FIRST OBSERVATIONS OF GRAVITATIONAL WAVE SIGNALS

Transcription

1 FIRST OBSERVATIONS OF GRAVITATIONAL WAVE SIGNALS GABRIELE VEDOVATO Istituto Nazionale di Fisica Nucleare Sezione di Padova ShanghaiTech Summer School Asiago Italy, 26 July

2 OUTLINE THE GRAVITATIONAL WAVES : A BIT OF HISTORY HOW THE GRAVITATIONAL WAVES ARE DETECTED THE SOURCES OF GRAVITATIONAL WAVES GW : THE DISCOVERY, THE ANALYSIS, THE SOURCE MORE GRAVITATIONAL WAVE EVENTS THE FUTURE

3 THE GRAVITATIONAL WAVES A BIT OF HISTORY

4 A century of General Relativity Einsten introduces the special relativity Space and Time are all part of what's called the space-time continuum Einstein introduces the strong equivalence principle For all physical laws: a gravitational field is locally equivalent to the pseudo-force experienced by an observer in a non-inertial (accelerated) frame of reference accelerated frame gravitational field

5 A century of General Relativity General Relativity Gravity is not a force but it is related to the curvature of space-time Matter tells space how to curve and space tells matter how to move. ( John Wheeler ) Gravitational Waves When massive objects move, the curvature of space-time must change to follow their new positions It takes time for space-time to react, as information can only propagate at the speed of light. There are therefore ripples in space-time These ripples in space-time are gravitational waves

6 A century of General Relativity 1916 General Relativity explains the "anomalous" precession of the perihelion of Mercury measured from model 1850 s General Relativity 5600 /century 5557 /century +43 /century 1919 Eddington observes the deflection of light by the Sun during the total solar ecplise General Relativity +1.8 It made Einstein and his theory of General Relativity world-famous

7 THE INDIRECT SEARCH OF GRAVITATIONAL WAVES In 1974, Hulse and Taylor discover the binary system PSR pulsar Taylor and Weisberg measured the decrease of the orbital period along many years They discovered that the decay period is in precise agreement with the loss of energy due to gravitational waves described by Einstein's general theory of relativity It is the first indirect evidence of the gravitational waves

8 THE DIRECT SEARCH : THE BARS 1960s 1990s Weber devised and constructed the first bar detector Cryogenic Bar Detectors One of these is AURIGA located at LNL near Padua EXPLORER AURIGA ALLEGRO NAUTILUS IGEC NIOBE Laboratori Nazionali di Legnaro, Padua International Gravitational Event Collaboration

9 THE DIRECT SEARCH : INTERFEROMETERS s First prototype (2m) LIGO, Virgo First proposal LIGO & Virgo start 2010 LIGO & Virgo upgrade Discovery! 2015 LIGO Advanced Virgo 2017 Virgo Advanced

10 HOW THE GRAVITATIONAL WAVES ARE DETECTED BY THE INTERFEROMETERS

11 HOW THEY INTERACT? Gravitational waves have two polarization components ( h +, h x ) that oscillate orthogonally to the direction of propagation. During the passage of a gravitational wave the space-time is deformed. h + h x L D L The objects are subjected to a variation D L proportional to the wave amplitude h and the length L of the object D L h L h D L L

12 HOW SMALL IS THE AMPLITUDE OF A GRAVITATIONAL WAVE? The observations until 2011 excluded wave amplitudes corresponding to relative variations greater than D L h L We must try to measure a distance that is 1000 times smaller than the atomic nucleus It is equivalent to a displacement of the diameter of a hair on a distance between the sun and alpha centaurs NUCLEUS ATOM The direct detection of a gravitational wave is a formidable scientific and technological EARTH TERRA challenge ALPHA CENTAURI

13 WHAT IS AN INTERFEROMETER? The interferometer is a very accurate instrument that uses light to measure differences in length MIRROR h BEAM SPLITTER MIRROR INTERFERENCE h L L 1 1 L L 2 2 Photodiode

14 LIGO Sky Sensitivity Each interferometer measures one linear combination of two polarization components h + h x ( F + F x are the detector s sky sensitivities for the h + h x components ) Directional sensitivity is broad, but several detectors are required to capture both polarizations

15 LIGO Spectral Sensitivity/Range LIGO range in O1 run (Sep,2015-Jan,2016) NS-NS ( 2x1.4 M ) 70:80 Mpc (initial LIGO: 20 Mpc) BH-BH ( 2x20 M ) 500:600 Mpc At ~40 Hz, Factor ~100 improvement Broadband, Factor ~3 improvement times the reach in distance translates into 27 times more volume of space accessible to LIGO than before

16 HOW DO THE INTERFEROMETERS WORKS? Credits: Marco Kraan, Nikhef

17 THE INTERFEROMETERS (NOW) Now Operational

18 LIGO Livingston Length = 4+4 Km

19 LIGO Hanford Length = 4+4 Km

20 VIRGO Length = 3+3 Km

21 WHAT DO THE DETECTORS SEE? ASTROPHYSICAL SOURCE GRAVITATIONAL WAVE Time(sec) DETECTOR The detected SIGNAL is buried in to the detector NOISE

22 Searching for GW in the data interferometers detect signals Fast Analysis ( minutes/hours ) GW Candidates are sent to the astronomers for EM follow-up Noise Data are analyzed Deep Analysis ( days/months ) The significance of the candidate events is computed Signal

23 ElectroMagnetic Follow-up The Multi-Messenger Astrophysics Swift X-ray, g-ray follow-up Swift Radio follow-up About 92 partners from 19 countries About 200 instruments covering the full spectrum from radio to very highenergy gamma-rays LIGO Hanford LIGO Livingston Gravitational Wave Detector Network Virgo Optical follow-up Image:

24 The Template Search Templates anticipated GR waveforms as a function of (limited) source parameters Short GRB light curve It finds the template that best fits data High Correlation confident detection & parameter estimation It needs exact source model may fail if theory does not match Nature

25 The Un-modeled Search Short GRB light curve It looks for excess power time frequency patterns consistent in multiple detectors It can search for un-modeled and un-expected sources High Cross Correlation

26 SOURCES OF GRAVITATIONAL WAVES NOT JUST BLACK HOLES

27 Source of Gravitational Waves Transient Signals Groun : ( ) sec Coalescing Binary Systems Neutron Star Neutron Star Neutron Star Black Hole Black Hole Black Hole Well modelled by General Relativity Bursts Asymmetric Core Collapse Supernovae Cosmic Strings Unknown??? Credit: AEI, CCT, LSU Unmodelled Credit: Chandra X-ray Observatory

28 Source of Gravitational Waves Continuous Sources Continuous Ground-based Signals Spinning Neutron Stars (Pulsars) Probe crustal deformations, equation of state Stochastic GW wave noise Incoherent background from primordial GWs or an ensemble of unphased sources Primordial GWs unlikely to detect, but it can bound in the Hz range NASA/WMAP Science Team

29 SEPTEMBER 14, :51 in Italy THE DISCOVERY

30 SEPTEMBER 14, :51 in Italy Numerical relativity simulation (SXS Collaboration, billion years ago

31 LIGO DETECT THE EVENT 7 milliseconds later LIGO HANFORD LIGO LIVINGSTONE SEPTEMBER 14, :51 in Italy

32 WHISPERS FROM THE COSMOS

33 Event Time Analysis ready 3 minutes later :50:45 UTC :53:51 UTC Very high SNR = 23.5 The fast analysis sends the alert

34 10 minutes later Arrival Time 11:51 Alert Time 11:53 GW : The First Shot

35 REAL or FAKE?

36 The announcement of the discovery : LIGO France David Cordova Reitze Gabriela Gonzales Gonzalez Rainer Weiss Kip Thorne NSF LIGO Director Portavoce LSC Spokesperson LIGO/MIT di LIGO/CIT Cofounder Cofounder /feb/11/we-did-it-scientists-announcediscovery-of-gravitational-waves-video February 11, 2016

37 GW THE ANALYSIS

38 LIGO HANFORD LIGO LIVINGSTONE The SIGNAL is extracted from the DATA recorded by the detectors

39 Is the SIGNAL the same in the two detectors? We overimpose the LIGO HANFORD signal to the LIGO LIVINGSTONE signal The signals coincide only partially

40 Is the SIGNAL the same in the two detectors? Google Map The sign of LIGO HANFORD signal is inverted because the detectors is rotated by ~ 90 degrees respect to LIGO LIVINGSTONE LIGO HANFORD Google Map LIGO LIVINGSTONE The LIGO HANFORD signal has arrived 7 milliseconds later respect to LIGO LIVINGSTONE

41 Is the SIGNAL the same in the two detectors? The sign of LIGO HANFORD signal is inverted because the detector is rotated by 90 degrees respect to LIGO LIVINGSTONE We invert the signal s sign in LIGO HANFORD The signals still don t coincide

42 Is the SIGNAL the same in the two detectors? The LIGO HANFORD signal has arrived 7 milliseconds later respect to LIGO LIVINGSTONE We anticipate the signal by 7 ms in LIGO HANFORD The signals coincide!!!

43 GW Skymap sent to the Astronomer Footprints of all reported observations cwb LIB BAYESTAR LALInference Large error region: 90% Confidence = 600 deg 2 Skymap was sent for EM follow up ApJ 826 (2016) L13 For Black Holes Merger there is a little expectation of detectable electromagnetic (EM) signature

44 GW : HOW SIGNIFICANT? Detectors are great, but environment is noisy. What is the probability to produce by chance a coincident event? The estimated probability that noise produce by chance a GW like event is less than 1 in years (Template Search) 1 in years (Unmodelled Search) no way GW can be a spurious noise, it is an astrophysical event!!!

45 GW THE SOURCE LIGO Open Science Center -

46 THE COALESCENT BLACK HOLES Inspiral Merging Ring Down The masses of the two black holes are 36 and 29 times the solar mass and radius repectively of 108 and 87 km 29M 36M The detected signal is in perfect agreement with the general relativity Before merging the two black holes have approached at ~ 350 km at a speed of ~ km/sec

47 THE FINAL BLACK HOLE The mass of the final black hole is 62 solar masses ( = 20 millions the earth mass ) The black hole radius ~ 183 km Asiago Turin Venice The energy converted in gravitational waves is about 3 [ = (36+29)-62 ] solar masses A peak power output about 50 times that of the whole visible universe!!!

48 GW SIMULATED Credits: SXS Simulating Extreme Spacetime Numerical relativity simulation (SXS Collaboration,

49 MORE GRAVITATIONAL WAVE EVENTS

50 Other events detected in the First Scientific Run

51 One more event detected in the Second Scientific Run The Masses First Event Reported June 1, 2017 Illustration: CXC/M.Weiss 1 Solar Mass = 333,000 Earth Masses! Second Event Third Event

52 The Signals M1 = 36 M - M2 = 29 M M1 = 23 M - M2 = 15 M PRX 6, (2016) M1 = 14 M - M2 = 7 M M1 = 31 M - M2 = 19 M

53 First Event 1.3 billion light years How Far? Second Event 1.4 billion Light years Third Event 3.0 billion light years

54 NEW ASTROPHYSICS What did we learn? 1. Stellar binary black holes exist 2. They form into binary pairs 3. They merge within the lifetime of the universe 4. The masses (M > 20 M ) are much larger than what was known about stellar mass black holes

55 A NEW WINDOW ON THE UNIVERSE Gravitational waves can help to explore great questions of physics 1. How do black holes form? 2. Is general relativity the correct description of gravity? 3. How does matter behave under the extreme conditions of temperature and pressure as those in neutron stars and supernovae?

56 AND NOW?

57 THE NEAR FUTURE Image Credit: Caltech/MIT/LIGO Lab VIRGO Approved! Expect more detections Significant improvements in the reconstruction of the signal Sky localization within few square degrees for full network

58 GW detections

59 WITH VIRGO = BETTER SKY LOCALIZATION Sky localization with the two LIGO detectors Adding simulated Virgo data with initial sensitivity GW LVT GW GW Credit: LIGO/Leo Singer (Milky Way image: Axel Mellinger) GW % credible areas from 600 deg 2 to deg 2

60 Visions of 3 rd generation detectors EINSTEIN TELESCOPE 10 km arm length, arranged in triangular configuration, cryogenic, underground ET will test the Einstein s gravity in strong field condition and it will be able to realize precision gravitational wave astronomy. Assuming technologies one should be able to achieve in years

61 elisa (2034) elisa is a constellation of three spacecraft, arranged in an equilateral triangle with sides 1 million km long, flying along an Earth-like heliocentric orbit. 2015: Impressive technological success of the LISA-Pathfinder demonstrator. It is focused on Hz frequency range, corresponding to: signals produced by very massive objects: coalescences of ~10 5 M S black holes Signal of lighter object (stellar mass black holes, BNS, stars) far from the coalescence

62 PULSAR TIMING ARRAY A pulsar timing array is a set of millisecond pulsars that can be used to detect and analyze gravitational waves in the frequency range of 10 9 to 10 6 Hz. The expected astrophysical sources are massive black hole binaries in the centers of merging galaxies, where tens of millions of solar masses are in orbit with a period between months and a few years. Globally there are three active pulsar timing array projects. Parkes Pulsar Timing Array European Pulsar Timing Array Nort American Nanohertz Gravitational Wave Observatory Pulsar

63 AND FINALLY

64 P R L HYSICAL EVIEW Ô ETTERS Member Subscription Copy Library or Other Institutional Use Pr ohibited Until 2017 Articles published week ending 12 FEBRUARY 2016 Published by American Physical Society Ô Volume 116, Number 6

65 Pasadena Marzo 2015 LIGO-Virgo Collaboration Meeting Kip Thorne talks about Interstellar I extent Kip Thorne s dedication to all of you Dedication for my son With best wishes for your studies of science. I hope you enjoy it as much as I have. Kip Thorne

66 Thanks!!! LNL-Padua 2016 Hannover 2015 AEI -Hannover 2015 The discovery notebook at LNL Paris 2017 The discovery node at CIT