Tagged: Caltech/MIT Advanced aLigo Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 4:06 pm on November 17, 2017 Permalink | Reply
    Tags: , , , , Caltech/MIT Advanced aLigo, , , GW170608   

    From AAS NOVA: “LIGO Finds Lightest Black-Hole Binary” 

    AASNOVA

    AAS NOVA

    1
    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Wednesday evening the Laser Interferometer Gravitational-wave Observatory (LIGO) collaboration quietly mentioned that they’d found gravitational waves from yet another black-hole binary back in June. This casual announcement reveals what is so far the lightest pair of black holes we’ve watched merge — opening the door for comparisons to the black holes we’ve detected by electromagnetic means.

    A Routine Detection

    2
    The chirp signal of GW170608 detected by LIGO Hanford and LIGO Livingston. [LIGO collaboration 2017]

    After the fanfare of the previous four black-hole-binary merger announcements over the past year and a half — as well as the announcement of the one neutron-star binary merger in August — GW170608 marks our entry into the era in which gravitational-wave detections are officially “routine”.

    GW170608, a gravitational-wave signal from the merger of two black holes roughly a billion light-years away, was detected in June of this year. This detection occurred after we’d already found gravitational waves from several black-hole binaries with the two LIGO detectors in the U.S., but before the Virgo interferometer came online in Europe and increased the joint ability of the detectors to localize sources.

    3
    Mass estimates for the two components of GW170608 using different models. [LIGO collaboration 2017]

    Overall, GW170608 is fairly unremarkable: it was detected by both LIGO Hanford and LIGO Livingston some 7 ms apart, and the signal looks not unlike those of the previous LIGO detections. But because we’re still in the early days of gravitational-wave astronomy, every discovery is still remarkable in some way! GW170608 stands out as being the lightest pair of black holes we’ve yet to see merge, with component masses before the merger estimated at ~12 and ~7 times the mass of the Sun.

    Why Size Matters

    With the exception of GW151226, the gravitational-wave signal discovered on Boxing Day last year, all of the black holes that have been discovered by LIGO/Virgo have been quite large: the masses of the components have all been estimated at 20 solar masses or more. This has made it difficult to compare these black holes to those detected by electromagnetic means — which are mostly under 10 solar masses in size.

    4
    GW170608 is the lowest-mass of the LIGO/Virgo black-hole mergers shown in blue. The primary mass is comparable to the masses of black holes we have measured by electromagnetic means (purple detections). [LIGO-Virgo/Frank Elavsky/Northwestern]

    One type of electromagnetically detected black hole are those in low-mass X-ray binaries (LMXBs). LMXBs consist of a black hole and a non-compact companion: a low-mass donor star that overflows its Roche lobe, feeding material onto the black hole. It is thought that these black holes form without significant spin, and are later spun up as a result of the mass accretion. Before LIGO, however, we didn’t have any non-accreting black holes of this size to observe for comparison.

    Now, detections like GW170608 and the Boxing Day event (which was also on the low end of the mass scale) are allowing us to start exploring spin distributions of non-accreting black holes to determine if we’re right in our understanding of black-hole spins. We don’t yet have a large enough comparison sample to make a definitive statement, but GW170608 is indicative of a wealth of more discoveries we can hope to find in LIGO’s next observing run, after a series of further design upgrades scheduled to conclude in 2018. The future of gravitational wave astronomy continues to look promising!

    Citation

    LIGO collaboration, submitted to ApJL. https://arxiv.org/abs/1711.05578

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    1

    AAS Mission and Vision Statement

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

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

    Adopted June 7, 2009

    Advertisements
     
  • richardmitnick 3:40 pm on November 17, 2017 Permalink | Reply
    Tags: , Black Hole Binaries Detected, Caltech/MIT Advanced aLigo, , GW170814, GW170817   

    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 .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    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: , All the Gold in the World, , , , Caltech/MIT Advanced aLigo, , , ,   

    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 .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    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 7:00 am on November 10, 2017 Permalink | Reply
    Tags: Caltech/MIT Advanced aLigo, Gravitatioal waves, Improve LIGO’s sensitivity with better coatings for its interferometers, , LIGO Scientific Collaboration Center for Coatings Research, ,   

    From Stanford: “LIGO mirror coatings get an upgrade with new Stanford-led national collaboration” 

    Stanford University Name
    Stanford University

    November 9, 2017
    Vicky Stein

    1
    Stanford is leading an effort to improve facilities that capture galaxy-shaking events like the recently revealed collision of two neutron stars. (Image credit: ikonacolor / Getty Images)

    Stanford scientists will lead a new national cooperative effort, the LIGO Scientific Collaboration Center for Coatings Research, to improve detection of gravitational waves at the twin LIGO facilities.


    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)

    LIGO, the Laser Interferometer Gravitational-wave Observatory, has a problem of scale: galaxy-shaking events like the recently revealed collision of two neutron stars happened so far away that the echoes took 130 million years to travel to our planet. A collision of black holes detected in 2015 was even farther, 1.3 billion light years away.

    By the time the effects of these massive events reach Earth, they are tiny enough that they can only be detected using the most sensitive equipment scientists could devise. Changes in distance (as detected over the sprawling four-kilometer arms of LIGO) caused by gravitational waves, said Stanford researcher Riccardo Bassiri, are “a thousand times smaller than the size of an atomic nucleus.”

    Any “noise” or molecular disarray introduced by the mirrors can completely obscure the faint signals from distant gravitational wave sources.

    “It’s quite amazing, this four-kilometer, massive piece of machinery – and the coatings on the mirrors play this key role in how many gravitational-wave events we can observe,” Bassiri said. In the end, the sensitivity of LIGO’s massive interferometers is limited by atomic-scale vibrations of molecules in the mirrors that reflect the facilities’ powerful lasers. These vibrations are known collectively as Brownian thermal noise. According to Bassiri, it will be the dominant noise source limiting LIGO’s sensitivity, and a major challenge to future generations of the facilities.

    The goal of the new center, comprising 10 US institutions and led at Stanford by Martin Fejer, professor of applied physics, will be to improve LIGO’s sensitivity with better coatings for its interferometers. Researchers hope to have new materials ready in time for the next update to the LIGO facilities in as soon as three years. If they are successful and halve the amount of thermal noise from the mirror coatings, they could expand the volume of the universe that LIGO can observe eight times over current capabilities.

    The coatings in question are comprised of multiple layers no larger than a few hundreds of nanometers in thickness each – hundreds of times thinner than a human hair. In the past, researchers have followed an iterative process, creating a new coating and then testing it, hoping to improve on previous versions.

    Through the new center, Stanford will be leading researchers and facilities across the country in what they hope will be a more targeted approach. For example, working with collaborators at the SLAC National Accelerator Laboratory’s Stanford Synchrotron Radiation Lightsource, scientists can inspect newly devised mirror coatings at an atomic level.

    With this critical mass of funding and participation, “rather than following this trial-and-error Edisonian approach, we can come to a materials-by-design process,” Bassiri said. “Ultimately, the reward of developing better coatings for LIGO will be to further enable exploration of the universe through gravitational wave astronomy.”

    The Center for Coatings Research is funded by the Gordon and Betty Moore Foundation and the National Science Foundation.

    The nine other US institutions that form the CCR are: American University; California State University, Los Angeles; California State University, Fullerton; Colorado State University; Hobart and William Smith Colleges; Syracuse University; University of California, Berkeley; University of Florida; and Whitman College.

    See the full article here .

    Please help promote STEM in your local schools.
    STEM Icon

    Stem Education Coalition

    Leland and Jane Stanford founded the University to “promote the public welfare by exercising an influence on behalf of humanity and civilization.” Stanford opened its doors in 1891, and more than a century later, it remains dedicated to finding solutions to the great challenges of the day and to preparing our students for leadership in today’s complex world. Stanford, is an American private research university located in Stanford, California on an 8,180-acre (3,310 ha) campus near Palo Alto. Since 1952, more than 54 Stanford faculty, staff, and alumni have won the Nobel Prize, including 19 current faculty members

    Stanford University Seal

     
  • richardmitnick 7:59 am on November 8, 2017 Permalink | Reply
    Tags: , , , , , Caltech/MIT Advanced aLigo, , 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 .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    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 2:02 pm on November 1, 2017 Permalink | Reply
    Tags: Caltech/MIT Advanced aLigo, , Jennifer Marshall, Texas A&M Astronomer Jennifer Marshall Witnesses Cosmic History in Chile, ,   

    From Texas A&M: Women in STEM – “Texas A&M Astronomer Jennifer Marshall Witnesses Cosmic History in Chile” 

    Texas A&M logo

    Texas A&M

    1

    Marshall (above and below), operating the Dark Energy Camera on the Blanco Telescope at the Cerro Tololo Inter-American Observatory in August 2017. The image displayed on the monitor is the gravitational wave event GW170817, the source just to the top left of the larger galaxy NGC 4993 in the center of the screen. (Credit: Erika Cook, Texas A&M University.)

    2

    “It was truly amazing. I felt so fortunate to be in the right place at the right time to help make perhaps one of the most significant observations of my career.”
    Dr. Jennifer Marshall, Texas A&M astronomer

    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

    August 17 dawned as the first day in an otherwise ordinary observing run for Texas A&M University astronomer Jennifer Marshall. She had arrived in Chile a few days earlier as part of another routine visit to the National Optical Astronomy Observatory’s (CTIO), distinguished solely by the fact that it happened to kick off the fifth and final year of the Dark Energy Survey (DES), a five-year international project led by the U.S. Department of Energy’s Fermi National Accelerator Laboratory to map one-eighth of the sky in unprecedented detail.

    CTIO Cerro Tololo Inter-American Observatory, CTIO Cerro Tololo Inter-American Observatory,approximately 80 km to the East of La Serena, Chile, at an altitude of 2200 meters

    However, just as swiftly as day turned to night and darkness descended over the Andes Mountains, Marshall found herself at the fateful crossroads of proximity and cosmic history, courtesy of one universally significant target of opportunity observation.

    By virtue of being in the right place at the right time, Marshall got to witness firsthand the fiery aftermath of a recently detected burst of gravitational waves, personally recording some of the initial images of the first confirmed explosion from two colliding neutron stars ever seen by astronomers.

    The discovery, historic because it marks the first cosmic event observed in both gravitational waves and light, was made using the U.S.-based Laser Interferometer Gravitational-Wave Observatory (LIGO); the Europe-based Virgo detector in Italy; and more than 60 ground- and space-based telescopes.


    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)

    During the course of seven days in Chile, Marshall watched the extraordinary event play out in real time through two telescopes — the 4-meter Victor M. Blanco Telescope at CTIO, then moving on to the 6.5-meter Magellan Telescope at nearby Las Campanas Observatory. She was the only astronomer present and observing for DES at Blanco during the unprecedented occurrence.

    3
    The Twin Magellan telescope domes on Cerro Manqui at 8370 feet (2450 m) above sea level. Each dome houses a 6.5-meter class telescope, with the Landon Clay telescope in the left dome and
    Walter Baade telescope in the right dome. The building connecting the two domes serves as a storage area for various instruments and a maintenance facility for realuminizing the mirrors.
    Note the tall, slender silo next to the domes. This is a differential image motion monitor (DIMM) telescope used to measure atmospheric seeing.

    “It is my observation that every telescope in Chile, including the two I was using, was pointed at this thing for the entire week,” Marshall said. “It was definitely the most important science I have ever had the opportunity to be involved in.”

    Images taken by Marshall using the 570-megapixel Dark Energy Camera (DECam) captured the flaring up and fading over time of a kilonova — an explosion similar to a supernova but on a smaller scale — that occurs when collapsed stars, called neutron stars, crash into each other, theoretically creating heavy radioactive elements.

    This particular violent merger, which occurred 130 million years ago in a galaxy (NGC 4993) relatively near our own Milky Way galaxy, is the source of the gravitational waves detected by the LIGO and the Virgo collaborations on Aug. 17. Although this is the fifth source of gravitational waves to be detected, it is unique because it is the first one with a visible electromagnetic counterpart observable by optical telescopes — the glowing aftermath of the collision of two neutron stars — as opposed to binary black holes, which are not expected to produce a remnant that can be seen through telescopes.

    Capitalizing on a Target of Opportunity

    When DES officials at Fermilab learned along with dozens of LIGO-affiliated collaborations and observatories around the world that a strong gravitational signal, named GW170817, had been detected at 7:41 a.m. CDT by two of LIGO’s three detectors — a find further corroborated by a gamma-ray burst detected by NASA’s Fermi Gamma-ray Space Telescope at roughly the same time — they sent out a target of opportunity observation notice that Marshall quickly seized upon.

    As she was observing at Blanco, Marshall was simultaneously collaborating via Skype with fellow DES scientists Marcelle Soares-Santos (Fermilab/Brandeis University), the DES principal investigator in charge of gravitational wave observations, and Daniel Holtz (University of Chicago), who is a member of both LIGO and DES. Coincidentally, Marshall also was sharing some of those nights via remote with Ting Li ’16, who earned her doctorate in astronomy at Texas A&M in 2016 working with Marshall and currently is a Lederman Fellow in Experimental Physics at Fermilab.

    “LIGO tells you the equivalent of, ‘If you look in this area of the sky, there might be something,'” Marshall explained. “Virgo helped narrow that area down to the extent that, instead of 100 square degrees, it was only 30. DECam has a large field of view of three square degrees, so we only had to look at 30 telescope pointings. I was there with Erika Cook, our Munnerlyn Astronomical Laboratory control systems engineer, and Marcus Sauseda, an undergraduate aerospace engineering major here at Texas A&M, and we took some quick, short exposures — a total of roughly one hour. I sent the data off, then went to bed. I woke up to an ecstatic email from Edo Berger at Harvard, who happens to be a longtime colleague from our postdoc days at The Observatories of the Carnegie Institution of Washington.”

    Armed with the crystal-clear images from DECam, for which Texas A&M astronomer Darren DePoy served as project scientist, Berger’s team went to work analyzing the phenomenon using several different resources, including NASA’s Hubble Space Telescope and Chandra X-ray Observatory. For her part, Marshall continued imaging the galaxy for five more nights at CTIO, watching the event fade rapidly and change in color from blue to red as the explosion quickly cooled down. She then spent a seventh night at Las Campanas, doing follow-up observation with the Magellan telescope, using a different spectrometer to enable more detailed study of the event in collaboration with Carnegie Observatories scientists Maria Drout and Ben Shappee.

    Jennifer Marshall may have been one of many astronomers observing GW170817 from both ground- and space-based telescopes on Aug. 17, but she likely was the only one who happened to have a film crew in tow. Check out this video produced by NOVA PBS, present at CTIO at the time, shooting footage for an upcoming segment on the Dark Energy Survey. Catch Marshall at the 0:45, 1:10 and 1:42 marks!

    Byproducts of a Binary Star Merger

    Understandable excitement aside, Marshall says this event is particularly interesting to her because it is directly related her research on r-process elements — the heavy elements that exist on Earth and are produced in theory as the byproducts of neutron star collisions and mergers. These observations show that the theory is accurate, providing the final piece of the puzzle regarding the origin of r-process elements.

    “This was the first time anyone has ever watched such an event play out from beginning to end, all thanks to LIGO,” Marshall said. “It was truly amazing. Watching science happen in real time is not something most astronomers get to experience. With the exception of supernovae and exoplanet studies, most things we work on take billions of years to play out. I felt so fortunate to be in the right place at the right time to help make perhaps one of the most significant observations of my career.”

    Marshall said one indication of just how well LIGO/Virgo is working is the amount of event follow-up requests, which are so numerous as a result of its second and most recent observing run since being upgraded via a program called Advanced LIGO that astronomers have been forced to prioritize.

    “There were actually several binary black hole mergers that same week that we didn’t bother to look at because the neutron star source was so much more important,” Marshall said. “We had absolutely no idea this was going to happen. Everyone was shocked, and understandably so, because it was truly unbelievable.”

    In addition to Marshall and DePoy, fellow Texas A&M astronomers and Mitchell Institute members Lucas Macri, Casey Papovich, Nicholas Suntzeff and Louis Strigari are full members of the 400-plus-member international DES collaboration that spans 26 institutions and seven countries as well as the gamut of science and engineering in the search for answers regarding the universe’s accelerated expansion. Texas A&M statistician James Long and Mitchell Institute Postdoctoral Fellow Peter Brown also are external collaborators.

    Publications Aplenty

    The LIGO-Virgo results are published today in the journal Physical Review Letters, while additional papers from the LIGO and Virgo collaborations and the astronomical community either have been submitted or accepted for publication in various journals.

    Six papers relating to the DECam discovery of the optical counterpart are planned for publication in The Astrophysical Journal. Preprints of all papers are available online.

    Marshall’s observations made during that fateful August week in Chile appear in a total of nine publications making their debut today, including the mega paper from LIGO that includes citations for 75 associated papers, in addition to two DES-related papers appearing in The Astrophysical Journal as well as two papers in the journal Science featuring the Las Campanas spectra and images. Beyond those, she is an author on three additional DES papers, including one that uses the binary neutron star merger event to derive the Hubble constant. DePoy and Li join her as co-authors on several of those papers by virtue of their status as fellow DES Builders. Finally, she is an author on the Transient Optical Robotic Observatory of the South (TOROS) Collaboration paper in The Astrophysical Journal Letters.

    “The August 17 binary neutron star merger event occurred in nearby galaxy NGC 4993, located at a distance of 39.5 megaparsecs from the Milky Way,” Marshall said. “This event will surely usher in a new field of science, the direct observational study of the formation of r-process elements starting now and being fueled by future discovery of similar events by LIGO and follow-up study by astronomers.”

    Read more on today’s announcement and its broader significance in the official press releases from LIGO/Virgo , DES/Fermilab, which include additional images along with animations and videos and from From UCSC: “Neutron stars, gravitational waves, and all the gold in the universe”, which tells the optical astronomy part of the story. This last, written by Tim Stephens is quite a production, complete with a 2.5 hour video of the press conference is not to be missed.

    Learn more about the Texas A&M Astronomy Group’s broader role in the imaging and analyses.

    For more information about Texas A&M astronomy, visit http://astronomy.tamu.edu.

    See the full article here .

    Please help promote STEM in your local schools.
    STEM Icon

    Stem Education Coalition
    Located in College Station, Texas, about 90 miles northwest of Houston and within a two to three-hour drive from Austin and Dallas.
    Home to more than 50,000 students, ranking as the sixth-largest university in the country, with more than 370,000 former students worldwide.
    Holds membership in the prestigious Association of American Universities, one of only 62 institutions with this distinction.
    More than $820 million in research expenditures generated by faculty-researchers
    Has an endowment valued at more than $5 billion, which ranks fourth among U.S. public universities and 10th overall.

     
  • richardmitnick 10:50 am on November 1, 2017 Permalink | Reply
    Tags: , Caltech/MIT Advanced aLigo, , , UCSC report   

    From FNAL: “Scientists spot explosive counterpart of LIGO/Virgo’s latest gravitational waves” 

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    October 16, 2017

    Science contact

    Josh Frieman, Director, Dark Energy Survey
    Fermilab
    frieman@fnal.gov
    847-274-0429

    Marcelle Soares-Santos, Assistant Professor
    Brandeis University
    marcelle@brandeis.edu
    773-757-8495

    Daniel Holz, Professor
    University of Chicago
    holz@uchicago.edu
    505-920-5751

    Edo Berger, Professor
    Harvard-Smithsonian Center for Astrophysics
    eberger@cfa.harvard.edu
    617-495-7914

    Media contact

    Andre Salles,
    Fermilab Office of Communication
    asalles@fnal.gov
    630-840-6733

    1
    Artist’s rendition of colliding neutron stars creating gravitational waves and a kilonova. Image: Fermilab

    Scientists using the Dark Energy Camera have captured images of the aftermath of a neutron star collision, the source of LIGO/Virgo’s most recent gravitational wave detection.

    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

    A team of scientists using the Dark Energy Camera (DECam), the primary observing tool of the Dark Energy Survey, was among the first to observe the fiery aftermath of a recently detected burst of gravitational waves, recording images of the first confirmed explosion from two colliding neutron stars ever seen by astronomers.

    Scientists on the Dark Energy Survey joined forces with a team of astronomers based at the Harvard-Smithsonian Center for Astrophysics (CfA) for this effort, working with observatories around the world to bolster the original data from DECam. Images taken with DECam captured the flaring-up and fading over time of a kilonova — an explosion similar to a supernova, but on a smaller scale — that occurs when collapsed stars (called neutron stars) crash into each other, creating heavy radioactive elements.

    This particular violent merger, which occurred 130 million years ago in a galaxy near our own (NGC 4993), is the source of the gravitational waves detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo collaborations on Aug. 17.


    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)

    This is the fifth source of gravitational waves to be detected — the first one was discovered in September 2015, for which three founding members of the LIGO collaboration were awarded the Nobel Prize in physics two weeks ago.

    This latest event is the first detection of gravitational waves caused by two neutron stars colliding and thus the first one to have a visible source. The previous gravitational wave detections were traced to binary black holes, which cannot be seen through telescopes. This neutron star collision occurred relatively close to home, so within a few hours of receiving the notice from LIGO/Virgo, scientists were able to point telescopes in the direction of the event and get a clear picture of the light.

    2
    The image on the left shows the kilonova (just above and to the left of the brightest galaxy) recorded by the Dark Energy Camera. The image on the right was taken several days later and shows that the kilonova has faded. Image: Dark Energy Survey

    “This is beyond my wildest dreams,” said Marcelle Soares-Santos, formerly of the U.S. Department of Energy’s Fermi National Accelerator Laboratory and currently of Brandeis University, who led the effort from the Dark Energy Survey side. “With DECam we get a good signal, and we can show how it is evolving over time. The team following these signals is a well-oiled machine, and though we did not expect this to happen so soon, we were ready for it.”

    The Dark Energy Camera is one of the most powerful digital imaging devices in existence. It was built and tested at Fermilab, the lead laboratory on the Dark Energy Survey, and is mounted on the National Science Foundation’s 4-meter Blanco telescope, part of the Cerro Tololo Inter-American Observatory in Chile, a division of the National Optical Astronomy Observatory. The DES images are processed at the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign.

    Texas A&M University astronomer Jennifer Marshall was observing for DES at the Blanco telescope during the event, while Fermilab astronomers Douglas Tucker and Sahar Allam were coordinating the observations from Fermilab’s Remote Operations Center. “It was truly amazing,” Marshall said. “I felt so fortunate to be in the right place at the right time to help make perhaps one of the most significant observations of my career.”

    The kilonova was first identified in DECam images by Ohio University astronomer Ryan Chornock, who instantly alerted his colleagues by email. “I was flipping through the raw data, and I came across this bright galaxy and saw a new source that was not in the reference image [taken previously],” he said. “It was very exciting.”

    Once the crystal clear images from DECam were taken, a team led by Professor Edo Berger, from CfA, went to work analyzing the phenomenon using several different resources. Within hours of receiving the location information, the team had booked time with several observatories, including NASA’s Hubble Space Telescope and Chandra X-ray Observatory.

    NASA/ESA Hubble Telescope

    NASA/Chandra Telescope

    3
    Composite picture of stars over the Cerro Tololo Inter-American Observatory in Chile. Photo: Reidar Hahn/Fermilab

    LIGO/Virgo works with dozens of astronomy collaborations around the world, providing sky maps of the area where any detected gravitational waves originated. The team from DES and CfA had been preparing for an event like this for more than two years, forging connections with other astronomy collaborations and putting procedures in place to mobilize as soon as word came down that a new source had been detected. The result is a rich data set that covers “radio waves to X-rays to everything in between,” Berger said.

    “This is the first event, the one everyone will remember,” Berger said. “I’m extremely proud of our entire group, who responded in an amazing way. I kept telling them to savor the moment. How many people can say they were there at the birth of a whole new field of astronomy?”

    Adding to the excitement of this observation, this latest gravitational wave detection correlates to a burst of gamma rays spotted by NASA’s Fermi Gamma-ray Space Telescope.

    NASA/Fermi Telescope


    NASA/Fermi LAT

    Combining these detections is like hearing thunder and seeing lightning for the very first time, and it opens up a world of new scientific discovery.

    “Each of these — the gravitational waves from merging neutron stars, the gamma ray burst and the optical counterpart — could have been separate groundbreaking discoveries, and each could have taken many years,” said Daniel Holz of the University of Chicago, who works on both the DES and LIGO collaborations. “In less than a day, we did it all. This has required many different communities working together to make it all happen. It’s so gratifying to have it be so successful.”

    This event also provides a completely new and unique way to measure the present expansion rate of the universe, the Hubble constant, something theorized by Holz and others. Just as astrophysicists use supernovae as “standard candles” (objects of the same intrinsic brightness) to measure cosmic expansion, kilonovae can be used as “standard sirens” (objects of known gravitational wave strength).

    LIGO/Virgo can use this to tell the distance to these events, while optical follow-up from DES and others determines the red shift or recession speed; their combination enables scientists to determine the present expansion rate. This new kind of measurement will assist the Dark Energy Survey in its mission to uncover more about dark energy, the mysterious force accelerating the expansion of the universe.

    “The Dark Energy Survey team has been working with LIGO for more than two years, refining their process of following up gravitational wave signals,” said Fermilab Director Nigel Lockyer. “It is immensely gratifying to be on the front lines of a discovery this significant, one that required the combined skills of many supremely talented people in many fields.”

    The Dark Energy Survey recently began the fifth and final year of its quest to map an area of the southern sky in unprecedented detail. Scientists on DES will use this data to learn more about the effect of dark energy over eight billion years of the universe’s history, in the process measuring 300 million galaxies, 100,000 galaxy clusters and 3,000 supernovae.

    Six papers relating to the DECam discovery of the optical counterpart are planned for publication in The Astrophysical Journal. Preprints of all papers are available here: https://www.darkenergysurvey.org/des-gravitational-waves-papers.

    “It is tremendously exciting to experience a rare event that transforms our understanding of the workings of the universe,” said France A. Córdova, director of the National Science Foundation (NSF), which funds LIGO and supports the observatory where DECam is housed. “This discovery realizes a long-standing goal many of us have had — that is, to simultaneously observe rare cosmic events using both traditional as well as gravitational-wave observatories. Only through NSF’s four-decade investment in gravitational-wave observatories, coupled with telescopes that observe from radio to gamma-ray wavelengths, are we able to expand our opportunities to detect new cosmic phenomena and piece together a fresh narrative of the physics of stars in their death throes.”

    The Dark Energy Survey is a collaboration of more than 400 scientists from 26 institutions in seven countries. Funding for the DES Projects has been provided by the U.S. Department of Energy Office of Science, U.S. National Science Foundation, Ministry of Science and Education of Spain, Science and Technology Facilities Council of the United Kingdom, Higher Education Funding Council for England, ETH Zurich for Switzerland, National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, Kavli Institute of Cosmological Physics at the University of Chicago, Center for Cosmology and AstroParticle Physics at Ohio State University, Mitchell Institute for Fundamental Physics and Astronomy at Texas A&M University, Financiadora de Estudos e Projetos, Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro, Conselho Nacional de Desenvolvimento Científico e Tecnológico and Ministério da Ciência e Tecnologia, Deutsche Forschungsgemeinschaft, and the collaborating institutions in the Dark Energy Survey, the list of which can be found at http://www.darkenergysurvey.org/collaboration.

    Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory, is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation.

    Fermilab is America’s premier national laboratory for particle physics and accelerator research. A U.S. Department of Energy Office of Science laboratory, Fermilab is located near Chicago, Illinois, and operated under contract by the Fermi Research Alliance LLC, a joint partnership between the University of Chicago and the Universities Research Association, Inc. Visit Fermilab’s website at http://www.fnal.gov and follow us on Twitter at @Fermilab.

    The DOE Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

    See the full article here .

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

    From UCSC: “Neutron stars, gravitational waves, and all the gold in the universe”

    5
    6

    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.

    7
    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)

    8
    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).

    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.

    9
    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.

    9
    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.”

    IN THIS REPORT

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

    10
    Graduate students and post-doctoral scholars at UC Santa Cruz played key roles in the dramatic discovery and analysis of colliding neutron stars.Astronomer Ryan Foley leads a team of young graduate students and postdoctoral scholars who have pulled off an extraordinary coup. Following up on the detection of gravitational waves from the violent merger of two neutron stars, Foley’s team was the first to find the source with a telescope and take images of the light from this cataclysmic event. In so doing, they beat much larger and more senior teams with much more powerful telescopes at their disposal.

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

    IN THIS REPORT

    Scientific Papers from the 1M2H Collaboration

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

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

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

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

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

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

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

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

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

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

    PRESS RELEASES AND MEDIA COVERAGE


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

    Credits

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

    See the full article here .

    UCO Lick Shane Telescope
    UCO Lick Shane Telescope interior
    Shane Telescope at UCO Lick Observatory, UCSC

    Lick Automated Planet Finder telescope, Mount Hamilton, CA, USA

    Lick Automated Planet Finder telescope, Mount Hamilton, CA, USA

    UC Santa Cruz campus
    The University of California, Santa Cruz, opened in 1965 and grew, one college at a time, to its current (2008-09) enrollment of more than 16,000 students. Undergraduates pursue more than 60 majors supervised by divisional deans of humanities, physical & biological sciences, social sciences, and arts. Graduate students work toward graduate certificates, master’s degrees, or doctoral degrees in more than 30 academic fields under the supervision of the divisional and graduate deans. The dean of the Jack Baskin School of Engineering oversees the campus’s undergraduate and graduate engineering programs.

    UCSC is the home base for the Lick Observatory.

    Lick Observatory's Great Lick 91-centimeter (36-inch) telescope housed in the South (large) Dome of main building
    Lick Observatory’s Great Lick 91-centimeter (36-inch) telescope housed in the South (large) Dome of main building

    Search for extraterrestrial intelligence expands at Lick Observatory
    New instrument scans the sky for pulses of infrared light
    March 23, 2015
    By Hilary Lebow
    1
    The NIROSETI instrument saw first light on the Nickel 1-meter Telescope at Lick Observatory on March 15, 2015. (Photo by Laurie Hatch) UCSC Lick Nickel telescope

    Astronomers are expanding the search for extraterrestrial intelligence into a new realm with detectors tuned to infrared light at UC’s Lick Observatory. A new instrument, called NIROSETI, will soon scour the sky for messages from other worlds.

    “Infrared light would be an excellent means of interstellar communication,” said Shelley Wright, an assistant professor of physics at UC San Diego who led the development of the new instrument while at the University of Toronto’s Dunlap Institute for Astronomy & Astrophysics.

    Wright worked on an earlier SETI project at Lick Observatory as a UC Santa Cruz undergraduate, when she built an optical instrument designed by UC Berkeley researchers. The infrared project takes advantage of new technology not available for that first optical search.

    Infrared light would be a good way for extraterrestrials to get our attention here on Earth, since pulses from a powerful infrared laser could outshine a star, if only for a billionth of a second. Interstellar gas and dust is almost transparent to near infrared, so these signals can be seen from great distances. It also takes less energy to send information using infrared signals than with visible light.

    5
    UCSC alumna Shelley Wright, now an assistant professor of physics at UC San Diego, discusses the dichroic filter of the NIROSETI instrument. (Photo by Laurie Hatch)

    Frank Drake, professor emeritus of astronomy and astrophysics at UC Santa Cruz and director emeritus of the SETI Institute, said there are several additional advantages to a search in the infrared realm.

    “The signals are so strong that we only need a small telescope to receive them. Smaller telescopes can offer more observational time, and that is good because we need to search many stars for a chance of success,” said Drake.

    The only downside is that extraterrestrials would need to be transmitting their signals in our direction, Drake said, though he sees this as a positive side to that limitation. “If we get a signal from someone who’s aiming for us, it could mean there’s altruism in the universe. I like that idea. If they want to be friendly, that’s who we will find.”

    Scientists have searched the skies for radio signals for more than 50 years and expanded their search into the optical realm more than a decade ago. The idea of searching in the infrared is not a new one, but instruments capable of capturing pulses of infrared light only recently became available.

    “We had to wait,” Wright said. “I spent eight years waiting and watching as new technology emerged.”

    Now that technology has caught up, the search will extend to stars thousands of light years away, rather than just hundreds. NIROSETI, or Near-Infrared Optical Search for Extraterrestrial Intelligence, could also uncover new information about the physical universe.

    “This is the first time Earthlings have looked at the universe at infrared wavelengths with nanosecond time scales,” said Dan Werthimer, UC Berkeley SETI Project Director. “The instrument could discover new astrophysical phenomena, or perhaps answer the question of whether we are alone.”

    NIROSETI will also gather more information than previous optical detectors by recording levels of light over time so that patterns can be analyzed for potential signs of other civilizations.

    “Searching for intelligent life in the universe is both thrilling and somewhat unorthodox,” said Claire Max, director of UC Observatories and professor of astronomy and astrophysics at UC Santa Cruz. “Lick Observatory has already been the site of several previous SETI searches, so this is a very exciting addition to the current research taking place.”

    NIROSETI will be fully operational by early summer and will scan the skies several times a week on the Nickel 1-meter telescope at Lick Observatory, located on Mt. Hamilton east of San Jose.

    The NIROSETI team also includes Geoffrey Marcy and Andrew Siemion from UC Berkeley; Patrick Dorval, a Dunlap undergraduate, and Elliot Meyer, a Dunlap graduate student; and Richard Treffers of Starman Systems. Funding for the project comes from the generous support of Bill and Susan Bloomfield.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    FNAL Icon
    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

     
  • richardmitnick 7:32 am on October 29, 2017 Permalink | Reply
    Tags: , , , Caltech/MIT Advanced aLigo, , ,   

    From ScienceNews: “What detecting gravitational waves means for the expansion of the universe” 

    ScienceNews bloc

    ScienceNews

    October 24, 2017
    Lisa Grossman

    Speed of spacetime ripples rules out some alternatives to dark energy.

    1
    BANG, FLASH Light waves and gravitational waves from a pair of colliding neutron stars reached Earth at almost the same time, ruling out theories about the universe based on predictions that the two kinds of waves might travel at different speeds. Illustration by Robin Dienel courtesy of the Carnegie Institution for Science.

    Ripples in spacetime travel at the speed of light. That fact, confirmed by the recent detection of a pair of colliding stellar corpses, kills a whole category of theories that mess with the laws of gravity to explain why the universe is expanding as fast as it is.

    On October 16, physicists announced that the Advanced Laser Interferometer Gravitational-Wave Observatory, LIGO, had detected gravitational waves from a neutron star merger (SN Online: 10/16/17).


    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)

    Also, the neutron stars emitted high-energy light shortly after merging. The Fermi space telescope spotted that light coming from the same region of the sky 1.7 seconds after the gravitational wave detection.

    NASA/Fermi Telescope


    NASA/Fermi LAT

    That observation showed for the first time that gravitational waves, the shivers in spacetime set off when massive bodies move, travel at the speed of light to within a tenth of a trillionth of a percent.

    Within a day, five papers were posted at arXiv.org mourning hundreds of expanding universe theories that predicted gravitational waves should travel faster than light — an impossibility without changes to Einstein’s laws of gravity. These theories “are very, very dead,” says the coauthor of one of the papers, cosmologist Miguel Zumalacárregui of the Nordic Institute for Theoretical Physics, or NORDITA, in Stockholm. “We need to go back to our blackboards and start thinking of other alternatives.”

    In the 1990s, observations of exploding stars showed that more distant explosions were dimmer than existing theories predicted. That suggested that the universe is expanding at an ever-increasing rate (SN: 10/22/11, p. 13). Cosmologists have struggled ever since to explain why.

    The most popular explanation for the speedup is that spacetime is filled with a peculiar entity dubbed dark energy. “You can think of it like a mysterious fluid that pushes everything apart and counteracts gravity,” says cosmologist Jeremy Sakstein of the University of Pennsylvania, coauthor of another new paper.

    Lambda-Cold Dark Matter, Accelerated Expansion of the Universe, Big Bang-Inflation (timeline of the universe) Date 2010 Credit: Alex MittelmannColdcreation

    In the simplest version of this theory, the density of this dark energy has not changed over the history of the universe, so physicists call it a cosmological constant. This doesn’t require any changes to gravity — which is good, because gravity has been well-tested inside the solar system.

    The cosmological constant idea matches observations of the wider universe, but it has some theoretical difficulties. Dark energy is about 120 orders of magnitude weaker than theorists calculate it should be (SN Online: 11/18/13), a mismatch that makes scientists uncomfortable.

    Also, different methods for measuring the rate of expansion come up with slightly different numbers (SN: 8/6/16, p. 10). Measurements based on exploding stars suggest that distant galaxies are speeding away from each other at 73 kilometers per second for each megaparsec (about 3.3 million light-years) of space between them. But observations based on the cosmic microwave background, ancient light that encodes information about the conditions of the early universe, found that the expansion rate is 67 km/s per megaparsec. The disagreement suggests that either one of the measurements is wrong, or the theory behind dark energy needs a tweak.

    So instead of invoking a substance to counteract gravity, theorists tried to explain the expanding universe by weakening gravity itself. Any modifications to gravity need to leave the solar system intact. “It’s quite hard to build a theory that accelerates the universe and also doesn’t mess up the solar system,” says cosmologist Tessa Baker of the University of Oxford, coauthor of still another paper.

    These theories take hundreds of forms. “This field of modified gravity theories is a zoo,” says Baker. Some suggest that gravity leaks out into extra dimensions of space and time. Many others account for the universe’s speedy spreading by adding a different mysterious entity — some unknown particle perhaps — that drains gravity’s strength as the universe evolves.

    But the new entity would have another crucial effect: It could slow the speed of light waves, similar to the way light travels more slowly through water than through air. That means that the best alternatives to dark energy required gravitational waves to travel faster than light — which they don’t.

    Justin Khoury, a theoretical physicist at the University of Pennsylvania who has worked on several of the alternative gravity theories but was not involved in the new papers, was surprised that one gravitational-wave observation ruled out so many theories at once. He’s hardly disappointed, though.

    “The fact that we’re learning something about dark energy because of this measurement is incredibly exciting,” he says.

    Observing gravitational waves and light waves at the same time offers a third, independent way to measure how fast the universe is expanding. For now, that rate lies frustratingly right between the two clashing measurements scientists already had, at 70 km/s per megaparsec. But it’s still imprecise. Once LIGO and other observatories have seen 10 or 20 more neutron star collisions, researchers should be able to tell which measurement is correct and figure out whether dark energy needs an update, Zumalacárregui says.

    “Gravitational waves may kill these models, but eventually they have the potential to tell us if this discrepancy is for real,” he says. “That’s something that is in itself very beautiful.”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

     
  • richardmitnick 6:05 am on October 24, 2017 Permalink | Reply
    Tags: , , , Caltech/MIT Advanced aLigo, , , , Production of gamma rays from merging neutron stars   

    From Princeton: “Steven S. Gubser: Thunder and Lightning from Neutron Star mergers” 

    Princeton University
    Princeton University

    October 18, 2017
    Steven S. Gubser

    As of late 2015, we have a new way of probing the cosmos: gravitational radiation. Thanks to LIGO (the Laser Interferometer Gravitational-wave Observatory) and its new sibling Virgo (a similar interferometer in Italy), we can now “hear” the thumps and chirps of colliding massive objects in the universe.


    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)

    Not for nothing has this soundtrack been described by LIGO scientists as “the music of the cosmos.” This music is at a frequency easily discerned by human hearing, from somewhat under a hundred hertz to several hundred hertz. Moreover, gravitational radiation, like sound, is wholly different from light. It is possible for heavy dark objects like black holes to produce mighty gravitational thumps without at the same time emitting any significant amount of light. Indeed, the first observations of gravitational waves came from black hole merger events whose total power briefly exceeded the light from all stars in the known universe. But we didn’t observe any light from these events at all, because almost all their power went into gravitational radiation.

    In August 2017, LIGO and Virgo observed a collision of neutron stars which did produce observable light, notably in the form of gamma rays. Think of it as cosmic thunder and lightning, where the thunder is the gravitational waves and the lightning is the gamma rays. When we see a flash of ordinary lightning, we can count a few seconds until we hear the thunder. Knowing that sound travels one mile in about five seconds, we can reckon how distant the event is. The reason this method works is that light travels much faster than sound, so we can think of the transmission of light as instantaneous for purposes of our estimate.

    Things are very different for the neutron star collision, in that the event took place about 130 million light years away, but the thunder and lightning arrived on earth pretty much simultaneously. To be precise, the thunder was first: LIGO and Virgo heard a basso rumble rising to a characteristic “whoop,” and just 1.7 seconds later, the Fermi and INTEGRAL experiments observed gamma ray bursts from a source whose location was consistent with the LIGO and Virgo observations.

    NASA/Fermi Telescope

    NASA/Fermi LAT

    ESA/Integral

    The production of gamma rays from merging neutron stars is not a simple process, so it’s not clear to me whether we can pin that 1.7 seconds down as a delay precisely due to the astrophysical production mechanisms; but at least we can say with some confidence that the propagation time of light and gravity waves are the same to within a few seconds over 130 million light years. From a certain point of view, that amounts to one of the most precise measurements in physics: the ratio of the speed of light to the speed of gravity equals 1, correct to about 14 decimal places or better.

    The whole story adds up much more easily when we remember that gravitational waves are not sound at all. In fact, they’re nothing like ordinary sound, which is a longitudinal wave in air, where individual air molecules are swept forward and backward just a little as the sound waves pass them by. Gravitational waves instead involve transverse disturbances of spacetime, where space is stretched in one direction and squeezed in another—but both of those stretch-squeeze directions are at right angles to the direction of the wave. Light has a similar transverse quality: It is made up of electric and magnetic fields, again in directions that are at right angles to the direction in which the light travels. It turns out that a deep principle underlying both Maxwell’s electromagnetism and Einstein’s general relativity forces light and gravitational waves to be transverse. This principle is called gauge symmetry, and it also guarantees that photons and gravitons are massless, which implies in turn that they travel at the same speed regardless of wavelength.

    It’s possible to have transverse sound waves: For instance, shearing waves in crystals are a form of sound. They typically travel at a different speed from longitudinal sound waves. No principle of gauge symmetry forbids longitudinal sound waves, and indeed they can be directly observed, along with their transverse cousins, in ordinary materials like metals. The gauge symmetries that forbid longitudinal light waves and longitudinal gravity waves are abstract, but a useful first cut at the idea is that there is extra information in electromagnetism and in gravity, kind of like an error-correcting code. A much more modest form of symmetry is enough to characterize the behavior of ordinary sound waves: It suffices to note that air (at macroscopic scales) is a uniform medium, so that nothing changes in a volume of air if we displace all of it by a constant distance.

    In short, Maxwell’s and Einstein’s theories have a feeling of being overbuilt to guarantee a constant speed of propagation. And they cannot coexist peacefully as theories unless these speeds are identical. As we continue Einstein’s hunt for a unified theory combining electromagnetism and gravity, this highly symmetrical, overbuilt quality is one of our biggest clues.

    The transverse nature of gravitational waves is immediately relevant to the latest LIGO / Virgo detection. It is responsible for the existence of blind spots in each of the three detectors (LIGO Hanford, LIGO Livingston, and Virgo). It seems like blind spots would be bad, but they actually turned out to be pretty convenient: The signal at Virgo was relatively weak, indicating that the direction of the source was close to one of its blind spots. This helped localize the event, and localizing the event helped astronomers home in on it with telescopes. Gamma rays were just the first non-gravitational signal observed: the subsequent light-show from the death throes of the merging neutron stars promises to challenge and improve our understanding of the complex astrophysical processes involved. And the combination of gravitational and electromagnetic observations will surely be a driver of new discoveries in years and decades to come.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition
    Princeton University Campus

    About Princeton: Overview

    Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

    Princeton Shield

     
  • richardmitnick 12:57 pm on October 17, 2017 Permalink | Reply
    Tags: , , , Caltech/MIT Advanced aLigo, , , ,   

    From Ethan Siegel: “Why Neutron Stars, Not Black Holes, Show The Future Of Gravitational Wave Astronomy” 

    From Ethan Siegel

    Oct 17, 2017

    2
    In the final moments of merging, two neutron stars don’t merely emit gravitational waves, but a catastrophic explosion that echoes across the electromagnetic spectrum. University of Warwick / Mark Garlick

    On August 17, the signals from two merging neutron stars reached Earth after a journey of 130 million light years. After an 11 billion year dance, these remnants of once-massive, blue stars that died in supernovae so long ago spiraled into one another after emitting enough gravitational radiation to see their orbits decay. As each one moves through the changing spacetime created by the gravitational field and motion of the other, its momentum changes, causing the two masses to orbit one another more closely over time. Eventually, they meet, and when they do, they undergo a catastrophic reaction: a kilonova. For the first time, we’ve recorded the inspiral and merger in the gravitational wave sky, noticing it in all three detectors (LIGO Livingston, LIGO Hanford, and Virgo), as well as in the electromagnetic sky, from gamma rays all the way through the optical and into the radio. At last, gravitational wave astronomy is now a part of astronomy.


    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)

    3
    From the very first binary neutron star system ever discovered, we knew that gravitational radiation was carrying energy away. It was only a matter of time before we found a system in the final stages of inspiral and merger. NASA (L), Max Planck Institute for Radio Astronomy / Michael Kramer

    We knew this had to happen eventually. Neutron stars have very large masses, estimated at over the mass of the Sun each, and very small sizes. Imagine an atomic nucleus that didn’t contain a handful, a few dozen, or even a few hundred protons and neutrons inside, but rather a star’s worth: 1057 of them. These incredible objects swoop through space, faster and faster, as the fabric of space itself bends and radiates due to their mutual presence. Pulsars in binary systems coalesce, and in the very final stages of inspiral, the strain they impose on a detector even a hundred million light years away can be detectable. We’ve seen the indirect evidence for decades: the decay of their mutual orbits. But the direct evidence, now available, changes everything.

    4
    The strain on the detectors, from the inspiral of the two neutron stars, can be clearly seen even visibly from the twin LIGO detectors. The less-sensitive Virgo detector provides incredibly accurate location information as well. B.P. Abbott et al., PRL 119, 161101 (2017)

    Each time these waves pass through your detector, they cause a slight expanding-and-contracting of the laser arms. Because the neutron star system is so thoroughly predictable, decaying at the rate predicted by Einstein’s equations, we know exactly how the frequency and amplitude of the inspiral ought to behave. Unlike black hole systems of higher masses, the frequency of these low-mass systems falls in the detectable range of the LIGO and Virgo detectors for much longer time periods. While the overwhelming majority of black hole-black hole mergers registered in the LIGO detectors for only a fraction of a second, these neutron stars, even at a distance of over 100 million light years, had their signals detected for almost half a minute!

    5
    This figure shows reconstructions of the four confident and one candidate (LVT151012) gravitational wave signals detected by LIGO and Virgo to date, including the most recent black hole detection GW170814 (which was observed in all three detectors). LIGO/Virgo/B. Farr (University of Oregon)

    This time, the Fermi gamma-ray satellite detected a transient burst, consistent with previously seen kilonovae, just 1.7 seconds after the arrival of the final “chirp” of the gravitational wave signal.

    NASA/Fermi Telescope


    NASA/Fermi LAT

    By time 11 hours had passed, the LIGO/Virgo team had pinpointed an area on the sky just 28 square degrees in size: the smallest localized region ever seen. Even though the neutron star signal was so much less intense in magnitude than the black hole signals were, the fact that the detectors had caught so many orbits gave the team the strongest signal to date: a signal-to-noise ratio of more than 32!

    6
    By adding in the data from the Virgo detector, even though the signal-to-noise ratio was low, we were able to make the greatest-precision detection of a gravitational wave source of all time. B.P. Abbott et al., PRL 119, 161101 (2017)

    By knowing where this signal was, we could then train our greatest optical, infrared, and radio telescopes on this site in the sky, where the galaxy NGC 4993 was located (at the correct distance). Over the next two weeks, we saw an electromagnetic counterpart to the gravitational wave source, and the afterglow of the gamma-ray burst that Fermi saw. For the first time, we had observed a neutron star merger in gravitational waves and across the light spectrum, confirming what theorists had suspected in spectacular fashion: that this is where the majority of the heaviest elements in the Universe originate.

    7
    Just hours after the gravitational wave signal arrived, optical telescopes were able to hone in on the galaxy home to the merger, watching the site of the blast brighten and fade in practically real-time.

    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

    But also encoded in this merger are a few incredible facts that you may not realize; facts that point the way to the future of gravitational wave astronomy.

    1.) Binary neutron stars barely spin at all! In isolation, neutron stars can be some of the most rapidly spinning objects in the Universe, up to a significant percentage of the speed of light. The fastest rotate over 700 times per second… but not in a binary system! The close presence of another large mass means that tidal forces are large, and hence the friction of one rotating body on another causes them both to slow down. By time they merge, neither one can be rotating at any appreciable speed, allowing us to constrain the orbital parameters from the gravitational wave signal extremely tightly.

    7
    Some of the most important parameters of the merging gravitational wave system were reported quite precisely, owing to the non-rotating nature of the neutron star-neutron star system. B.P. Abbott et al., PRL 119, 161101 (2017)

    2.) At least 28 Jupiter masses’ worth of material was converted into energy via E = mc2. We’ve never seen neutron star-neutron star mergers in gravitational waves before. In black hole-black hole systems of equivalent mass, up to 5% of the total mass gets converted into energy. In neutron star systems, its expected to be less, because the collision occurs between nuclei, not between singularities; the two masses can’t get as close. Still, at least 1% of the total mass was converted into pure energy via Einstein’s mass-energy equivalence, a very impressive and large amount of energy!

    8
    All massless particles travel at the speed of light, including the photon, gluon and gravitational waves, which carry the electromagnetic, strong nuclear and gravitational interactions, respectively. NASA/Sonoma State University/Aurore Simonnet

    3.) Gravitational waves move at exactly the speed of light! Before this detection, we never had a gravitational wave and a light signal simultaneously identifiable to compare with one another. After a journey of 130 million light years, the first electromagnetic signal from this detection arrived just 1.7 seconds after the peak of the gravitational wave signal. That means, at most, the difference between the speed of gravity and the speed of light is about 0.12 microns-per-second, or 0.00000000000004%. It’s anticipated that these two speeds are exactly equal, and the delay of the light signal comes from the fact that the light-producing reactions in the neutron star take a second or two to reach the surface.

    8
    The galaxy NGC 4993, located 130 million light years away, had been imaged many times before. But just after the August 17, 2017 detection of gravitational waves, a new transient source of light was seen: the optical counterpart of a neutron star-neutron star merger. P.K. Blanchard / E. Berger / Pan-STARRS / DECam

    Pann-STARS telescope, U Hawaii, Mauna Kea, Hawaii, USA, 4,207 m (13,802 ft) above sea level

    4.) A faster response time is possible! By time we first located the three-dimensional place on the sky where the electromagnetic signal was, twelve hours had passed. Sure, we were able to observe the optical counterpart immediately, but it would’ve been better to get in on the ground floor. As automated analysis improves, as well as the synchronization of all three detectors, the better we’ll do. Over the coming years, LIGO will get slightly more sensitive, Virgo will do better, and two additional LIGO-like detectors, KAGRA in Japan and LIGO-India, will come online. Instead of half a day, we may be soon talking about response times in a matter of minutes or even seconds.

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

    LIGO-India in the Hingoli district in western India

    9
    On the ground, a noise ‘glitch’ in the LIGO Livingston detector meant that the automated software failed to extract the signal, requiring manual intervention. B.P. Abbott et al., PRL 119, 161101 (2017)

    5.) Going to space will be the ultimate in gravitational wave observing. Here on the ground, part of the reason it took so long to find the location was that in Livingston, LA, there was a “noise” glitch: something caused the detector on the ground to vibrate. As a result, the automated software couldn’t extract the true signal, and manual intervention was required. The LIGO-Virgo team did an amazing job, but were these detectors in space, this wouldn’t even have been an issue in the first place. There is no seismic noise in the abyss of interplanetary space.

    ESA/eLISA space based the future of gravitational wave research

    10
    Neutron stars, when they merge, can exhibit gravitational wave and electromagnetic signals simultaneously, unlike black holes.
    Dana Berry / Skyworks Digital, Inc.

    Unlike merging black holes, inspiraling and merging neutron stars:

    Can be seen for a much longer time, due to their low masses,
    Will emit electromagnetic counterparts, allowing for the gravitational and electromagnetic skies to be unified,
    Are far more numerous, with the only reason we’ve seen more black holes is due to the increased range for them,
    And can be used to learn information about the Universe, such as the speed of gravity, that black holes cannot teach us.
    The delay of around 11 hours from the merger to the first optical and infrared signatures isn’t due to physics, but due to our own instrumental limitations here. As our analysis techniques improve, and more events are discovered, we’ll learn exactly how long it takes before visible light signatures are created by neutron star-neutron star mergers.

    At last, the origin of the heavy elements are confirmed; the speed of gravity is definitively known; and the gravitational wave and electromagnetic skies are one. Any doubters of LIGO now have the independent confirmation they’ve been clamoring for, and there is no ambiguity left. The future of astronomy includes gravitational waves, and that future is here, today. Congratulations, one and all. Today, all of Earth is the beneficiary of this incredible knowledge.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

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

     
c
Compose new post
j
Next post/Next comment
k
Previous post/Previous comment
r
Reply
e
Edit
o
Show/Hide comments
t
Go to top
l
Go to login
h
Show/Hide help
shift + esc
Cancel
%d bloggers like this: