Searching for gravitational waves with LIGO

Transcription

1 Searching for gravitational waves with LIGO An introduction to LIGO and a few things gravity wave Michael Landry LIGO Hanford Observatory California Institute of Technology Spokane Astronomical Society Nov 2, 2007

2 LIGO in 30 seconds 1. Gravitational Waves: Not EM waves, not particles 2. Gravitational Waves: Never before directly detected 2

3 Gravitational wave astronomy in 30 seconds 3

4 Talk overview Sources» What are gravitational waves?» Why look for them?» Sources: what makes them? Observatories» LIGO. Networks. Interferometers» Overview of a Michelson interferometer» Some LIGO installations» Strain curves and Science mode running Briefly! Einstein@home: a search for continuous gravitational waves 4

5 Gravity: the Old School Sir Isaac Newton, who invented the theory of gravity and all the math needed to understand it 5

6 Newton s theory: good, but not perfect! Mercury s orbit precesses around the sun-each year the perihelion shifts 560 arcseconds per century But this is 43 arcseconds per century too much! (discovered 1859) This is how fast the second hand on a clock would move if one day lasted 4.3 billion years! Urbain Le Verrier, discoverer of Mercury s perihelion shift anomaly Image from St. Andrew s College Mercury Sun Image from Jose Wudka perihelion6

7 Einstein s Answer: General Relativity Picture from Northwestern U. Space and time (spacetime) are curved. Matter causes this curvature Space tells matter how to move This looks to us like gravity 7

8 Space is curved. Really. Not only the path of matter, but even the path of light is affected by gravity from massive objects A massive object shifts apparent position of a star Einstein Cross Photo credit: NASA and ESA 8

9 Important Signature of Gravitational Waves Gravitational waves shrink space along one axis perpendicular to the wave direction as they stretch space along another axis perpendicular both to the shrink axis and to the wave direction. 9

10 Why look for Gravitational Radiation? Because it s there! (presumably) Test General Relativity:» Quadrupolar radiation? Travels at speed of light?» Unique probe of strong-field gravity Gain different view of Universe:» Sources cannot be obscured by dust / stellar envelopes» Detectable sources some of the most interesting, least understood in the Universe» Opens up entirely new non-electromagnetic spectrum 10

11 What s left behind when a star dies? Stars live Stars die Ordinary star Supernova And sometimes they leave behind exotic corpses Neutron stars, pulsars (credit : W. Feimer/STSI) Black holes (credit : NASA/CXC/A. Hobart) 11

12 What might make Gravitational Waves? Compact binary inspiral: chirps» NS-NS waveforms are well described» BH-BH need better waveforms Supernovae / GRBs: bursts» burst signals in coincidence with signals in electromagnetic radiation / neutrinos» all-sky untriggered searches too Cosmological Signal: stochastic background Pulsars in our galaxy: periodic» search for observed neutron stars» all-sky search (computing challenge) 12

13 Compact binary inspirals Sources I Neutron-star binary inspiral: Black-hole binary inspiral: 13

14 Orbital decay : strong indirect evidence Neutron Binary System Hulse & Taylor PSR Timing of pulsars Emission of gravitational waves 17 / sec ~ 8 hr Neutron Binary System separated by ~2x10 6 km m 1 = 1.44m ; m 2 = 1.39m ; ε = Prediction from general relativity spiral in by 3 mm/orbit rate of change orbital period 14

15 Orbital decay : strong indirect evidence Neutron Binary System Hulse & Taylor PSR Timing of pulsars Emission of gravitational waves 17 / sec See Tests of General Relativity from Timing the Double Pulsar Science Express, Sep The only double-pulsar system know, PSR J A/B provides an update to this result. Orbital parameters of the double-pulsar system agree with those predicted by GR to 0.05% ~ 8 hr Neutron Binary System separated by ~2x10 6 km m 1 = 1.44m ; m 2 = 1.39m ; ε = Prediction from general relativity spiral in by 3 mm/orbit rate of change orbital period 15

16 Burst sources: supernovae Sources II Spacequake should preceed optical display by ½ day Leaves behind compact stellar core, e.g., neutron star, black hole Strength of waves depends on asymmetry in collapse Credit: Dana Berry, NASA Observed neutron star motions indicate some asymmetry present Simulations do not succeed from initiation to explosions 16

17 Supernova: Death of a Massive Star Spacequake should preceed optical display by ½ day Leaves behind compact stellar core, e.g., neutron star, black hole Strength of waves depends on asymmetry in collapse Credit: Dana Berry, NASA Observed neutron star motions indicate some asymmetry present Simulations do not succeed from initiation to explosions 17

18 Stochastic background Sources III A stochastic GW background may be: i) an analog of the CMB (discovered by Penzias and Wilson, measured by COBE and WMAP) ii) a summation of sources from a more recent (astrophysical) epoch Credit: Bell Telephone Laboratories Credit: WMAP science team, NASA 18

19 Neutron and quark stars Sources IV Continuous GW may be due to: i) neutron stars ii) quark stars with some form of asymmetry 19

20 Gravitational-Wave Emission May be the Regulator for Accreting Neutron Stars Neutron stars spin up when they accrete matter from a companion Observed neutron star spins max out at ~700 Hz Gravitational waves are suspected to balance angular momentum from accreting matter Credit: Dana Berry, NASA 20

21 Gravitational-Wave Emission May be the Regulator for Accreting Neutron Stars Neutron stars spin up when they accrete matter from a companion Observed neutron star spins max out at ~700 Hz Gravitational waves are suspected to balance angular momentum from accreting matter Credit: Dana Berry, NASA 21

22 Sketch of a Michelson Interferometer End Mirror End Mirror Beam Splitter Laser Viewing Screen 22

23 Gravitational Wave Detection Suspended Interferometers» Suspended mirrors in free-fall» Michelson IFO is natural GW detector Fabry-Perot cavity 4km» Broad-band response (~50 Hz to few khz) g.w. output port» Waveform information (e.g., chirp reconstruction) power recycling mirror LIGO design length sensitivity: m 23

24 Sensing the Effect of a Gravitational Wave Gravitational wave changes arm lengths and amount of light in signal Change in arm length is meters, or about 2/10,000,000,000,000,000 inches Laser signal 24

25 LIGO sites LIGO (Washington) (4km and 2km) LIGO (Louisiana) (4km) Funded by the National Science Foundation; operated by Caltech and MIT; the research focus for more than 500 LIGO Scientific Collaboration members worldwide. 25

26 The LIGO Observatories LIGO Hanford Observatory (LHO) H1 : 4 km arms H2 : 2 km arms 10 ms LIGO Livingston Observatory (LLO) L1 : 4 km arms Adapted from The Blue Marble: Land Surface, Ocean Color and Sea Ice at visibleearth.nasa.gov NASA Goddard Space Flight Center Image by Reto Stöckli (land surface, shallow water, clouds). Enhancements by Robert Simmon (ocean color, compositing, 3D globes, animation). Data and technical support: MODIS Land Group; MODIS Science Data Support Team; MODIS Atmosphere Group; MODIS Ocean Group Additional data: USGS EROS Data Center (topography); USGS Terrestrial Remote Sensing Flagstaff Field Center (Antarctica); Defense Meteorological Satellite Program (city lights) 26

27 An International Network of Interferometers Simultaneously detect signal (within msec) LIGO GEO Virgo TAMA detection confidence locate the sources AIGO (proposed) decompose the polarization of gravitational waves 27

28 Vacuum Chambers Provide Quiet Homes for Mirrors View inside Corner Station Standing at vertex beam splitter 28

29 All-Solid-State Nd:YAG Laser Custom-built 10 W Nd:YAG Laser, joint development with Lightwave Electronics (now commercial product) Cavity for defining beam geometry, joint development with Stanford Frequency reference cavity (inside oven) 29

30 Core Optics Suspension and Control Optics suspended as simple pendulums Shadow sensors & voice-coil actuators provide damping and control forces Mirror is balanced on 30 micron diameter wire to 1/100 th degree of arc 30

31 Evacuated Beam Tubes Provide Clear Path for Light Vacuum required: <10-9 Torr 31

32 Evacuated Beam Tubes Provide Clear Path for Light Bakeout facts: 4 loops to return current, 1 gauge 1700 amps to reach temperature bake temp 140 degrees C for 30 days 400 thermocouples to ensure even heating each site has 4.8km of weld seams full vent of vacuum: ~ 1GJ of energy Vacuum required: <10-9 Torr 32

33 Seismic Isolation Springs and Masses damped spring cross section 33

34 LIGO detector facilities Seismic Isolation Multi-stage (mass & springs) optical table support gives 10 6 suppression Pendulum suspension gives additional 1 / f 2 suppression above ~1 Hz Transfer function Horizontal 10-6 Vertical Frequency (Hz) 34

35 Interferometer Length Control System (photodiode) 4km Multiple Input / Multiple Output Three tightly coupled cavities Employs adaptive control system that evaluates plant evolution and reconfigures feedback paths and gains during lock acquisition 35

36 Calibrated output: LIGO noise history 80kpc 1Mpc 15Mpc S1 S2 S3 S4 S5 - current Curves are calibrated interferometer output: spectral content of the gravity-wave channel 36

37 The road to design sensitivity 37

38 Time line Inauguration First Lock Full Lock all IFO Now 4K strain noise at 150 Hz [Hz-1/2] Engineering E2 Science E3 E5 E7 E8 E9 E10 E11 S1 S2 First Science Data S3 S4 Coincident science runs with GEO and TAMA S5 Runs 38

39 LIGO Hanford control room 39

40 Like but for LIGO/GEO data American Physical Society (APS) publicized as part of World Year of Physics (WYP) 2005 activities Use infrastructure/help from developers for the distributed computing parts (BOINC) Goal: pulsar searches using ~1 million clients. Support for Windows, Mac OSX, Linux clients From our own clusters we can get ~ thousands of CPUs. From Einstein@home hope to get order(s) of magnitude more at low cost Great outreach and science education tool Currently : ~160,000 active users corresponding to about 85Tflops, about 200 new users/day 40

41 What would a pulsar look like? Post-processing step: find points on the sky and in frequency that exceeded threshold in many of the sixty ten-hour segments Software-injected fake pulsar signal is recovered below Simulated (software) pulsar signal in S3 data 41

42 Final S3 analysis results WITH INJECTIONS WITHOUT INJECTIONS Data: hour stretches of the best H1 data Post-processing step on centralized server: find points in sky and frequency that exceed threshold in many of the sixty ten-hour segments analyzed Hz band shows no evidence of strong pulsar signals in sensitive part of the sky, apart from the hardware and software injections. There is nothing in our backyard. Outliers are consistent with instrumental lines. All significant artifacts away from r.n=0 are ruled out by follow-up studies. 42

43 Summary remarks LIGO achieved design sensitivity in Nov 05, a major milestone LIGO/GEO then launched the coincident S5 science run, which is to ran until Sep 30, 2007 Host of searches underway: analyses ongoing of S3, S4, and S5 data no detections yet! Future:» Enhanced LIGO upgrade slated for fall 2007-spring 2009, factor of 2-3 in sensitivity improvement» Advanced LIGO upgrade slated for ~2011 to dramatically improve sensitivity We should be detecting gravitational waves regularly within the next 10 years! 43

44 A hope for the near future: The Beginning of a New Astronomy LIGO - Virgo LIGO+ Virgo+ AdvLIGO AdvVirgo 44