DOCSLIB.ORG

Gravitational Waves WARNING!!!!

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text

Load more

Gravitational Waves WARNING!!!! ⚫ Terminology is treacherous! ⚫ There are gravitational waves (our topic) and there are gravity waves (a topic for a surfing class). Mix them to your peril. Gravitational waves ⚫ Movie The History ⚫ The history of gravitational waves is rocky. Einstein argued in 1916 that gravitational waves must exist – if the space-time is dynamic, there must be ripples on it. ⚫ Einstein derived the approximate formula for the gravitational waves from two orbiting bodies. ⚫ In 1922 Eddington (that one) argued that gravitational waves were not real and just a mathematical artefact. The History ⚫ In 1936 Einstein wrote a paper with Nathan Rosen reversing his original view; they concluded that all gravitational waves should collapse into black holes. ⚫ The paper was submitted to Physics Review but was returned after the referee pointed out a mistake in it. ⚫ Einstein got berserk in response, writing an angry letter to the editor and promising never to publish in Physics Review again. The History ⚫ Einstein was later persuaded by Infeld of his mistake and corrected the paper. Rosen never conceded. ⚫ In 1957 Richard Feymann (a very famous particle physicist) presented a “sticky bead” argument that convinced most people that gravitational waves are real. The Challenge ⚫ The primary challenge with gravitational waves is that in GR there is no (unambiguous) mathematical expression for its energy. ⚫ Since locally space-time is Minkowski, in the local inertial reference frame the energy of gravitational waves is zero. I.e., that energy is non-local, one cannot claim that the energy of gravitational waves is … at his location, only that the total energy is such and such. Detecting Gravitational Waves 1919-2000 ⚫ The experimental pioneer was Joseph Weber (also a discoverer of the physical principle for a laser). ⚫ He spent most of his life building more and more sophisticated devices for detecting gravitational waves, but never succeeded (although he claimed that he did and was publicly called “insane” for that). ⚫ One of his apparatus even went to the moon on Apollo 17 mission. First Indirect Detection ⚫ In 1993, Russell Hulse and Joseph Taylor received the Nobel Prize in Physics for the discovery and observation of the Hulse-Taylor binary pulsar, which offered the first indirect evidence of the existence of gravitational waves. The End of the Road ⚫ A 50-year long searched ended on Feb 11, 2016! Rainer Weiss Barry Barish Kip Thorne LIGO ⚫ Laser Interferometer Gravitational Observatory LIGO: How It Works ⚫ The main principle is the same as in the Michelson-Morley interferometer. ⚫ Arm length is 4km. ⚫ Initial laser power is 20W, eventually amplified to 100 kW. ⚫ Number of times light bounces back and forth: 280. LIGO ⚫ How it works: LIGO ⚫ Started in 2002. Nothing was detected by 2010. ⚫ Had a major refurbishing into Advanced LIGO until 2015. ⚫ Advanced LIGO had the first detection announced in 2016. ⚫ By 2020 some ~30 detections have been made. ⚫ https://www.gw-openscience.org/eventapi/html/ LIGO: How It Measures GW ⚫ The change of the length of a 4 km arm is 10-18 m. ⚫ This precision is just barely enough to find the signal. ⚫ https://blackholehunter.org/game.html LIGO: Results ⚫ T LIGO: Results ⚫ Why does LIGO find only big BHs and X-ray observers find only small ones? Astronomer’s Bane: Selection Effects ⚫ With one method we always see just one side of the whole story. LIGO: Kilonova ⚫ The GW170817 event had an optical counterpart – they called it a “kilonova”. Future ⚫ LIGO-India (INDIGO), ~2024 ⚫ LIGO A+, ~2026 ⚫ Second refurbishing of LIGO: “LIGO Voyager”, 2028 ⚫ “Einstein Telescope” (Europe), 10 km arms ⚫ LISA: Light Interferometer Space Antenna, ~2034 LISA ⚫ Three spacecraft “flying-in-formation”, arm length is 2.5 million km. ⚫ The arm length is not fixed, variations in length need to be accounted for all the time. ⚫ Light travel time between satellites is significant. ⚫ Science goals: detect mergers of supermassive black holes, compact object binaries before merger, cosmic background. LISA Pathfinder ⚫ A small satellite launched in 2015 to test some of LISA technologies, including measuring positions of free-floating test masses to 0.01 nanometers. ⚫ Exceeded expectations by almost a factor of 10..
Recommended publications
  • The Second-Order Correction to the Energy and Momentum in Plane Symmetric Gravitational Waves Like Spacetimes

    The Second-Order Correction to the Energy and Momentum in Plane Symmetric Gravitational Waves Like Spacetimes

    S S symmetry Article The Second-Order Correction to the Energy and Momentum in Plane Symmetric Gravitational Waves Like Spacetimes Mutahir Ali *, Farhad Ali , Abdus Saboor, M. Saad Ghafar and Amir Sultan Khan Department of Mathematics, Kohat University of Science and Technology, Kohat 26000, Pakistan; [email protected] (F.A.); [email protected] (A.S.); [email protected] (M.S.G.); [email protected] (A.S.K.) * Correspondence: [email protected] Received: 5 December 2018; Accepted: 22 January 2019; Published: 13 February 2019 Abstract: This research provides second-order approximate Noether symmetries of geodetic Lagrangian of time-conformal plane symmetric spacetime. A time-conformal factor is of the form ee f (t) which perturbs the plane symmetric static spacetime, where e is small a positive parameter that produces perturbation in the spacetime. By considering the perturbation up to second-order in e in plane symmetric spacetime, we find the second order approximate Noether symmetries for the corresponding Lagrangian. Using Noether theorem, the corresponding second order approximate conservation laws are investigated for plane symmetric gravitational waves like spacetimes. This technique tells about the energy content of the gravitational waves. Keywords: Einstein field equations; time conformal spacetime; approximate conservation of energy 1. Introduction Gravitational waves are ripples in the fabric of space-time produced by some of the most violent and energetic processes like colliding black holes or closely orbiting black holes and neutron stars (binary pulsars). These waves travel with the speed of light and depend on their sources [1–5]. The study of these waves provide us useful information about their sources (black holes and neutron stars).
  • Nobel Laureates Endorse Joe Biden

    Nobel Laureates Endorse Joe Biden

    Nobel Laureates endorse Joe Biden 81 American Nobel Laureates in Physics, Chemistry, and Medicine have signed this letter to express their support for former Vice President Joe Biden in the 2020 election for President of the United States. At no time in our nation’s history has there been a greater need for our leaders to appreciate the value of science in formulating public policy. During his long record of public service, Joe Biden has consistently demonstrated his willingness to listen to experts, his understanding of the value of international collaboration in research, and his respect for the contribution that immigrants make to the intellectual life of our country. As American citizens and as scientists, we wholeheartedly endorse Joe Biden for President. Name Category Prize Year Peter Agre Chemistry 2003 Sidney Altman Chemistry 1989 Frances H. Arnold Chemistry 2018 Paul Berg Chemistry 1980 Thomas R. Cech Chemistry 1989 Martin Chalfie Chemistry 2008 Elias James Corey Chemistry 1990 Joachim Frank Chemistry 2017 Walter Gilbert Chemistry 1980 John B. Goodenough Chemistry 2019 Alan Heeger Chemistry 2000 Dudley R. Herschbach Chemistry 1986 Roald Hoffmann Chemistry 1981 Brian K. Kobilka Chemistry 2012 Roger D. Kornberg Chemistry 2006 Robert J. Lefkowitz Chemistry 2012 Roderick MacKinnon Chemistry 2003 Paul L. Modrich Chemistry 2015 William E. Moerner Chemistry 2014 Mario J. Molina Chemistry 1995 Richard R. Schrock Chemistry 2005 K. Barry Sharpless Chemistry 2001 Sir James Fraser Stoddart Chemistry 2016 M. Stanley Whittingham Chemistry 2019 James P. Allison Medicine 2018 Richard Axel Medicine 2004 David Baltimore Medicine 1975 J. Michael Bishop Medicine 1989 Elizabeth H. Blackburn Medicine 2009 Michael S.
  • Ripples in Spacetime

    Ripples in Spacetime

    editorial Ripples in spacetime The 2017 Nobel prize in Physics has been awarded to Rainer Weiss, Barry C. Barish and Kip S. Thorne “for decisive contributions to the LIGO detector and the observation of gravitational waves”. It is, frankly, difficult to find something original to say about the detection of gravitational waves that hasn’t been said already. The technological feat of measuring fluctuations in the fabric of spacetime less than one-thousandth the width of an atomic nucleus is quite simply astonishing. The scientific achievement represented by the confirmation of a century-old prediction by Albert Einstein is unique. And the collaborative effort that made the discovery possible — the Laser Interferometer Gravitational-Wave Observatory (LIGO) — is inspiring. Adapted from Phys. Rev. Lett. 116, 061102 (2016), under Creative Commons Licence. Rainer Weiss and Kip Thorne were, along with the late Ronald Drever, founders of the project that eventually became known Barry Barish, who was the director Last month we received a spectacular as LIGO. In the 1960s, Thorne, a black hole of LIGO from 1997 to 2005, is widely demonstration that talk of a new era expert, had come to believe that his objects of credited with transforming it into a ‘big of gravitational astronomy was no interest should be detectable as gravitational physics’ collaboration, and providing the exaggeration. Cued by detections at LIGO waves. Separately, and inspired by previous organizational structure required to ensure and Virgo, an interferometer based in Pisa, proposals, Weiss came up with the first it worked. Of course, the passion, skill and Italy, more than 70 teams of researchers calculations detailing how an interferometer dedication of the thousand or so scientists working at different telescopes around could be used to detect them in 1972.
  • Joseph Weber's Contribution to Gravitational Waves and Neutrinos

    Joseph Weber's Contribution to Gravitational Waves and Neutrinos

    Firenze University Press www.fupress.com/substantia Historical Article New Astronomical Observations: Joseph Weber’s Contribution to Gravitational Waves Citation: S. Gottardo (2017) New Astronomical Observations: Joseph and Neutrinos Detection Weber’s Contribution to Gravitational Waves and Neutrinos Detection. Sub- stantia 1(1): 61-67. doi: 10.13128/Sub- stantia-13 Stefano Gottardo Copyright: © 2017 S. Gottardo.This European Laboratory for Nonlinear Spectroscopy (LENS), 50019 Sesto Fiorentino (Flor- is an open access, peer-reviewed arti- ence), Italy cle published by Firenze University E-mail: [email protected] Press (http://www.fupress.com/substan- tia) and distribuited under distributed under the terms of the Creative Com- Abstract. Joseph Weber, form Maryland University, was a pioneer in the experimen- mons Attribution License, which per- tal research of gravitational waves and neutrinos. Today these two techniques are very mits unrestricted use, distribution, and promising for astronomical observation, since will allow to observe astrophysical phe- reproduction in any medium, provided nomena under a new light. We review here almost 30 years of Weber’s career spent the original author and source are on gravity waves and neutrinos; Weber’s experimental results were strongly criticized credited. by the international community, but his research, despite critics, boosted the brand Data Availability Statement: All rel- new (in mid-sixties of last century) research field of gravity waves to become one of evant data are within the paper and its the most important in XXI century. On neutrino side, he found an unorthodox way Supporting Information files. to reduce the size of detectors typically huge and he claimed to observe neutrinos flux with a small pure crystal of sapphire.
  • Science & ROGER PENROSE

    Science & ROGER PENROSE

    Science & ROGER PENROSE Live Webinar - hosted by the Center for Consciousness Studies August 3 – 6, 2021 9:00 am – 12:30 pm (MST-Arizona) each day 4 Online Live Sessions DAY 1 Tuesday August 3, 2021 9:00 am to 12:30 pm MST-Arizona Overview / Black Holes SIR ROGER PENROSE (Nobel Laureate) Oxford University, UK Tuesday August 3, 2021 9:00 am – 10:30 am MST-Arizona Roger Penrose was born, August 8, 1931 in Colchester Essex UK. He earned a 1st class mathematics degree at University College London; a PhD at Cambridge UK, and became assistant lecturer, Bedford College London, Research Fellow St John’s College, Cambridge (now Honorary Fellow), a post-doc at King’s College London, NATO Fellow at Princeton, Syracuse, and Cornell Universities, USA. He also served a 1-year appointment at University of Texas, became a Reader then full Professor at Birkbeck College, London, and Rouse Ball Professor of Mathematics, Oxford University (during which he served several 1/2-year periods as Mathematics Professor at Rice University, Houston, Texas). He is now Emeritus Rouse Ball Professor, Fellow, Wadham College, Oxford (now Emeritus Fellow). He has received many awards and honorary degrees, including knighthood, Fellow of the Royal Society and of the US National Academy of Sciences, the De Morgan Medal of London Mathematical Society, the Copley Medal of the Royal Society, the Wolf Prize in mathematics (shared with Stephen Hawking), the Pomeranchuk Prize (Moscow), and one half of the 2020 Nobel Prize in Physics, the other half shared by Reinhard Genzel and Andrea Ghez.
  • Recent Observations of Gravitational Waves by LIGO and Virgo Detectors

    Recent Observations of Gravitational Waves by LIGO and Virgo Detectors

    universe Review Recent Observations of Gravitational Waves by LIGO and Virgo Detectors Andrzej Królak 1,2,* and Paritosh Verma 2 1 Institute of Mathematics, Polish Academy of Sciences, 00-656 Warsaw, Poland 2 National Centre for Nuclear Research, 05-400 Otwock, Poland; [email protected] * Correspondence: [email protected] Abstract: In this paper we present the most recent observations of gravitational waves (GWs) by LIGO and Virgo detectors. We also discuss contributions of the recent Nobel prize winner, Sir Roger Penrose to understanding gravitational radiation and black holes (BHs). We make a short introduction to GW phenomenon in general relativity (GR) and we present main sources of detectable GW signals. We describe the laser interferometric detectors that made the first observations of GWs. We briefly discuss the first direct detection of GW signal that originated from a merger of two BHs and the first detection of GW signal form merger of two neutron stars (NSs). Finally we present in more detail the observations of GW signals made during the first half of the most recent observing run of the LIGO and Virgo projects. Finally we present prospects for future GW observations. Keywords: gravitational waves; black holes; neutron stars; laser interferometers 1. Introduction The first terrestrial direct detection of GWs on 14 September 2015, was a milestone Citation: Kro´lak, A.; Verma, P. discovery, and it opened up an entirely new window to explore the universe. The combined Recent Observations of Gravitational effort of various scientists and engineers worldwide working on the theoretical, experi- Waves by LIGO and Virgo Detectors.
  • LIGO's Unsung Heroes : Nature News & Comment

    LIGO's Unsung Heroes : Nature News & Comment

    NATURE | NEWS LIGO's unsung heroes Nature highlights just a few of the people who played a crucial part in the discovery of gravitational waves — but didn’t win the Nobel Prize. Davide Castelvecchi 09 October 2017 Corrected: 19 October 2017 Joe McNally/Getty LIGO hunts gravitational waves with the help of two laser interferometers — and hundreds of people. Expand Every October, the announcements of the Nobel Prizes bring with them some controversy. This year’s physics prize — in recognition of the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the United States — was less debated than most. The three winners — Kip Thorne and Barry Barish, both at the California Institute of Technology (Caltech) in Pasadena, and Rainer Weiss at the Massachusetts Institute of Technology (MIT) in Cambridge — had attracted near-universal praise for their roles in the project’s success. But the award has still put into stark relief the difficulty of singling out just a few individuals from the large collaborations of today’s 'Big Science'. The LIGO collaboration uses two giant laser interferometers to listen for deformations in space-time caused by some of the Universe’s most cataclysmic events. Physicists detected their first gravitational waves — interpreted as being produced by the collision of two black holes more than a billion years ago — in September 2015. The resulting paper, published in February 20161, has a mind-boggling 1,004 authors. Some of those are members of the LIGO Laboratory, the Caltech–MIT consortium that manages LIGO’s two interferometers in Louisiana and Washington State. But the list also includes the larger LIGO Scientific Collaboration: researchers from 18 countries, some of which — such as Germany and the United Kingdom — have made crucial contributions to the detectors.
  • Rainer Weiss, Professor of Physics Emeritus and 2017 Nobel Laureate

    Rainer Weiss, Professor of Physics Emeritus and 2017 Nobel Laureate

    Giving to the Department of Physics by Erin McGrath RAINER WEISS ’55, PHD ’62 Bryce Vickmark Rai Weiss has established a fellowship in the Physics Department because he is eternally grateful to his advisor, the late Jerrold Zacharias, for all that he did for Rai, so he knows firsthand the importance of supporting graduate students. Rainer Weiss, Professor of Physics Emeritus and 2017 Nobel Laureate. Rainer “Rai” Weiss was born in Berlin, Germany in 1932. His father was a physician and his mother was an actress. His family was forced out of Germany by the Nazis since his father was Jewish and a Communist. Rai, his mother and father fled to Prague, Czecho- slovakia. In 1937 a sister was born in Prague. In 1938, after Chamberlain appeased Hitler by effectively giving him Czechoslovakia, the family was able to obtain visas to enter the United States through the Stix Family in St. Louis, who were giving bond to professional Jewish emigrants. When Rai was 21 years-old, he visited Mrs. Stix and thanked her for what she had done for his family. The family immigrated to New York City. Rai’s father had a hard time passing the medi- cal boards because of his inability to answer multiple choice exams. His mother, who Rai says “held the family together,” worked in a number of retail stores. Through the services of an immigrant relief organization Rai received a scholarship to attend the prestigious Columbia Grammar School. At the end of 1945, when Rai was 13 years old, he became fascinated with electronics and music.
  • Report 2018/2019 ETH Institute for Theoretical Studies

    Report 2018/2019 ETH Institute for Theoretical Studies

    Report 2018/2019 ETH Institute for Theoretical Studies ETH-ITS Table of Contents Foreword 5 The ETH Institute for Theoretical Studies 6 History and aims 6 Fellows at the ITS 6 Collaborations 7 Activities 8 Meetings, talks, minicourses 8 The ITS Science Colloquium 10 Programme 2018–2019 11 Fellows’ seminar 12 Programme 2018–2019 12 Awards 13 Fellows’ report 14 Outlook 22 People at the ETH-ITS 24 Director 24 Coordinator 24 Board of Patrons 24 Advisory Committee 24 2013–2017 2017–2019 Fellows 2014–2019 25 Senior Fellows Junior Fellows (with current affiliation of former Junior Fellows) Contact 27 Clausiusstrasse 47, the address of the ETH Institute for Theoretical Studies. 4 Foreword The academic year 2018/2019 was in several ways special for the Institute for Theoretical Studies. Firstly, it experimen- ted a new way of functioning, dedicating a semester to the interdisciplinary subject of «modular forms, periods and scattering amplitudes», hosting over forty physicists and mathematicians, with a school, a workshop and other events involving several young scientists and putting into contact participants with scientists of ETH. Secondly, the Institute was evaluated by an international committee, who was very positively impressed by the achievements of the Institute and gave interesting suggestions for improvement. Thirdly, on a more personal note, this was my last year as the director of the ETH-ITS; the last six years were an intense period in which I had the unique opportunity to meet scientists in a variety of subjects who are shaping their respective disciplines. I thank the donors for making this possible, the Fellows of the Institute for their excellent scientific contributions, the school board of ETH Zurich for their continuous support, the Advisory Committee for its commitment and advice, and Christina Buchmann, who is retiring this year as coordinator, for her invaluable help and competence in running the Institute.
  • The Titans of the Cosmos

    The Titans of the Cosmos

    FALL 2018 Titans of the Cosmos Exploring the Mysteries of Neutron Star Mergers & Supermassive Black Holes 10 | Educating the next generation of innovators in science and industry 16 | Berkeley leads the way in data science education Research Highlights, Department News & More CONTENTS CHAIR’SLETTER RESEARCH HIGHLIGHTS2 Recent breakthroughs in faculty-led investigations PHOTO: BEN AILES PHOTO: TITANS OF THE COSMOS Fall classes are underway, our introductory courses ON THE COVER: Exploring the Mysteries of are packed, and we have good news on several fronts. Berkeley astrophysicist Daniel Kasen's research group uses Neutron Star Mergers and On July 1 we welcomed our newest faculty member, supercomputers at the National Supermassive Black Holes condensed matter theorist Mike Zalatel. In August the Energy Research Scientific Com- puting Center at LBNL to model 2018 Academic Rankings of World Universities were cosmic explosions. See page 4. announced, with Berkeley Physics second, between MIT CHAIR and Stanford – fine company. In September we learned Wick Haxton 4 that Professor Barbara Jacak will be awarded the 2019 MANAGING EDITOR & Tom Bonner Prize of the American Physical Society for DIRECTOR OF DEVELOPMENT her leadership of the PHENIX detector at Brookhaven’s Rachel Schafer Relativistic Heavy Ion Collider, and new graduate stu- CONTRIBUTING EDITOR & dent Nick Sherman will receive the LeRoy Apker Award SCIENCE WRITER for outstanding undergraduate research in theoretical Devi Mathieu PHYSICS INNOVATORS condensed matter and mathematical physics. Most re- DESIGN 10INITIATIVE cently, Assistant Professor Norman Yao has been named Sarah Wittmer Educating the Next a Packard Fellow, one of the most prestigious awards CONTRIBUTORS Generation of Innovators available in STEM disciplines.
  • A Brief History of Gravitational Waves

    A Brief History of Gravitational Waves

    Review A Brief History of Gravitational Waves Jorge L. Cervantes-Cota 1, Salvador Galindo-Uribarri 1 and George F. Smoot 2,3,4,* 1 Department of Physics, National Institute for Nuclear Research, Km 36.5 Carretera Mexico-Toluca, Ocoyoacac, Mexico State C.P.52750, Mexico; [email protected] (J.L.C.-C.); [email protected] (S.G.-U.) 2 Helmut and Ana Pao Sohmen Professor at Large, Institute for Advanced Study, Hong Kong University of Science and Technology, Clear Water Bay, 999077 Kowloon, Hong Kong, China. 3 Université Sorbonne Paris Cité, Laboratoire APC-PCCP, Université Paris Diderot, 10 rue Alice Domon et Leonie Duquet 75205 Paris Cedex 13, France. 4 Department of Physics and LBNL, University of California; MS Bldg 50-5505 LBNL, 1 Cyclotron Road Berkeley, CA 94720, USA. * Correspondence: [email protected]; Tel.:+1-510-486-5505 Abstract: This review describes the discovery of gravitational waves. We recount the journey of predicting and finding those waves, since its beginning in the early twentieth century, their prediction by Einstein in 1916, theoretical and experimental blunders, efforts towards their detection, and finally the subsequent successful discovery. Keywords: gravitational waves; General Relativity; LIGO; Einstein; strong-field gravity; binary black holes 1. Introduction Einstein’s General Theory of Relativity, published in November 1915, led to the prediction of the existence of gravitational waves that would be so faint and their interaction with matter so weak that Einstein himself wondered if they could ever be discovered. Even if they were detectable, Einstein also wondered if they would ever be useful enough for use in science.
  • Rainer Weiss Year: 1972 Journal Citation: Quarterly Progress Report, Research Laboratory of Electronics (MIT) No

    Rainer Weiss Year: 1972 Journal Citation: Quarterly Progress Report, Research Laboratory of Electronics (MIT) No

    Author: Rainer Weiss Year: 1972 Journal Citation: Quarterly Progress Report, Research Laboratory of Electronics (MIT) No. 105, p.54. Title: Electronically Coupled Broadband Gravitational Antenna nLtr Cli/x = .*= /( 6\"iue lSApr'tla (v. GR-rvIT-{TrOriRESE-{P.CH) B. ELECTROAIAGNETICALLY COUPLED BR OADBAND GR.{,VIT.{TIONAL A\TE:i\A l. Intro duction The prediction of gravitational radiarion that travels at the speed of Ught has been an essential part of every gravitational theory since the discovery of special relativiiy. ^I In !918, Einstein, usirg a rveak-field appPoxirnationin bis very successful geometrical theory of gravity (the general theory of relativity), indicated the form that gravitational waves would take rn ihis theorj- and demonstrated that systems with titne-variant mass quadrupole moments u,ou]d lose energy by gravitational radiation. It was evident to Einstein that since gravitationaf radiation is extremely weak, the most likely measurable radiatj,on woulci come from astronomi,cal sources. For many years the subject of gravj.tational radiation remained the province of a few dedicated theorists; however, the recen! discovery of the pulsars and the pioneering and controve:'sial experiments of Weber-'' at the Universitt' of Maryland have engendered a new interest in ihe field. Weber has reported coincldent excitarions in two gravitational anter/tras separaied 1000 km. These antelrnas are high-Q resonard ba.rs tuned to 1.6 kHz. He attributes these excitattons to puLsesof graviiadonal radiadon emitted by broadband sources con- cenirated nesr the eenter of our galaxy. If Weberrs i$terpretatj.on of these events is corlect, the:'e is ar e!:ormous flnx of gravitationaL fadiation incident on the Earth.