LISA reflectors, Advantages and Disadvantages

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1 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 1

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4 Some PSRB parameters Character Keplerian Post-Keplerian General Relativity Parameter Orbital period Eccentricity Projected semi-major axis Periastron precession Time dilation + grav. redshift Orbital period decay rate Pulsar mass Companion mass Orbit inclination Value P = hours e = a sin i = light sec = deg / year = sec Ṗ = ± m p = M m c = M sin i = th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 4

5 PSRB consequences PSRB is a strongly relativistic system GR correctly predicts all post-keplerian parameters Gravitational redshift and time dilation Perihelion advance Shapiro time delays Emission of Gravitational Wave Radiation GWs from the binalry pulsar: Compelling evidence of their existence, Not indirect, but incomplete GW emission frequency: ~ 70 μhz Current GW emission amplitude: ~ Calculated lifetime: ~ 300,000,000 years 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 5

6 GW Astronomy Therefore: Relevant GW sources are far from Earth Detection poses a formidable problem Benefit of detection: GWs carry undistorted news from source interiors GW sources are often classified in four groups: Burst, or short duration signals Periodic, or long duration signals Stochastic backgrounds Other, unforeseen signals GW detection will thus spawn a new branch of Astronomy: GW Astronomy 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 6

7 GW telescopes: basics Free test masses at rest before GW comes: m l 0 m Incoming GW causes relative distance changes: m l(t) m l t = l 0 δl = l 0[ h t ] δl 2 δl 2 where h t =[h x 0,t cos 2 h x 0,t sin 2 ] sin 2 GW amplitudes are measured in metres/metre. For envisaged sources, h ~ th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 7

8 Acoustic GW detectors The idea of these devices is to link the proof masses by a spring: l t 2β l t Ω 2 [l t l 0 ] = 1 2 ḧ t l 0 GW signals get selectively amplified near frequency Ω. 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 8

9 Acoustic GW detectors: NAUTILUS Resonance: ~1 khz Single capacitive transducer Sensitivity: ~ Dilution refrigerator: 50 mk 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 9

10 Acoustic GW detectors: Spheres PHC Isotropic, multi-mode, mode-channels Mario Schenberg, Brazil mini-grail, Netherlands 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 10

11 Interferometric GW detectors Idea of interferometric detectors is to sense δl by inteferometry: δ = 2 ω Ω h 0sin Ω L 2 c, Ω ω Note optimum arm-length: L = λ GW 2 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 11

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13 Suspension towers, central building 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 13

14 The VIRGO site: Cascina (Pisa) Te North pipe Power recycling mirror 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 14

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17 GW telescopes: Earth vs. space based Ground based (VIRGO & LIGO) GW freq 10 Hz < f < 2 khz Main signals are pulsed Rates uncertain Space based (LISA) GW freq 0.1 mhz < 1 Hz Long (years) duration signals Ibid., but some signals guaranteed SNRs tight SNRs can be as high as 1000 Data analysis very complex Data archives huge (because of high freq) No hardware limits Highly serviceable, upgradable Long lifetime Data analysis (hopefully) less complex Data archives much more manageable Very stringent hardware constraints Not serviceable, minor upgrades Reduced lifetime These complement each other in a common objective 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 17

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20 LISA sensitivity 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 20

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22 Binary system of SMBHs NGC 6240 Hubble-Spitzer, optical + IR X-ray, Chandra 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 22

23 Detectability of SMBH binaries 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 23

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25 But, how is LISA conceived to make all this possible!? 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 25

26 LISA orbit 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 26

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34 LISA interferometry 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 34

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36 There are two MOSAs in each of the three spacecraft. Each MOSA: serves its individual interferometer arm optically connect with its remote counterpart pivots around a vertical axis to maintain correct beam direction The main elements of each MOSA are: an Optical Bench (OB) a Gravitational Reference Sensor Head a 40 cm diameter telescope 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 36

37 Time delay interferometry LISA s laser (1.064 m) is cavity-stabilised to have frequency fluctuations below within the MBW. S f 1/2 < 30 Hz/ Hz If two interferometer arms have mismatched lengths by L then laser frequency fluctuations f mimic TM displacements x: x = f f L LISA is required to have a displacement noise below 10 pm/ Hz, hence L should be kept below L < 100 m. Yet L gets as large as 60,000 km!!! 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 37

38 Time delay interferometry TDI is a post-processing technique for removing (at least) laser frequency noise. This is done by defining (a wealth of) TDI variables which contain no frequency noise, yet retain GW signals: L 1 L 2 L 1 L 2 L 1 L 2 Michelson (no f-noise) Kennedy-Thorndike (f-noise) Sagnac (f-noise cancellation) 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 38

39 Time delay interferometry Let (t) be phase at the beam splitter (vertex). Then, e.g., In arm 1: In arm 2: () t ( t 2 L ) () t 1 1 () t ( t 2 L ) () t 2 2 Off-line, the following TDI variable can be constructed: Xt () [ ( t 2 L) ()] t [ ( t 2 L) ()] t which is readily seen to be free of any phase noise, while still containing (GW) signals. There are more TDI combinations, but a strong requirement is precise knowledge of arm-lenghs at the given times. 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 39

40 LISA is really challenging......and expensive!! 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 40

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42 LISA PathFinder 1. One LISA arm is squeezed to 30 centimetres: 30 cm LTP Objectives : Drag-free Interferometry Diagnostics TM charging Telemetry Data processing 2. Relax sensitivity by one order of magnitude, also in band: 14[ S Δa ω mHz 2] ω/2π ms 2 Hz 1/2, 1mHz ω/2π 30 mhz 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 42

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44 LPF orbit Lagrange L1 Travel time: ~3 months Mission lifetime: ~6 months 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 44

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46 Drag-free sequence 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 46

47 Drag-free sequence 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 47

48 Drag-free sequence 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 48

49 Drag-free sequence 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 49

50 Drag-free sequence 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 50

51 Drag-free sequence 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 51

52 Drag-free sequence 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 52

53 Drag-free sequence 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 53

54 Beveled vertexes Notch 46 mm Au 70% + Pt 30%, 1.96 kg Test Mass EH interior, gap = 4 mm 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 54

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58 Precision thermometers Precision magnetometers The DMU Rad Mon 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 58

59 DRB, 11-Feb-2010, Friedrichshafen D Kolbe ASD I Lloro ICE A Lobo ICE H Abele ASD Bengt J ESA G Kahl ASD U Denskat ASD X Llamas NTE 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 59

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61 Final remarks GWs are a unique and unexplored new way to scrutinise the Universe GWs are the last open issue in GR so far GW detection is a very challenging problem: almost 50 years since first attempts by Joe Weber LISA strongly depends on success of LISA PathFinder, scheduled for a 2013 launch. System integration is already proceeding Important parts of LPF will be transferred to LISA, including: Local metrology system Most of LPF GRS Diagnostics items while other parts need feasible improvement with affordable effort. Some of these are already under study, while the mission formulation (Astrium Germany) is essentially complete Ground-based are upgrading to new generation detectors, strongly enhancing probability of sighting in the next 5 years or so 39th Winter Meeting FP, Canfranc 9-ii-2011 A. Lobo, Gravitational Waves 61