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  • richardmitnick 4:00 pm on December 20, 2017 Permalink | Reply
    Tags: Advanced Virgo, , , , Update on Neutron Star Smash-Up: Jet Hits a Roadblock   

    From Caltech: “Update on Neutron Star Smash-Up: Jet Hits a Roadblock” 

    Caltech Logo

    Caltech

    12/20/2017

    Whitney Clavin
    (626) 395-1856
    wclavin@caltech.edu

    1
    On August 17, 2017, observatories around the world witnessed the collision of two neutron stars. At first, many scientists thought a narrow high-speed jet, directed away from our line of sight, or off-axis, was produced (diagram at left). But observations made at radio wavelengths now indicate the jet hit surrounding material, producing a slower-moving, wide-angle outflow, dubbed a cocoon (pink structure at right). Credit: NRAO/AUI/NSF/D. Berry

    Radio observations are illuminating what happened during recent gravitational-wave event.

    Millions of years ago, a pair of extremely dense stars, called neutron stars, collided in a violent smash-up that shook space and time. On August 17, 2017, both gravitational waves—ripples in space and time—and light waves emitted during that neutron star merger finally reached Earth. The gravitational waves came first and were detected by the twin detectors of the National Science Foundation (NSF)-funded Laser Interferometry Gravitational-wave Observatory (LIGO), aided by the European Virgo observatory.


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

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

    ESA/eLISA the future of gravitational wave research

    1
    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)

    The light waves were observed seconds, days, and months later by dozens of telescopes on the ground and in space.

    Now, scientists from Caltech and several other institutions are reporting that light with radio wavelengths continues to brighten more than 100 days after the August 17 event. These radio observations indicate that a jet, launched from the two neutron stars as they collided, is slamming into surrounding material and creating a slower-moving, billowy cocoon.

    “We think the jet is dumping its energy into the cocoon,” says Gregg Hallinan, an assistant professor of astronomy at Caltech. “At first, people thought the material from the collision was coming out in a jet like a firehose, but we are finding that that the flow of material is slower and wider, expanding outward like a bubble.”

    The findings, made with the Karl G. Jansky Very Large Array in New Mexico, the Australia Telescope Compact Array, and the Giant Metrewave Radio Telescope in India, are reported in a new paper in the December 20 online issue of the journal Nature. The lead author is Kunal Mooley (PhD ’15), formerly of the University of Oxford and now a Jansky Fellow at Caltech.

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

    CSIRO ATCA at the Paul Wild Observatory, about 25 km west of the town of Narrabri in rural NSW about 500 km north-west of Sydney, AU

    GMRT Radio Telescope, located near Pune, India

    The new data argue against a popular theory describing the aftermath of the neutron star merger—a theory that proposes the event created a fast-moving and beam-like jet thought to be associated with extreme blasts of energy called gamma-ray bursts, and in particular with short gamma-ray bursts, or sGRBs. Scientists think that sGRBs, which pop up every few weeks in our skies, arise from the merger of a pair of neutron stars or the merger of a neutron star with a black hole (an event that has yet to be detected by LIGO). An sGRB is seen when the jet points exactly in the direction of Earth.


    A hydrodynamical simulation shows a cocoon breaking out of the neutron star merger. This model explains the gamma-ray, X-ray, ultraviolet, optical, infrared, and radio data gathered by the GROWTH team from 18 telescopes around the world. Credit: Ehud Nakar (Tel Aviv), Ore Gottlieb (Tel Aviv), Leo Singer (NASA), Mansi Kasliwal (Caltech), and the GROWTH collaboration.

    On August 17, NASA’s Fermi Gamma-ray Space Telescope and the European INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) missions detected gamma rays just seconds after the neutron stars merged.

    NASA/Fermi LAT


    NASA/Fermi Telescope

    ESA/Integral

    The gamma rays were much weaker than what is expected for sGRBS, so the researchers reasoned that a fast and narrowly focused jet was produced but must have been pointed slightly askew from the direction of Earth, or off-axis.

    The radio emission—originally detected 16 days after the August 17 event and still measurable and increasing in strength as of December 2—tells a different story. If the jet had been fast and beam-like, the radio light would have weakened with time as the jet lost energy. The fact that the brightness of the radio light is increasing instead suggests the presence of a cocoon that is choking the jet. The reason for this is complex, but it has to do with the fact that the slower-moving, wider-angle material of the cocoon gives off more radio light than the faster-moving, sharply focused jet material.

    “It’s like the jet was fogged out,” says Mooley. “The jet may be off-axis, but it is not a simple pointed beam or as fast as some people thought. It may be blocked off by material thrown off during the merger, giving rise to a cocoon and emitting light in many different directions.”

    This means that the August 17 event was not a typical sGRB as originally proposed.

    “Standard sGRBs are 10,000 times brighter than we saw for this event,” says Hallinan. “Many people thought this was because the gamma-ray emission was off-axis and thus much weaker. But it turns out that the gamma rays are coming from the cocoon rather than the jet. It is possible that the jet managed to eventually break out through the cocoon, but we haven’t seen any evidence for this yet. It is more likely that it got trapped and snuffed out by the cocoon.”

    The possibility that a cocoon was involved in the August 17 event was originally proposed in a study led by Caltech’s Mansi Kasliwal (MS ’07, PhD ’11), assistant professor of astronomy, and colleagues. She and her team from the NSF-funded Global Relay of Observatories Watching Transients Happen (GROWTH) project observed the event at multiple wavelengths using many different telescopes.

    “The cocoon model explains puzzling features we have observed in the neutron star merger,” says Kasliwal. “It fits observations across the electromagnetic spectrum, from the early blue light we witnessed to the radio waves and X-rays that turned on later. The cocoon model had predicted that the radio emission would continue to increase in brightness, and that’s exactly what we see.”

    The researchers say that future observations with LIGO, Virgo, and other telescopes will help further clarify the origins and mechanisms of these extreme events. The observatories should be able to detect additional neutron star mergers—and perhaps eventually, mergers of neutron stars and black holes.

    Work at Caltech on this study was funded by the NSF, the Sloan Research Foundation, and Research Corporation for Science Advancement. Other Caltech authors are Kishalay De, a graduate student, and Shri Kulkarni, George Ellery Hale Professor of Astronomy and Planetary Science.

    See the full article here .

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

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  • richardmitnick 3:40 pm on November 17, 2017 Permalink | Reply
    Tags: Advanced Virgo, Black Hole Binaries Detected, , , GW170814,   

    From LIGO via Manu: “LIGO and Virgo announce the detection of a black hole binary merger from June 8, 2017” 


    Manu Garcia, a friend from IAC.

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

    LIGO Scientific Collaboration

    News Release • November 15, 2017

    1
    Black Hole Binaries Detected

    Scientists searching for gravitational waves have confirmed yet another detection from their fruitful observing run earlier this year. Dubbed GW170608, the latest discovery was produced by the merger of two relatively light black holes, 7 and 12 times the mass of the sun, at a distance of about a billion light-years from Earth. The merger left behind a final black hole 18 times the mass of the sun, meaning that energy equivalent to about 1 solar mass was emitted as gravitational waves during the collision.

    This event, detected by the two NSF-supported LIGO detectors at 02:01:16 UTC on June 8, 2017 (or 10:01:16 pm on June 7 in US Eastern Daylight time), was actually the second binary black hole merger observed during LIGO’s second observation run since being upgraded in a program called Advanced LIGO. But its announcement was delayed due to the time required to understand two other discoveries: a LIGO-Virgo three-detector observation of gravitational waves from another binary black hole merger (GW170814) on August 14, and the first-ever detection of a binary neutron star merger (GW170817) in light and gravitational waves on August 17.

    A paper describing the newly confirmed observation, “GW170608: Observation of a 19-solar-mass binary black hole coalescence,” authored by the LIGO Scientific Collaboration and the Virgo Collaboration has been submitted to The Astrophysical Journal Letters. Additional information for the scientific and general public can be found at http://www.ligo.org/detections/GW170608.php.

    A fortuitous detection

    The fact that researchers were able to detect GW170608 involved some luck.

    A month before this detection, LIGO paused its second observation run to open the vacuum systems at both sites and perform maintenance. While researchers at LIGO Livingston, in Louisiana, completed their maintenance and were ready to observe again after about two weeks, LIGO Hanford, in Washington, encountered additional problems that delayed its return to observing.

    On the afternoon of June 7 (PDT), LIGO Hanford was finally able to stay online reliably and staff were making final preparations to once again “listen” for incoming gravitational waves. As part of these preparations, the team at Hanford was making routine adjustments to reduce the level of noise in the gravitational-wave data caused by angular motion of the main mirrors. To disentangle how much this angular motion affected the data, scientists shook the mirrors very slightly at specific frequencies. A few minutes into this procedure, GW170608 passed through Hanford’s interferometer, reaching Louisiana about 7 milliseconds later.

    LIGO Livingston quickly reported the possible detection, but since Hanford’s detector was being worked on, its automated detection system was not engaged. While the procedure being performed affected LIGO Hanford’s ability to automatically analyze incoming data, it did not prevent LIGO Hanford from detecting gravitational waves. The procedure only affected a narrow frequency range, so LIGO researchers, having learned of the detection in Louisiana, were still able to look for and find the waves in the data after excluding those frequencies. For this detection, Virgo was still in a commissioning phase; it started taking data on August 1.

    More to learn about black holes

    GW170608 is the lightest black hole binary that LIGO and Virgo have observed – and so is one of the first cases where black holes detected through gravitational waves have masses similar to black holes detected indirectly via electromagnetic radiation, such as X-rays.

    This discovery will enable astronomers to compare the properties of black holes gleaned from gravitational wave observations with those of similar-mass black holes previously only detected with X-ray studies, and fills in a missing link between the two classes of black hole observations.

    Despite their relatively diminutive size, GW170608’s black holes will greatly contribute to the growing field of “multimessenger astronomy,” where gravitational wave astronomers and electromagnetic astronomers work together to learn more about these exotic and mysterious objects.

    What’s next

    The LIGO and Virgo detectors are currently offline for further upgrades to improve sensitivity. Scientists expect to launch a new observing run in fall 2018, though there will be occasional test runs during which detections may occur.

    LIGO and Virgo scientists continue to study data from the completed O2 observing run, searching for other events already “in the can,” and are preparing for the greater sensitivity expected for the fall O3 observing run.

    See the full article here .

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    About the LSC

    The LIGO Scientific Collaboration (LSC) is a group of scientists seeking to make the first direct detection of gravitational waves, use them to explore the fundamental physics of gravity, and develop the emerging field of gravitational wave science as a tool of astronomical discovery. The LSC works toward this goal through research on, and development of techniques for, gravitational wave detection; and the development, commissioning and exploitation of gravitational wave detectors.

    The LSC carries out the science of the LIGO Observatories, located in Hanford, Washington and Livingston, Louisiana as well as that of the GEO600 detector in Hannover, Germany. Our collaboration is organized around three general areas of research: analysis of LIGO and GEO data searching for gravitational waves from astrophysical sources, detector operations and characterization, and development of future large scale gravitational wave detectors.

    Founded in 1997, the LSC is currently made up of more than 1000 scientists from dozens of institutions and 15 countries worldwide. A list of the participating universities.

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

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

    VIRGO Gravitational Wave interferometer, near Pisa, Italy
    VIRGO Gravitational Wave interferometer, near Pisa, Italy

     
  • richardmitnick 9:45 am on November 15, 2017 Permalink | Reply
    Tags: Advanced Virgo, , , , , , , ,   

    From Swinburne University: “Research captures wonders of the universe, and imaginations” 

    Swinburne U bloc

    Swinburne University

    15 November 2017
    Lea Kivivali
    +61 3 9214 5428
    lkivivali@swin.edu.au

    1
    An illustration of two merging neutron stars from the US National Science Foundation | Image: AFP

    One of the great things about science is that the money we invest in research often brings a return through commercially useful discoveries or advances that improve the quality of life for us all.

    Even in my field of astrophysics, research discoveries have been made that led to huge practical benefits. For example, Wi-Fi, which all of us use every day, is the result of CSIRO mastery of fourier techniques that were being used for both astrophysics and applied research.

    But astrophysics also reveals inherent wonders about the universe, and in this past year we have hit some phenomenal goals.

    On October 17, for the first time, scientists measured the violent death spiral of two dense neutron stars — the dense cores of stars that have exploded and died — as they collided at nearly the speed of light, creating what many called the greatest fireworks show in the universe.

    ____________________________________________________________________________________________________________________

    UC Santa Cruz

    UC Santa Cruz

    14

    A UC Santa Cruz special report

    Tim Stephens

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

    2
    The first optical image of a gravitational wave source was taken by a team led by Ryan Foley of UC Santa Cruz using the Swope Telescope at the Carnegie Institution’s Las Campanas Observatory in Chile. This image of Swope Supernova Survey 2017a (SSS17a, indicated by arrow) shows the light emitted from the cataclysmic merger of two neutron stars. (Image credit: 1M2H Team/UC Santa Cruz & Carnegie Observatories/Ryan Foley)

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

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

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

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

    THE MERGER

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

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


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

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

    ESA/eLISA the future of gravitational wave research

    1
    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

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

    3
    The UC Santa Cruz team found SSS17a by comparing a new image of the galaxy N4993 (right) with images taken four months earlier by the Hubble Space Telescope (left). The arrows indicate where SSS17a was absent from the Hubble image and visible in the new image from the Swope Telescope. (Image credits: Left, Hubble/STScI; Right, 1M2H Team/UC Santa Cruz & Carnegie Observatories/Ryan Foley)

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


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

    ALL THE GOLD IN THE UNIVERSE

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

    4
    The violent merger of two neutron stars is thought to involve three main energy-transfer processes, shown in this diagram, that give rise to the different types of radiation seen by astronomers, including a gamma-ray burst and a kilonova explosion seen in visible light. (Image credit: Murguia-Berthier et al., Science)

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

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

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

    RIPPLES IN THE FABRIC OF SPACE-TIME

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

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

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

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

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

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

    Not only did we see the collision, we could hear it as the two stars, each the size of a city, completed 4000 orbits in the last 100 seconds of their cosmic dance.

    It was a landmark discovery from an international team that included almost 100 Australian scientists and it resonated with the public in a way that only black holes, dying stars and fireballs in the universe can do. It was science at its most impressive, almost inconceivable yet intensely fascinating. It also reminded us that basic science — the science that isn’t immediately geared towards industrial applications — remains immensely important.

    A century ago, Albert Einstein realised that gravity could be mimicked by acceleration — that light bent when passing near massive objects, and that the fabric of space-time could be shaken by the acceleration of the stars and planets.

    A natural consequence of his theory was that stars beyond a certain density would collapse to become black holes, terrifying objects that possessed such strong gravity that not even light could escape them. He also predicted that the stars and planets emitted a strange and mysterious new form of radiation known as gravitational waves. But was Einstein right? Did black holes exist and did his equations correctly describe their behaviour? Does time really stand still in their vicinity and do gravitational waves permeate the universe? These are questions that are incredibly fundamental to how the universe ultimately works but that Einstein thought were impossible to verify experimentally.

    It appears completely ludicrous to even think about trying to do experiments on black holes when you realise that you’d have to shrink the Earth into a ball just 2cm in diameter for it to become one. For our sun the black hole diameter seems more achievable, more like 6km — except when you learn that the sun weighs about 300,000 Earths and about 18 billion tonnes has to fit in every cubic centimetre.

    This year’s Nobel prize winners in physics (Rainer Weiss, Kip Thorne and Barry Barish) realised that it was possible to build a machine that could hypothetically detect colliding black holes or their ultra-dense cousins, neutron stars, in the nearest million galaxies — should they exist and ever collide. Their detector, called Advanced LIGO, was the first to have a realistic chance of detecting the ripples in space-time induced by Einstein’s gravitational waves.

    The technology behind this facility is staggering. More than 1000 people from around the world have contributed to the instruments, which fire powerful lasers at pairs of mirrors (beautifully polished in Australia) hanging from complex suspensions 4km away in the world’s largest vacuum tubes. Australia is one of four countries in the project.

    When Advanced LIGO began its science operations in September 2015, it started listening for tremors in the fabric of space-time for the first time.

    Remarkably, it wasn’t long before LIGO saw a burst of gravitational waves from two black holes as they destroyed each other in the last few orbits of a death spiral that probably had been under way for billions of years.

    Black holes are deceptively simple objects, defined by their mass, spin and charge, and the pair involved in the September 2015 event were about 1300 million light years away.

    Their detection proved that gravitational waves existed and that black holes 30 times the mass of our sun did too. For the first time scientists got to experiment with gravity in the vicinity of a black hole.

    In August this year the first pair of merging neutron stars were seen by LIGO. Neutron stars are so dense that a teaspoon weighs a billion tonnes, but when they collide they produce an explosion that briefly creates a fireball in the sky. This event proved Einstein’s postulate that the speed of gravity and the speed of light were equivalent, to four parts in 10,000 trillion — one of the most precise confirmations of a physical law in the history of physics.

    Last Thursday the Australian Research Council Centre of Excellence in Gravitational Wave Discovery was opened by federal Education Minister Simon Birmingham. The centre, which has been operating since April, has been born in a year that will likely go down in history as a monumental one for astrophysics.

    The existence of the centre, and the excitement surrounding gravitational wave science, is testament to those who believe that basic science, the science of discovery, is a goal unto itself. This year, the LIGO gravitational wave detectors acted like a stethoscope, allowing us to listen to the vibrations in the fabric of space-time.

    The appeal of the resultant science — which may not have any immediate monetary worth — is fascinating because it is truly universal, intangible and priceless.

    See the full article here .

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    Swinburne U Campus

    Swinburne is a large and culturally diverse organisation. A desire to innovate and bring about positive change motivates our students and staff. The result is in an institution that grows and evolves each year.

     
  • richardmitnick 7:59 am on November 8, 2017 Permalink | Reply
    Tags: Advanced Virgo, , , , , , , More on GW170817: Black Hole Popcorn and the Gravitational Wave Background   

    From astrobites: “More on GW170817: Black Hole Popcorn and the Gravitational Wave Background” 

    Astrobites bloc

    astrobites

    Nov 8, 2017
    Lisa Drummond
    Title: GW170817: Implications for the Stochastic Gravitational-Wave Background from Compact Binary Coalescences
    Authors: The LIGO Scientific Collaboration and The Virgo Collaboration
    Status: arXiv.org, open access

    On August 17, 2017, a cosmic event was observed for the first time ever via both gravitational and electromagnetic waves! The event – named GW170817 – was produced by the cataclysmic collision of two neutron stars.


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

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

    ESA/eLISA the future of gravitational wave research

    1
    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)

    1
    The merger of two neutron stars generated a bright kilonova observed by UC Santa Cruz astronomers, as depicted in this artist’s illustration. (Credit: Illustration by Robin Dienel courtesy of the Carnegie Institution for Science)

    There is certainly no shortage of papers written about this historic multi-messenger detection. Here is the list of 67 preprints released on the day of the announcement of the binary neutron star coalescence. In this bite, we will be discussing the implications of GW170817 for the stochastic gravitational wave background, which is the random gravitational wave signal generated by an abundance of weak, unresolved sources.

    When will we detect the background?

    Probably the most important question answered in this paper is: when will we actually observe this background? The LIGO/VIRGO collaboration has determined that an astrophysical gravitational wave background could be detected at a statistically significant level after 18 months of observation time. However, this is the most optimistic possible case. Happily, there are reasons to believe we could detect it even earlier! There are likely to be additional compact object mergers (on top of BBH and BNS) out there, for example black hole-neuton star binaries, which could boost the background signal further. Also, specialised searches that have been cleverly designed especially for the task of gravitational wave background detection could be more sensitive to the signal.

    Searching for an individual, resolvable chirp in LIGO data is like searching for a needle in a haystack; most of the data is of no interest and discarded, with the exception of the tiny volume of data that happens to contain the chirp. In contrast, for the purposes of analysing the stochastic background, all the data is useful. In this sense, detecting the background would be a serious step forward for gravitational wave physics.

    See the full article here .

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    What do we do?

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

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

     
  • richardmitnick 11:23 am on September 4, 2017 Permalink | Reply
    Tags: Advanced Virgo, , , Constructive interference: CERN and gravitational waves   

    From CERN: “Constructive interference: CERN and gravitational waves” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead

    CERN

    4 Sep 2017
    Stefania Pandolfi

    1
    Gravitational waves as emitted during a black hole merger. (Image credit: S. Ossokine, A. Buonanno, Max Planck Institute for Gravitational Physics, Simulating eXtreme Spacetimes project, D. Steinhauser, Airborne Hydro Mapping GmbH)

    What do gravitational waves – ripples in the fabric of space-time caused by violent energetic processes in the universe – have to do with particle physics? At first sight, not much. But on 1 September scientists from the gravitational-wave community and CERN met to identify technology parallels.

    As CERN works towards a major upgrade of the Large Hadron Collider (LHC), the High Luminosity LHC, gravitational wave scientists are also contemplating major upgrades to current facilities. These will enrich the vista of the universe opened up in February 2016 when the Laser Interferometer Gravitational-wave Observatory (LIGO) and Virgo collaborations announced the long-awaited first detection of gravitational waves, 100 years after their prediction by Einstein’s theory of gravity: general relativity.

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Gravitational waves were detected using large “interferometers”. These L-shaped tubes with 4-km-long arms contain a series of mirrors and lasers that are sensitive to any slight distortion in the apparatus caused by a passing gravitational wave.


    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project


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

    ESA/eLISA the future of gravitational wave research

    Now the gravitational-wave community is exploring several technologies to improve the sensitivity of the current observatories.

    “Technological R&D and design efforts for third-generation gravitational detectors may have interesting overlaps both with CERN capabilities and possible future directions,” says Barry Barish of the California Institute of Technology, one of the founders of the LIGO experiment.

    Next-generation interferometers could have much longer arms, be located underground to reduce seismic noise, or be cooled to cryogenic temperatures to reduce thermal interference. Expertise in vacuum, cryogenics and control systems is therefore of particular relevance, as well as how to deal with large volumes of data. CERN can also offer insights into how to organise the large international collaborations necessary to design, build and operate tomorrow’s gravitational wave observatories.

    More precise observations of the gravitational fingerprints of the most energetic phenomena in our universe may also help CERN in its quest to understand the fundamental constituents of matter. Collisions of black holes or neutron stars and supernovae explosions, for example, could shed light on open questions such as the nature of dark matter, the limits of the validity of general relativity and the behaviour of matter at extreme densities and pressures.

    “Overall, we had a healthy exchange of ideas that opened the door to the exploration of possible further synergies and joint work,” said Barish.

    See the full article here.

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    Meet CERN in a variety of places:

    Quantum Diaries
    QuantumDiaries

    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS
    CERN ATLAS New

    ALICE
    CERN ALICE New

    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    LHC

    CERN LHC Map
    CERN LHC Grand Tunnel

    CERN LHC particles

    Quantum Diaries

     
  • richardmitnick 6:42 am on August 29, 2017 Permalink | Reply
    Tags: Advanced Virgo, , , , , , , Rumors swirl that LIGO snagged gravitational waves from a neutron star collision,   

    From Science News: “Rumors swirl that LIGO snagged gravitational waves from a neutron star collision” 

    ScienceNews bloc

    ScienceNews

    August 25, 2017
    Emily Conover

    1
    CRASH AND FLASH Rumors suggest that LIGO may have detected gravitational waves from a new source: colliding neutron stars (illustrated). Such cataclysms are expected to generate a high-energy flash of light, called a gamma-ray burst (yellow jets). Several telescopes made observations seemingly in search of light from such events.

    Speculation is running rampant about potential new discoveries of gravitational waves, just as the latest search wound down August 25.

    Publicly available logs from astronomical observatories indicate that several telescopes have been zeroing in on one particular region of the sky, potentially in response to a detection of ripples in spacetime by the Advanced Laser Interferometer Gravitational-Wave Observatory, LIGO.


    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project


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

    ESA/eLISA the future of gravitational wave research

    These records have raised hopes that, for the first time, scientists may have glimpsed electromagnetic radiation — light — produced in tandem with gravitational waves. That light would allow scientists to glean more information about the waves’ source. Several tweets from astronomers reporting rumors of a new LIGO detection have fanned the flames of anticipation and amplified hopes that the source may be a cosmic convulsion unlike any LIGO has seen before.

    “There is a lot of excitement,” says astrophysicist Rosalba Perna of Stony Brook University in New York, who is not involved with the LIGO collaboration. “We are all very anxious to actually see the announcement.”

    An Aug. 25 post on the LIGO collaboration’s website announced the end of the current round of data taking, which began November 30, 2016. Virgo, a gravitational wave detector in Italy, had joined forces with LIGO’s two on August 1 (SN Online: 8/1/17).


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    The three detectors will now undergo upgrades to improve their sensitivity. The update noted that “some promising gravitational-wave candidates have been identified in data from both LIGO and Virgo during our preliminary analysis, and we have shared what we currently know with astronomical observing partners.”

    When LIGO detects gravitational waves, the collaboration alerts astronomers to the approximate location the waves seemed to originate from. The hope is that a telescope could pick up light from the aftermath of the cosmic catastrophe that created the gravitational waves — although no light has been found in previous detections.


    SPIRAL IN Two neutron stars orbit one another and spiral inward until they merge in this animation. The collision emits gravitational waves and a burst of light.

    Since mid-August, seemingly in response to a LIGO alert, several telescopes have observed a section of sky around the galaxy NGC 4993, located 134 million light-years away in the constellation Hydra. The Hubble Space Telescope has made at least three sets of observations in that vicinity, including one on August 22 seeking “observations of the first electromagnetic counterparts to gravitational wave sources.”

    NASA/ESA Hubble Telescope

    Likewise, the Chandra X-ray Observatory targeted the same region of sky on August 19.

    NASA/Chandra Telescope

    And records from the Gemini Observatory’s telescope in Chile indicate several potentially related observations, including one referencing “an exceptional LIGO/Virgo event.”


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

    “I think it’s very, very likely that LIGO has seen something,” says astrophysicist David Radice of Princeton University, who is not affiliated with LIGO. But, he says, he doesn’t know whether its source has been confirmed as merging neutron stars.

    LIGO scientists haven’t commented directly on the veracity of the rumor. “We have some substantial work to do before we will be able to share with confidence any quantitative results. We are working as fast as we can,” LIGO spokesperson David Shoemaker of MIT wrote in an e-mail.

    See the full article here .

    Science News is edited for an educated readership of professionals, scientists and other science enthusiasts. Written by a staff of experienced science journalists, it treats science as news, reporting accurately and placing findings in perspective. Science News and its writers have won many awards for their work; here’s a list of many of them.

    Published since 1922, the biweekly print publication reaches about 90,000 dedicated subscribers and is available via the Science News app on Android, Apple and Kindle Fire devices. Updated continuously online, the Science News website attracted over 12 million unique online viewers in 2016.

    Science News is published by the Society for Science & the Public, a nonprofit 501(c) (3) organization dedicated to the public engagement in scientific research and education.

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  • richardmitnick 9:41 am on May 29, 2017 Permalink | Reply
    Tags: Advanced Virgo, , , Background of gravitational waves expected from binary black hole events like GW150914, , , ,   

    From LIGO: “Background of gravitational waves expected from binary black hole events like GW150914” 

    LSC LIGO Scientific Collaboration

    LIGO Scientific Collaboration

    5.29.17 Presentation
    No writer credit found


    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project


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

    ESA/eLISA the future of gravitational wave research

    Introduction
    It is an amazing time in the field of gravitational-wave astronomy—the observation of gravitational waves by the Advanced LIGO detectors from a binary black hole merger is an event of tremendous scientific significance. A century ago, Einstein developed general relativity and predicted the existence of gravitational waves. This first direct detection of gravitational waves, the so-called “GW150914” event, is a confirmation of Einstein’s theory and is the first direct observation of a pair of black holes merging to form a single black hole. The observation of GW150914, and future observations of binary black hole mergers, will provide new insights about massive black holes in the relatively nearby part of our Universe.

    GW150914 will not be the only event of its type in the Universe. It can be expected that, on average, binary black hole mergers occur at some rate. When these mergers happen within a couple of billion light-years from the Earth, they will likely be directly observed by Advanced LIGO (and soon to come, Advanced Virgo, and ESA eLISA). Events that are further than this will just appear as random noise in the gravitational-wave detectors (like static on an old-fashioned TV), too small to be individually directly measured. However, it will be possible to observe the sum of binary black hole mergers that have happened throughout the history of our observable Universe.

    What is a gravitational-wave background?
    Gravitational waves are ripples in spacetime predicted by Einstein’s theory of general relativity. Gravitational waves are produced by accelerating objects of any size, including us humans. Most of these waves, however, are far too weak to experimentally detect. In general, we can only hope to observe gravitational waves produced by the most massive objects moving close to the speed of light, such as the binary black holes that produced GW150914.

    For every nearby, loud event like GW150914, there are many more that are too far away to be individually detected by Advanced LIGO. The gravitational waves from these distant binary black holes instead combine to create a relatively quiet “popcorn” background of gravitational waves. As a pair of black holes merges, it produces a short burst of gravitational waves lasting just a few tenths of a second. These mostly-quiet individual bursts are separated in time, and arrive at Earth at an average rate of about one every 15 minutes. Their exact arrival times, though, are randomly distributed, just like the random popping of individual kernels of popcorn.

    A popcorn background is an example of a broader category of gravitational-wave signal called a stochastic background. In general, stochastic backgrounds are formed by the combination of many unresolvable sources. Unresolvable sources are those which we cannot distinguish individually, either because they are too quiet (as in the case of a popcorn background described above) or because there are simply too many occurring at once. Detecting a stochastic background is something like listening to voices in a crowded room. Aside from the loudest people and those standing nearest to you, you can hear the remaining conversations blend together into a continuous hum.

    What can it tell us?
    Gravitational waves are expected to have been created throughout the history of the Universe. Depending on when they were produced, gravitational-wave backgrounds can be classified into two basic categories: cosmological and astrophysical. Cosmological backgrounds are predicted to have been produced by sources that existed in the very early Universe just a few seconds after the Big Bang, while astrophysical backgrounds are predicted to have been produced by systems of massive stars such as the neutron stars and black holes that we see today. Most likely, contributions to the gravitational-wave background from astrophysical sources will dominate cosmological ones. The gravitational-wave signal produced by a population of binary black holes like GW150914 is an example of an astrophysical background.

    The strength of the gravitational-wave background at different frequencies strongly depends on the type of sources that produce them. Thus, depending on the type of gravitational-wave background we detect, we may learn about the state of the Universe just a few moments after the Big Bang or how the Universe is evolving in more recent times. In addition, looking at whether the signal is stronger from certain directions on the sky or is uniformly spread out will give us information about the distribution of the sources that produced the background.

    What does GW150914 mean for a gravitational-wave background? Why is this interesting?
    GW150914 was a single event. Its gravitational waves were from the merger of two black holes, having masses of about 29 times and 36 times the mass of the Sun, forming a single black hole with a mass of about 62 times the Sun’s mass. The large component masses of the black holes making up GW150914 suggest that the unresolved popcorn signal from the population of binary black holes is probably stronger than most astrophysicists originally thought. This means we have a better chance of measuring this background with the Advanced LIGO and Virgo detectors. We will have to analyze the data for several years, but it may be possible to eventually measure the signal.

    How do we detect these gravitational waves?
    Although the individual signals from the binary black hole mergers have a characteristic shape, the signals from distant sources will be too weak to be individually detected and the arrival times of the popcorn-like bursts will be random. This means that the standard searches that look for single events like GW150914 won’t work for detecting the relatively quiet popcorn signal from the population of binary black hole mergers throughout the Universe. So we need to take a different approach (described below) to detect the waves from these unresolvable sources.

    It is hard to search for a weak random signal using data from a single detector because the detector noise itself is also random. So instead we compare (“correlate”) data from pairs of detectors, e.g., the two LIGO detectors in Hanford, WA and Livingston, LA. The random gravitational-wave signal will be the same (“correlated”) in both detectors, while the detector noise will not (since the detectors are widely separated and most noise sources due to the environment are local to the detectors). Thus we can use this similarity (“correlation”) to distinguish the gravitational-wave signal from unwanted detector noise.

    Moreover, by performing this correlation over the whole duration of the run (which could be months or years), we build up the signal relative to the noise by including the contribution of the events that occur (on average) once every 15 minutes. The more data we have to analyze, the better it is for this type of search.

    Estimating the gravitational-wave background based on what we’ve learned from GW150914
    A number of factors contribute to how many binary black hole systems will form in the Universe. An important long-term research question will be to try and describe how systems like GW150914 were created. For example, maybe the two original black holes in GW150914 evolved from a binary star system, where the two stars orbiting one another were very massive. Or perhaps the system was created in a globular cluster (a group of stars tightly bound together by gravity) where one could imagine many interactions taking place that would make initially small black holes evolve into larger ones. The most massive stars are short-lived and often produce black holes upon their death, so knowing the birth rate of massive stars is important. Star formation rates depend on the amount of matter present, and its constituents; was there just hydrogen and helium present when the star was formed, or were there other elements as well? Also, how long did the two black holes take to get close enough to collide? All of these ingredients contribute to the different binary black hole formation models that we considered.

    If we detect a stochastic gravitational-wave background in the future, we will not be able to distinguish between different models describing how these binary black hole systems were created. We will, however, be able to contribute to understanding how often these mergers happen in the far away Universe. Future measurements of individual mergering black holes will provide a better estimate of how often these types of events take place in the nearby Universe and more information on the masses of the black holes. Combining what we learn from a stochastic background with measurements from individual events may help distinguish between different formation pathways for binary black holes.

    Implications for the future
    The GW150914 event suggests that merger rates and masses of binary black holes are on the high end of the range of earlier predictions. This means that a gravitational-wave background due to merging black holes is expected to be larger as well. There are sizable uncertainties associated with the strength of this background, but detecting it may be within reach of the advanced detectors at their peak sensitivity. Looking to the future, the next generation of gravitational-wave detectors might be able combine measurements of a gravitational-wave background with measurements of individual black hole mergers to distinguish how black holes may come to orbit one another.

    Glossary

    Astrophysical background A stochastic background of gravitational waves produced by sources such as neutron stars and black holes.
    Black hole A region of space-time caused by an extremely compact mass where the gravity is so intense it prevents anything, including light, from leaving.
    Correlation The amount of similarity between two sets of data. For example, the comparison of data from pairs of gravitational-wave detectors in order to search for weak signals (like a stochastic background) that are shared (“correlated”) between the two instruments.
    Cosmological background A stochastic background of gravitational waves produced by sources such as those in the very early Universe in the instant after the Big Bang.
    Globular cluster A very dense group of stars bound together by gravity.
    Neutron star An extremely dense object which remains after the collapse of a massive star.
    Popcorn background The combination effects of bursts of gravitational waves from all binary black holes too distant to be directly observed. These bursts arrive at Earth at random times, like the popping of individual kernels of corn.
    Spacetime An interwoven continuum of space and time.
    Stochastic background A gravitational-wave signal formed from the combination of many individually unresolvable sources. Sources are unresolvable if they are too weak to be directly observed or if too many overlap at once, like conversations in a loud, crowded room.
    Stochastic Randomly determined; having a random pattern that may be analyzed statistically but may not be predicted precisely.

    Read more:

    Freely readable preprint of the publication describing the analysis
    Data used for this analysis
    Advanced LIGO
    Advanced Virgo

    See the full article here .

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    About the LSC

    The LIGO Scientific Collaboration (LSC) is a group of scientists seeking to make the first direct detection of gravitational waves, use them to explore the fundamental physics of gravity, and develop the emerging field of gravitational wave science as a tool of astronomical discovery. The LSC works toward this goal through research on, and development of techniques for, gravitational wave detection; and the development, commissioning and exploitation of gravitational wave detectors.

    The LSC carries out the science of the LIGO Observatories, located in Hanford, Washington and Livingston, Louisiana as well as that of the GEO600 detector in Hannover, Germany. Our collaboration is organized around three general areas of research: analysis of LIGO and GEO data searching for gravitational waves from astrophysical sources, detector operations and characterization, and development of future large scale gravitational wave detectors.

    Founded in 1997, the LSC is currently made up of more than 1000 scientists from dozens of institutions and 15 countries worldwide. A list of the participating universities.

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

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

    VIRGO Gravitational Wave interferometer, near Pisa, Italy
    VIRGO Gravitational Wave interferometer, near Pisa, Italy

     
  • richardmitnick 1:09 pm on September 9, 2016 Permalink | Reply
    Tags: Advanced Virgo, , , , , ,   

    From Symmetry: “A tale of two black holes” 

    Symmetry Mag

    Symmetry

    09/09/16
    Liz Kruesi

    1
    LIGO

    The historic detection of gravitational waves announced earlier this year breathed new life into a theory that’s been around for decades: that black holes created in the first second of the universe might make up dark matter. It also inspired a new idea: that those so-called primordial black holes could be contributing to a diffuse background light.

    The connection between these perhaps seemingly disparate areas of astronomy were tied together neatly in a theory from Alexander Kashlinsky, an astrophysicist at NASA’s Goddard Spaceflight Center. And while it’s an unusual idea, as he says, it could be proven true in only a few years.

    Mapping the glow

    Kashlinsky’s focus has been on a residual infrared glow in the universe, the accumulated light of the earliest stars. Unfortunately, all the stars, galaxies and other bright objects in the sky—the known sources of light—oversaturate this diffuse glow. That means that Kashlinsky and his colleagues have to subtract them out of infrared images to find the light that’s left behind.

    They’ve been doing precisely that since 2005, using data from the Spitzer space telescope to arrive at the residual infrared glow: the cosmic infrared background (CIB).

    NASA/Spitzer Telescope
    “NASA/Spitzer Telescope

    Cosmic Infrared Background, Credit: Michael Hauser (Space Telescope Science Institute), the COBE/DIRBE Science Team, and NASA)
    Cosmic Infrared Background, Credit: Michael Hauser (Space Telescope Science Institute), the COBE/DIRBE Science Team, and NASA

    Other astronomers followed a similar process using Chandra X-ray Observatory data to map the cosmic X-ray background (CXB), the diffuse glow of hotter cosmic material and more energetic sources.

    NASA/Chandra Telescope
    NASA/Chandra Telescope

    Cosmic X-ray Background, imagine.gsfc.nasa.gov
    Cosmic X-ray Background, imagine.gsfc.nasa.gov

    In 2013, Kashlinsky and colleagues compared the CIB and CXB and found correlations between the patchy patterns in the two datasets, indicating that something is contributing to both types of background light. So what might be the culprit for both types of light?

    “The only sources that could be coherent across this wide range of wavelengths are black holes,” he says.

    To explain the correlation they found, roughly 1 in 5 of the sources had to be black holes that lived in the first few hundred million years of our universe. But that ratio is oddly large.

    “For comparison,” Kashlinsky says, “in the present populations, we have 1 in 1000 of the emitting sources that are black holes. At the peak of star formation, it’s 1 in 100.”

    He wasn’t sure how the universe could have ever had enough black holes to produce the patterns his team saw in the CIB and CXB. Then the Laser Interferometric Gravitational-wave Observatory (LIGO) discovered a pair of strange beasts: two roughly-30-solar-mass black holes merging and emitting gravitational waves.

    LSC LIGO Scientific Collaboration
    Caltech/MIT Advanced aLigo Hanford, WA, USA installation
    Caltech/MIT Advanced aLigo Hanford, WA, USA installation
    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA
    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA
    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project
    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    A few months later, Kashlinsky saw a study led by Simeon Bird analyzing the possibility that the black holes LIGO had detected were primordial—formed in the universe’s first second. “And it just all came together,” Kashlinsky says.

    Gravitational secrets

    The crucial ripples in space-time picked up by the LIGO detector on September 14, 2015, came from the last dance of two black holes orbiting each other and colliding. One black hole was 36 times the sun’s mass, the other 29 times. Those black-hole weights aren’t easy to make.

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

    The majority of the universe’s black holes are less than about 15 solar masses and form as massive stars collapse at the end of their lives. A black hole weighing 30 solar masses would have to start from a star closer to 100 times our sun’s mass—and nature seems to have a hard time making stars that enormous. To compound the strangeness of the situation, the LIGO detection is from a pair of those black holes. Scientists weren’t expecting such a system, but the universe has a tendency to surprise us.

    Bird and his colleagues from Johns Hopkins University next looked at the possibility that those black holes formed not from massive stars but instead during the universe’s first fractions of a second. Astronomers haven’t yet seen what the cosmos looked like at that time, so they have to rely on theoretical models.

    In all of these models, the early universe exists with density variations. If there were regions of very high-contrasting density, those could have collapsed into black holes in the universe’s first second. If those black holes were at least as heavy as mountains when they formed, they’d stick around until today, dark and seemingly invisible and acting through the gravitational force. And because these primordial black holes formed from density perturbations, they wouldn’t be comprised of protons and neutrons, the particles that make up you, me, stars and, thus, the material that leads to normal black holes.

    All of those characteristics make primordial black holes a tempting candidate for the universe’s mysterious dark matter, which we believe makes up some 25 percent of the universe and reveals itself only through the gravitational force. This possible connection has been around since the 1970s, and astronomers have looked for hints of primordial black holes since. Even though they’ve slowly narrowed down the possibilities, there are a few remaining hiding spots—including the region where the black holes that LIGO detected fall, between about 20 and 1000 solar masses.

    Astronomers have been looking for explanations of what dark matter is for decades. The leading theory is that it’s a new type of particle, but searches keep coming up empty. On the other hand, we know black holes exist; they stem naturally from the theory of gravity.

    “They’re an aesthetically pleasing candidate because they don’t need any new physics,” Bird says.

    A glowing contribution

    Kashlinsky’s newest analysis took the idea of primordial black holes the size that LIGO detected and looked at what that population would do to the diffuse infrared light of the universe. He evolved a model of the early universe, looking at how the first black holes would congregate and grow into clumps. These black holes matched the residual glow of the CIB and, he found, “would be just right to explain the patchiness of infrared background by sources that we measured in the first couple hundred million years of the universe.”

    This theory fits nicely together, but it’s just one analysis of one possible model that came out of an observation of one astrophysical system. Researchers need several more pieces of evidence to say whether primordial black holes are in fact the dark matter. The good news is LIGO will soon begin another observing run that will be able to see black hole collisions even farther away from Earth and thus further back in time. The European gravitational wave observatory VIRGO will also come online in January, providing more data and working in tandem with LIGO.

    VIRGO Collaboration bloc
    VIRGO interferometer EGO Campus
    VIRGO interferometer EGO Campus, in Cascina, Italy

    More cases of gravitational waves from black holes around this 30-solar-masses range could add evidence that there is a population of primordial black holes. Bird and his colleague Ilias Cholis suggest looking for a more unique signal, though, in future gravitational-wave data. For two primordial black holes to become locked in a binary system and merge, they would likely be gravitationally captured during a glancing interaction, which could result in a signal with multiple frequencies or tones at any one moment.

    “This is a rare event, but it would be very characteristic of our scenario,” Cholis says. “In the next 5 to 10 years, we might see one.”

    This smoking-gun signature, as they call it, would be a strong piece of evidence that primordial black holes exist. And if such objects are floating around our universe, it might not be such a stretch to connect them to dark matter.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 6:48 am on July 2, 2016 Permalink | Reply
    Tags: Advanced Virgo, , , ,   

    From Durham: “It’s not easy being green…” 

    Durham U bloc

    Durham University

    30 June 2016
    No writer credit found

    what colours tell us about galaxy evolution.

    1
    No image caption. No image credit.

    Scientists may have answered why green galaxies are rare in our Universe and why their colour could reveal a troubled past.

    An international team of scientists, led from Durham’s Institute for Computational Cosmology (ICC), used new computer modelling of the Universe to investigate the colours that galaxies have and what those colours might tell us about how galaxies evolve.

    Using the state-of-the-art EAGLE simulations, the researchers modelled how both the ages of stars in galaxies and what those stars are made from translate into the colour of light that they produce.

    The research team said its simulations showed that colours of galaxies can also help diagnose how they evolve.

    Important stage in galaxy evolution

    While red and blue galaxies are relatively common, rare green galaxies are likely to be at an important stage in their evolution, when they are rapidly turning from blue – when new stars and planets are being born – to red as stars begin to burn themselves out.

    The research funded by the Science and Technology Facilities Council (STFC) and the European Research Council (ERC) is being presented at the Royal Astronomical Society’s National Astronomy Meeting in Nottingham, UK.

    Lead researcher James Trayford, PhD student in the ICC at Durham University, said: “Galaxies emit a healthy blue glow while new stars and planets are being born. However, if the formation of stars is halted galaxies turn red as stars begin to age and die.

    “In the real Universe we see many blue and red galaxies, but these intermediate ‘green’ galaxies are more rare.

    “This suggests that the few green galaxies we catch are likely to be at a critical stage in their evolution; rapidly turning from blue to red.”

    Dramatic changes in colour

    Because stars form from dense gas, a powerful process is needed to rapidly destroy their gas supply and cause such dramatic changes in colour, the research found.

    James added: “In a recent study we followed simulated galaxies as they changed colour, and investigated what processes caused them to change.

    “We typically find that smaller green galaxies are being violently tossed around by the gravitational pull of a massive neighbour, causing their gas supply to be stripped away.

    “Meanwhile, bigger green galaxies may self-destruct as immense explosions triggered by super-massive black holes at their centres can blow dense gas away.”

    Hope for green galaxies

    However, the research found that there was some hope for green galaxies as a lucky few might absorb a fresh supply of gas from their surroundings.

    This can revive the formation of stars and planets, and restore galaxies to a healthy blue state.

    James said: “By using simulations to study how galaxy colours change, we can speed up the process of galaxy evolution from the billions of years it takes in the real Universe to just a matter of days in a computer.

    “This means we don’t just see galaxy colours frozen in time, we can watch them evolve. Another advantage is that we can remove unwanted factors that may change the colours we see, such as pesky dust clouds that can prevent light escaping from galaxies.

    “As the EAGLE simulations we use represent a new level of realism, we can have greater confidence in applying these results to the real Universe.”

    See the full article here .

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    Durham U campus

    Durham University is distinctive – a residential collegiate university with long traditions and modern values. We seek the highest distinction in research and scholarship and are committed to excellence in all aspects of education and transmission of knowledge. Our research and scholarship affect every continent. We are proud to be an international scholarly community which reflects the ambitions of cultures from around the world. We promote individual participation, providing a rounded education in which students, staff and alumni gain both the academic and the personal skills required to flourish.

     
  • richardmitnick 10:00 pm on January 19, 2016 Permalink | Reply
    Tags: , Advanced Virgo, , ,   

    From LIGO: “Planning for a bright tomorrow: prospects for gravitational-wave astronomy with Advanced LIGO and Advanced Virgo” 

    Advanced Ligo

    Advanced LIGO

    LSC LIGO Scientific Collaboration

    VIRGO Collaboration bloc

    Where do you see yourself in five years? This is a dreaded interview question. It is hard to predict where you will end up in the future, as you never know what opportunities (or setbacks) you will encounter or how your interests will change. However, it is a good idea to have a plan, to think about what you want to accomplish so you can set yourself goals. Scientific collaborations also have to think about the future, and it is just as hard for us to do so. Often, we are trying to do things for the very first time so it can be difficult to judge how long they will take; however, with so many people from all around the world involved, it is extremely useful to have a plan so that we can co-ordinate our efforts.

    LIGO and Virgo have thought about where we want to be in five (and more) years, and have written up an answer. This might not be much use for job interviews, but should let other astrophysicists know what to expect. A plan was first produced back in 2013, and now we are updating it with our progress. The good news is that we are currently right on target! In fact, we are near the upper end of our expectations.

    Temp 1

    Temp 2

    Our current plan for how the sensitivity of the Advanced LIGO and Advanced Virgo detectors will progress with time. The curves on the plots show the expected strain noise across the spectrum of gravitational-wave frequencies; the strain is a good measure of the sensitivity of the detectors to gravitational waves. The lower the sensitivity curve on the plots, the better we are at measuring gravitational waves (the easier it is to detect quieter signals, like those from sources further away). We cannot predict exactly how things will go, but these are our current best estimates. The BNS-optimized curve is an idea to specially tune the detectors to search for binary neutron stars, which are expected to be one of the most common sources.

    Temp 3
    A plausible time-line for how LIGO and Virgo detectors will operate over the coming decade. Dates become more uncertain the further they are in the future. The colored bars correspond to observing runs, with the colors matching those in the sensitivity plots above. Between observing runs, we work on tuning our detectors to improve their sensitivity, and have engineering runs where we test the instruments and check that we understand how they behave while running.

    The Advanced LIGO detectors officially began their first observing run, which is called O1, on 18 September 2015.

    Temp 4
    A simulated sky map for the location of a binary neutron-star merger that could be seen in O1 (Berry et al. 2015). Darker reds indicate more probable positions and the star indicates the true location. The map allows astronomers to decide where to point their telescopes in order to have the best chance of seeing an electromagnetic counterpart. With only two detectors, we localize the source to somewhere in a circle on a sky from which the gravitational-wave signal would pass through our detectors at times that match our measurements. In these map projections, the circles look like long, extended arcs of reddish color (where the posterior probability density is high).

    The detectors are not yet at final sensitivity, but are roughly four times more sensitive than the pre-Advanced LIGO best. It is a long and complicated process to improve our gravitational-wave detectors. Rather than wait until they are at their final sensitivity before beginning observations, we plan to carry out several observing runs along the way. This is done because we are excited to start the search for gravitational waves as soon as possible; because we want to gain experience operating our detectors in stable, undisturbed observing state, and because we want to test out our data-analysis methods. Figuring out how to extract all the information we can from our data (while checking carefully for any gravitational waves that might be present) is just as tricky as getting the instruments working in the first place. O1 is planned to last for four months, closing mid-January 2016. Then work will start on upgrading the instruments for our second observing run, which is called O2; those upgrades will be informed by what we have learned about the instruments during O1. O2 will start in 2016 and last around six months. Hopefully, around this time Advanced LIGO will be joined by Advanced Virgo. Following O2 we will upgrade again, before observing for nine months in our third observing run, which is called (you can probably guess) O3. Each upgrade should improve the sensitivities of our detectors and increase our chances of detecting gravitational waves. Eventually, if all goes according to plan, both Advanced LIGO and Advanced Virgo will be running at full sensitivity by 2021.

    It is not just those impatient for the first direct detection of gravitational waves who are interested in the Advanced LIGO and Advanced Virgo observing plans. Many other astronomers are also keen to look for an explosion (or its afterglow) that accompanies a gravitational-wave event. These explosions are called electromagnetic counterparts, as observations are made with electromagnetic radiation (such as visible light, radio or gamma-rays) as well as with gravitational radiation (gravitational waves). The detection of both electromagnetic and gravitational radiation from the same source enables a more complete understanding of the physics, and simultaneous observations like these are called multi-messenger astronomy.. Some gravitational-wave sources, like merging neutron stars, may come with an accompanying electromagnetic signal while others, like merging black holes, probably do not (although that would make it more exciting if an electromagnetic counterpart were discovered). To plan their observations, astronomers need to know when we will be looking for gravitational waves and how much of the sky they will need to cover.

    When localising sources on the sky, gravitational-wave detectors work much like ears locating the source of a sound. The time difference between the signal arriving at different detectors gives information about where it came from. Adding Advanced Virgo to the network will made a huge difference in locating the source! There is also a plan to put a LIGO detector in India to enhance the network further, and within the next few years the LIGO and Virgo detectors will also be joined by a Japanese detector KAGRA that is currently under construction. The localization on the sky will improve as the detector network advances. Adding more detectors to the network will also increase the fraction of the time that we have the two or more detectors observing (which we need to make a detection). However, improving the detectors’ sensitivity will also make the network sensitive to more distant gravitational-wave sources, which would have fainter electromagnetic counterparts. Astronomers have a difficult challenge ahead of them.

    The one thing we cannot plan for is exactly when a gravitational-wave signal will pass through the Earth. However, each step of progress in detector sensitivity and data analysis increases our chance of making a detection. LIGO, Virgo and KAGRA will be detecting gravitational-wave signals soon, and perhaps there will be electromagnetic counterparts too.

    Glossary

    Electromagnetic radiation: Visible light stretches from red to violet, but outside the range our eyes can see this spectrum continues. Beyond red light there is infra-red, microwaves and radio waves, and beyond violet there is ultraviolet, X rays and gamma rays. This is the spectrum of electromagnetic radiation, and astronomers use each part of the spectrum to learn more about the Universe. All electromagnetic radiation takes the form of ripples in electric and magnetic fields, and differ in their frequency or wavelength (the length of a ripple).
    Gravitational radiation: Ripples in space-time created by accelerating massive objects. Like electromagnetic radiation, they travel at the speed of light. They are predicted by Einstein’s theory of general relativity and are commonly known as gravitational waves. If you would like to know more, you have come to the right place! Try looking at our other pages on gravitational-wave science.

    Read more:

    Free preprint of the paper on the arXiv

    See the full article here .

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