping, novel algorithm development and software sustainability to accelerate scientific discovery over the next decade and more.”

    Additional project collaborators include Columbia University; the Center for Advanced Computing and Department of Astronomy at Cornell University; Las Cumbres Observatory, a California-based network of observatories; Michigan State University; Pennsylvania State University; the University of California, Santa Barbara; the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign; and the Texas Advanced Computing Center at the University of Texas at Austin.

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    The University of Washington is one of the world’s preeminent public universities. Our impact on individuals, on our region, and on the world is profound — whether we are launching young people into a boundless future or confronting the grand challenges of our time through undaunted research and scholarship. Ranked number 10 in the world in Shanghai Jiao Tong University rankings and educating more than 54,000 students annually, our students and faculty work together to turn ideas into impact and in the process transform lives and our world. For more about our impact on the world, every day.
    So what defines us —the students, faculty and community members at the University of Washington? Above all, it’s our belief in possibility and our unshakable optimism. It’s a connection to others, both near and far. It’s a hunger that pushes us to tackle challenges and pursue progress. It’s the conviction that together we can create a world of good. Join us on the journey.

  • richardmitnick 9:49 am on October 2, 2019 Permalink | Reply
    Tags: , , , Collision between a black hole and a neutron star?, , , Multi-messenger astrophysics,   

    From Symmetry: “Chasing gravitational waves” 

    Symmetry Mag
    From Symmetry<

    Diana Kwon

    A. Tonita, L. Rezzolla/Goethe University of Frankfurt​, &​ F. Pannarale/Sapienza University of Rome

    When LIGO and Virgo detected the echoes that likely came from a collision between a black hole and a neutron star, dozens of physicists began a hunt for the signal’s electromagnetic counterpart.

    Around mid-afternoon on August 14, a pulse passed simultaneously through the laser beams of three enormous gravitational-wave detectors, the twin locations of the Laser Interferometer Gravitational-Wave Observatory, or LIGO, in Louisiana and Washington, and the Virgo detector in Italy.

    MIT /Caltech Advanced aLigo

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

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

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Almost immediately, alerts beeped smartphones, tablets and laptops to life around the globe. Many of the physicists who saw this notification immediately dropped what they were doing and dashed to their computers to investigate.

    What they soon hoped to find was the first optical evidence that they were detecting a collision between a black hole and a neutron star.

    Scientists may have detected violent collision between neutron star, black hole

    An ear on the universe

    All objects with mass—including stars, planets and even humans—emit gravitational waves when they change speed or direction. But most gravitational waves are much too weak to detect. Even highly sensitive instruments like LIGO and Virgo, which are akin to microphones that hear signals from all directions, can only identify very “loud” gravitational waves caused by exceptionally massive objects that are accelerating rapidly.

    So far, the gravitational waves detected have all come from compact binaries, or two massive objects spiraling around and smashing into one another. There are three different types of pairings in a compact binary—two black holes, two neutron stars, or a neutron star and a black hole.

    Since black holes are more massive than neutron stars, their clashes generate the loudest gravitational waves. Because of this, they are the easiest to find. After their first two observing runs, the LIGO-Virgo collaboration announced official detections of 10 colliding black hole pairs.

    Neutron star-neutron star mergers, called kilonovae, are the quietest of the three. In October 2017, scientists announced the first observation of such a collision.

    It was the first successful use of LIGO-Virgo in multi-messenger astronomy, in which cosmological phenomena are examined through multiple types of signals, such as gravitational waves and electromagnetic sources like X-rays, radio waves and light.

    LIGO and Virgo send out an alert each time they hear an interesting signal to allow scientists at other observatories to immediately point their instruments at the spot in the sky where the signal most likely originated to collect as much data as possible about the source.

    The alert that went out after the neutron star merger mobilized scientists at telescopes around the world, including the DECam, a US Department of Energy-funded instrument mounted onto the National Science Foundation-funded 4-meter Blanco Telescope in Chile; the Very Large Array in New Mexico; and the Fermi Gamma-Ray Space Telescope orbiting our planet. Together, their observations helped provide evidence for a long-standing hypothesis that heavy elements such as gold and uranium were formed in the cosmic explosions that occur when two neutron stars crash.

    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

    Timeline of the Inflationary Universe WMAP

    The Dark Energy Survey (DES) is an international, collaborative effort to map hundreds of millions of galaxies, detect thousands of supernovae, and find patterns of cosmic structure that will reveal the nature of the mysterious dark energy that is accelerating the expansion of our Universe. DES began searching the Southern skies on August 31, 2013.

    According to Einstein’s theory of General Relativity, gravity should lead to a slowing of the cosmic expansion. Yet, in 1998, two teams of astronomers studying distant supernovae made the remarkable discovery that the expansion of the universe is speeding up. To explain cosmic acceleration, cosmologists are faced with two possibilities: either 70% of the universe exists in an exotic form, now called dark energy, that exhibits a gravitational force opposite to the attractive gravity of ordinary matter, or General Relativity must be replaced by a new theory of gravity on cosmic scales.

    DES is designed to probe the origin of the accelerating universe and help uncover the nature of dark energy by measuring the 14-billion-year history of cosmic expansion with high precision. More than 400 scientists from over 25 institutions in the United States, Spain, the United Kingdom, Brazil, Germany, Switzerland, and Australia are working on the project. The collaboration built and is using an extremely sensitive 570-Megapixel digital camera, DECam, mounted on the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory, high in the Chilean Andes, to carry out the project.

    Over six years (2013-2019), the DES collaboration used 758 nights of observation to carry out a deep, wide-area survey to record information from 300 million galaxies that are billions of light-years from Earth. The survey imaged 5000 square degrees of the southern sky in five optical filters to obtain detailed information about each galaxy. A fraction of the survey time is used to observe smaller patches of sky roughly once a week to discover and study thousands of supernovae and other astrophysical transients.

    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)

    NASA/Fermi LAT

    NASA/Fermi Gamma Ray Space Telescope

    “That event was unbelievably exciting and scientifically rich,” says Daniel Holz, an astrophysicist at the University of Chicago and a member of both LIGO and DES-GW. “The thrill of being part of that was incredible.”

    LIGO and Virgo have released dozens of public alerts about potential detections since the beginning of their third observing run this April. To date, these include potential observations of 20 binary black holes, 4 binary neutron stars, and 2 neutron star-black holes—but none of the these has been seen with a separate electromagnetic signal.

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

    Masses in the Stellar Graveyard LIGO Virgo| Frank Elavsky | Northwestern

    The alerts are sent out almost immediately after the detectors pick up on a promising signal. In addition to identifying the potential candidate and its location on the sky, the notifications include a false alarm rate that portrays the likelihood that the proposed event was real. As researchers conduct further analyses on the data, the collaboration publishes updated estimates. If the signal turns out to be mere noise, they release a retraction.

    A needle in a haystack

    After the alert this August, the Slack channel for DES-GW, a group of scientists who use DECam to search for the optical counterparts of gravitational waves, was abuzz with chatter.

    At first, the gravitational wave was only classified as a “mass gap” detection, a signal from a pair of objects that was between the mass of the lightest black hole and the heaviest neutron star. This suggested the gravitational wave came from a new type of source, says Antonella Palmese, a postdoc at Fermilab and a member of DES-GW. But it could have been a merger between two unusually small black holes, in which case, it would be invisible to an instrument like DECam.

    After further analysis of the gravitational wave data, LIGO and Virgo scientists were able to categorize the signal as most likely a clash between a black hole and a neutron star. Although the collaboration hasn’t yet announced an official detection, their alert classified the event with greater than 99% confidence. It was their clearest gravitational-wave signal from a black hole-neutron star merger yet.

    “The moment when we got really excited and were all over our laptops was when we received the classification that it was a black hole-neutron star merger,” Palmese says. “In that case, you might expect the material from the neutron star to emit some electromagnetic counterpart that we can observe from our telescopes.”

    Once they received the classification, the group immediately got to work analyzing the information provided from the gravitational wave observatories and making plans to take data of their own with DECam as soon as possible. “We had to jump into action right away to try to do the observation,” says Marcelle Soares-Santos, an astrophysicist at Brandeis University who was at home when she received the first LIGO-Virgo message on her phone. “We managed to be on the sky in less than 24 hours.”

    According to the alert, the slice of sky that the signal could have originated from was tiny, providing astronomers with a clear target at which to point their instruments.

    “It was clear from the beginning that this event was special,” Soares-Santos says. “Several of us ended up staying up multiple nights because we were observing the same area of the sky multiple times.”

    Continuing the chase

    To identify optical counterparts of the source, DES-GW scientists look for transients: short-lived bursts of electromagnetic energy. Over the course of seven observing nights, DES-GW identified approximately 23 potential sources for the gravitational waves. Over the last few weeks, the group has been examining each of these to try to rule out the possibility that they are other celestial objects.

    One of the most common contaminants in these candidates are supernovae. Physicists can identify whether an object is a supernova by observing how long it takes to disappear. Unlike a black hole-neutron star merger, which would fade quickly, the aftermath of these stellar explosions usually remains in the sky for around a month or more.

    Finding the optical counterpart of the black hole-neutron star collision would be exciting for several reasons. First of all, this would be the first detection of such an event, so it could help reveal how such a process happens—whether the neutron star is ripped apart by a black hole or swallowed in one fell swoop. By observing this process, physicists could learn about the material that neutron stars are made of, which is the densest matter in the universe. These mergers may also help researchers better understand which elements are generated during this process.

    At this point, enough time has passed that it’s unlikely that DES-GW will identify the optical counterpart to the gravitational waves produced from this likely neutron star-black hole collision. Still, even without the detection, the data gathered at electromagnetic instruments can be helpful. For example, it suggests that instead of colliding, the neutron star may simply have been swallowed by the black hole instead, leaving no visible signs.

    More observations of neutron star-black hole mergers will be necessary to determine how, exactly, this process is happening. Scientists don’t yet know for sure when LIGO-Virgo will hear another gravitational wave coming from this type of event. But there are still several months to go during the current observing run, so physicists are anticipating another detection that will be worth pursuing.

    “This was the most exciting event this season so far,” Soares-Santos says. “But I wouldn’t bet it’s the last.”

    See the full article here .


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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 9:24 am on March 1, 2019 Permalink | Reply
    Tags: , , , , , , Multi-messenger astrophysics,   

    From “Physics”: “Synopsis: How to Test a Space-Based Gravitational-Wave Detector” 

    Physics LogoAbout Physics

    Physics Logo 2

    From “Physics”

    February 28, 2019
    Christopher Crockett

    Researchers propose a device to verify the performance of the laser-based equipment that will fly on the Laser Interferometer Space Antenna.

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

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

    The European Space Agency is moving ahead with plans to launch a gravitational-wave detector called “LISA” into space. LISA, which stands for Laser Interferometer Space Antenna, will listen for gravitational waves that are currently undetectable from ground-based facilities such as the Laser Interferometer Gravitational-Wave Observatory. Catching these subtle spacetime ripples will require instrumentation with phenomenally stringent precision. Now, researchers have developed a device to test a core piece of LISA’s laser-based technology and ensure that it meets the requisite performance requirements.

    D. Penkert/Max Planck Institute for Gravitational Physics

    Max Planck Institute for Gravitational Physics

    The planned LISA detector consists of three spacecrafts flying in triangle formation. Incoming gravitational waves will change the 2.5 million kilometers between each spacecraft by a few trillionths of a meter. To track those changes, the spacecraft will look for phase shifts in the laser light they receive from their two companions, a feat requiring precise measuring instruments with exceptionally low noise and low distortion.

    To test the precision of LISA’s phase-shift-measuring hardware, Thomas Schwarze and colleagues at the Max Planck Institute for Gravitational Physics in Germany built and trialed a calibration device. Their device consists of three lasers whose beams interfere with each other in such a way that their phases—after being extracted by a prototype of LISA’s phase-measuring hardware—should cancel each other out. Any nonzero value reported reflects noise or distortion introduced by the phase-measuring hardware.

    Others have suggested using three-laser setups to test LISA’s detectors, but the team’s device introduces an order of magnitude less noise than other proposals. With further refinements to their setup—such as swapping out photodetectors for models with lower noise—the team envisions that they could reduce measurement noise further. Doing that, they say, could enable their setup to serve as a critical performance check for LISA’s hardware.

    This research is published in Physical Review Letters.

    See the full article here .


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    Stem Education Coalition

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

  • richardmitnick 3:29 pm on October 26, 2018 Permalink | Reply
    Tags: , , , , , Gravitational waves could soon provide measure of universe’s expansion, Multi-messenger astrophysics, ,   

    From University of Chicago: “Gravitational waves could soon provide measure of universe’s expansion” 

    U Chicago bloc

    From University of Chicago

    Oct 22, 2018
    Louise Lerner

    Image by Robin Dienel/The Carnegie Institution for Science

    UChicago scientists estimate, based on LIGO’s quick first detection of a first neutron star collision, that they could have an extremely precise measurement of the universe’s rate of expansion within five to ten years. [Too bad for me, I’ll be long gone.]

    Twenty years ago, scientists were shocked to realize that our universe is not only expanding, but that it’s expanding faster over time.

    Pinning down the exact rate of expansion, called the Hubble constant after famed astronomer and UChicago alumnus Edwin Hubble, has been surprisingly difficult. Since then scientists have used two methods to calculate the value, and they spit out distressingly different results. But last year’s surprising capture of gravitational waves radiating from a neutron star collision offered a third way to calculate the Hubble constant.

    Edwin Hubble at Caltech Palomar Samuel Oschin 48 inch Telescope, (credit: Emilio Segre Visual Archives/AIP/SPL)

    That was only a single data point from one collision, but in a new paper published Oct. 17 in Nature, three University of Chicago scientists estimate that given how quickly researchers saw the first neutron star collision, they could have a very accurate measurement of the Hubble constant within five to ten years.

    “The Hubble constant tells you the size and the age of the universe; it’s been a holy grail since the birth of cosmology. Calculating this with gravitational waves could give us an entirely new perspective on the universe,” said study author Daniel Holz, a UChicago professor in physics who co-authored the first such calculation from the 2017 discovery. “The question is: When does it become game-changing for cosmology?”

    In 1929, Edwin Hubble announced that based on his observations of galaxies beyond the Milky Way, they seemed to be moving away from us—and the farther away the galaxy, the faster it was receding. This is a cornerstone of the Big Bang theory, and it kicked off a nearly century-long search for the exact rate at which this is occurring.

    To calculate the rate at which the universe is expanding, scientists need two numbers. One is the distance to a faraway object; the other is how fast the object is moving away from us because of the expansion of the universe. If you can see it with a telescope, the second quantity is relatively easy to determine, because the light you see when you look at a distant star gets shifted into the red as it recedes. Astronomers have been using that trick to see how fast an object is moving for more than a century—it’s like the Doppler effect, in which a siren changes pitch as an ambulance passes.

    Major questions in calculations

    But getting an exact measure of the distance is much harder. Traditionally, astrophysicists have used a technique called the cosmic distance ladder, in which the brightness of certain variable stars and supernovae can be used to build a series of comparisons that reach out to the object in question.

    Cosmic Distance Ladder, skynetblogs

    “The problem is, if you scratch beneath the surface, there are a lot of steps with a lot of assumptions along the way,” Holz said.

    Perhaps the supernovae used as markers aren’t as consistent as thought. Maybe we’re mistaking some kinds of supernovae for others, or there’s some unknown error in our measurement of distances to nearby stars. “There’s a lot of complicated astrophysics there that could throw off readings in a number of ways,” he said.

    The other major way to calculate the Hubble constant is to look at the cosmic microwave background [CMB]—the pulse of light created at the very beginning of the universe, which is still faintly detectable.

    CMB per ESA/Planck

    While also useful, this method also relies on assumptions about how the universe works.

    The surprising thing is that even though scientists doing each calculation are confident about their results, they don’t match. One says the universe is expanding almost 10 percent faster than the other. “This is a major question in cosmology right now,” said the study’s first author, Hsin-Yu Chen, then a graduate student at UChicago and now a fellow with Harvard University’s Black Hole Initiative.

    Then the LIGO detectors picked up their first ripple in the fabric of space-time from the collision of two stars last year.

    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)

    This not only shook the observatory, but the field of astronomy itself: Being able to both feel the gravitational wave and see the light of the collision’s aftermath with a telescope gave scientists a powerful new tool. “It was kind of an embarrassment of riches,” Holz said.

    Gravitational waves offer a completely different way to calculate the Hubble constant. When two massive stars crash into each other, they send out ripples in the fabric of space-time that can be detected on Earth. By measuring that signal, scientists can get a signature of the mass and energy of the colliding stars. When they compare this reading with the strength of the gravitational waves, they can infer how far away it is.

    This measurement is cleaner and holds fewer assumptions about the universe, which should make it more precise, Holz said. Along with Scott Hughes at MIT, he suggested the idea of making this measurement with gravitational waves paired with telescope readings in 2005. The only question is how often scientists could catch these events, and how good the data from them would be.

    Illustration by A. Simon
    Unlike previous LIGO detections of black holes merging, the two neutron stars that collided sent out a bright flash of light—making it visible to telescopes on Earth.

    [ See https://sciencesprings.wordpress.com/2017/10/20/from-ucsc-neutron-stars-gravitational-waves-and-all-the-gold-in-the-universe/ ]

    ‘It’s only going to get more interesting’

    The paper predicts that once scientists have detected 25 readings from neutron star collisions, they’ll measure the expansion of the universe within an accuracy of 3 percent. With 200 readings, that number narrows to 1 percent.

    “It was quite a surprise for me when we got into the simulations,” Chen said. “It was clear we could reach precision, and we could reach it fast.”

    A precise new number for the Hubble constant would be fascinating no matter the answer, the scientists said. For example, one possible reason for the mismatch in the other two methods is that the nature of gravity itself might have changed over time. The reading also might shed light on dark energy, a mysterious force responsible for the expansion of the universe.

    “With the collision we saw last year, we got lucky—it was close to us, so it was relatively easy to find and analyze,” said Maya Fishbach, a UChicago graduate student and the other author on the paper. “Future detections will be much farther away, but once we get the next generation of telescopes, we should be able to find counterparts for these distant detections as well.”

    The LIGO detectors are planned to begin a new observing run in February 2019, joined by their Italian counterparts at VIRGO. Thanks to an upgrade, the detectors’ sensitivities will be much higher—expanding the number and distance of astronomical events they can pick up.

    “It’s only going to get more interesting from here,” Holz said.

    The authors ran calculations at the University of Chicago Research Computing Center.

    Funding: Kavli Foundation, John Templeton Foundation, National Science Foundation.

    See the full article here .


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    One of the world’s premier academic and research institutions, the University of Chicago has driven new ways of thinking since our 1890 founding. Today, UChicago is an intellectual destination that draws inspired scholars to our Hyde Park and international campuses, keeping UChicago at the nexus of ideas that challenge and change the world.

    University of Chicago

    An intellectual destination

    One of the world’s premier academic and research institutions, the University of Chicago has driven new ways of thinking since our 1890 founding. Today, UChicago is an intellectual destination that draws inspired scholars to our Hyde Park and international campuses, keeping UChicago at the nexus of ideas that challenge and change the world.

    The University of Chicago is an urban research university that has driven new ways of thinking since 1890. Our commitment to free and open inquiry draws inspired scholars to our global campuses, where ideas are born that challenge and change the world.

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  • richardmitnick 1:37 pm on July 13, 2018 Permalink | Reply
    Tags: , , , Biggest neutrino event ever from IceCube, , , IceCube-170922A, Multi-messenger astrophysics, ,   

    The Great Neutrino Catch: A Bunch of Articles 


    U Wisconsin ICECUBE neutrino detector at the South Pole

    IceCube employs more than 5000 detectors lowered on 86 strings into almost 100 holes in the Antarctic ice NSF B. Gudbjartsson, IceCube Collaboration

    Lunar Icecube

    IceCube DeepCore annotated

    IceCube PINGU annotated

    DM-Ice II at IceCube annotated


    From Nature Magazine Single subatomic particle illuminates mysterious origins of cosmic rays

    When a subatomic particle from space streaked through Antarctica last September, astrophysicists raced to find the source.

    13 July 2018
    Davide Castelvecchi

    A single subatomic particle detected at the South Pole last September is helping to solve a major cosmic mystery: what creates electrically charged cosmic rays, the most energetic particles in nature.

    Follow-up studies by more than a dozen observatories suggest that researchers have, for the first time, identified a distant galaxy as a source of high-energy neutrinos

    This discovery could, in turn, help scientists pin down the still mysterious source of protons and atomic nuclei that arrive to Earth from outer space, collectively called cosmic rays. The same mechanisms that produce cosmic rays should also make high-energy neutrinos.

    Multiple teams of researchers from around the world describe the neutrino’s source in at least seven papers released on 12 July.

    “Everything points to this as the ultra-bright, energetic source — a gorgeous source,” says Elisa Resconi, an astroparticle physicist at the Technical University of Munich in Germany.

    Astrophysicists have proposed a number of scenarios for astrophysical phenomena that could produce both high-energy neutrinos and their electrically charged counterparts: protons and atomic nuclei collectively called cosmic rays. But until now, they had not managed to unambiguously trace any of these particles back to their source. This is especially difficult with cosmic rays, whose electric charges make their paths curve on their way to Earth, whereas neutrinos travel in straight lines.

    The finding also underscores the promise of ‘multi-messenger’ astronomy, a nascent field that combines signals from different types of observatory to pin down details of celestial events.

    Muon alert

    The story began on 22 September 2017, when an electrically charged particle called a muon streaked through the Antarctic ice cap at close to the speed of light. IceCube — an array of more than 5,000 sensors buried in a cubic kilometre’s worth of ice — detected flashes of light that the muon produced in its wake. The particle appeared to emerge from below the detector — an orientation that indicated that it was the decay product of a neutrino that had come from below the horizon. Muons can only travel so far inside matter, whereas neutrinos often pass through the entire planet unimpeded; most of the ones that IceCube detects have crashed with a particle inside Earth to produce a muon (see ‘Neutrino observatory’).

    Within seconds, a computer cluster at the US National Science Foundation’s Amundsen–Scott South Pole Station, which sits atop Earth’s southernmost point, had reconstructed the precise path of the particle and recognized that the muon had come from a highly energetic neutrino; 43 seconds after the event, the station sent an automated alert to a network of astronomers via a satellite link. It tagged the neutrino as IceCube-170922A.

    After receiving the alert, Derek Fox, an astrophysicist at Pennsylvania State University in University Park, quickly secured observing time on the X-ray observatory Swift, which orbits Earth.

    NASA Neil Gehrels Swift Observatory

    Fox had created the automated alert system two years before, precisely in the hope that researchers could follow up on events such as this one.

    He and his team found nine sources of high-energy X-rays close to where the neutrino had come from. Among them was an object called TXS 0506+056. This was a blazar, a galaxy with a supermassive black hole at the centre and a known source of γ-rays. In a blazar, the black hole stirs gas up to temperatures of millions of degrees and shoots it out of its poles in two highly collimated jets, one of which points in the direction of the Solar System. Fox’s team announced its findings to the astronomical community the next day after.


    Flare up

    In the following days, another team inspected data from the Large Area Telescope (LAT) aboard NASA’s Fermi Gamma-ray Space Telescope.

    NASA/Fermi LAT

    NASA/Fermi Gamma Ray Space Telescope

    LAT constantly sweeps the sky, and among other things monitors about 2,000 blazars. These objects go through periods of increased activity that can last weeks or months, during which they become unusually bright. “When we looked at the region that IceCube said the neutrino came from, we noticed that this blazar had been flaring more than ever before,” says Regina Caputo, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who is Fermi-LAT’s analysis coordinator.

    On 28 September, the Fermi-LAT team sent out an alert to reveal this finding. It was at that point that other astronomers got very excited. IceCube has detected about a dozen such high-energy neutrinos each year since it started operating in 2010, but none had been associated with a particular source in the sky. “That’s what made the hair stand at the back of the neck,” Fox says.

    Still, the association between the neutrino and the TXS blazar flare could have been a coincidence. To make the case stronger, researchers from both IceCube and Fermi-LAT calculated the odds that the flare and the neutrino were related, rather than coming from the same direction in the sky by chance.

    “We had to calculate the chance that random neutrinos in the sky come from one of the known gamma-ray sources, and the likelihood that it was flaring at that time,” says Anna Franckowiak, an astroparticle physicist at the German Electron Synchrotron (DESY) in Zeuthen who is a member of both IceCube and Fermi-LAT. She and her collaborators found that likelihood to be good, though not at the level of statistical significance required for claiming a discovery in physics.

    Evidence hunt

    Finding more neutrinos and gamma rays detected during a previous flare from the same blazar would boost the evidence for TXS 0506+056 being the source. In November, IceCube researchers found that the observatory had recorded an excess of neutrinos coming from the same direction in the sky between late 2014 and 2015.

    Resconi, who is a senior member of IceCube, got so excited by the discovery that she got lost while driving to a Nick Cave concert after work. “I ended up in the open countryside. My colleagues now tease me that next time we see a neutrino source, who knows where I will end up.”

    Soon though, the researchers realized that this apparent flare did not seem to show up in Fermi-LAT data. “That news came as a wet blanket,” Resconi says. But in a separate study, she and her collaborators found hints of a TXS flare during that period, but with gamma rays of energies that were mostly too high for Fermi-LAT to detect.

    A major missing piece of information was the blazar’s distance from Earth, says Simona Paiano of the Astronomical Observatory of Padua in Italy. To measure it, she and her team booked 15 hours of observing time on the world’s largest optical telescope, the 10.4-metre Gran Telescopio Canarias on La Palma, one of Spain’s Canary Islands.

    Gran Telescopio Canarias at the Roque de los Muchachos Observatory on the island of La Palma, in the Canaries, Spain, sited on a volcanic peak 2,267 metres (7,438 ft) above sea level

    They found it to be around 1.15 billion parsecs (3.78 billion light years) away.

    Together, the data pinpoint the likely source, says Kyle Cranmer, a particle physics and data-analysis expert at New York University, but “the observation isn’t unambiguous”, he says. “More follow-up is needed to conclusively establish blazars as a source of high-energy neutrinos.

    Researchers hope that this is only the first of many multi-messenger events of this kind.They are especially looking forward to detecting neutrinos together with gravitational waves. The celebrated collision of two neutron stars that was discovered using gravitational waves in August 2017 should have produced neutrinos as well, but IceCube did not detect any. But if the TXS blazar flares up again, it might be possible to detect more high-energy neutrinos and other kinds of radiation coming from it.

    From Astronomy Magazine

    July 12, 2018
    Michelle Hampson

    The rare detection of a high-energy neutrino hints at how these strange particles are created.

    Four billion years ago, an immense galaxy with a black hole at its heart spewed forth a jet of particles at nearly the speed of light. One of those particles, a neutrino that is just a fraction of the size of a regular atom, traversed across the universe on a collision course for Earth, finally striking the ice sheet of Antarctica last September. Coincidentally, a neutrino detector planted by scientists within the ice recorded the neutrino’s charged interaction with the ice, which resulted in a blue flash of light lasting just a moment. The results are published today in the journal Science.

    This detection marks the second time in history that scientists have pinpointed the origins of a neutrino from outside of our solar system. And it’s the first time they’ve confirmed that neutrinos are created in the supermassive black holes at the centers of galaxies — a somewhat unexpected source.

    Neutrinos are highly energetic particles that rarely ever interact with matter, passing through it as though it weren’t even there. Determining the type of cosmological events that create these particles is critical for understanding the nature of the universe. But the only confirmed source of neutrinos, other than our Sun, is a supernova that was recorded in 1987.

    Physicists have a number of theories about what sort of astronomical events may create neutrinos, with some suggesting that blazars could be a source. Blazars are massive galaxies with black holes at their center, trying to suck in too much matter at once, causing jets of particles to be ejected outward at incredible speeds. Acting like the giant counterparts to terrestrial particle accelerators, blazar jets are believed to produce cosmic rays that can in turn create neutrinos.

    “This [detection] in particular is a chance of nature,” says Darren Grant, a lead scientist of the team that first discovered the high-energy neutrino, as part of the neutrino detection project IceCube. “There’s a blazar there that just happened to turn on at the right time and we happened to capture it. It’s one of those eureka moments. You hope to experience those a few times in your career and this was one of them, where everything aligned.”

    Blazars are active supermassive black holes sucking in immense amounts of material, which form swirling accretion disks and generate high-powered particle jets that churn out particles that astronomers have believed eventually result in neutrinos. DESY, Science Communication Lab

    A cosmic messenger

    On September 22, 2017, the neutrino reached the Antarctica ice sheet, passing by an ice crystal at just the right angle to cause a subatomic particle (called a muon) to be created from the interaction. The resulting blue flash was recorded by one of IceCube’s 5,160 detectors, embedded within the ice. Grant was in the office when the detection occurred. This neutrino was about 300 million times more energetic than those that are emitted by the Sun.

    Grant and his colleague briefly admired the excellent image depicting the trajectory of the muon, which provides basic information necessary to begin tracing back the neutrino’s origin. However, they weren’t overly excited quite yet. His team observes about 10 to 20 high-energy neutrinos each year, but the right combination of events — in space, time and energy, for example — is required to precisely pinpoint the source of the neutrino. Such an alignment had eluded scientists so far. As Grant’s team began their analysis, though, they began to narrow in on a region: an exceptionally bright blazar called TXS 0506+056.

    Upon the detection, an automatic alert was sent to other astronomy teams around the world, which monitor various incoming cosmic signals, such as radio and gamma rays. A few days later a team of scientists using the MAGIC telescope in the Canary Islands responded with some exciting news: the arrival of the neutrino had coincided with a burst of gamma rays – which are extremely energetic photons – also coming from the direction of TXS 0506+056.

    MAGIC Cherenkov telescope array at the Roque de los Muchachos Observatory on the island of La Palma, in the Canaries, Spain, sited on a volcanic peak 2,267 metres (7,438 ft) above sea level

    Other teams analyzing the region following the initial detection observed changes in X-ray emissions and radio signals too. Collectively, the data is a huge step forward for physicists in understanding blazars, and high-energy cosmological events in general.

    John Learned of University of Hawaii, Manoa, who was not involved in the study, says that the data linking the blazar as the source is “overwhelmingly convincing” and he emphasizes the importance of this finding. “This is the realization of many long-standing scientific dreams. Neutrinos at high energies can tell us about the guts of these extremely luminous objects … The implications of the finding are that we are now finally … [able] to see inside the most dense and luminous objects, and to further our grasp of the ‘deus ex machina’ which drives them and powers these awesome phenomena.”

    For example, this detection also provides the first evidence that a blazar can produce the high-energy protons needed to generate neutrinos such as the one IceCube saw. Sources of high-energy protons also remain largely a mystery, so the identification of one such source is another big step forward for astronomers. “It’s really quite convincing that we’ve unlocked one piece of that puzzle,” says Grant.

    Gems from the past

    And it gets even better. “We looked back at [archival] data [that had been collected since 2010], in the direction of this particular blazar source, and what we discovered was really quite remarkable,” Grant says. A barrage of high-energy neutrinos and gamma rays from TXS 0506+056 reached Earth in late 2014 and early 2015. At the time, IceCube’s real-time alert system was not fully functioning, so other scientific teams were not aware of the detection. But now these previous neutrinos are on scientists’ radar, providing a more long-term glimpse into the life of a blazar.

    “That was really icing on the cake, because what [the archived data indicated] was that the source had been active in neutrinos in the past, and then again, with this very high-energy neutrino in September — those are the pieces that really start to come together, to make a picture of what’s happening there,” explains Grant.

    The alert IceCube sent once the neutrino’s interaction with the ice was detected resulted in follow-up observations from about 20 Earth- and space-based observatories. This immense effort resulted in the clear identification of a distant blazar as the source of the neutrino — as well as gamma rays, X-rays, radio emission, and optical light.
    Nicolle R. Fuller/NSF/IceCube

    Previous coverage https://sciencesprings.wordpress.com/2018/07/12/from-nrao-via-newswise-vla-gives-tantalizing-clues-about-source-of-energetic-cosmic-neutrino/

    The data also reveal that radio emissions from TXS 0506+056 gradually increased in the 18 months leading up to the September neutrino detection. Greg Sivakoff, an associate professor at the University of Alberta who helped analyze the data, says one possibility is that the black hole began to consume surrounding matter much faster during this time, causing the jet of particles being emitted to speed up. He says, “If the jet gets too fast too quickly, it might run into some of its own material, creating what astronomers call a shock. Shocks have long been used in astronomy to explain how particles are accelerated to high energies. We are not sure that this is the answer yet, but this may be part of the story.”

    Scientists are continuing to monitor TXS 0506+056, hoping to learn more about this colossal event. One team conducted a detailed analysis to determine how far away the blazar is from us, astounded to discover that it is a whopping four billion light years away. While TXS 0506+056 was always considered a bright object in the sky, this luminosity at such a distance makes it one of the brightest objects in the universe. No doubt future studies of this powerful blazar will yield valuable insights into the most energetic events to occur in our universe.

    Learned says, “We are just opening a new door and I would love to be able to say what we shall find beyond. But I guarantee that initiating this new means of observing the universe will bring surprises and new insights. In an extreme analogy it is like asking Galileo what his new astronomical telescope will reveal.”

    From UCSC: VERITAS supplies critical piece to neutrino discovery puzzle

    July 12, 2018
    Megan Watzke, CfA

    Potential connection between blazar and neutrino detection by IceCube observatory marks a new advance in multi-messenger astrophysics

    CfA/VERITAS, a major ground-based gamma-ray observatory with an array of four 12m optical reflectors for gamma-ray astronomy in the GeV – TeV energy range. Located at Fred Lawrence Whipple Observatory, Mount Hopkins, Arizona, US in AZ, USA, Altitude 2,606 m (8,550 ft)

    One of the telescopes in the Very Energetic Radiation Imaging Telescope Array System (VERITAS), Located at Fred Lawrence Whipple Observatory, Mount Hopkins, Arizona, US in AZ, USA. VERITAS is operated and managed by the Smithsonian Astrophysical Observatory. (Photo by Wystan Benbow)

    The VERITAS array has confirmed the detection of gamma rays from the vicinity of a supermassive black hole. While these detections are relatively common for VERITAS, this black hole is potentially the first known astrophysical source of high-energy cosmic neutrinos, a type of ghostly subatomic particle.

    On September 22, 2017, the IceCube Neutrino Observatory, a cubic-kilometer neutrino telescope located at the South Pole, detected a high-energy neutrino of potential astrophysical origin. However, the observation of a single neutrino by itself is not enough for IceCube to claim the detection of a source. For that, scientists needed more information.

    Very quickly after the detection by IceCube was announced, telescopes around the world including VERITAS (which stands for the “Very Energetic Radiation Imaging Telescope Array System”) swung into action to identify the source. The VERITAS, MAGIC [above], and H.E.S.S. gamma-ray observatories all looked at the neutrino position.

    HESS Cherenkov Telescope Array, located on the Cranz family farm, Göllschau, in Namibia, near the Gamsberg searches for cosmic rays, altitude, 1,800 m (5,900 ft)

    In addition, two gamma-ray observatories that monitor much of the sky at lower and higher energies also provided coverage.

    These follow-up observations of the rough IceCube neutrino position suggest that the source of the neutrino is a blazar, which is a supermassive black hole with powerful outflowing jets that can change dramatically in brightness over time. This blazar, known as TXS 0506+056, is located at the center of a galaxy about 4 billion light years from Earth.

    “We know that the blazar jet is accelerating particles to very high energies, but it is difficult to tell from gamma rays alone if it is accelerating just electrons or also protons and heavier nuclei,” said David Williams, adjunct professor of physics at UC Santa Cruz and the Santa Cruz Institute for Particle Physics (SCIPP) and a member of the VERITAS collaboration. “If the blazar is a neutrino source, that’s a smoking gun for protons, because high-energy protons colliding with gas produce pions, which decay into neutrinos,” he said.

    Initially, NASA’s Fermi Gamma-ray Space Telescope [above] observed that TXS 0506+056 was several times brighter than usually seen in its all-sky monitoring. Eventually, the MAGIC observatory made a detection of much higher-energy gamma rays within two weeks of the neutrino detection, while VERITAS, H.E.S.S., and HAWC did not see the blazar in any of their observations during the two weeks following the alert.

    Given the importance of higher-energy gamma-ray detections in identifying the possible source of the neutrino, VERITAS continued to observe TXS 0506+056 over the following months, through February 2018, and revealed the source but at a dimmer state than what was detected by MAGIC.

    “The VERITAS detection shows us that the gamma-ray brightness of the source changes, which is a signature of a blazar,” said Wystan Benbow of the Smithsonian Astrophysical Observatory (SAO), which operates and manages VERITAS. “Finding a link between an astrophysical source and a neutrino event could open yet another window of exploration to the extreme universe.”

    Cosmic rays

    The detection of gamma rays coincident with neutrinos is tantalizing, since both particles must be produced in the generation of cosmic rays. Since they were first detected over 100 years ago, cosmic rays—highly energetic particles that continuously rain down on Earth from space—have posed an enduring mystery. What creates and launches these particles across such vast distances? Where do they come from?

    “The potential connection between the neutrino event and TXS 0506+056 would shed new light on the acceleration mechanisms that take place at the core of these galaxies and provide clues on the century-old question of the origin of cosmic rays,” said coauthor and VERITAS spokesperson Reshmi Mukherjee of Barnard College, Columbia University in New York.

    “Astrophysics is entering an exciting new era of multi-messenger observations, in which celestial sources are being studied through the detection of the electromagnetic radiation they emit across the spectrum, from radio waves to high-energy gamma rays, in combination with non-electromagnetic means, such as gravitational waves and high-energy neutrinos,” said coauthor Marcos Santander of the University of Alabama in Tuscaloosa, who led the study.

    A paper describing the deep VERITAS observations of TXS 0506+056 (“VERITAS Observations of the BL Lac Object TXS 0506+056”) has been accepted for publication in The Astrophysical Journal Letters and appears online on July 12, 2018. A paper on the IceCube and initial gamma-ray observations, including VERITAS’s, appears in the latest issue of the journal Science.

    “This is a terrific step forward in multi-messenger astrophysics,” said Williams, who worked on the analysis of the VERITAS data and coordinated the VERITAS contributions to the Science paper.

    VERITAS is a ground-based facility located at the SAO’s Fred Lawrence Whipple Observatory in southern Arizona. It consists of an array of four 12-meter optical telescopes that can detect gamma rays via the extremely brief flashes of blue “Cherenkov” light created when gamma rays are absorbed in the Earth’s atmosphere. The VERITAS Collaboration consists of about 80 scientists from 20 institutions in the United States, Canada, Germany and Ireland.

    The Fermi-LAT Collaboration [above], which also played an important role in this research, includes researchers at the Santa Cruz Institute for Particle Physics at UC Santa Cruz.

    From ESA INTEGRAL joins multi-messenger campaign to study high-energy neutrino source

    12 July 2018
    Erik Kuulkers
    ESA INTEGRAL Project Scientist
    European Space Agency
    Tel: +31 6 30249526
    Email: Erik.Kuulkers@esa.int

    Carlo Ferrigno
    INTEGRAL Science Data Centre
    University of Geneva, Switzerland
    Email: Carlo.Ferrigno@unige.ch

    Volodymyr Savchenko
    INTEGRAL Science Data Centre
    University of Geneva, Switzerland
    Email: Volodymyr.Savchenko@unige.ch

    Francis Halzen
    IceCube Principal Investigator
    University of Wisconsin–Madison, USA
    Email: francis.halzen@icecube.wisc.edu

    Sílvia Bravo Gallart
    IceCube Press Office
    University of Wisconsin–Madison, USA
    Email: silvia.bravo@icecube.wisc.edu

    Markus Bauer
    ESA Science Communication Officer
    Tel: +31 71 565 6799
    Mob: +31 61 594 3 954
    Email: markus.bauer@esa.int

    An international team of scientists has found first evidence of a source of high-energy neutrinos: a flaring active galaxy, or blazar, 4 billion light years from Earth. Following a detection by the IceCube Neutrino Observatory on 22 September 2017, ESA’s INTEGRAL satellite joined a collaboration of observatories in space and on the ground that kept an eye on the neutrino source, heralding the thrilling future of multi-messenger astronomy.


    Neutrinos are nearly massless, ‘ghostly’ particles that travel essentially unhindered through space at close to the speed of light [1]. Despite being some of the most abundant particles in the Universe – 100 000 billion pass through our bodies every second – these electrically neutral, subatomic particles are notoriously difficult to detect because they interact with matter incredibly rarely.

    While primordial neutrinos were created during the Big Bang, more of these elusive particles are routinely produced in nuclear reactions across the cosmos. The majority of neutrinos arriving at Earth derive from the Sun, but those that reach us with the highest energies are thought to stem from the same sources as cosmic rays – highly energetic particles originating from exotic sources outside the Solar System.

    Unlike neutrinos, cosmic rays are charged particles and so their path is bent by magnetic fields, even weak ones. The neutral charge of neutrinos instead means they are unaffected by magnetic fields, and because they pass almost entirely through matter they can be used to trace a straight path all the way back to their source.

    Acting as ‘messengers’, neutrinos directly carry astronomical information from the far reaches of the Universe. Over the past decades, several instruments have been built on Earth and in space to decode their messages, though detecting these particles is no easy feat. In particular, the source of high-energy neutrinos has, until now, remained unproven.

    On 22 September 2017, one of these high-energy neutrinos arrived at the IceCube Neutrino Observatory at the South Pole [2]. The event was named IceCube-170922A.

    The IceCube observatory, which encompasses a cubic kilometre of deep, pristine ice, detects neutrinos through their secondary particles, muons. These muons are produced on the rare occasion that a neutrino interacts with matter in the vicinity of the detector, and they create tracks, kilometres in length, as they pass through layers of Antarctic ice. Their long paths mean their position can be well defined, and the source of the parent neutrino can be pinned down in the sky.

    During the 22 September event, a traversing muon deposited 22 TeV of energy in the IceCube detector. From this, scientists estimated the energy of the parent neutrino to be around 290 TeV, indicating a 50 percent chance that it had an astrophysical origin beyond the Solar System.

    When the origin of a neutrino cannot be robustly identified by IceCube, like in this case, multi-wavelength observations are required to investigate its source. So, following the detection, IceCube scientists circulated the coordinates in the sky of the neutrino’s origin, inferred from their observations, to a worldwide network of ground and space-based observatories working across the full electromagnetic spectrum.

    These included NASA’s Fermi gamma-ray space telescope [above] and the Major Atmospheric Gamma-Ray Imaging Cherenkov (MAGIC) [above] on La Palma, in the Canary Islands, which looked to this portion of the sky and found the known blazar, TXS 0506+056, in a ‘flaring’ state – a period of intense high-energy emission – at the same time the neutrino was detected at the South Pole.

    Blazars are the central cores of giant galaxies that host an actively accreting supermassive black-hole at their heart, where matter spiralling in forms a hot, rotating disc that generates enormous amounts of energy, along with a pair of relativistic jets.

    These jets are colossal columns that funnel radiation, photons and particles – including neutrinos and cosmic rays – tens of light years away from the central black hole at speeds very close to the speed of light. A specific feature of blazars is that one of these jets happens to point towards Earth, making its emission appear exceptionally bright.

    Scientists around the world began observing this blazar – the likely source of the neutrino detected by IceCube – in a variety of wavelengths, from radio waves to high-energy gamma rays. ESA’s INTEGRAL gamma-ray observatory was part of this international collaboration [3].

    “This is a very important milestone to understanding how high-energy neutrinos are produced,” says Carlo Ferrigno from the INTEGRAL Science Data Centre at the University of Geneva, Switzerland.

    “There have been previous claims that blazar flares were associated with the production of neutrinos, but this, the first confirmation, is absolutely fundamental. This is an exciting period for astrophysics,” he adds.

    INTEGRAL, which surveys the sky in hard X-rays and soft gamma rays, is also sensitive to transient high-energy sources across the whole sky. At the time the neutrino was detected, it did not record any burst of gamma rays from the location of the blazar, so scientists were able to rule out prompt emissions from certain sources, such as a gamma-ray burst.

    After the neutrino alert from IceCube, INTEGRAL pointed to this area of the sky on various occasions between 30 September and 24 October 2017 with its wide-field instruments, and it did not observe the blazar to be in a flaring state in the hard X-ray or soft gamma-ray range.

    The fact that INTEGRAL could not detect the source in the follow-up observations provided significant information about this blazar, allowing scientists to place a useful upper limit on its energy output during this period.

    “INTEGRAL was important in constraining the properties of this blazar, but also in allowing scientists to exclude other neutrino sources such as gamma-ray bursts,” explains Volodymyr Savchenko from the INTEGRAL Science Data Centre, who led the analysis of the INTEGRAL data.

    With facilities spread across the globe and in space, scientists now have the capability to detect a plethora of ‘cosmic messengers’ travelling vast distances at extremely high speeds, in the form of light, neutrinos, cosmic rays, and even gravitational waves.

    “The ability to globally marshal telescopes to make a discovery using a variety of wavelengths in cooperation with a neutrino detector like IceCube marks a milestone in what scientists call multi-messenger astronomy,” says Francis Halzen from the University of Wisconsin–Madison, USA, lead scientist for the IceCube Neutrino Observatory.

    By combining the information gathered by each of these sophisticated instruments to investigate a wide range of cosmic processes, the era of multi-messenger astronomy has truly entered the phase of scientific exploitation.

    ESA’s high-energy space telescopes are fully integrated into this network of large multi-messenger collaborations, as demonstrated during the recent detection of gravitational waves with a corresponding gamma-ray burst – the latter detected by INTEGRAL – released by the collision of two neutron stars, and in the subsequent follow-up campaign, with contributions by INTEGRAL as well as the XMM-Newton X-ray observatory.

    ESA/XMM Newton

    Pooling resources from these and other observatories is key for the future of astrophysics, fostering our ability to decode the messages that reach us from across the Universe.

    “INTEGRAL is the only observatory available in the hard X-ray and soft gamma-ray domain that has the ability to perform dedicated imaging and spectroscopy, as well as having an instantaneous all-sky view at any time,” notes Erik Kuulkers, INTEGRAL project scientist at ESA.

    “After more than 15 years of operations, INTEGRAL is still at the forefront of high-energy astrophysics.”

    [1] Described by Frederick Reines, one of the scientists who made the first neutrino detection, as “… the most tiny quantity of reality ever imagined by a human being,” one neutrino is estimated to contain one millionth of the mass of an electron.

    [2] The IceCube Collaboration is funded primarily by the National Science Foundation and is operated by a team headquartered at the University of Wisconsin–Madison, USA. The research efforts, including critical contributions to the detector operation, are supported by funding agencies in Australia, Belgium, Canada, Denmark, Germany, Japan, New Zealand, Republic of Korea, Sweden, Switzerland, the United Kingdom, and the USA.

    [3] These results are detailed in the paper Multimessenger observations of a flaring blazar coincident with high-energy neutrino IceCube-170922A by The IceCube, Fermi-LAT, MAGIC, AGILE, ASAS-SN, HAWC, H.E.S.S, INTEGRAL, Kanata, Kiso, Kapteyn, Liverpool telescope, Subaru, Swift/NuSTAR, VERITAS, and VLA/17B-403 teams, published in Science. DOI:10.1126/science.aat1378

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