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  • richardmitnick 1:35 pm on August 28, 2021 Permalink | Reply
    Tags: "Collaborations sets new constraints on cosmic strings", Caltech/MIT aLIGO, , KAGRA Collaboration, , ,   

    From Caltech/MIT aLIGO, VIRGO and KAGRA via Phys.org: “Collaborations sets new constraints on cosmic strings” 

    From Caltech/MIT aLIGO, VIRGO Collaboration and KAGRA Collaboration

    via

    Phys.org

    From phys.org

    August 27, 2021

    1
    Credit: Unsplash/CC0 Public Domain

    The LIGO/Virgo/KAGRA Collaboration, a large group of researchers at different institutes worldwide, has recently set the strongest constraints on cosmic strings to date, using the Advanced LIGO/Virgo full O3 dataset. This dataset contains the latest gravitational waves data detected by a network of three interferometers located in United States and in Italy.

    “We wanted to use the most current data of the third observing run (O3 dataset) to put constraints on cosmic strings,” Prof. Mairi Sakellariadou of King’s College London (UK), who is part of the LIGO-Virgo Collaboration, told Phys.org.

    Field theories predict that as the Universe expands and its temperature drops, it undergoes a series of phase transitions followed by spontaneously broken symmetries, which may leave behind topological defects, relics of the previous, more symmetrical phase of the Universe.

    “Just to give you an example, if you take water in its liquid form and you decrease the temperature below zero degrees Celcius, it will solidify,” Sakellariadou said. “Inside an ice cube, you can see filaments where the water is in the liquid form. This phenomenon may also happen in the Universe.” One-dimensional topological defects are referred to as cosmic strings. While particle physics models predict the existence of cosmic strings, there is currently no observational confirmation of their existence.

    “The heavier cosmic strings are, the stronger their gravitational effects will be,” Sakellariadou said. By analyzing observational data, we can put constraints on the parameter that tells us how heavy these objects are, in other words the epoch of cosmic string formation.”

    Setting constraints on cosmic strings also allows researchers to constraint particle physics models and cosmological scenarios. Using gravitational wave data, researchers are able to test particle physics models at energy scales that cannot be reached by accelerators like the Large Hadron Collider at CERN.

    “Constraints also depend on which model of cosmic strings we are using for the string loop distribution, which is dictated by involved numerical simulations” Sakellariadou said.

    So far, researchers have developed two possible numerical simulations. The first one was put forward several years ago by Bouchet, Lorenz, Ringeval and Sakellariadou, while the second was developed by Blanco-Pillado, Olum and Shlaer.

    Recently, Auclair, Ringeval, Sakellariadou and Steer developed a new analytic string loop model that interpolates between the two developed in the past with numerical simulations. This new model has been used for the first time in putting constraints on cosmic strings using gravitational wave data from the last observing run of the LIGO/Virgo/KAGRA collaboration.

    Remarkably, the recent constraints set by the LIGO/Virgo/KAGRA collaboration are stronger than the ones put by Big Bang nucleosynthesis, pulsar-timing array, or cosmic microwave background data. They have also improved on previous constraints set by LIGO/Virgo by 1 to 2 orders of magnitude.

    “As more data becomes available, we will be able to put even stronger constraints. From a theoretical point of view, however, it is also important to build and investigate new cosmic string models, and examine the implications of our work for particle physics beyond the Standard Model and cosmological scenarios”, Sakellariadou said.

    The research was published in Physical Review Letters.

    See the full article here .

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  • richardmitnick 4:12 pm on July 28, 2021 Permalink | Reply
    Tags: "On the hunt for 'hierarchical' black holes", Black holes-detected by their gravitational wave signal as they collide with other black holes-could be the product of much earlier parent collisions., Caltech/MIT aLIGO, , , , ,   

    From University of Birmingham (UK) : “On the hunt for ‘hierarchical’ black holes” 

    From University of Birmingham (UK)

    27 July 2021

    Beck Lockwood,
    Press Office, University of Birmingham,
    Tel: +44 (0)781 3343348.
    r.lockwood@bham.ac.uk

    Black holes-detected by their gravitational wave signal as they collide with other black holes-could be the product of much earlier parent collisions.

    1
    Credit: Riccardo Buscicchio.

    1
    Credit: CC0 Public Domain.

    Such an event has only been hinted at so far, but scientists at the University of Birmingham in the UK, and Northwestern University (US), believe we are getting close to tracking down the first of these so-called ‘hierarchical’ black holes.

    In a review paper, published in Nature Astronomy, Dr Davide Gerosa, of the University of Birmingham, and Dr Maya Fishbach of Northwestern University (US), suggest that recent theoretical findings together with astrophysical modelling and recorded gravitational wave data will enable scientists to accurately interpret gravitational wave signals from these events.

    Since the first gravitational wave was detected by the LIGO and Virgo detectors in September 2015, scientists have produced increasingly nuanced and sophisticated interpretations of these signals.

    There is now fervent activity to prove the existence of so-called ‘hierarchical mergers’ although the detection of GW190521 in 2019 – the most massive black hole merger yet detected – is thought to be the most promising candidate so far.

    “We believe that most of the gravitational waves so far detected are the result of first generation black holes colliding,” says Dr Gerosa. “But we think there’s a good chance that others will contain the remnants of previous mergers. These events will have distinctive gravitational wave signatures suggesting higher masses, and an unusual spin caused by the parent collision.”

    Understanding the characteristics of the environment in which such objects might be produced will also help narrow the search. This must be an environment with a large number of black holes, and one that is sufficiently dense to retain the black holes after they have merged, so they can go on and merge again.

    These could be, for example, nuclear star clusters, or accretion disks – containing a flow of gas, plasma and other particles – surrounding the compact regions at the centre of galaxies.

    “The LIGO and Virgo collaboration has already discovered more than 50 gravitational wave events,” says Dr Fishbach. “This will expand to thousands over the next few years, giving us so many more opportunities to discover and confirm unusual objects like hierarchical black holes in the universe.”

    See the full article here .

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    University of Birmingham (UK) has been challenging and developing great minds for more than a century. Characterised by a tradition of innovation, research at the University has broken new ground, pushed forward the boundaries of knowledge and made an impact on people’s lives. We continue this tradition today and have ambitions for a future that will embed our work and recognition of the Birmingham name on the international stage.

    The University of Birmingham is a public research university located in Edgbaston, Birmingham, United Kingdom. It received its royal charter in 1900 as a successor to Queen’s College, Birmingham (founded in 1825 as the Birmingham School of Medicine and Surgery), and Mason Science College (established in 1875 by Sir Josiah Mason), making it the first English civic or ‘red brick’ university to receive its own royal charter. It is a founding member of both the Russell Group (UK) of British research universities and the international network of research universities, Universitas 21.

    The student population includes 23,155 undergraduate and 12,605 postgraduate students, which is the 7th largest in the UK (out of 169). The annual income of the institution for 2019–20 was £737.3 million of which £140.4 million was from research grants and contracts, with an expenditure of £667.4 million.

    The university is home to the Barber Institute of Fine Arts, housing works by Van Gogh, Picasso and Monet; the Shakespeare Institute; the Cadbury Research Library, home to the Mingana Collection of Middle Eastern manuscripts; the Lapworth Museum of Geology; and the 100-metre Joseph Chamberlain Memorial Clock Tower, which is a prominent landmark visible from many parts of the city. Academics and alumni of the university include former British Prime Ministers Neville Chamberlain and Stanley Baldwin, the British composer Sir Edward Elgar and eleven Nobel laureates.

    Scientific discoveries and inventions

    The university has been involved in many scientific breakthroughs and inventions. From 1925 until 1948, Sir Norman Haworth was Professor and Director of the Department of Chemistry. He was appointed Dean of the Faculty of Science and acted as Vice-Principal from 1947 until 1948. His research focused predominantly on carbohydrate chemistry in which he confirmed a number of structures of optically active sugars. By 1928, he had deduced and confirmed the structures of maltose, cellobiose, lactose, gentiobiose, melibiose, gentianose, raffinose, as well as the glucoside ring tautomeric structure of aldose sugars. His research helped to define the basic features of the starch, cellulose, glycogen, inulin and xylan molecules. He also contributed towards solving the problems with bacterial polysaccharides. He was a recipient of the Nobel Prize in Chemistry in 1937.

    The cavity magnetron was developed in the Department of Physics by Sir John Randall, Harry Boot and James Sayers. This was vital to the Allied victory in World War II. In 1940, the Frisch–Peierls memorandum, a document which demonstrated that the atomic bomb was more than simply theoretically possible, was written in the Physics Department by Sir Rudolf Peierls and Otto Frisch. The university also hosted early work on gaseous diffusion in the Chemistry department when it was located in the Hills building.

    Physicist Sir Mark Oliphant made a proposal for the construction of a proton-synchrotron in 1943, however he made no assertion that the machine would work. In 1945, phase stability was discovered; consequently, the proposal was revived, and construction of a machine that could surpass proton energies of 1 GeV began at the university. However, because of lack of funds, the machine did not start until 1953. The DOE’s Brookhaven National Laboratory (US) managed to beat them; they started their Cosmotron in 1952, and had it entirely working in 1953, before the University of Birmingham.

    In 1947, Sir Peter Medawar was appointed Mason Professor of Zoology at the university. His work involved investigating the phenomenon of tolerance and transplantation immunity. He collaborated with Rupert E. Billingham and they did research on problems of pigmentation and skin grafting in cattle. They used skin grafting to differentiate between monozygotic and dizygotic twins in cattle. Taking the earlier research of R. D. Owen into consideration, they concluded that actively acquired tolerance of homografts could be artificially reproduced. For this research, Medawar was elected a Fellow of the Royal Society. He left Birmingham in 1951 and joined the faculty at University College London (UK), where he continued his research on transplantation immunity. He was a recipient of the Nobel Prize in Physiology or Medicine in 1960.

     
  • richardmitnick 9:24 am on September 17, 2019 Permalink | Reply
    Tags: , , , Caltech/MIT aLIGO, , , , Ringing black holes,   

    From Science News: “Gravitational waves from a ringing black hole support the no-hair theorem” 

    From Science News

    September 16, 2019
    Emily Conover

    General relativity suggests the spacetime oddities can be fully described by their mass and spin.

    1

    After two black holes collide and meld into one, the new black hole “rings” (illustrated), emitting gravitational waves before settling down into a quiet state. M. Isi/MIT, NASA

    For black holes, it’s tough to stand out from the crowd: Donning a mohawk is a no-no.

    Ripples in spacetime produced as two black holes merged into one suggest that the behemoths have no “hair,” scientists report in the Sept. 13 Physical Review Letters. That’s another way of saying that, as predicted by Einstein’s general theory of relativity, black holes have no distinguishing characteristics aside from mass and the rate at which they spin (SN: 9/24/10).

    “Black holes are very simple objects, in some sense,” says physicist Maximiliano Isi of MIT.

    Detected by the Advanced Laser Interferometer Gravitational-Wave Observatory, LIGO, in 2015, the spacetime ripples resulted from a fateful encounter between two black holes, which spiraled around each other before crashing together to form one big black hole (SN: 2/11/16).

    MIT /Caltech Advanced aLigo

    In the aftermath of that coalescence, the newly formed big black hole went through a period of “ringdown.” It oscillated over several milliseconds as it emitted gravitational waves, similar to the way a struck bell vibrates and makes sound waves before eventually quieting down.

    Reverberating black holes emit gravitational waves not at a single frequency, but with additional, short-lived frequencies known as overtones — much like a bell rings with multiple tones in addition to its main pitch.

    Measuring the ringing black hole’s main frequency as well as one overtone allowed the researchers to compare those waves with the prediction for a hairless black hole. The results agreed within 20 percent.

    That result still leaves some wiggle room for the no-hair theorem to be proved wrong. But, “It’s a clear demonstration that the method works,” says physicist Leo Stein of the University of Mississippi in Oxford, who was not involved with the research. “And hopefully the precision will increase as LIGO improves.”

    The researchers also calculated the mass and spin of the black hole, using only waves from the ringdown period. The figures agreed with the values estimated from the entire event — including the spiraling and merging of the original two black holes — and so reinforced the idea that the resulting black hole’s behavior was determined entirely by its mass and spin.

    But just as a mostly bald man may sport a few strands, black holes could reveal some hair on closer inspection. If they do, that might lead to a solution to the information paradox, a puzzle about what happens to information that falls into a black hole (SN: 5/16/14). For example, in a 2016 attempt to resolve the paradox, physicist Stephen Hawking and colleagues suggested that black holes might have “soft hair” (SN: 4/3/18).

    “It could still be that these objects have more mysteries to them that will only be revealed by future, more sensitive measurements,” Isi says.

    See the full article here .


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  • richardmitnick 10:45 am on July 13, 2019 Permalink | Reply
    Tags: "What Are Intermediate-Mass Black Holes?", , , , , Caltech/MIT aLIGO, ,   

    From Discover Magazine: “What Are Intermediate-Mass Black Holes?” 

    DiscoverMag

    From Discover Magazine

    July 12, 2019
    Jake Parks

    1
    The hunt for intermediate-mass black holes (IMBH) has picked up over recent years, and there are now dozens of promising candidates. This artist’s concept depicts a 2,200 solar mass IMBH suspected to reside in the heart of the globular cluster 47 Tucanae, located some 15,000 light-years from Earth. (Credit: B. Kiziltan/T. Karacan)

    Black holes have long served as fodder for science fiction — and for good reason. These unimaginably dense objects contain so much matter trapped in such a small volume that their gravity prevents even light from escaping their surfaces.

    Although the first prediction of a black hole was made nearly 250 years ago by the English philosopher and clergyman John Michell, the first black hole candidate, Cygnus X-1, wasn’t discovered until 1971. Since then, astronomers have tirelessly chipped away at countless questions related to these once-mythical beasts. But one of the most basic and enduring questions remains: Do they come in all sizes?

    Small and Large, or Small to large?

    Over the past few decades, astronomers have compiled loads of evidence for the existence of black holes at both ends of the mass spectrum. Researchers have uncovered small black holes that weigh just a few to 100 times the mass of the sun, as well as supermassive black holes that can reach billions of times the mass of their star-sized brethren.

    Stellar-mass black holes are thought to form when a relatively massive star dies in spectacular fashion. As the exhausted star burns through its final traces of fuel, its immense gravity causes it to collapse in on itself. If the collapsing star isn’t too big, the infalling material rebounds off the star’s dense core. This causes a supernova explosion, often leaving behind a tiny white dwarf or neutron star. But if the surviving remnant is greater than about three solar masses, not even tightly packed neutrons can prevent the city-sized core from continuing to collapse into a stellar-mass black hole.

    On the other hand, there’s another class of black holes known as supermassive black holes, which serve as the central gravitational anchors of most, if not all, large galaxies. Though supermassive black holes are anywhere from millions to billions of times the mass of the sun, they pack all that matter into a region roughly the size of a single star. There are many lines of evidence that indicate these cosmic behemoths are common throughout the universe, but exactly how and when they formed still remains a mystery.

    But what about the in-betweeners? Shouldn’t there should be a class of mid-sized black holes that split the difference between stellar-mass and supermassive black holes? These cosmic middleweights, which would range from about 100 to 1 million solar masses — though the specific range varies depending on who you ask — are referred to as intermediate-mass black holes (IMBHs). And although astronomers have found several compelling IMBH candidates spread throughout the universe, the jury is still out on whether they truly exist. However, the evidence is beginning to pile up.

    2
    Located roughly 290 million light-years from Earth, the edge-on spiral galaxy ESO 243-49 is thought to harbor one of the first strong candidates for an intermediate-mass black hole, HLX-1. The black hole (circled) was found near the edge of the galaxy within a cluster of young stars. (Credit: NASA/ESA/S. Farrell (University of Sydney and University of Leicester))

    NASA/ESA Hubble Telescope

    Is Proof Out There?

    Though conclusive proof of IMBHs remains elusive, over the past few decades, there have been a number of studies that have uncovered intriguing evidence hinting at the existence of these not-so-big, not-so-small black holes.

    For example, in 2003, researchers used the ESA’s XMM-Newton space observatory to identify two strong, distinct X-rays sources in the nearby starburst galaxy NGC 1313. Because black holes tend to ferociously gobble up material that gets too close and belch out high-energy radiation, they are some of the strongest known emitters of X-rays. And by pinpointing NGC 1313’s X-ray sources and studying how they periodically flash, in 2015, researchers were able to constrain the mass of one of the galaxy’s suspected black holes, known as NGC 1313 X-1 [The Astrophysical Journal Letters]. They calculated it’s about 5,000 times the mass of the Sun, give or take about 1,000 solar masses, which would put it firmly in the mass range of an intermediate-mass black hole.

    Likewise, in 2009, researchers uncovered even stronger evidence for the existence of a medium-sized black hole [Nature] . Located some 290 million light-years away near the edge of the galaxy ESO 243-49, the team observed an incredibly bright X-ray source called HLX-1 (Hyper-Luminous X-ray source 1) [Astronomy] that did not have an optical counterpart. This suggests the object is not simply a star or background galaxy. Additionally, the researchers found HLX-1’s X-ray signature varied with time, suggesting a black hole is brightening every time a nearby star makes a close approach, feeding gas to the black hole and causing brief outbursts of X-rays that then slowly fade away. Based on the brightness of the observed flashes, the researchers calculated a minimum mass of the black hole of about 500 times the mass of the Sun, though some estimates put its weight closer to 20,000 solar masses [The Astrophysical Letters].

    “Such a detection is essential,” said lead author Sean Farrell of the University of Leicester after the discovery [ScienceDaily]. “While it is already known that stellar-mass black holes are the remnants of massive stars, the formation mechanisms of supermassive black holes are still unknown.” Farrell went on to explain that “the identification of HLX-1 is therefore an important step towards a better understanding of the formation of the supermassive black holes that exist at the center of the Milky Way and other galaxies.

    More recently, astronomers have started to uncover strong evidence of wandering intermediate-mass black holes lurking near the heart of the Milky Way. For example, in January 2019, astronomers used the Atacama Large Millimeter/submillimeter Array (ALMA) to trace streams of gas orbiting an invisible object, thought to be an IMBH [The Astrophysical Journal Letters] , with an apparent mass of about 32,000 times the mass of the Sun.

    Located a scant 23 light-years from the Milky Way’s supermassive black hole, Sagittarius A*, the discovery suggests the newfound IMBH could merge with the roughly 4-million-solar-mass Sagittarius A* in the not-too-distant future. To help bolster the case for IMBHs wandering through the Milky Way, the researchers hope to use other oddly-orbiting gas clouds to probe our galaxy for more mid-sized black holes tucked away in gas-dominated regions.

    3
    So far, the LIGO and Virgo gravitational-wave detectors have teamed up to uncover 20 stellar-mass black holes in the process of merging to form black holes ranging from about 20 to 80 solar masses. Although LIGO-Virgo has not uncovered any IMBHs (over 100 solar masses), researchers are optimistic about spotting them in the future. (Credit: LIGO-Virgo/Frank Elavsky/Northwestern)

    The Hunt for IMBHs

    Moving forward, researchers will rely on a variety of methods to uncover a slew of more mid-sized black holes. By doing so, they not only hope to prove that IMBHs truly exist, but more importantly, they want to use IMBHs to help piece together how large black holes grow and evolve over time.

    Fortunately, astronomers are now in a prime position to do just that. Thanks to the recent successes of the LIGO-Virgo gravitational-wave project — which has identified 20 stellar-mass black holes [MPIGP] by probing the universe for gravitational waves that are produced when black holes merge — researchers have a new method for searching for small to mid-sized black holes.

    Although the LIGO-Virgo collaboration has yet to uncover gravitational waves from mergers between black holes larger than about 40 solar masses, according to the LIGO website [https://www.ligo.org/science/Publication-O1O2IMBH/index.php], “in [the] future, with improvement in [the] sensitivity of gravitational wave detector[s], we will have a better understanding of the frequency of IMBH mergers. The third observing run has started collecting data from April 1, 2019, and gravitational-wave scientists are very hopeful to observe these elusive sources soon!”

    So stay tuned, because over the next few years, we may find definitive proof of the missing link between small and super-sized black holes. And if we do, it will finally put this cosmic conundrum to rest once and for all. Only then will we be able to stop debating the existence of IMBHs, and instead focus on unraveling their origin stories, as well as those of supermassive black holes.

    See the full article here .

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  • richardmitnick 12:44 pm on June 24, 2019 Permalink | Reply
    Tags: "NASA’s Fermi mission reveals record-setting gamma-ray bursts", , , , , Caltech/MIT aLIGO, ,   

    From Stanford University: “NASA’s Fermi mission reveals record-setting gamma-ray bursts” 

    Stanford University Name
    From Stanford University

    June 13, 2019

    1
    NASA/DOE/FermiLAT Collaboration

    NASA/Fermi Gamma Ray Space Telescope

    NASA/Fermi LAT

    Stanford has played a leading role in compiling Fermi’s gamma-ray bursts catalogs ever since the space observatory launched nearly 11 years ago.

    For 10 years, NASA’s Fermi Gamma-ray Space Telescope has scanned the sky for gamma-ray bursts (GRBs), the universe’s most luminous explosions. A new catalog of the highest-energy blasts provides scientists with fresh insights into how they work.

    “Fermi is an ongoing experiment that keeps producing good science,” said Nicola Omodei, an astrophysicist at Stanford University’s School of Humanities and Sciences. “GRBs are really one of the most spectacular astronomical events that we witness.”

    The catalog was published in the June 13 edition of The Astrophysical Journal. More than 120 authors contributed to the paper, which was led by Omodei and Giacomo Vianello at Stanford, Magnus Axelsson at Stockholm University in Sweden, and Elisabetta Bissaldi at the National Institute of Nuclear Physics and Polytechnic University in Bari, Italy.

    Stanford has played a leading role in compiling Fermi’s GRB catalogs ever since the space observatory launched nearly 11 years ago. “All of the analysis tools and methods that led to the preperation of the catalogs were developed at Stanford and SLAC,” Omodei said. “We’ve continued to refine the analysis techniques and increase the sensitivity of the Fermi Large Area Telescope (LAT) to GRBs. For every GRB, we can characterize its duration, its temporal behavior, and its spectral properties.”

    GRBs emit gamma rays, the highest-energy form of light. Most GRBs occurs when some types of massive stars run out of fuel and collapse to create new black holes. Others happen when two neutron stars, superdense remnants of stellar explosions, merge. Both kinds of cataclysmic events create jetfers of particles that move near the speed of light. The gamma rays are produced in collisions of fast-moving material inside the jets and when the jets interact with the environment around the star.

    Astronomers can distinguish the two GRB classes by the duration of their lower-energy gamma rays. Short bursts from neutron star mergers last less than 2 seconds, while long bursts typically continue for a minute or more. The new catalog, which includes 17 short and 169 long bursts, describes 186 events seen by Fermi’s Large Area Telescope (LAT) LAT over the last 10 years.

    Fermi observes these powerful bursts using two instruments. The LAT sees about one-fifth of the sky at any time and records gamma rays with energies above 30 million electron volts (MeV) — millions of times the energy of visible light. The Gamma-ray Burst Monitor (GBM) sees the entire sky that isn’t blocked by Earth and detects lower-energy emission. All told, the GBM has detected more than 2,300 GRBs so far.

    Included in Fermi’s latest observation set are a number of record-setting and intriguing events, including the shortest burst ever recorded (GRB 081102B, which lasted just one-tenth of a second), the longest burst in the catalog (GRB 160623A, which remained illuminated for 10 hours), and the farthest known burst (GRB 080916C, located 12.2 billion light-years away in the constellation Carina).

    Also included in the new catalog is GRB 170817A, the first burst to have both its light and gravitational waves captured simultaneously. Light from the event — a product of two neutron stars crashing together — was recorded by Fermi’s GBM instrument, while the spacetime ripples it generated were detected by the Laser Interferometer Gravitational Wave Observatory (LIGO), the Virgo interferometer.


    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

    Gravity is talking. Lisa will listen. Dialogos of Eide

    ESA/eLISA the future of gravitational wave research

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


    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 that LIGO and VIRGO have begun another observation period, the astrophysics community will be on the lookout for more joint GRB and gravitational wave events” said Judy Racusin, a co-author and Fermi deputy project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “This catalog was a monumental team effort, and the result helps us learn about the population of these events and prepares us for delving into future groundbreaking finds.”

    The Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership managed by NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Fermi was developed in collaboration with the U.S. Department of Energy, with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

    See the full article here .


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    Stanford University campus. No image credit

    Stanford University

    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 2:34 pm on April 2, 2019 Permalink | Reply
    Tags: , , , , Caltech/MIT aLIGO, , , , , ,   

    From University of Chicago: “How to use gravitational waves to measure the expansion of the universe” 

    U Chicago bloc

    From University of Chicago

    Mar 28, 2019
    Louise Lerner


    Prof. Daniel Holz discusses a new way to calculate the Hubble constant, a crucial number that measures the expansion rate of the universe and holds answers to questions about the universe’s size, age and history. Video by UChicago Creative

    Ripples in spacetime lead to new way to determine size and age of universe.

    On the morning of Aug. 17, 2017, after traveling for more than a hundred million years, the aftershocks from a massive collision in a galaxy far, far away finally reached Earth.

    These ripples in the fabric of spacetime, called gravitational waves, tripped alarms at two ultra-sensitive detectors called LIGO, sending texts flying and scientists scrambling.


    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

    Gravity is talking. Lisa will listen. Dialogos of Eide

    ESA/eLISA the future of gravitational wave research

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


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

    One of the scientists was Prof. Daniel Holz at the University of Chicago. The discovery had provided him the information he needed to make a groundbreaking new measurement of one of the most important numbers in astrophysics: the Hubble constant, which is the rate at which the universe is expanding.

    The Hubble constant holds the answers to big questions about the universe, like its size, age and history, but the two main ways to determine its value have produced significantly different results. Now there was a third way, which could resolve one of the most pressing questions in astronomy—or it could solidify the creeping suspicion, held by many in the field, that there is something substantial missing from our model of the universe.

    “In a flash, we had a brand-new, completely independent way to make a measurement of one of the most profound quantities in physics,” said Holz. “That day I’ll remember all my life.”

    As LIGO and its European counterpart VIRGO turn back on on April 1, Holz and other scientists are preparing for more data that could shed light on some of the universe’s biggest questions.

    Universal questions

    We’ve known the universe is expanding for a long time (ever since eminent astronomer and UChicago alum Edwin Hubble made the first measurement of the expansion in 1929, in fact),

    Edwin Hubble looking through a 100-inch Hooker telescope at Mount Wilson in Southern California, 1929 discovers the Universe is Expanding

    but in 1998, scientists were stunned to discover that the rate of expansion is not slowing as the universe ages, but actually accelerating over time. In the following decades, as they tried to precisely determine the rate, it has become apparent that different methods for measuring the rate produce different answers.

    One of the two methods measures the brightness of supernovae–exploding stars– in distant galaxies;

    Standard Candles to measure age and distance of the universe from supernovae NASA

    the other looks at tiny fluctuations in the cosmic microwave background [CMB], the faint light left over from the Big Bang.

    CMB per ESA/Planck

    ESA/Planck 2009 to 2013

    Scientists have been working for two decades to boost the accuracy and precision for each measurement, and to rule out any effects which might be compromising the results; but the two values still stubbornly disagree by almost 10 percent.

    2
    A neutron star collision causes detectable ripples in the fabric of spacetime, which are called gravitational waves. Photo courtesy of Aurore Simonnet

    Because the supernova method looks at relatively nearby objects, and the cosmic microwave background is much more ancient, it’s possible that both methods are right—and that something profound about the universe has changed since the beginning of time.

    “We don’t know if one or both of the other methods have some kind of systematic error, or if they actually reflect a fundamental truth about the universe that is missing from our current models,” said Holz. “Either is possible.”

    Holz saw the possibility for a third, completely independent way to measure the Hubble constant—but it would depend on a combination of luck and extreme feats of engineering.

    The ‘standard siren’

    In 2005, Holz wrote a paper [NJP] with Scott Hughes of Massachusetts Institute of Technology suggesting that it would be possible to calculate the Hubble constant through a combination of gravitational waves and light. They called these sources “standard sirens,” a nod to “standard candles”, which refers to the supernovae used to make the Hubble constant measurement.

    But first it would take years to develop technology that could pick up something as ephemeral as ripples in the fabric of spacetime. That’s LIGO: a set of enormous, extremely sensitive detectors that are tuned to pick up the gravitational waves that are emitted when something big happens somewhere in the universe.

    The Aug. 17, 2017 waves came from two neutron stars, which had spiraled around and around each other in a faraway galaxy before finally slamming together at close to the speed of light. The collision sent gravitational waves rippling across the universe and also released a burst of light, which was picked up by telescopes on and around Earth.

    Neutron star collision-Robin Dienel-The Carnegie Institution for Science

    3
    Prof. Daniel Holz writes out the formula for the Hubble constant, which measures the rate at which the universe is expanding.

    That burst of light was what sent the scientific world into a tizzy. LIGO had picked up gravitational wave readings before, but all the previous ones were from collisions of two black holes, which can’t be seen with conventional telescopes.

    But they could see the light from the colliding neutron stars, and the combination of waves and light unlocked a treasure trove of scientific riches. Among them were the two pieces of information Holz needed to make his calculation of the Hubble constant.

    How does the method work?

    To make this measurement of the Hubble constant, you need to know how fast an object—like a newly collided pair of neutron stars—is receding away from Earth, and how far away it was to begin with. The equation is surprisingly simple. It looks like this: The Hubble constant is the velocity of the object divided by the distance to the object, or H=v/d.

    Somewhat counterintuitively, the easiest part to calculate is how fast the object is moving. Thanks to the bright afterglow given off by the collision, astronomers could point telescopes at the sky and pinpoint the galaxy where the neutron stars collided. Then they can take advantage of a phenomenon called redshift: As a faraway object moves away from us, the color of the light it’s giving off shifts slightly towards the red end of the spectrum. By measuring the color of the galaxy’s light, they can use this reddening to estimate how fast the galaxy is moving away from us. This is a century-old trick for astronomers.

    The more difficult part is getting an accurate measure of the distance to the object. This is where gravitational waves come in. The signal the LIGO detectors pick up gets interpreted as a curve, like this:

    4
    The signal picked up by the LIGO detector in Louisiana, as it caught the waves from two neutron stars colliding far away in space, forms a distinctive curve. Courtesy of LIGO

    The shape of the signal tells scientists how big the two stars were and how much energy the collision gave off. By comparing that with how strong the waves were when they reached Earth, they could infer how far away the stars must have been.

    The initial value from just this one standard siren came out to be 70 kilometers per second per megaparsec. That’s right in between the other two methods, which find about 73 (from the supernova method) and 67 (from the cosmic microwave background).

    Of course, that initial standard siren measurement is only from one data point, and large uncertainties remain. But the LIGO detectors are turning back on after an upgrade to boost their sensitivity. Nobody knows how often neutron stars collide, but Holz (along with former student Hsin-Yu Chen and current student Maya Fishbach) wrote a paper estimating that the gravitational wave method may provide a revolutionary, extremely precise measurement of the Hubble constant within five years.

    “As time goes on, we’ll observe more and more of these binary neutron star mergers, and use them as standard sirens to steadily improve our estimate of the Hubble constant. Depending on where our value falls, we might confirm one method or the other. Or we might find an entirely different value,” Holz said. “No matter what we find, it’s gonna be interesting—and will be an important step in learning more about our universe.”

    See the full article here .

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    Please help promote STEM in your local schools.

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    U Chicago Campus

    An intellectual destination

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

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

    We empower individuals to challenge conventional thinking in pursuit of original ideas. Students in the College develop critical, analytic, and writing skills in our rigorous, interdisciplinary core curriculum. Through graduate programs, students test their ideas with UChicago scholars, and become the next generation of leaders in academia, industry, nonprofits, and government.

    UChicago research has led to such breakthroughs as discovering the link between cancer and genetics, establishing revolutionary theories of economics, and developing tools to produce reliably excellent urban schooling. We generate new insights for the benefit of present and future generations with our national and affiliated laboratories: Argonne National Laboratory, Fermi National Accelerator Laboratory, and the Marine Biological Laboratory in Woods Hole, Massachusetts.

    The University of Chicago is enriched by the city we call home. In partnership with our neighbors, we invest in Chicago’s mid-South Side across such areas as health, education, economic growth, and the arts. Together with our medical center, we are the largest private employer on the South Side.

    In all we do, we are driven to dig deeper, push further, and ask bigger questions—and to leverage our knowledge to enrich all human life. Our diverse and creative students and alumni drive innovation, lead international conversations, and make masterpieces. Alumni and faculty, lecturers and postdocs go on to become Nobel laureates, CEOs, university presidents, attorneys general, literary giants, and astronauts.

     
  • richardmitnick 1:31 pm on January 24, 2019 Permalink | Reply
    Tags: "When Black Holes Collide", , , , , , Caltech/MIT aLIGO,   

    From Caltech: “When Black Holes Collide” 

    Caltech Logo

    From Caltech

    01/24/2019

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

    1
    A simulated picture of two merging black holes, each about 30 solar masses. This is approximately what a human would see if they could travel in spaceship to take a closer look at merging black holes.
    Credit: SXS, the Simulating eXtreme Spacetimes (SXS) project (http://www.black-holes.org)

    Physicists use supercomputers and AI to create the most accurate model yet of black hole mergers.

    One of the most cataclysmic events to occur in the cosmos involves the collision of two black holes. Formed from the deathly collapse of massive stars, black holes are incredibly compact—a person standing near a stellar-mass black hole would feel gravity about a trillion times more strongly than they would on Earth. When two objects of this extreme density spiral together and merge, a fairly common occurrence in space, they radiate more power than all the stars in the universe.

    “Imagine taking 30 suns and packing them into a region the size of Hawaii. Then take two such objects and accelerate them to half the speed of light and make them collide. This is one of the most violent events in nature,” says Vijay Varma, a graduate student at Caltech.

    In a new study in the January 11 issue of the journal Physical Review Letters, Varma and his colleagues report the most accurate computer model yet of the end stage of black hole mergers, a period when a new, more massive black hole has formed. The model, which was aided by supercomputers and machine-learning, or artificial intelligence (AI) tools, will ultimately help physicists perform more precise tests of Einstein’s general theory of relativity.

    “We can predict what’s left after a black hole merger—properties of the final black hole such as its spin and mass—with an accuracy 10 to 100 times better than what was possible before,” says co-author Davide Gerosa, an Einstein Postdoctoral Fellow in Theoretical Astrophysics at Caltech. “This is important because tests of general relativity depend on how well we can predict the end states of black hole mergers.”

    The research is related to a larger effort to study black holes with LIGO, the Laser Interferometer Gravitational-wave Observatory, which made history in 2015 by making the first direct detection of gravitational waves emitted by a black hole merger. Since then, LIGO has detected nine additional black hole mergers.

    Gravitational waves are ripples in space and time, first predicted by Einstein more than 100 years ago. Gravity itself, according to general relativity, is a warping of the fabric of spacetime. When massive objects like black holes accelerate through spacetime, they generate gravitational waves.

    One of the goals of LIGO and the thousands of scientists analyzing its data is to better understand the physics of black hole collisions—and to use these data, in turn, to assess whether Einstein’s general theory of relativity still holds true under these extreme conditions. A breakdown of the theory might open the door to new types of physics not yet imagined.

    But creating models of colossal events like black hole collisions has proved to be a daunting task. As the colliding black holes become very close to one another, just seconds before the final merger, their gravitational fields and velocities become extreme and the math becomes far too complex for standard analytical approaches.

    “When it comes to modeling these sources, one can use the pen-and-paper approach to solve Einstein’s equations during the early stages of the merger when the black holes are spiraling toward each other,” says Varma. “However, these schemes break down near the merger. Simulations using the equations of general relativity are the only means to predict the outcome of the merger process accurately.”

    That is where supercomputers help out. The team took advantage of nearly 900 black hole merger simulations previously run by the Simulating eXtreme Spacetimes (SXS) group using the Wheeler supercomputer at Caltech (supported by the Sherman Fairchild Foundation) and the Blue Waters supercomputer at the National Center for Supercomputing Applications (NCSA) at the University of Illinois at Urbana-Champaign. The simulations took 20,000 hours of computing time. The Caltech scientists’ new machine-learning program, or algorithm, learned from the simulations and helped create the final model.

    “Now that we have built the new model, you don’t need to take months,” says Varma. “The new model can give you answers about the end state of mergers in milliseconds.”

    The researchers say that their model will be of particular importance in a few years, as LIGO and other next-generation gravitational-wave detectors become more and more precise in their measurements. “Within the next few years or so, gravitational-wave detectors will have less noise,” says Gerosa. “The current models of the final black hole properties won’t be precise enough at that stage, and that’s where our new model can really help out.”

    The Physical Review Letters study, titled “High-accuracy mass, spin, and recoil predictions of generic black-hole merger remnants,” was funded by the Sherman Fairchild Foundation, the National Science Foundation, NASA, the Brinson Foundation, and Caltech. Other authors includealumnus Leo Stein (BS ’06) of the University of Mississippi and formerly a postdoctoral scholar at Caltech; François Hébert, a postdoctoral scholar at Caltech; and Hao Zhang of the University of Pennsylvania and formerly a Summer Undergraduate Research Fellow (SURF) at Caltech.


    3
    LIGO and Virgo Announce Four New Detections
    The observatories are also releasing their first catalog of gravitational-wave events
    4
    5

    On Saturday, December 1, scientists attending the Gravitational Wave Physics and Astronomy Workshop in College Park, Maryland, presented new results from the National Science Foundation’s LIGO (Laser Interferometer Gravitational-Wave Observatory) and the European- based VIRGO gravitational-wave detector regarding their searches for coalescing cosmic objects, such as pairs of black holes and pairs of neutron stars. The LIGO and Virgo collaborations have now confidently detected gravitational waves from a total of 10 stellar-mass binary black hole mergers and one merger of neutron stars, which are the dense, spherical remains of stellar explosions. Six of the black hole merger events had been reported before, while four are newly announced.

    From September 12, 2015, to January 19, 2016, during the first LIGO observing run since undergoing upgrades in a program called Advanced LIGO, gravitational waves from three binary black hole mergers were detected. The second observing run, which lasted from November 30, 2016, to August 25, 2017, yielded one binary neutron star merger and seven additional binary black hole mergers, including the four new gravitational-wave events being reported now. The new events are known as GW170729, GW170809, GW170818, and GW170823, in reference to the dates they were detected.

    All of the events are included in a new catalog, also released Saturday, with some of the events breaking records. For instance, the new event GW170729, detected in the second observing run on July 29, 2017, is the most massive and distant gravitational-wave source ever observed. In this coalescence, which happened roughly 5 billion years ago, an equivalent energy of almost five solar masses was converted into gravitational radiation.

    GW170814 was the first binary black hole merger measured by the three-detector network, and allowed for the first tests of gravitational-wave polarization (analogous to light polarization).

    The event GW170817, detected three days after GW170814, represented the first time that gravitational waves were ever observed from the merger of a binary neutron star system. What’s more, this collision was seen in gravitational waves and light, marking an exciting new chapter in multi-messenger astronomy, in which cosmic objects are observed simultaneously in different forms of radiation.

    One of the new events, GW170818, which was detected by the global network formed by the LIGO and Virgo observatories, was very precisely pinpointed in the sky. The position of the binary black holes, located 2.5 billion light-years from Earth, was identified in the sky with a precision of 39 square degrees. That makes it the next best localized gravitational-wave source after the GW170817 neutron star merger.

    Caltech’s Albert Lazzarini, Deputy Director of the LIGO Laboratory, says “The release of four additional binary black hole mergers further informs us of the nature of the population of these binary systems in the universe and better constrains the event rate for these types of events.”

    “In just one year, LIGO and VIRGO working together have dramatically advanced gravitational- wave science, and the rate of discovery suggests the most spectacular findings are yet to come,” says Denise Caldwell, Director of NSF’s Division of Physics. “The accomplishments of NSF’s LIGO and its international partners are a source of pride for the agency, and we expect even greater advances as LIGO’s sensitivity becomes better and better in the coming year.”

    “The next observing run, starting in Spring 2019, should yield many more gravitational-wave candidates, and the science the community can accomplish will grow accordingly,” says David Shoemaker, spokesperson for the LIGO Scientific Collaboration and senior research scientist in MIT’s Kavli Institute for Astrophysics and Space Research. “It’s an incredibly exciting time.”

    “It is gratifying to see the new capabilities that become available through the addition of Advanced Virgo to the global network,” says Jo van den Brand of Nikhef (the Dutch National Institute for Subatomic Physics) and VU University Amsterdam, who is the spokesperson for the Virgo Collaboration. “Our greatly improved pointing precision will allow astronomers to rapidly find any other cosmic messengers emitted by the gravitational-wave sources.” The enhanced pointing capability of the LIGO-Virgo network is made possible by exploiting the time delays of the signal arrival at the different sites and the so-called antenna patterns of the interferometers.

    “The new catalog is another proof of the exemplary international collaboration of the gravitational wave community and an asset for the forthcoming runs and upgrades”, adds EGO Director Stavros Katsanevas.

    The scientific papers describing these new findings, which are being initially published on the arXiv repository of electronic preprints, present detailed information in the form of a catalog of all the gravitational wave detections and candidate events of the two observing runs as well as describing the characteristics of the merging black hole population. Most notably, we find that almost all black holes formed from stars are lighter than 45 times the mass of the Sun. Thanks to more advanced data processing and better calibration of the instruments, the accuracy of the astrophysical parameters of the previously announced events increased considerably.

    Laura Cadonati, Deputy Spokesperson for the LIGO Scientific Collaboration, says “These new discoveries were only made possible through the tireless and carefully coordinated work of the detector commissioners at all three observatories, and the scientists around the world responsible for data quality and cleaning, searching for buried signals, and parameter estimation for each candidate — each a scientific specialty requiring enormous expertise and experience.”

    The Collaborations

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

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

    Related Links

    Paper: “GWTC-1: A Gravitational-Wave Transient Catalog of Compact Binary Mergers Observed by LIGO and Virgo during the First and Second Observing Runs”

    Paper: “Binary Black Hole Population Properties Inferred from the First and Second Observing Runs of Advanced LIGO and Advanced Virgo”

    Papers available on the arXiv and the LIGO DCC, https://dcc.ligo.org/

    Media Contacts

    Valerio Boschi
    
Virgo-EGO Communication Office
    valerio.boschi@ego-gw.it; +39 050 752 463

    Antonella Varaschin
    
INFN Communications Office
    antonella.varaschin@presid.infn.it; +39 06 68400360

    Kimberly Allen

    Director of Media Relations and Deputy Director, MIT News Office
    allenkc@mit.edu; +1 617-253-2702

    Whitney Clavin

    Senior Content and Media Strategist
    Caltech Communications
    wclavin@caltech.edu; +1 626-395-1856

    John Toon

    Institute Research and Economic Development Communications
    Georgia Institute of Technology

    john.toon@comm.gatech.edu; +1 404-894-6986

    Amanda Hallberg Greenwell
    
Head, Office of Legislative and Public Affairs
    National Science Foundation
    agreenwe@nsf.gov; +1 703-292-8070

    See the full article here .

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


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.


    Stem Education Coalition

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

    Caltech campus


    Caltech campus

     
  • richardmitnick 9:23 am on October 19, 2018 Permalink | Reply
    Tags: , , , Caltech/MIT aLIGO, , Cosmic microwave background radiation. Stephen Hawking Center for Theoretical Cosmology U Cambridge, , Measuring the Age of the Universe   

    From Harvard-Smithsonian Center for Astrophysics: “Measuring the Age of the Universe” 

    Harvard Smithsonian Center for Astrophysics


    From Harvard-Smithsonian Center for Astrophysics

    Inflationary Universe. NASA/WMAP


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

    1

    October 17, 2018

    Tyler Jump
    Public Affairs
    Harvard-Smithsonian Center for Astrophysics
    +1 617-495-7462
    tyler.jump@cfa.harvard.edu

    The single most important puzzle in today’s cosmology (the study of the universe as a whole) can be summarized in one question: How old is it? For nearly a century — since the discoveries by Einstein, Hubble, LeMaitre and others led to the big bang model of creation — we have known the answer. It is about 13.8 billion years old (using current data). But in just the past decade the two alternative measurement methods have narrowed the uncertainties in their results to a few percent to reach a stunning conclusion: The two do not agree with each other. Since both methods are based on exactly the same model and equations, our understanding of the universe is somehow wrong — perhaps fundamentally so.

    Enter the most exciting technical achievement in astronomy for decades, the detection of gravitational waves (GW) caused by the mergers of black holes or neutron stars with each other by LIGO-Virgo, soon to be joined by other similar GW detection facilities in other countries.


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

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

    ESA/eLISA the future of gravitational wave research

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

    The solution to the cosmological dilemma is likely to be settled soon by these instruments according to a new Nature paper by Hsin-Yu Chen of Harvard’s Black Hole Initiative, Maya Fishbach and Daniel E. Holz of the University of Chicago. The authors describe how upcoming detections of GW will have enough statistics to settle the question of age, forcing either one or the other (or perhaps even both) methods to re-think their basic understanding, or possibly even forcing a new variation of the When and How of the creation.

    The two currently conflicting methods rely on observations of vastly different parts of the cosmic order. The first method measures and models the cosmic microwave background radiation (the CMBR method) produced by the universe when, after about 380,000 years, it cooled down and allowed neutral hydrogen atoms to form and light to propagate without scattering.

    Cosmic microwave background radiation. Stephen Hawking Center for Theoretical Cosmology U Cambridge

    The second method, the one used by Hubble and interpreted by LeMaitre, measures galaxies. This method takes advantage of the expansion of the universe to correlate a galaxy’s distance with its recession velocity, the so-called Hubble-LeMaitre Law, and to derive the Hubble-LeMaitre parameter which describes how long these galaxies have been in motion, related to the age of the universe. All astronomers today rely on this expression to obtain the distances to galaxies too far away to measure directly but whose velocities are easily seen in the Doppler shifts (the redshift) of their spectral lines. While the most familiar use of the parameter is to obtain the age of the universe, its value influences all the other parameters in the cosmological model (about nine of them) which together also explain the shape and expansion character of the universe.

    Hubble calibrated his set of distances with nearby galaxies, but today we are capable of seeing galaxies so remote their light has been traveling to us for over ten billion years. Supernovae (SN), or at least those whose brightness is thought to be well understood, can be seen at great distances and so have been used to bootstrap the distance scale calibration outward from Hubble’s original neighborhood. There are subtle complexities in SN that are not well understood, however, resulting in an uncertainty that has been getting smaller as our understanding of them has improved. Today those uncertainties are small enough to exclude the comparable result from CMBR measurements.

    The GW method of distance measurement is completely independent of both galaxy and CMBR methods. General relativity alone provides the intrinsic strength of the GW signal from its peculiar ringing signal, and its observed strength provides a direct measure of its distance. (The velocity information is obtained from the redshift of atomic lines in the host galaxy). Dr. Chen and her colleagues simulated 90,000 merger events in binary black hole or binary neutron star systems, including the host galaxy properties, and included likely selection effects and other complexities. The GW strength, for example, depends on our viewing angle of inclination of the merger, while the number of events to expect is only roughly constrained by the detections so far. Including these and similar uncertainties, the astronomers conclude that within the next five years it is likely that the GW method will fix the Hubble-LeMaitre parameter (that is, the age of the universe) to a precision of 2%, and to 1% in a decade, good enough to exclude one or even both of the other methods. The new paper’s conclusions are bolstered by the fact that one paper using the GW method to estimate an age has already appeared. It had an uncertainty of between 11.9 billion years to 15.7 billion years, spanning both the current CMBR and galaxy values. But the new paper shows that in five years another roughly fifty GW events will be detected and these should be enough to settle the matter … and usher in a new era in precision cosmology.

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

     
  • richardmitnick 8:58 pm on May 13, 2018 Permalink | Reply
    Tags: , , , Caltech/MIT aLIGO, , , ,   

    From Northwestern University: “Dozens of binaries from Milky Way’s globular clusters could be detectable by LISA” 

    Northwestern U bloc
    From Northwestern University

    May 11, 2018
    Megan Fellman

    Next-generation gravitational wave detector in space will complement LIGO on Earth.

    ESA/eLISA space based the future of gravitational wave research

    The historic first detection of gravitational waves from colliding black holes far outside our galaxy opened a new window to understanding the universe. A string of detections — four more binary black holes and a pair of neutron stars — soon followed the Sept. 14, 2015, observation.

    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.”

    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)

    5
    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.

    7
    David Coulter, graduate student

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

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

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

    8
    Charles Kilpatrick, postdoctoral scholar

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

    9
    Ariadna Murguia-Berthier, graduate student

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

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

    10
    Matthew Siebert, graduate student

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

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

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

    11
    César Rojas Bravo, graduate student

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

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

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

    12
    Yen-Chen Pan, postdoctoral scholar

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

    13
    Enia Xhakaj, graduate student

    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.

    Press releases:

    UC Santa Cruz Press Release

    UC Berkeley Press Release

    Carnegie Institution of Science Press Release

    LIGO Collaboration Press Release

    National Science Foundation Press Release

    Media coverage:

    The Atlantic – The Slack Chat That Changed Astronomy

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

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

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

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

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

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

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

    Scientific American – Gravitational Wave Astronomers Hit Mother Lode

    Nature – Colliding stars spark rush to solve cosmic mysteries

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

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

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

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

    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

    Dark Energy Survey


    Dark Energy Camera [DECam], built at FNAL


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

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

    Noted in the vdeo but not in te article:

    NASA/Chandra Telescope

    NASA/SWIFT Telescope

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

    Prompt telescope CTIO Chile

    NASA NuSTAR X-ray telescope

    Now, another detector is being built to crack this window wider open. This next-generation observatory, called LISA, is expected to be in space in 2034, and it will be sensitive to gravitational waves of a lower frequency than those detected by the Earth-bound Laser Interferometer Gravitational-Wave Observatory (LIGO).

    A new Northwestern University study predicts dozens of binaries (pairs of orbiting compact objects) in the globular clusters of the Milky Way will be detectable by LISA (Laser Interferometer Space Antenna). These binary sources would contain all combinations of black hole, neutron star and white dwarf components. Binaries formed from these star-dense clusters will have many different features from those binaries that formed in isolation, far from other stars.

    The study is the first to use realistic globular cluster models to make detailed predictions of LISA sources. “LISA Sources in Milky-Way Globular Clusters” was published today, May 11, by the journal Physical Review Letters.

    “LISA is sensitive to Milky Way systems and will expand the breadth of the gravitational wave spectrum, allowing us to explore different types of objects that aren’t observable with LIGO,” said Kyle Kremer, the paper’s first author, a Ph.D. student in physics and astronomy in Northwestern’s Weinberg College of Arts and Sciences and a member of a computational astrophysics research collaboration based in Northwestern’s Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA).

    In the Milky Way, 150 globular clusters have been observed so far. The Northwestern research team predicts one out of every three clusters will produce a LISA source. The study also predicts that approximately eight black hole binaries will be detectable by LISA in our neighboring galaxy of Andromeda and another 80 in nearby Virgo.

    Before the first detection of gravitational waves by LIGO, as the twin detectors were being built in the United States, astrophysicists around the world worked for decades on theoretical predictions of what astrophysical phenomena LIGO would observe. That is what the Northwestern theoretical astrophysicists are doing in this new study, but this time for LISA, which is being built by the European Space Agency with contributions from NASA.

    “We do our computer simulations and analysis at the same time our colleagues are bending metal and building spaceships, so that when LISA finally flies, we’re all ready at the same time,” said Shane L. Larson, associate director of CIERA and an author of the study. “This study is helping us understand what science is going to be contained in the LISA data.”

    A globular cluster is a spherical structure of hundreds of thousands to millions of stars, gravitationally bound together. The clusters are some of the oldest populations of stars in the galaxy and are efficient factories of compact object binaries.

    The Northwestern research team had numerous advantages in conducting this study. Over the past two decades, Frederic A. Rasio and his group have developed a powerful computational tool — one of the best in the world — to realistically model globular clusters. Rasio, the Joseph Cummings Professor in Northwestern’s department of physics and astronomy, is the senior author of the study.

    The researchers used more than a hundred fully evolved globular cluster models with properties similar to those of the observed globular clusters in the Milky Way. The models, which were all created at CIERA, were run on Quest, Northwestern’s supercomputer cluster. This powerful resource can evolve the full 12 billion years of a globular cluster’s life in a matter of days.

    NASA (ATP grant NNX14AP92G) and the National Science Foundation (grant AST-1716762) supported the research.

    Other authors of the paper include Sourav Chatterjee and Katelyn Breivik, both of Northwestern and CIERA, and Carl L. Rodriguez, of the MIT-Kavli Institute for Astrophysics and Space Research.

    See the full article here

    See the full article here .

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Northwestern South Campus
    South Campus

    On May 31, 1850, nine men gathered to begin planning a university that would serve the Northwest Territory.

    Given that they had little money, no land and limited higher education experience, their vision was ambitious. But through a combination of creative financing, shrewd politicking, religious inspiration and an abundance of hard work, the founders of Northwestern University were able to make that dream a reality.

    In 1853, the founders purchased a 379-acre tract of land on the shore of Lake Michigan 12 miles north of Chicago. They established a campus and developed the land near it, naming the surrounding town Evanston in honor of one of the University’s founders, John Evans. After completing its first building in 1855, Northwestern began classes that fall with two faculty members and 10 students.
    Twenty-one presidents have presided over Northwestern in the years since. The University has grown to include 12 schools and colleges, with additional campuses in Chicago and Doha, Qatar.

    Northwestern is recognized nationally and internationally for its educational programs.

     
  • richardmitnick 9:07 am on April 18, 2018 Permalink | Reply
    Tags: , , , , Caltech/MIT aLIGO, , Triple Threat: Uncovering Triple Systems with Gravitational Waves   

    From astrobites: “Triple Threat: Uncovering Triple Systems with Gravitational Waves” 

    Astrobites bloc

    astrobites

    Apr 17, 2018
    Lisa Drummond

    Title: Detecting triple systems with gravitational wave observations
    Authors: Yohai Meiron, Bence Kocsis, Abraham Loeb
    Status: The Astrophysical Journal, open access

    The Laser Interferometer Gravitational-Wave Observatory (LIGO) collaboration has been receiving a lot of press in recent years, with a run of groundbreaking gravitational wave (GW) detections (most recently, a neutron star binary!), capturing the excitement of the astrophysics community and general public alike.

    All of the gravitational waves detected so far have been produced by compact binary mergers. This series of LIGO discoveries begs the question – where are the gravitational waves produced by triples? Triple systems are not uncommon in astrophysics – but how would we distinguish a standard compact binary coalescence signal from one produced by a tight binary in orbit around a triple companion? Todays’ paper tackles this question by identifying signatures of the triple that are apparent in the GW signal.

    What is a hierarchical triple system?

    Triple systems consist of three celestial bodies orbiting each other simultaneously. A physical triple system usually exhibits a hierarchical structure. Two of the objects form a close binary, called the inner binary, and the third companion lies on the outskirts, orbiting at distance that far exceeds the length of the inner binary separation.

    1
    Figure 1: A schematic of a stellar triple system. The inner binary (denoted with yellow arrows) orbits a third companion (blue arrows). Image from http://wondergressive.com/triple-star-system-new-gravity/.

    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.

     
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