Probing the Universe for Gravitational Waves

Transcription

1 Probing the Universe for Gravitational Waves Barry C. Barish Caltech Crab Pulsar University of Illinois 16-Feb-06

2 General Relativity the essential idea G μν = 8πΤ μν Gravity is not a force, but a property of space Overthrew & time Objects Concentrations follow the the 19 of th shortest mass -century or path energy concepts through distort of» this absolute Spacetime = 3 spatial and time dimensions + time (warp) warped spacetime spacetime; path is the same for» all Perception objects of space or time is relative 16-Feb-06 LIGO - University of Illinois 2

3 After several hundred years, a small crack in Newton s theory.. perihelion shifts forward an extra +43 /century compared to Newton s theory 16-Feb-06 LIGO - University of Illinois 3

4 A new prediction of Einstein s theory Light from distant stars are bent as they graze the Sun. The exact amount is predicted by Einstein's theory. 16-Feb-06 LIGO - University of Illinois 4

5 Confirming Einstein. bending of light A massive object shifts apparent position of a star Observation made during the solar eclipse of 1919 by Sir Arthur Eddington, when the Sun was silhouetted against the Hyades star cluster 16-Feb-06 LIGO - University of Illinois 5

6 A Conceptual Problem is solved! Newton s Theory instantaneous action at a distance Einstein s Theory information carried by gravitational radiation at the speed of light 16-Feb-06 LIGO - University of Illinois 6

7 Einstein s Theory of Gravitation Gravitational waves are necessary consequence of Special Relativity with its finite speed for information transfer Gravitational waves come from the acceleration of masses and propagate away from their sources as a space-time warpage at the speed of light gravitational radiation binary inspiral of compact objects 16-Feb-06 LIGO - University of Illinois 7

8 Einstein s Theory of Gravitation gravitational waves Using Minkowski metric, the information about space-time curvature is contained in the metric as an added term, h μν. In the weak field limit, the equation can be described with linear equations. If the choice of gauge is the transverse traceless gauge the formulation becomes a familiar wave equation 1 c t 2 2 ( 2 2 ) h μν = 0 The strain h μν takes the form of a plane wave propagating at the speed of light (c). Since gravity is spin 2, the waves have two components, but rotated by 45 0 instead of 90 0 from each other. h h ( t z / c) + hx ( t z / c) = + 16-Feb-06 LIGO - University of Illinois 8 μν

9 The Evidence T h e For Gravitational Waves Russel A. Hulse Source: Discovered and Studied Pulsar System PSR with Radio Telescope Joseph H.Taylor Jr 16-Feb-06 LIGO - University of Illinois 9

10 The evidence for gravitational waves Hulse & Taylor 17 / sec Neutron binary system separation = 10 6 miles m 1 = 1.4m m 2 = 1.36m e = period ~ 8 hr Prediction from general relativity PSR Timing of pulsars spiral in by 3 mm/orbit rate of change orbital period 16-Feb-06 LIGO - University of Illinois 10

11 Indirect evidence for gravitational waves 16-Feb-06 LIGO - University of Illinois 11

12 Direct Detection Gravitational Wave Astrophysical Source Detectors in space LISA Terrestrial detectors LIGO, TAMA, Virgo, AIGO 16-Feb-06 LIGO - University of Illinois 12

13 Gravitational Waves in Space LISA Three spacecraft, each with a Y-shaped payload, form an equilateral triangle with sides 5 million km in length. 16-Feb-06 LIGO - University of Illinois 13

14 Network of Interferometers LIGO GEO Virgo TAMA decompose detection locate the the confidence polarization sources of gravitational waves AIGO 16-Feb-06 LIGO - University of Illinois 14

15 The frequency range of astronomy EM waves studied over ~16 orders of magnitude» Ultra Low Frequency radio waves to high energy gamma rays 16-Feb-06 LIGO - University of Illinois 15

16 Frequencies of Gravitational Waves The diagram shows the sensitivity bands for LISA and LIGO 16-Feb-06 LIGO - University of Illinois 16

17 Gravitational Wave Detection free masses h = strain amplitude of grav. waves h = ΔL/L ~ L = 4 km ΔL ~ m Laser Interferometer laser 16-Feb-06 LIGO - University of Illinois 17

18 Interferometer optical vacuum layout suspended, seismically isolated test masses mode cleaner 4 km laser various optics 10 W 6-7 W 4-5 W W 9-12 kw 200 mw photodetector GW channel 16-Feb-06 LIGO - University of Illinois 18

19 Hanford Observatory LIGO Laser Interferometer Gravitational-wave Observatory MIT Caltech Livingston Observatory 16-Feb-06 LIGO - University of Illinois 19

20 LIGO Livingston, Louisiana 4 km 16-Feb-06 LIGO - University of Illinois 20

21 LIGO Hanford Washington 4 km 2 km 16-Feb-06 LIGO - University of Illinois 21

22 LIGO Beam Tube Minimal enclosure Reinforced concrete No services 1.2 m diameter - 3mm stainless 50 km of weld 65 ft spiral welded sections Girth welded in portable clean room in the field 16-Feb-06 LIGO - University of Illinois 22

23 Vacuum Chambers vibration isolation systems» Reduce in-band seismic motion by 4-6 orders of magnitude» Compensate for microseism at 0.15 Hz by a factor of ten» Compensate (partially) for Earth tides 16-Feb-06 LIGO - University of Illinois 23

24 LIGO vacuum equipment 16-Feb-06 LIGO - University of Illinois 24

25 Seismic Isolation suspension system Suspension assembly for a core optic Support structure is welded tubular stainless steel Suspension wire is 0.31 mm diameter steel music wire Fundamental violin mode frequency of 340 Hz 16-Feb-06 LIGO - University of Illinois 25

26 LIGO Optics fused silica Surface uniformity < 1 nm rms Scatter < 50 ppm Absorption < 2 ppm ROC matched < 3% Internal mode Q s > 2 x 10 6 Caltech data CSIRO data 16-Feb-06 LIGO - University of Illinois 26

27 Core Optics installation and alignment 16-Feb-06 LIGO - University of Illinois 27

28 Lock Acquisition 16-Feb-06 LIGO - University of Illinois 28

29 Tidal Compensation Data Tidal evaluation 21-hour locked section of S1 data Predicted tides Feedforward Feedback Residual signal on voice coils Residual signal on laser 16-Feb-06 LIGO - University of Illinois 29

30 Controlling angular degrees of freedom 16-Feb-06 LIGO - University of Illinois 30

31 Interferometer Noise Limits Seismic Noise test mass (mirror) Quantum Noise Residual gas scattering "Shot" noise Radiation pressure LASER Wavelength & amplitude fluctuations Beam splitter photodiode 16-Feb-06 LIGO - University of Illinois 31 Thermal (Brownian) Noise

32 What Limits LIGO Sensitivity? Seismic noise limits low frequencies Thermal Noise limits middle frequencies Quantum nature of light (Shot Noise) limits high frequencies Technical issues - alignment, electronics, acoustics, etc limit us before we reach these design goals 16-Feb-06 LIGO - University of Illinois 32

33 Evolution of LIGO Sensitivity S1: 23 Aug 9 Sep 02 S2: 14 Feb 14 Apr 03 S3: 31 Oct 03 9 Jan 04 S4: 22 Feb 23 Mar 05 S5: 4 Nov Feb-06 LIGO - University of Illinois 33

34 Commissioning /Running Time Line Inauguration First Lock Full Lock all IFO Now 4K strain noise x10-23 at 150 Hz [Hz -1/2 ] Engineering E2 Science E3 E5 E7 E8 E9 E10 E11 S1 S2 First Science Data S3 S4 S5 Runs 16-Feb-06 LIGO - University of Illinois 34

35 Equivalent strain noise (Hz -1/2 ) Entering S5 Rms strain in 100 Hz BW: 0.4x10-21 H1, 20 Oct 05 L1, 30 Oct 05 SRD curve Frequency (Hz) 16-Feb-06 LIGO - University of Illinois 35

36 S5 Run Plan and Outlook Interferometer duty cycles Goal is to collect at least a year s data of coincident operation at the science goal sensitivity Expect S5 to last about 1.5 yrs S5 will not be completely handsoff Run S2 S3 S4 L1 37% 22% 75% 85% 90% H1 74% 69% 81% 85% 90% H2 58% 63% 81% 85% 90% 3- way 22% 16% 57% S5 Target SRD goal 70% 75% 16-Feb-06 LIGO - University of Illinois 36

37 Science Runs Virgo Andromeda Milky Cluster Way A Measure of Progress NN Binary Inspiral Range E8 ~ 5 kpc S1 ~ 100 kpc S2 ~ 0.9Mpc S3 ~ 3 Mpc Goal ~ 14 Mpc 16-Feb-06 LIGO - University of Illinois 37

38 Astrophysical Sources Compact binary inspiral: chirps» NS-NS waveforms are well described» BH-BH need better waveforms» search technique: matched templates Supernovae / GRBs: bursts» burst signals in coincidence with signals in electromagnetic radiation» prompt alarm (~ one hour) with neutrino detectors Pulsars in our galaxy: periodic» search for observed neutron stars (frequency, doppler shift)» all sky search (computing challenge)» r-modes Cosmological Signal stochastic background 16-Feb-06 LIGO - University of Illinois 38

39 Compact Binary Collisions» Neutron Star Neutron Star waveforms are well described» Black Hole Black Hole need better waveforms» Search: matched templates chirps 16-Feb-06 LIGO - University of Illinois 39

40 Template Bank Covers desired region of mass param space Calculated based on L1 noise curve Templates placed for max mismatch of δ = templates Second-order post-newtonian 16-Feb-06 LIGO - University of Illinois 40

41 Optimal Filtering frequency domain Transform data to frequency domain : Generate template in frequency domain : ~ h ( f ) ~ s ( f ) Correlate, weighting by power spectral density of noise: ~ s ( f ) h S ( f ~ * h z( t) = 4 0 z( t) ( f ) ) Then inverse Fourier transform gives you the filter output at all times: ~ ~ s ( f ) h S ( f h ( f ) ) Find maxima of over arrival time and phase Characterize these by signal-to-noise ratio (SNR) and effective distance * e 2πi f t df 16-Feb-06 LIGO - University of Illinois 41

42 Matched Filtering 16-Feb-06 LIGO - University of Illinois 42

43 Inspiral Searches Mass BBH Search S3/S PBH MACHO S3/S4 BNS S3/S Spin is important Detection templates S3 High mass ratio Coming soon Physical waveform follow-up S3/S4 Inspiral-Burst S4 10 Mass

44 Binary Neutron Star Search Results (S2) Physical Review D, In Press cumulative number of events Rate < 47 per year per Milky-Way-like galaxy signal-to-noise ratio squared 16-Feb-06 LIGO - University of Illinois 44

45 Binary Black Hole Search 16-Feb-06 LIGO - University of Illinois 45

46 Binary Inspiral Search: LIGO Ranges inary neutron star range inary black hole range 16-Feb-06 LIGO - University of Illinois Image: R. Powell 46

47 Astrophysical Sources Compact binary inspiral: chirps» NS-NS waveforms are well described» BH-BH need better waveforms» search technique: matched templates Supernovae / GRBs: bursts» burst signals in coincidence with signals in electromagnetic radiation» prompt alarm (~ one hour) with neutrino detectors Pulsars in our galaxy: periodic» search for observed neutron stars (frequency, doppler shift)» all sky search (computing challenge)» r-modes Cosmological Signal stochastic background 16-Feb-06 LIGO - University of Illinois 47

48 Detection of Burst Sources Known sources -- Supernovae & GRBs» Coincidence with observed electromagnetic observations.» No close supernovae occurred during the first science run» Second science run We analyzed the very bright and close GRB Unknown phenomena» Emission of short transients of gravitational radiation of unknown waveform (e.g. black hole mergers). 16-Feb-06 LIGO - University of Illinois 48

49 Unmodeled Bursts GOAL search for waveforms from sources for which we cannot currently make an accurate prediction of the waveform shape. METHODS Raw Data Time-domain high pass filter Time-Frequency Plane Search TFCLUSTERS Pure Time-Domain Search SLOPE frequency 8Hz 0.125s time 16-Feb-06 LIGO - University of Illinois 49

50 Blind procedure gives one event candidate» Event immediately found to be correlated with airplane over-flight Burst Search Results 16-Feb-06 LIGO - University of Illinois 50

51 Burst Source - Upper Limit 16-Feb-06 LIGO - University of Illinois 51

52 Gamma-Ray Bursts short and long Short burst GRB Long burst GRB Optical counterpart Optical counterpart HST Image Credit: Derek Fox NASA Image Possible scenario for short GRBs: neutron star/black hole collision Credit: Dana Berry/NASA 16-Feb-06 LIGO - University of Illinois 52

53 Astrophysical Sources signatures Compact binary inspiral: chirps» NS-NS waveforms are well described» BH-BH need better waveforms» search technique: matched templates Supernovae / GRBs: bursts» burst signals in coincidence with signals in electromagnetic radiation» prompt alarm (~ one hour) with neutrino detectors Pulsars in our galaxy: periodic» search for observed neutron stars (frequency, doppler shift)» all sky search (computing challenge)» r-modes Cosmological Signal stochastic background 16-Feb-06 LIGO - University of Illinois 53

54 Detection of Periodic Sources Pulsars in our galaxy: periodic» search for observed neutron stars» all sky search (computing challenge)» r-modes Frequency modulation of signal due to Earth s motion relative to the Solar System Barycenter, intrinsic frequency changes. Amplitude modulation due to the detector s antenna pattern. 16-Feb-06 LIGO - University of Illinois 54

55 Pulsars: Target Sources Accreting Neutron Stars Wobbling Neutron Stars Credit: Dana Berry/NASA Credit: M. Kramer Bumpy Neutron Star 16-Feb-06 LIGO - University of Illinois 55

56 Directed Pulsar Search 28 Radio Sources 16-Feb-06 LIGO - University of Illinois 56

57 Detection of Periodic Sources Known Pulsars in our galaxy Frequency modulation of signal due to Earth s motion relative to the Solar System Barycenter, intrinsic frequency changes. Amplitude modulation due to the detector s antenna pattern. NEW RESULT 28 known pulsars NO gravitational waves e < (no mountains > 10 cm ALL SKY SEARCH enormous computing challenge 16-Feb-06 LIGO - University of Illinois 57

58 LIGO Pulsar Search using home pc s BRUCE ALLEN Project Leader Univ of Wisconsin Milwaukee LIGO, UWM, AEI, APS 16-Feb-06 LIGO - University of Illinois 58

59 Astrophysical Sources Compact binary inspiral: chirps» NS-NS waveforms are well described» BH-BH need better waveforms» search technique: matched templates Supernovae / GRBs: bursts» burst signals in coincidence with signals in electromagnetic radiation» prompt alarm (~ one hour) with neutrino detectors Pulsars in our galaxy: periodic» search for observed neutron stars (frequency, doppler shift)» all sky search (computing challenge)» r-modes Cosmological Signal stochastic background 16-Feb-06 LIGO - University of Illinois 59

60 Signals from the Early Universe stochastic background Cosmic Microwave background WMAP Feb-06 LIGO - University of Illinois 60

61 Signals from the Early Universe Strength specified by ratio of energy density in GWs to total energy density needed to close the universe: Ω (f) GW = dρgw d(lnf) Detect by cross-correlating output of two GW detectors: First LIGO Science Data ρ 1 critical Hanford - Livingston 16-Feb-06 LIGO - University of Illinois 61

62 Stochastic Background Search (S3) Physical Review Letters, In Press Fraction of Universe s energy in gravitational waves: (LIGO band) 16-Feb-06 LIGO - University of Illinois 62

63 Results Stochastic Backgrounds 16-Feb-06 LIGO - University of Illinois 63

64 Gravitational Waves from the Early Universe results projected E7 S1 S2 LIGO Adv LIGO 16-Feb-06 LIGO - University of Illinois 64

65 Astrophysical Results Chirps» S2: 355 hours of coincident (2X, 3X) interferometer operation» Sensitive to D ~ 2 Mpc (NG = 1.14 Milky Way Equiv. Galaxies)» R90% < 50 events/year/mweg (1 Msun < M1,2 < 3 Msun) Bursts» S1: For h > 10-18, R90% < 2/day (limited by observation time)» Minimum h ~ 2 x 10-19» S2: 50% detection efficiency h ~ Periodic, or CW» S2: (LIGO and GEO600) interferometers -- Targeted 28 known pulsars» h < 1.7 x (J D)» e < 4.5 x 10-6 (J )» Crab limit on h within 30X of spindown rate, if spindown were due to GW emission» All sky search ---- Einstein@Home Stochastic background» S2: 387 hours of cross-correlation measurements for H-L Ω GW < / in band 50 Hz < f < 300 Hz (preliminary)» S3: 240 hours of cross-correlation measurements for H-L, H-H» Sensitivity estimated to be Ω GW < 5 x Hz < f < 250 Hz» 16-Feb-06 Sensitivity estimated to LIGO be - University Ω GW < of Illinois 5 x Hz < f < Hz

66 Gravitational Wave Astronomy LIGO will provide a new way to view the dynamics of the Universe 16-Feb-06 LIGO - University of Illinois 66