Probing the Dark Side of the Universe with Gravitational Waves

Transcription

1 Probing the Dark Side of the Universe with Gravitational Waves Martin Hendry Astronomy and Astrophysics Group and Institute for Gravitational Research SUPA, Dept of Physics and Astronomy, University of Glasgow, UK 1

2 Outline of talk 2 Introduction: what are gravitational waves? Astrophysical motivation: possible sources and overview of science case GW detection: general principles; noise limitations; and current status (ground-based) The advent of GW astronomy: some examples Coming attractions (next 5 years) and future developments (next 20 years) Case study: cosmology with GW sources

3 Who am I? 3 Jim Hough and Ron Drever, 1978 Institute for Gravitational Research ~50 research staff and students, with activity spanning advanced materials, optics and interferometry, data analysis, for groundand space-based GW detectors.

4 4 Who am I? William Thompson (Lord Kelvin)

5 5 Who am I? There is nothing new to be discovered in physics now. William Thompson (Lord Kelvin) All that remains is more and more precise measurement (1900)

6 6 Gravity in Einstein s s Universe The greatest feat of human thinking about nature, the most amazing combination of philosophical penetration, physical intuition and mathematical skill. Max Born G = κt µν µν Spacetime curvature Matter (and energy)

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8 8 Gravity in Einstein s s Universe Spacetime tells matter how to move, and matter tells spacetime how to curve

9 Gravitational Waves 9 Produced by violent acceleration of mass in: neutron star binary coalescences black hole formation and interactions cosmic string vibrations in the early universe (?) and in less violent events: pulsars binary stars Gravitational waves ripples in the curvature of spacetime that carry information about changing gravitational fields or fluctuating strains in space of amplitude h where: h L = 2 L

10 Gravitational Waves: possible sources 10 Pulsed Compact Binary Coalescences: NS/NS; NS/BH; BH/BH Stellar Collapse (asymmetric) to NS or BH Continuous Wave Pulsars Low mass X-ray binaries (e.g. SCO X1) Modes and Instabilities of Neutron Stars Stochastic Inflation Cosmic Strings

11 Science goals of the gravitational wave field 11 Fundamental physics and GR What are the properties of gravitational waves? Is general relativity the correct theory of gravity? Is GR still valid under strong-gravity conditions? Are Nature s black holes the black holes of GR? How does matter behave under extremes of density and pressure? Cosmology What is the history of the accelerating expansion of the Universe? Were there phase transitions in the early Universe?

12 Science goals of the gravitational wave field 12 Astronomy and astrophysics How abundant are stellar-mass black holes? What is the central engine that powers GRBs? Do intermediate mass black holes exist? Where and when do massive black holes form and how are they connected to galaxy formation? What happens when a massive star collapses? Do spinning neutron stars emit gravitational waves? What is the distribution of white dwarf and neutron star binaries in the galaxy? How massive can a neutron star be? What makes a pulsar glitch? What causes intense flashes of X- and gammaray radiation in magnetars? What is the star formation history of the Universe?

13 Evidence for gravitational waves 13 Indirect detection from orbital decay of binary pulsar: Hulse & Taylor PSR

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15 15 How can we detect them? L L Gravitational wave amplitude h ~ L Sensing the induced excitations of a large bar is one way to measure this L + L Field originated with J. Weber looking for the effect of strains in space on aluminium bars at room temperature Claim of coincident events between detectors at Argonne Lab and Maryland subsequently shown to be false

16 How can we detect them? 16 L + L Jim Hough and Ron Drever, March 1978

17 17 32 yrs on - Interferometric ground-based detectors

18 18 It s all done with mirrors Michelson Interferometer Mirror laser Beam splitter Observer

19 19 It s all done with mirrors CONSTRUCTIVE (BRIGHT) Michelson Interferometer + path 1 laser + path 2 DESTRUCTIVE (DARK)

20 20 Detecting gravitational waves GW produces quadrupolar distortion of a ring of test particles Dimensionless strain h = 2 L L Expect movements of less than m over 4km

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22 Principal limitations to sensitivity ground based detectors 22 Photon shot noise (improves with increasing laser power) and radiation pressure (becomes worse with increasing laser power) There is an optimum light power which gives the same limitation expected by application of the Heisenberg Uncertainty Principle the Standard Quantum limit Seismic noise (relatively easy to isolate against use suspended test masses) Gravitational gradient noise, - particularly important at frequencies below ~10 Hz Thermal noise (Brownian motion of test masses and suspensions) All point to long arm lengths being desirable LIGO 4km; Virgo 3km; GEO 600m, TAMA 300m

23 23 Ground based Detector Network audio frequency range LIGO Hanford GEO600 TAMA, CLIO 600 m 4 km 2 km LIGO LIGO Livingston Livingston VIRGO 300 m 100 m 3 km 4 km P. Shawhan, LIGO-G v1

24 Sources the gravitational wave spectrum 24 Gravity gradient wall ADVANCED GROUND - BASED DETECTORS

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26 LISA: Laser Interferometric Space Antenna 26 LISA a joint ESA/NASA Mission to study Black hole physics, and much more, in the frequency range 10-4 Hz Hz After first studies in 1980s, M3 proposal for 4 S/C ESA/NASA collaborative mission in 1993 LISA selected as ESA Cornerstone in S/C NASA/ESA LISA appears in 1997 Baseline concept unchanged ever since!

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28 Pulsar Timing: nano-hz search for stochastic background and super-massive black hole coalescences 28 North America Full data sharing Australia Multi-country Courtesy G. Hobbs

29 Pulsar timing arrays as a probe of GWs 29 Gravitational waves distort spacetime as they propagate. A periodic gravitational wave passing across the line of sight to a pulsar will produce a periodic variation in the time of arrival (TOA) of pulses. If the strain along the line-of-sight is h, then the fractional change in the pulse arrival rate due to the gravitational wave just depends on the strain at emission and reception.

30 30 Real progress in GW astronomy over past few years Operation of six ground based interferometers (in addition to three cryogenic bar detectors) Advances in waveform predictions from Numerical Relativity Significant advances in Space Borne Detectors LISA and DECIGO Pulsar Timing coming to the fore Importance of Multi-messenger Astronomy Using wider interest in relativity, cosmology and fundamental physics to bring science to schools and the public.

31 31 Current Status 1 -LIGO now at design sensitivity

32 32 Current status 2: the advent of GW astronomy Initial Science Runs Complete (LIGO, Virgo, GEO 600, TAMA) Upper Limits set on a range of sources (no detections as yet) Coalescing Binary Systems Neutron stars, low mass black holes, and NS/BS systems Bursts galactic asymmetric core collapse supernovae cosmic strings??? Credit: AEI, CCT, LSU NASA/WMAP Science Team Cosmic GW background stochastic, incoherent background Credit: Chandra X-ray Observatory unlikely to detect, but can bound in the Hz range Casey Reed, Penn State Continuous Sources Spinning neutron stars probe crustal deformations, quarki-ness

33 Example: The Crab Pulsar Beating the Spin Down Limit 33 Remnant from supernova in year 1054 Spin frequency ν EM = 29.8 Hz ν gw = 2 ν EM = 59.6 Hz observed luminosity of the Crab nebula accounts for < 1/2 spin down power spin down due to: electromagnetic braking particle acceleration GW emission? Abbott, et al., Beating the spin-down limit on gravitational wave emission from the Crab pulsar, Ap. J. Lett. 683, L45- L49, (2008). LIGO S5 result: h < 3.9 x GW amplitude ~ 4X below spin down limit Upper limit on the ellipticity: ε < 2.1 x 10-4 GW energy upper limit < 6% of radiated energy is in GWs

34 Example: GRB070201, Not a Binary Merger in M31 34 Refs: GCN: X-ray emission curves (IPN) M31 The Andromeda Galaxy by Matthew T. Russell Date Taken: 10/22/ /2/2005 Location: Black Forest, CO Equipment: RCOS 16" Ritchey-Chretien Bisque Paramoune ME AstroDon Series I Filters SBIG STL-11000M

35 Example: GRB070201, Not a Binary Merger in M31 35 Inspiral (matched filter search: Binary merger in M31 scenario excluded at >99% level Abbott, et al. Implications for the Origin of GRB from LIGO Observations, Ap. J., 681: (2008). Inspiral Exclusion Zone 50% Exclusion of merger at 75% larger distances 90% Burst search: (1<m 1 <3 M sun ) Cannot exclude an SGR in M31 SGR in M31 is the current best explanation for this emission Upper limit: 8x10 50 ergs (4x10-4 M Ÿ c 2 ) (emitted within 100 ms for isotropic emission of energy in GW at M31 distance) D. Reitze 25% 99%

36 36 Example: The Stochastic GW Background, Beating BBN An isotropic stochastic GW background could come from: Primordial universe (inflation) Incoherent sum of point emitters isotropically distributed over the sky 2 c αβ Energy density: ρ = < h& αβh & GW > 32πG Log-frequency spectrum: Ω GW ( f ) = 1 ρ crit dρgw d(ln f ) Strain spectral density: S ( f ) 3H = 10π 2 0 ΩGW ( f ) 2 3 f Nature, August 20 th 2009 Published S5/VSR1 result, 95% C.L. limit: Ω 0, LIGO < 6.9 x 10-6 UL consistent with no GW stochastic background (null result) D. Reitze

37 37 Current status 3: coming attractions! Enhancements to LIGO and Virgo at end of commissioning aimed at a factor of two improvement in sensitivity meanwhile GEO, LIGO and cryogenic bar detectors have maintained astrowatch New science runs recently started (July 7 th 2009) 2 nd generation detectors Advanced LIGO fully funded (10 to 15 x improved sensitivity, operational ~2014) For Comparison: Neutron Star Binaries: Advanced Virgo close to approval Initial LIGO (S5): ~15 Mpc rate ~1/50yr Adv LIGO: ~ 200 Mpc rate ~ 40/year Black Hole Binaries (Less Certain): Initial LIGO (S5): ~100 Mpc rate ~1/100yr Adv LIGO: ~ 1 Gpc rate ~ 20/year GEO-HF conversion starting D. Reitze

38 Future developments on the ground 38 Need a network of detectors for good source location and improve overall sensitivity Second Generation Network Advanced LIGO/Advanced Virgo/Geo-HF/LCGT/AIGO LCGT under review (proposed cryo, underground interferometer in Kamioka mine) AIGO plans progressing (proposed interferometer in Western Australia)

39 39 Networking Sky coverage at >50% maximum sensitivity L/H+L/L L/H+L/L+V L/H+L/L+V+LCGT LIGO Hanford & Livingston LIGO Hanford & Livingston + Virgo LIGO Hanford & Livingston + Virgo + LCGT Bernard Schutz, AEI

40 Future developments on the ground 40 Third Generation Network Incorporating Low Frequency Detectors Third-generation underground facilities are aimed at having excellent sensitivity from ~1 Hz to ~10 4 Hz. This will greatly expand the new frontier of gravitational wave astrophysics. Recently begun: Three year-long European design study, with EU funding, underway for a 3rd-generation gravitational wave facility, the Einstein Telescope (ET). Goal: 100 times better sensitivity than first generation instruments.

41 Future developments on the ground 41 Third Generation Network Incorporating Low Frequency Detectors Third-generation underground facilities are aimed at having excellent sensitivity from ~1 Hz to ~10 4 Hz. This will greatly expand the new frontier of gravitational wave astrophysics. Recently begun: Three year-long European design study, with EU funding, underway for a 3rd-generation gravitational wave facility, the Einstein Telescope (ET). Goal: 100 times better sensitivity than first generation instruments.

42 Future developments on the ground 42 Third Generation Network Incorporating Low Frequency Detectors

43 Future developments in space 43 LISA (Laser Interferometer Space Antenna) 10-4 Hz 10-1 Hz Our first priority for a space based mission Mission Description 3 spacecraft in Earth-trailing solar orbit, separated by 5 x10 6 km. Gravitational waves are detected by measuring change in proper distance between fiducial masses in each spacecraft using laser interferometry Partnership between NASA and ESA Launch date: soon after 2020?...

44 Future developments in space 44 LISA (Laser Interferometer Space Antenna) 10-4 Hz 10-1 Hz Our first priority for a space based mission Mission Description 3 spacecraft in Earth-trailing solar orbit, separated by 5 x10 6 km. Gravitational waves are detected by measuring change in proper distance between fiducial masses in each spacecraft using laser interferometry Partnership between NASA and ESA Launch date: soon after 2020?...

45 Future developments in space 45 LISA (Laser Interferometer Space Antenna) 10-4 Hz 10-1 Hz Our first priority for a space based mission LISA : A Universe Full of Strong Gravitational Wave Sources Massive Black Hole Binary (BHB) inspiral and merger (10s 100s) Ultra compact binaries (thousands) Extreme Mass Ratio Inspiral (EMRI) (hundreds) Cosmic backgrounds, superstring bursts? K. Danzmann 45

46 46 State of the Universe: September 2009 Some key questions for cosmology: What is driving the cosmic acceleration? Why is 96% of the Universe strange matter and energy? Is dark energy = Λ? How, and when, did galaxies evolve? Big bang + inflation + gravity = LSS? What rôle could gravitational waves play in answering these questions?

47 47 Gravitational Wave Sources as Cosmological Probes Much recent interest in Standard Sirens : e.g. SMBHs at cosmological distances, for which D L can in principle be determined to exquisite accuracy. Inspiral waveform strongly dependent on SMBH masses. Since amplitude falls off linearly with (luminosity) distance, measured strain determines the distance of the source to high precision. Long tail due to parameter degeneracies Holz and Hughes 2005

48 48 Gravitational Wave Sources as Cosmological Probes What could we do with standard sirens? Completely independent, gravitational, calibration of the distance scale and the Hubble parameter Useful adjunct to existing constraints from CMBR, BAO, subject to completely different systematic errors. High precision probe of w(z) Extension of H (z) beyond the reach of SNIe and BAO. Are these goals realistic?...

49 49 Gravitational Wave Sources as Cosmological Probes Currently three major issues: Identification of E-M counterpart Impact of weak lensing Predicting merger event rates

50 50 Gravitational Wave Sources as Cosmological Probes Identifying an E-M counterpart: GWs are redshifted, just like E-M radiation. Hence we determine (very precisely) ( 1+ z) If our goal is to probe e.g. how varies with we can assume and break the z D L z degeneracy. (See e.g. Hughes 02, Sesana et al. 07, 08) D L z If we want to use sirens to measure, we must observe the E-M counterpart. For this we need an accurate sky position!

51 51 Gravitational Wave Sources as Cosmological Probes So what exactly can we do with sirens?... Adapted from Holz & Hughes (2005)

52 52 Gravitational Wave Sources as Cosmological Probes So what exactly can we do with sirens?... Adapted from Holz & Hughes (2005)

53 53 Gravitational Wave Sources as Cosmological Probes GW sources will be (de-)magnified by weak lensing due to LSS. Same treatment as for SN [ See e.g. Misner, Thorne & Wheeler; Varvella et al (2004), Takahashi (2006) ]. However, WL has much greater impact for sirens, because of their much smaller intrinsic scatter. Weak lensing may also limit identification of E-M counterpart

54 54 Gravitational Wave Sources as Cosmological Probes But what will the counterpart signatures be, and when would we see them? Much detailed modelling required. See e.g. Kocsis et al (2008) Periodic variations in flux during inspiral phase, correlated with variations in potential (c.f. OJ287) Viscous dissipation of GW energy released during coalescence Shocks induced by sudden mass loss during final GW burst Shocks induced by a supersonic GW recoil kick Infall of gas onto SMBH merged remnant Before GW peak hours / days days / weeks months / years years

55 55 Gravitational Wave Sources as Cosmological Probes But what will the counterpart signatures be, and when would we see them? Much detailed modelling required. See e.g. Kocsis et al (2008) Periodic variations in flux during inspiral phase, correlated with variations in potential (c.f. OJ287) Viscous dissipation of GW energy released during coalescence Shocks induced by sudden mass loss during final GW burst Shocks induced by a supersonic GW recoil kick Infall of gas onto SMBH merged remnant Before GW peak hours / days days / weeks months / years years Strong argument for multimessenger approach

56 What could be done from the ground? 56 Dalal et al. (2006): Short-duration GRBS, due to NS-NS mergers, will also be observed by ALIGO network. First optical observation of a NS- NS merger? GRB (Perley et al 2008)

57 What could be done from the ground? 57 Dalal et al. (2006): Short-duration GRBS, due to NS-NS mergers, will also be observed by ALIGO network. Beaming of GRBs (blue curves), aligned with GW emission, could boost GW SNR. All-sky monitoring of GRBs + 1 year operation of ALIGO network H 0 to ~2%?

58 What can be done from the ground? 58 Nissanke et al. (2009): Very thorough treatment. Considers impact of: siren true distance; no. of detectors in network; Identifies strong degeneracy between distance and inclination. Need E-M observations / beaming assumption to break this? D L to 10 30% at 600 Mpc (NS-NS); 1400 Mpc (NS-BH). Competitive with traditional distance ladder ; probe of peculiar velocities?

59 Looking ahead to the Einstein Telescope 59 Sathyaprakash et al. (2009): ~10 6 NS-NS mergers observed by ET. Assume that E-M counterparts observed for ~1000 GRBs, 0 < z < 2. Weak lensing De-lensed Fit,, Competitive with traditional methods

60 And even further ahead to BBO 60

61 And even further ahead to BBO 61 BBO schematic Cutler and Holz (2009): ~3 x 10 5 sirens observed, with unique E-M counterparts, for 0 < z < 5. Extremely good angular resolution, even at z = 5! Robust E-M identification of host galaxy, for determining redshift

62 And even further ahead to BBO 62 Cutler and Holz (2009): ~3 x 10 5 sirens observed, with unique E-M counterparts, for 0 < z < 5. Simulated Hubble diagram, including effects of lensing

63 And even further ahead to BBO 63 Hubble constant to ~0.1% w 0 to ~1%, w a to ~10%

64 And even further ahead to BBO 64 Hubble constant to ~0.1% w 0 to ~1%, w a to ~10% All of this lies far ahead, but the key is to work on development of the science case now

65 Opening a new window on the Universe 65

66 Opening a new window on the Universe 66 Gravitational Waves????