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Detection of gravitational waves Miquel Nofrarias Institut de - - PowerPoint PPT Presentation

May 09, 2023 143 likes •673 views

Detection of gravitational waves Miquel Nofrarias Institut de Cincies de lEspai (IEEC-CSIC) Gravity gradient Coupling of the suspended test mass with density fluctuations Dominant source comes from seismic surface waves near the

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Detection of gravitational waves

Miquel Nofrarias Institut de Ciències de l’Espai (IEEC-CSIC)

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GW detection - M. Nofrarias ICE 02/07/18

Gravity gradient

  • Coupling of the suspended test mass with density fluctuations
  • Dominant source comes from seismic surface waves near the location of

the test mass

  • Solutions to these come from active isolation (using seismograph) to

underground facilities

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Parametric instabilities

  • Energy can couple from the optical modes resonating in the cavity to the

acoustic modes in the test mass

  • Solution is design to avoid this instabilities.
  • Suppression can be achieved, for instance, by means of thermal

compensation

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Parametric instabilities - thermal compensation

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Active isolation

  • Test mass required to be located ~10-6 of

a wavelength

  • Residual motion is ~ microns
  • makes difficult to lock on mirror

because large forces need to be applied

  • Makes it impossible to act on the test

mass

  • noise limit on the actuator typically

10-9 of the max signal to be applied

  • 10-9 x 10-6 = 10-15 (large!)
  • Two options: either reduce residual

motion or attenuate test mass motion by means of control stages

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Active isolation

  • The equation of motion for a suspended

pendulum

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  • We use the error signal
  • Our transfer function is then
  • Suppression factor
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Ultra low frequency pre-isolator

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Equation of motion for inverted pendulum Equation of motion for folded pendulum

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Inverted pendulum dynamics

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VIRGO Superattentuator

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External Injection Bench - Seismic Attenuation System

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Suspended detection benches (Virgo)

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Suspended detection benches (Virgo)

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LIGO

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Resonant mass/Acoustic detectors

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Acoustic detectors

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Weber pioneering work

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  • Consider an harmonic oscillator driven by

gravitational waves

  • Derive equations of motion
  • Exploit piezoelectric effect: stress

in a piezoelectric will induce a signal that can be recorded, measure this and you can compute terms of the Riemann

  • As suggested by Dirac, what if

anomalies in Earth rotation would be due to gravitational wave radiation? 5 x 108 erg/cm2 :’The

Earth rotation is not a useful detector unless the anomaly can be reduced’

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Resonant mass detectors network

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Resonant bar

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Resonant bar

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Sensitivity to GW sources

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  • Energy deposited in a resonant antenna
  • Total intrinsic noise of the antenna
  • Optimal result reaching the amplifier limit KBTN
  • Quantum limit
  • M = 1200kg, D = 3m, ωs =900Hz => TN = 0.04 uK , hmin = 10-21
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Sensitivity to GW sources

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Spherical GW detectors

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Omnidirectional GW detectors

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  • Various geometries proposed for omnidirectional GW detectors
  • Truncated Icosahedron (TIGA)
  • Pentagonal Hexacontahedron (PHC)
  • Some interesting properties derived from the geometry. In particular,

multimode analysis. PHC, for instance, shown to differentiate GR from BD theories from the monopole

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Omnidirectional GW detectors

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What can we learn about GW Physics with an elastic spherical antenna? J.A. Lobo PRD (1995)

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DUAL wideband proposal

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The gravitational wave spectra

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Pulsar Timing Array

  • A pulsar timing network of ~100

pulsars each with better than 100 ns timing precision

  • Observing with weekly regular

cadence would enable nHz – μHz band

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LISA recent chronology

  • 2011 Apr: “ESA has ended the partnership with NASA

because NASA is financially unable to participate when ESA's funding is available” R. Stebbins (NASA).

  • 2013 Nov: ESA selects ‘The Gravitational Universe’ as

scientific theme for L3 mission slot.

  • 2016 Feb: LIGO announcement (and LISA Pathfinder

successfully releases TMs in free-fall)

  • 2016 Nov: ESA call for mission proposals for the L3 slot

(1.000 ME, 2034)

  • 2017 Jan: LISA Consortium submits its proposal
  • 2017 Jun: ESA officially selects LISA as L3 mission of its

scientific programme

  • 2017 Jul-Dec: LISA phase 0 study. Output: Payload

Description Document (PDD)

  • 2018 June: LISA Phase A kick off (2 years).

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It’s a long story…

NASA studies GWI (Gravity Wave Interferometer), an interferometer with a total launch mass of 16.4 t, which included four 1000kg test masses. The total cost of the project was estimated at that time to be $ 49.5 M

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  • R. Weiss, P.L. Bender, C.W. Misner and R.V. Pound, in Report of the Sub-Panel on Relativity

and Gravitation, Management and Operations Working Group for Shuttle Astronomy, (NASA, Washington, DC, 1976).

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LISA schedule

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The LISA mission concept

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LISA is the concept selected for ESA L3 mission slot (2034, 1000M€) LISA (Laser Interferometer Space Antenna)

Constellation of 3 satellites in heliocentric orbit Space-craft are drag-free, ie. it follows a test mass inside which is in nominal free fall Micro-newton thrusters steers the space-frat to be entered around the test mass Differential arm-length measured by laser interferometry

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Black Hole Astronomy in the 2030s

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Future EM

  • bs.

SKA,

Redshift, z

Future ground Current ground

Mass [log M/Mo]

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Thermo-elastic modelling workshop

LISA science case

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L I S A P a t h fi n d e r

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Thermo-elastic modelling workshop

LISA measurement concept

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LISA challenges — MOSA

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Going to 20uHz requires 14h measurements. Many things move, so it requires:

very high pointing accuracy: 5 nrad/√Hz imaging systems and very good alignment between Optical Bench, Telescope and test mass (order of a few 10 μm)

The MOSA has to follow the constellation ‘breathing’, then

necessary a backlink fiber harness with 100+ cables must be continuously moved

One pm is 10-6 of a wavelength

stray light with an amplitude of 10-6 compared to the wanted light produces pm errors

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LISA challenges — Gravitational Reference Sensor

  • Requirements on the test mass:
  • Allow TM to be a 3 fm/s2/Hz1/2 level

geodesic reference (relaxed 1/f2 from 20 mHz to 400 mHz)

  • Allow TM to be used as a mirror for < 10

pm/Hz1/2 IFO readout

  • Forces applied to the test mass dominate

noise budget at low frequency

  • Cold gas: initially 4 tanks 50kg each pulling
  • utwards on two TMs.
  • Cannot deplete fuel without unbalancing g
  • n two TMs
  • Costs ~ hundreds pm/s2 in differential

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LISA challenges — interferometry

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Beam expands to 15 km → only 1 nW received in telescope

Very accurate pointing (sub-μrad) required → complicated link acquisition

One-way light travel time is about 8 seconds, spacecraft are moving

phasemeter needs to take into account Doppler and implement tracking schemes

Difference between transmit and receive directions, changing over time

Need point-ahead mechanism in the

  • ptical path

Laser frequency noise couples into measurement with enormous amplification

Time-Delay Interferometry (TDI)

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LISA challenges — Time Delay Interferometry (TDI)

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TDI is essential to remove frequency noise in post-processing

Suppresses frequency noise by several orders of magnitude Fundamental step in post-processing LISA telemetry Based on pioneering work at JPL, Tinto et al. (1999) technique to ‘synthesize’ an equal arm interferometer, relying in accurate knowledge of satellite constellation

TDI impacts in mission design since it requires:

sub-m knowledge of absolute arm lengths ns-accurate time-stamping ranging function of phasemeter special requirements on spacecraft timing and clocks

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LISA Pathfinder — paving the way for LISA

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LPF - exploded view

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Gravitational Reference Sensor

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Gravitational Reference Sensor

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LISA Pathfinder

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Four interferometers in total

x1 x12 Reference Frequency

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Optical Metrology - heterodyne interferometer

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LPF - dynamics and control scheme

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LPF - dynamics and control scheme

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Armano et al. (LPF collaboration) Phys. Rev. D (accepted) Guidance signals applied to the system MCMC parameter estimation

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LISA Pathfinder: tracking spacetime

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LISA Pathfinder launch campaign

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The Vega launcher

  • P80: Vega’s first stage is powered by a large single-piece solid rocket motor

containing 87,710 kg. of HTPB 1912 solid propellant. This solid rocket motor delivers maximum vacuum thrust of 3,015 kN and burns for 110 seconds prior to being jettisoned at an altitude of about 55 km.

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  • ZEFIRO: Vega’s second and third stages use

Zefiro solid rocket motors. These two stages, each 1.9 meters in diameter, The Zefiro-Z23 stage is 8.39 meters long, and is loaded with 23,820 kg. of HTPB 1912 solid propellant, providing maximum vacuum thrust of 1,120 kN. It operates for 77 seconds in average.

  • AVUM (Attitude & Vernier Upper Module) has a

bipropellant propulsion system to provide orbital injection, and a monopropellant propulsion system for roll and attitude control. It is designed to inject different payloads into different orbits, and ensures the fine pointing of satellites prior to separation. The AVUM contains about 577 kg. of liquid propellant (UDMH/NTO), distributed in four tanks. It is powered by an engine derived from the re-ignitable RD-869, providing 2.45 kN of thrust. It also has two sets of three monopropellant thrusters to control roll and attitude.

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Cruise phase to L1

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LISA Pathfinder results: free fall

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Armano et al. (LPF collaboration) Sub-femto-g free fall for space-based gravitational wave observatories: LISA pathfinder results. Phys. rev. lett. 116 (2016)

Brownian Interferometer noise Force on test mass and artifacts

LISA pathfinder appreciably constrains collapse models

  • Phys. Rev. D 95, 084054

Experimental bounds on collapse models from gravitational wave detectors

  • Phys. Rev. D 95, 084054
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LISA Pathfinder results: free fall

SMBH merge (M = 5 x 106, z=2) f = 0.02 mHz: 35d before coalesce (SNR 50) f = 0.8 mHz: coalescence (SNR 1400) Armano et al. (LPF collaboration) Beyond required LISA free-fall performance: new LISA Pathfinder results down to 20 μHz Phys. Rev. Lett. 120 (2018)