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Keith Riles University of Michigan

To Catch a Wave – The Hunt for Gravitational Radiation with LIGO. Keith Riles University of Michigan. REU seminar June 24, 2013. Outline. Nature & Generation of Gravitational Waves Detecting Gravitational Waves with the LIGO Detector Data Runs and Results to Date

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Keith Riles University of Michigan

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  1. To Catch a Wave – The Hunt for Gravitational Radiation with LIGO Keith Riles University of Michigan REU seminar June 24, 2013

  2. Outline • Nature & Generation of Gravitational Waves • Detecting Gravitational Waves with the LIGO Detector • Data Runs and Results to Date • Looking Ahead – Advanced LIGO

  3. Example: Ring of test masses responding to wave propagating along z Nature of Gravitational Waves • Gravitational Waves = “Ripples in space-time” • Perturbation propagation similar to light (obeys same wave equation!) • Propagation speed = c • Two transverse polarizations - quadrupolar: +andx • Amplitude parameterized by (tiny) dimensionless strain h: ΔL ~ h(t) x L

  4. 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 • Detectable sources some of the most interesting, least understood in the Universe • Opens up entirely new non-electromagnetic spectrum

  5. What will the sky look like? Has BICEP-2 seen fossil GWs?

  6. Generation of Gravitational Waves • Radiation generated by quadrupolar mass movements: (with Imn = quadrupole tensor, r = source distance) • Example: Pair of 1.4 Msolar neutron stars in circular orbit of radius 20 km (imminent coalescence) at orbital frequency 400 Hz gives 800 Hz radiation of amplitude:

  7. 17 / sec · · ~ 8 hr Generation of Gravitational Waves • Strong indirect evidence for GW generation: Taylor-Hulse Pulsar System (PSR1913+16) • Two neutron stars (one=pulsar) in elliptical 8-hour orbit • Measured periastron advance quadratic in time in agreement with absolute GR prediction  Orbit decay due to GW energy loss

  8. Generation of Gravitational Waves Can we detect this radiation directly? NO - freq too low Must wait ~300 My for characteristic “chirp”:

  9. What makes Gravitational Waves? • Compact binary inspiral: “chirps” • NS-NS waveforms are well described • Recent progress on BH-BH waveforms • Supernovae / GRBs: “bursts” • burst signals in coincidence with signals in electromagnetic radiation / neutrinos • all-sky untriggered searches too • Pulsars in our galaxy: “periodic” • search for observed neutron stars • all-sky search (computing challenge) • Cosmological Signals“stochastic background”

  10. Generation of Gravitational Waves Most promising periodic source:Rotating Neutron Stars (e.g., pulsar) But axisymmetric object rotating about symmetry axis Generates NO radiation Need an asymmetry or perturbation: • Equatorial ellipticity (e.g., – mm-high “mountain”): h α εequat • Poloidal ellipticity (natural) + wobble angle (precessing star): h α εpol x Θwobble (precession due to differentLand Ωaxes)

  11. Periodic Sources Serious technical difficulty: Doppler frequency shifts • Frequency modulation from earth’s rotation (v/c ~ 10-6) • Frequency modulation from earth’s orbital motion (v/c ~ 10-4) Additional, related complications: • Daily amplitude modulation of antenna pattern • Spin-down of source • Orbital motion of sources in binary systems Modulations / drifts complicate analysis enormously: • Simple Fourier transform inadequate • Every sky direction requires different demodulation  All-sky survey at full sensitivity = Formidable challenge

  12. Periodic Sources of GW But two substantial benefits from modulations: • Reality of signal confirmed by need for corrections • Corrections give precise direction of source • Difficult to detect spinning neutron stars! • But search is nonetheless intriguing: • Unknown number of electromagnetically quiet, undiscovered neutron stars in our galactic neighborhood • Realistic values for ε unknown • A nearby source could be buried in the data, waiting for just the right algorithm to tease it into view

  13. Outline • Nature & Generation of Gravitational Waves • Detecting Gravitational Waves with the LIGO Detector • Data Runs and Results to Date • Preparing for Advanced LIGO

  14. Top view Gravitational Wave Detection • Suspended Interferometers (IFO’s) • Suspended mirrors in “free-fall” • Michelson IFO is “natural” GW detector • Broad-band response (~50 Hz to few kHz) •  Waveform information (e.g., chirp reconstruction)

  15. The Global Interferometer Network The three (two) LIGO, Virgo and GEO interferometers are part of a Global Network. Multiple signal detections will increase detection confidence and provide better precision on source locations and wave polarizations V1 L1 G1 GEO K1 LIGO Virgo H1, H2 KAGRA LIGO – India (approved)

  16. LIGO Observatories Hanford Observation of nearly simultaneous signals 3000 km apart rules out terrestrial artifacts Livingston

  17. LIGO Detector Facilities • Stainless-steel tubes • (1.24 m diameter, ~10-8 torr) • Gate valves for optics isolation • Protected by concrete enclosure Vacuum System

  18. LIGO Detector Facilities LASER • Infrared (1064 nm, 10-W) Nd-YAG laser from Lightwave (now commercial product!) • Elaborate intensity & frequency stabilization system, including feedback from main interferometer Optics • Fused silica (high-Q, low-absorption, 1 nm surface rms, 25-cm diameter) • Suspended by single steel wire • Actuation of alignment / position via magnets & coils

  19. 102 100 10-2 10-6 Horizontal 10-4 10-6 10-8 Vertical 10-10 LIGO Detector Facilities Seismic Isolation • Multi-stage (mass & springs) optical table support gives 106 suppression • Pendulum suspension gives additional 1 / f 2 suppression above ~1 Hz

  20. achieved What Limits the Sensitivityof the Interferometers? • Seismic noise & vibration limit at low frequencies • Atomic vibrations (Thermal Noise) inside components limit at mid frequencies • Quantum nature of light (Shot Noise) limits at high frequencies • Myriad details of the lasers, electronics, etc., can make problems above these levels • Best design sensitivity: • ~ 3 x 10-23 Hz-1/2 @ 150 Hz < 2 x 10-23

  21. The road to design sensitivity at Hanford…

  22. Retrofit with active feed-forward isolation system (using technology developed for Advanced LIGO) • Fixed Solution: Harder road at Livingston… Livingston Observatory located in pine forest popular with pulp wood cutters Spiky noise (e.g. falling trees) in 1-3 Hz band creates dynamic range problem for arm cavity control  40% livetime

  23. LIGO Scientific Collaboration • University of Michigan • University of Minnesota • The University of Mississippi • Massachusetts Inst. of Technology • Monash University • Montana State University • Moscow State University • National Astronomical Observatory of Japan • Northwestern University • University of Oregon • Pennsylvania State University • Rochester Inst. of Technology • Rutherford Appleton Lab • University of Rochester • San Jose State University • Univ. of Sannio at Benevento, and Univ. of Salerno • University of Sheffield • University of Southampton • Southeastern Louisiana Univ. • Southern Univ. and A&M College • Stanford University • University of Strathclyde • Syracuse University • Univ. of Texas at Austin • Univ. of Texas at Brownsville • Trinity University • Universitat de les Illes Balears • Univ. of Massachusetts Amherst • University of Western Australia • Univ. of Wisconsin-Milwaukee • Washington State University • University of Washington • Australian Consortiumfor InterferometricGravitational Astronomy • The Univ. of Adelaide • Andrews University • The Australian National Univ. • The University of Birmingham • California Inst. of Technology • Cardiff University • Carleton College • Charles Sturt Univ. • Columbia University • Embry Riddle Aeronautical Univ. • Eötvös Loránd University • University of Florida • German/British Collaboration forthe Detection of Gravitational Waves • University of Glasgow • Goddard Space Flight Center • Leibniz Universität Hannover • Hobart & William Smith Colleges • Inst. of Applied Physics of the Russian Academy of Sciences • Polish Academy of Sciences • India Inter-University Centrefor Astronomy and Astrophysics • Louisiana State University • Louisiana Tech University • Loyola University New Orleans • University of Maryland • Max Planck Institute for Gravitational Physics

  24. Michigan LIGO Group Members Old fogeys: Dick Gustafson, Keith Riles Graduate students: Santiago Caride, Grant Meadors, Jaclyn Sanders Undergraduates / high school students: Weigang Liu, Daniel Mantica, Pranav Rao, Curtis Rau / David Groden Graduated Ph.D. students: Dave Chin (now medical physicist) Vladimir Dergachev*(now postdoc at Caltech) Evan Goetz*(now postdoc at Albert Einstein Institute – Hanover, Germany) Former undergraduates: Jamie Rollins*(Caltech postdoc) Alistair Hayden (Boston U.) Joseph Marsano(Chicago postdoc)Michael La Marca(Arizona State G.S.) Jake Slutsky*(A.E.I. postdoc) Phil Szepietowski (U. Virginia postdoc) Tim Bodiya*(MIT G.S.) Courtney Jarman (Wisconsin G.S.) Ramon Armen (industry) Alex Nitz* (Syracuse G.S.) *Continued GW research after graduating

  25. Michigan Group – Main Efforts • Search for Periodic Sources (rotating neutron stars) • Riles, Caride, Meadors, Sanders, Liu, Mantica, Rao • Detector Characterization (instrumentation, software) • Riles, Gustafson, Caride, Meadors, Liu, Groden • Commissioning & Noise Reduction • Gustafson, Meadors, Sanders (when in residence at Hanford) • Controls System Development • Gustafson • Public Outreach • Riles, Meadors, Rau

  26. LIGO Scientific Collaboration • University of Michigan • University of Minnesota • The University of Mississippi • Massachusetts Inst. of Technology • Monash University • Montana State University • Moscow State University • National Astronomical Observatory of Japan • Northwestern University • University of Oregon • Pennsylvania State University • Rochester Inst. of Technology • Rutherford Appleton Lab • University of Rochester • San Jose State University • Univ. of Sannio at Benevento, and Univ. of Salerno • University of Sheffield • University of Southampton • Southeastern Louisiana Univ. • Southern Univ. and A&M College • Stanford University • University of Strathclyde • Syracuse University • Univ. of Texas at Austin • Univ. of Texas at Brownsville • Trinity University • Universitat de les Illes Balears • Univ. of Massachusetts Amherst • University of Western Australia • Univ. of Wisconsin-Milwaukee • Washington State University • University of Washington • Australian Consortiumfor InterferometricGravitational Astronomy • The Univ. of Adelaide • Andrews University • The Australian National Univ. • The University of Birmingham • California Inst. of Technology • Cardiff University • Carleton College • Charles Sturt Univ. • Columbia University • Embry Riddle Aeronautical Univ. • Eötvös Loránd University • University of Florida • German/British Collaboration forthe Detection of Gravitational Waves • University of Glasgow • Goddard Space Flight Center • Leibniz Universität Hannover • Hobart & William Smith Colleges • Inst. of Applied Physics of the Russian Academy of Sciences • Polish Academy of Sciences • India Inter-University Centrefor Astronomy and Astrophysics • Louisiana State University • Louisiana Tech University • Loyola University New Orleans • University of Maryland • Max Planck Institute for Gravitational Physics

  27. GEO600 • Work closely with the GEO600 Experiment (Germany / UK / Spain) • Arrange coincidence data runs when commissioning schedules permit • GEO members are full members of the LIGO Scientific Collaboration • Data exchange and strong collaboration in analysis now routine • Major partners in proposed Advanced LIGO upgrade 600-meter Michelson Interferometer just outside Hannover, Germany

  28. Virgo Have begun collaborating with Virgo colleagues (Italy/France) Took data in coincidence for parts of last two science runs Data exchange and joint analysis Will coordinate closely on detector upgrades and future data taking 3-km Michelson Interferometer just outside Pisa, Italy

  29. Outline • Nature & Generation of Gravitational Waves • Detecting Gravitational Waves with the LIGO Detector • Data Runs and (small sampling of ) Results to Date • Looking Ahead – Advanced LIGO

  30. Data Runs Have carried out a series of Engineering Runs (E1–E14) and Science Runs(S1—S6) interspersed with commissioning & upgrades S1 run: 17 days (Aug / Sept 2002)– Rough but good practice S2 run: 59 days (Feb—April 2003)– Many good results • S3 run: • 70 days (Oct 2003 – Jan 2004) -- Ragged • S4 run: • 30 days (Feb—March 2005) – Another good run • S5 run: • 23 months (Nov 2005 – Sept 2007) – Great! • S6 run: • “16” months (Jul 2009 – Oct 2010) – Better sensitivity but uneven

  31. hrms = 3 10-22 S1  S5 Sensitivities

  32. “Enhanced LIGO” (July 2009 – Oct 2010) Displacement spectral noise density Factor of 2 improvement above 300 Hz S5 S6

  33. Searching for Gravity Waves Today Short-Lived Long-Lived Known waveform Binary Inspirals Continuous waves (NS-NS, NS-BH, BH-BH)(Spinning NS) BurstsStochastic background (Supernovae, “mergers”)(Cosmological, astrophysical) Spinning black-hole / SGR ringdowns Young pulsars high-mass inspirals (glitchy) Unknown waveform

  34. Chandra image Model Searching for continuous waves Crab Pulsar Bayesian PDF Use coherent, 9-month, time-domain matched filter Strain amplitude h0 • Upper limits on GW strain amplitude h0 • Single-template, uniform prior: 3.4 × 10–25 • Single-template, restricted prior: 2.7 × 10–25 • Multi-template, uniform prior: 1.7 × 10–24 • Multi-template, restricted prior: 1.3 × 10–24 Implies that GW emission accountsfor ≤ 4% of totalspin-down power Ap. J. Lett 683 (2008) 45

  35. Searching for continuous waves Same algorithm applied to 195 known pulsars over LIGO S5/S6 and Virgo VSR2/VSR4 data • Lowest upper limit on strain: h0 < 2.1 × 10−26 • Lowest upper limit on ellipticity: • ε < 6.7 × 10-8 • Crab limit at 1% of total energy loss • Vela limit at 10% of total energy loss arXiv:1309.4027 (Sept 2013)

  36. Searching for continuous waves • All-sky search for unknown isolated neutron stars Linearly polarized Semi-coherent, stacks of 30-minute, demodulated power spectra (“PowerFlux”) Circularly polarized Carried out by Michigan graduate student Vladimir Dergachev (now at Caltech) • Phys. Rev. Lett. 102 (2009) 111102

  37. Recent results Semi-coherent, stacks of 30-minute, demodulated power spectra (“PowerFlux”) Latest full-S5 all-sky results Astrophysical reach Phys. Rev. D85 (2012) 022001

  38. Searching for continuous waves First all-sky search for unknown binary CW sources Uses TwoSpect* algorithm: Sample spectrogram (30-minute FFTs) for simulated strong signal (Earth’s motion already demodulated) Result of Fourier transforming each row of spectrogram  Concentrates power in orbital harmonics *E. Goetz & K. Riles, CQG 28 (2011) 215006

  39. Searching for continuous waves Initial search uses 30-minute FFTs  Favors longer orbital periods: Mod. Depth (Hz)  Period (hr)  Search is severely computationally bound Upper limits based on summing power in harmonics Templates used only in follow-up Not so limited in directed searches, e.g., for Scorpius X-1

  40. GEO-600 Hannover • LIGO Hanford • LIGO Livingston • Current search point • Current search coordinates • Known pulsars • Known supernovae remnants http://www.einsteinathome.org/ Your computer can help too!

  41. Outline • Nature & Generation of Gravitational Waves • Detecting Gravitational Waves with the LIGO Detector • Data Runs and Results to Date • Looking Ahead – Advanced LIGO

  42. Looking Ahead • Both LIGO and Virgo underwent significant upgrades since first joint science run (S5/VSR1): • Initial LIGO  “Enhanced LIGO” • Initial Virgo  “Virgo +” LIGO schedule: S6 data run July 2009 – October 2010 Began Advanced LIGO installation October 2010  Aim for first data run fall (summer?) 2015 Virgo schedule: VSR2/3 data runs July 2009 – October 2010 Virgo+ upgrade ongoing VSR4 data run – Summer 2011 Began Advanced Virgo installation fall 2011  On schedule for 2016 data run

  43. Advanced LIGO • Increased laser power: • 10 W  200 W Improved shot noise (high freq) Higher-Q test mass: Fused silica with better optical coatings Lower internal thermal noise in band Increased test mass: 10 kg  40 kg Compensates increased radiation pressure noise

  44. Advanced LIGO New suspensions: Single  Quadruple pendulum Lower suspensions thermal noise in bandwidth Improved seismic isolation: Passive  Active Lowers seismic “wall” to ~10 Hz

  45. Advanced LIGO • Neutron Star Binaries: • Average range ~ 200 Mpc • Most likely rate ~ 40/year The science from the first 3 hours of Advanced LIGO should be comparable to 1 year of initial LIGO (Range x ~10  Volume x ~1000) But that sensitivity will not be achieved instantly… arXiv: 1304.0670

  46. Summary • Bottom line: • No GW signal detected yet  • But • Not all S5-6 VSR1-4 searches completed • Advanced LIGO / Virgo will bring major sensitivity improvements with orders of magnitude increase in expected event rates

  47. Extra Slides

  48. With Fabry-Perot arm cavities • Recycling mirror matches losses, enhances effective power by ~ 50x 4 km Fabry-Perot cavity recycling mirror 150 W LASER/MC 20000 W (~0.5W) LIGO Interferometer Optical Scheme Michelson interferometer end test mass 6W

  49. Generation of Gravitational Waves Coalescence rate estimates based on two methods: • Use known NS/NS binaries in our galaxy (three!) • A priori calculation from stellar and binary system evolution  Large uncertainties! For initial LIGO design “seeing distance” (~15 Mpc): Expect 1/(70 y) to 1/(4 y)  Will need Advanced LIGO to ensure detection

  50. Tony Mezzacappa -- Oak Ridge National Laboratory Generation of Gravitational Waves Super-novae (requires asymmetry in explosions) Examples of SN waveforms May not know exactly what to look for – must be open-minded with diverse algorithms

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