ONDE GRAVITAZIONALI la nuova era della fisica

Transcription

1 ONDE GRAVITAZIONALI la nuova era della fisica Andrea Chincarini Istituto Nazionale di Fisica Nucleare Collaborazione LIGO-VIRGO

2 14 Sep 2015: First detection of Gravitational Waves! 229,000 paper downloads from APS in the first 24 hours, servers down! Phys. Rev. Lett. 116, (2016) Binary black holes do exist! and we can listen to them coalesce This is the birth of gravitational wave astronomy 2

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4 What are GW? GW are not the same thing as light: they are not part of the e.m. spectrum (radio waves, infrared, visible light, ultraviolet, x-rays ) 4

5 Newton vs. Einstein media

6 Einstein vs. Newton A new picture What are GWs? a necessary consequence of Special Relativity ripples in space-time due to cosmic cataclisms quadrupolar distortions of distances between freely falling masses finite speed for information transfer gravitational waves come from the acceleration of masses and propagate away from their sources as a space-time warp field at the speed of light space-time tells matter how to move, and matter tells space-time how to curve 6

7 How did we know GWs exist? Binary Pulsar GR prediction The Nobel Prize in Physics 1993 Russell A. Hulse, Joseph H. Taylor Jr. Ok, but how to directly detect it? J. M. Weisberg, J. H. Taylor, 7

8 Gravitational waves are hard to detect they are very very very weak What is the Effect of GWs? Squeeze and stretch the space [and time] in the directions perpendicular to the propagation strain h = ΔL/L What is the plausible strain? Even for the most tremendous events in Universe, h~10-21 media-06 8

9 With h = ΔL/L ~10-21, even with test masses L~km far apart, displacement is ΔL~10-18 m Reminder: Diameter of human hair: Diameter of atom: Diameter of atomic nucleus: Diameter of proton: 10-5 m m m m ΔL~10-18 m looks rather... small media-07 9

10 another way of looking at it Let s suppose you pour a glass of wine into the ocean. What is the rise of sea-level you get? 10

11 Ocean surface: 70% x 4pi x R_earth2 = 0.7 x 4 x 3.14 x (6.37x106 m)2 ~ 3.6 x 1014 m2 Glass volume: ~ 0.25x10-3 m3 Ocean rise: delta_h~ V_glass/Ocean surface ~ 1x10-18m This is the kind of displacement we need to detect 11

12 DETECTING GWs 12

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16 Using light as a ruler 16 media-08

17 Michelson (with additions) 4 optical resonators arranged around Michelson IFO Michelson-Morley experiment (1887): Accuracy: 10-8 m (10-9 relative) media m arm-length Advanced Interferometer: Accuracy: m (~10-23 relative), 100Hz BW 3-4 km arm-length 17

18 ...and a bit closer To reality... 18

19 Meet the Villain: Noise! Doesn t matter how sensitive you are, if your noise is billions of times your signal Credits: Stephen Fairhurst 19

20 What Limits 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 20 media-10-11

21 Coping with Noise Low frequency range: Dominated by seismic noise Managed by suspending the mirrors from extreme vibration isolators (attenuation > 10^12) Technical noises of different nature are the real challenge in this range Ultimate limit for ground-based detectors: gravity gradient noise 21

22 Newtonian Noise Credit: M. Lorenzini 12

23 Superattenuatorsors 23

24 Coping with Noise Thermal noise Intermediate frequency range: Dominated by thermal noise of mirror coatings and suspensions 24

25 Mid frequency range: Dominated by thermal noise of mirror coatings and suspensions Coping with Noise Thermal noise Reduced by: Larger beam spot (sample larger mirror surface) Test masses suspended by fused silica fibers (low mechanical losses) Mirror coatings engineered for low losses 25

26 Mirrors 35cm 20cm 42Kg The surface figure of the polished test masses is such that with a mirror as large as EmiliaRomagna, highest mountains would be 1mm 26

27 The real thing Advanced Virgo 27

28 Advanced Virgo In a nutshell: Advanced Virgo (AdV): upgrade of the Virgo interferometric detector of gravitational waves Participated by scientists from Italy and France (former founders of Virgo), The Netherlands, Poland and Hungary Funding approved in Dec 2009 First science data scheduled in European countries 19 labs, ~200 authors APC Paris ARTEMIS Nice EGO Cascina INFN Firenze-Urbino INFN Genova INFN Napoli INFN Perugia INFN Pisa INFN Roma La Sapienza INFN Roma Tor Vergata INFN Trento-Padova LAL Orsay ESPCI Paris LAPP Annecy LKB Paris LMA Lyon NIKHEF Amsterdam POLGRAW(Poland) RADBOUD Uni. Nijmegen RMKI Budapest 28

29 Inside one arm 29

30 Central building 30

31 End test masses 31

32 Beam splitter 32

33 Virgo INPUT TEST MASS PAYLOAD LVC, Budapest, Sep 2, 2015 G Losurdo - AdV Project Leader 33 33

34 FIRST MINITOWER BENCH (SIB2) INTEGRATED 34 34

35 Better seismic isolation Better test masses and suspension Higher power laser

36 ial t i In Oanc O v LIG Ad LIG ed Advanced detectors 10X better amplitude sensitivity Event rate (reach)3 ~ 1000X greater 1 day of observation with Advanced LIGO = 1 year with Initial LIGO 36

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39 THE EVENT GW

40 September 14, :50:45 CET LIGO Hanford Observatory LIGO Livingston Observatory Initial detection made by a low latency searches for generic GW transients: Coherent WaveBurst Reported within 3 minutes after data acquisition media-12 40

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42 GW has = 23.6 (largest signal), corresponding to false alarm rate less than 1 per 203,000 years or significance > 5.1 σ 42

43 Why black holes? Binary neutron stars excluded Binary made by one BH and one NS? If so, MBH very large Coalescence takes place at lower frequencies NS-BH binary excluded media-13 ~ ~ 210 km 43

44 Joint observations with astronomers LVC called for EM observers to join a follow-up program LIGO and Virgo share promptly with astronomers interesting triggers; up to a few at current sensitivity Provide limited directional information, promptly estimated Big participation to GW observation: 24 groups carried out observations Challenging! Source location with large uncertainty ~ 600 deg2 44

45 Sky location Source location with large uncertainty ~ 600 deg2 45

46 Why is our error box so large? t n e v e d te la u Sim Two interferometers (HL), each with poor directionality, determine by time delay an annulus in the sky with folding in amplitude information we can do a bit better (in the RHS, a simulation with a BNS event) 46

47 How do we cope? With telescope time.. A sky map produced by LIGO and Virgo is tiled with multiple observations, searching for transients Looking for fading objects, repeat observations after days 47

48 In the design LIGO-Virgo network, GW could have been localized to ~20 deg2 48

49 The advanced GW detector network: Advanced LIGO Hanford 2015 Advanced LIGO Livingston 2015 LIGO Livingston Observatory Louisiana, USA KAGRA 2017 Advanced Virgo 2016 VIRGO Observatory, Cascina, Italy LIGO-India 2022 LIGO Hanford Observatory Washington, USA 49 49

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51 16 February 2016 LISA Pathfinder has released both test masses!

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53 Further reading Paper on the detection Phys. Rev. Lett. 116, (2016) Companion papers Open data On GW detection with interferometer On Advanced Virgo detector On aligo detectors On close-future evolution of GW detectors 53

54 Thank you The European Gravitational Observatory is a consortium of: 54

55 James Clerk Maxwell 1864, announced his electromagnetic theory of light 55