LISALaser Interferometer Space Antenna

LISA Laser Interferometer Space Antenna

Gravitational Physics Program

Jo van den Brand

NIKHEF – ET Meeting April 2006

LISA

Introduction

Einstein gravity :

Gravity as a geometry

Space and time are physical objects

8

G _   T _

Gravitational waves

• Dynamical part of gravitation, all space is filled

• Very large energy, almost no interaction

• Ideal information carrier, almost no scattering or attenuation

• The entire Universe has been transparant for GWs, all

the way back to the Big Bang

Meten van afstanden

De afstand tussen twee punten x

en x

3 3

2

0 0

( )

ds g x dx dx g dx dx

 

   

 

 

 

 

  

Voorbeeld 1: Vlakke ruimte, 2 dimensies, cartesische coordinaten

1 2

11 22

( , ) ( , ) en x x  x y g  g  1, g _  0 als    ,

2 ( 1 2 ) ( 2 2 ) ( ) 2 ( ) 2

ds  dx  dx  dx  dy

Euclidische metriek in rechthoekige

coordinaten is dus g

= 

LISA

Meten van afstanden

Voorbeeld 2: Vlakke ruimte, 2 dimensies, poolcoordinaten

1 2 1 2

11 22

( , ) ( , ) en x x  r  g  1, g  ( ) , x g _  0 als    ,

2 ( ) 2 2 ( ) 2

ds  dr  r d 

Voorbeeld 3: Vlakke ruimte, 3 dimensies, sferische coordinaten

1 2 3 1 2 1 2 2

11 22 33

( , , ) ( , , ) en x x x  r   g  1, g  ( ) , x g  ( sin x x )

2 ( ) 2 2 ( ) 2 ( sin ) ( 2 ) 2

ds  dr  r d   r  d 

Voorbeeld 4: Minkowski ruimte, 4 dimensies, cartesische coordinaten

0 1 2 3

( , , , ) ( , , , ) en x x x x  ct x y z g 00  1, g _kk   1

2 2 2 2 2 2

ds  c dt  dx  dy  dz

Metriek functie van energie en impuls: G _ =8T _

Gravitational waves `squeeze’ space: small effects

Proper distance between x

and x

+dx

Plane GW propagating in z-direction Define

Wave equation

Amplitude, frequency and duration

LISA

Evidence for Gravitational Waves

 PSR 1913+16

– R. Hulse, J. Taylor (1974)

– 2 neutron stars

– 1 Pulsar → get the orbital parameters

– Orbital period decreases

– Energy loss due to GW emission

– Good agreement with GR

Bar detectors: IGEC collaboration

Built to detect gravitational waves from compact objects

LISA

Mini-GRAIL: a spherical `bar’ in Leiden

Interferometric detectors: an international dream

GEO600 (British-German) Hanover, Germany

LIGO (USA)

Hanford, WA and Livingston, LA

LISA

Network of Interferometers

LIGO

detection confidence

GEO Virgo

TAMA

AIGO locate the sources

decompose the polarization of

gravitational waves

Interferometer as GW detector

 Principle: Measure distances between free test masses

– Michelson interferometer

– Test masses = Interferometer mirrors

– Sensitivity: h = L/L

– We need large interferometer – For Virgo L = 3 km

2 L   hL 2 

L   hL



Suspended

mirror Suspended

mirror

Virgo: CNRS+INFN

( ESPCI-Paris, INFN-Firenze/Urbino, INFN-Napoli, INFN-Perugia, INFN-Pisa, INFN-Roma,LAL-Orsay,

LAPP-Annecy, LMA-Lyon, OCA-Nice)

+ NIKHEF joining

LISA

Interferometer Concept

As a wave passes, the arm lengths

change in different

ways….

…causing the interference pattern

to change at the

photodiode Suspended

Masses

VIRGO Optical Scheme

Laser 20 W

Input Mode Cleaner (144 m)

Power Recycling

3 km long Fabry-Perot Cavities

Output Mode

Cleaner (4 cm)

LISA

Virgo – inside the central building

Mirror suspension

High quality fused silica mirrors

• 35 cm diameter, 10 cm thickness, 21 kg mass

• Substrate losses ~1 ppm

• Coating losses <5 ppm

• Surface deformation ~l/100

Superattenuators

Possible contributions:

 Virgo+ will use

monolithic suspension

 Input-mode cleaner

suspension

NIKHEF: Linear alignment of VIRGO

N W

EOM

 Phase modulation of input beam

 Demodulation of photodiode signals at different output beams

– => longitudinal error signals

 Quadrant diodes in output beams

– => Alignment information

– (differential wavefront sensing)

 Anderson-Giordano technique

– 2 quadrant diodes after arm cavities

LISA

Linear alignment setup

Sensitivity evolution

LIGO started

LISA

Virgo compared to LIGO

Virgo-LIGO joint analysis

 Working group for burst and inspiral events

 Up to now work on simulated data :

– Project “1a”: Compare analysis pipelines on the same data sets.

– Project “2b”: Study the advantages of 3 sites for astrophysical sources

– Sky location, Detection efficiency

 3 talks and papers (GWDAW9 and Amaldi 6)

Burst from galactic

center

LISA

Virgo- Bars joint analysis

 AURIGA, ROG

 Burst events and Stochastic signals

 Project starting with software injection

– 4 hours of data

– Plan for analysis C6 &C7

GW Source: Coalescing Binary

 End of the life of compact binary systems

– Neutron Stars or Black Hole

 Rare events:

– ~ 0.1 event/year (@20Mpc) ±1 order of magnitude

 Typical amplitude (NS-NS): h ~ 10

@20 Mpc

 “Known” waveform

– Search with matched filtering

– General Relativity test

– Standard candles: get the distance from the waveform

– Coincidence with short gamma ray burst?

LISA

GW source : Supernovae

 Non-spherical star collapse

 Impulsive events

– Duration < 10ms

 Waveform and amplitude difficult to predict

h << 10

@ 10 Mpc (?)

 Rates:

– 10/year in the Virgo cluster

 Required coincidences

– GW, Optic, neutrino detectors

Example of expected

waveforms

 Rotating asymmetric neutron star

 GW Amplitude function of the unknown asymmetry

–

ε = star asymmetry = ??

–

Upper limit set by the pulsar spin down

 A few pulsars around a few 100 Hz

–

Only 800 pulsars plotted out of 10

in the galaxy

 Weak signal but could be integrated for months

–

But a complex problem due to the Doppler effect

GW Source: pulsars

 

 



 



 



 



 



 



 



 

 ^ _{ 6}

2 2

45 27

10 200

10 10 10

3 

Hz f cm

g I r

h kpc ^zz

N

LISA

Detection of Periodic Sources

• Pulsars in our galaxy: “periodic”

• search for observed neutron stars

28 Radio Sources

h ~ GIf ²  _e /cr < 10 ^-24

Periodic Sources – all sky search – Roma / NIKHEF

• Doppler shifts

• Frequency modulation: due to Earth’s motion relative to the Solar System Barycenter, intrinsic frequency changes

• Amplitude modulation: due to the detector’s antenna pattern.

• The original frequency is 100 Hz and the maximum variation fraction is of the order of 0.0001

• Note the daily variations.

• Because of the frequency

variation, the energy of the

wave doesn’t go in a single

LISA

Optimal detection by re-sampling procedure

• Use a non-uniform sampling of the received data: if the sampling frequency is proportional to the (varying) received frequency, the

samples, seen as uniform, represent a constant frequency sinusoid and the energy goes only in one bin of their FFT.

• Every point of the sky (and every spin-down or spin-up behavior) needs a particular re-sampling and FFT.

Original data:

The frequency is varying, we sample non-uniformly

(about 13 samples per period).

The non-uniform samples, seen as uniform, give a perfect sinusoid and the

periodogram of the samples has a single “excited” bin.

1 year FFT length (number of points) 3.1E+10

Sky points 3.1E+13

Spin-down points (1st ) 3.1E+06

Spin-down points (2nd ) 3.2E+02

Freq. points (500 Hz) 1.6E+10

Total points 4.8E+32

Comp. power (Tflops) 3.6E+19

ALL SKY SEARCH

enormous computing challenge

VIRGO - Next steps

 2006: Commissioning + data taking

– Alignment, controls,…

– A science run by the end of 2006 (coincidence with LIGO-S5) ?

 2007

– Data taking/Commissioning/Upgrades

 2008-9: Virgo +

– 50W laser, New electronics, New mirrors ? (not yet decided)

 2011(?): Advanced Virgo

– 200W laser? New beam geometry? New mirrors?...

LISA

Third generation detector

Rüdiger, ‘85

 Two order of magnitude compared to initial Virgo

 Underground site

 Multiple interferometers:

– 3 Interferometers; triangular configuration?

– 10 km long

– 2 polarization + redundancy

 Design study part of ILIAS & FP7

 Construction: 2010-16 ?

Gravitational wave antenna in space - LISA

– 3 spacecraft in Earth-trailing solar orbit separated by 5 x10

km.

– Measure changes in distance between fiducial masses in each spacecraft

– Partnership between NASA and ESA

– Launch date ~2016+

LISA

Complementarity of Space- & Ground- Based Detectors

Rotating Neutron Stars

Difference of 10

in wavelength:

Like difference between X-rays and IR!

VIRGO LISA

LISA will see all the compact white-dwarf and

neutron-star binaries in the Galaxy (Schutz)

LISA – Technical contributions NL

SRON

 Test equipment for position sensor read-out electronics in on-ground tests of the satellite system

 Simulation software modules of the position sensors, used in system simulations

TNO-TPD

 Test equipment of the Laser Optical Bench

 Decaging Mechanism (TBC)

Bradford Engineering

 Cold Gas propulsion (TBC)

NIKHEF

 ASIC development for read-out electronics

LISA

LISA Science Goals & Sources

Observational Targets:

• Merging supermassive black holes

• Merging intermediate- mass/seed black holes

• Gravitational captures by supermassive black holes

• Galactic and verification binaries

• Cosmological backgrounds Science Objectives:

• Determine the role of massive black holes in galaxy evolution, including the origin of seed black holes

• Make precision tests of Einstein’s Theory of Relativity

• Determine the population of ultra- compact binaries in the Galaxy

• Probe the physics of the early

universe

 Production: fundamental physics in the early universe - Inflation, phase transitions, topological defects

- String-inspired cosmology, brane-world scenarios

 Spectrum: slope, peaks give masses of key particles & energies of transitions.

 A TeV phase transition would have left radiation in LISA band.

LISA

Logistics

 SRON

– Netherlands Institute for Space Research

 Radboud Universiteit Nijmegen

– Department of astrophysics

 NIKHEF

– National institute for nuclear and particle physics

 Vrije Universiteit - Amsterdam

– Subatomic physics group

Interest expressed by astronomy groups of both Leiden & Utrecht Universities

Henk Jan Bulten & Gijs Nelemans (RUN) – DAST

representatives NL for LISA (ESA)

Summary

 Collaborate on LISA and VIRGO

– Component of our particle-astrophysics initiative

– Exciting new physics program at NIKHEF

 NIKHEF commitment

– NIKHEF

– Thomas Bauer, Harry van der Graaf, Jan Willem van Holten – Sipho van der Putten – OIO

– VU

– Jo van den Brand, Henk Jan Bulten, Tjeerd Ketel – Gideon Koekoek - AIO

– Technical impact

– Mechanical engineering, Electronics and ASIC design, GRID

 Negotiate with SRON, LISA and VIRGO

LISA

LISA Pathfinder

TM1

TM2

Optical bench

Sensor housings

Dimensions: 640 mm x 375 mm x 375 mm

 Goal: demonstrate free-fall of a proofmass, i.e. isolation from non- gravitational disturbances.

 Method: laser interferometry between two proof masses (PMs)

Virgo: What for?

 First (?) direct observation of gravity waves

 Better understanding of gravity

–

GW produce in high density area

–

Strong field

–

Tests GR

 Open a new window on the universe

–

GW very weakly absorbed

–

Standard candle: Hubble constant

–

GW + Gamma Ray Bursts?

–

Supernova understanding?

–

Neutron stars/black hole physics?

–

Early universe picture??

The future ?

Next Virgo steps

 2006

– Interferometer restart: 1 Month

– New sensitivity curve: February ?

– Recycled ITF commissioning: 3 Months

– Start data taking during weed-ends and nights

– Noise hunting: 4 Months

– Start a Science Run (NS-NS horizon around 15/2.5 Mpc?)

– Data taking > 30% of the time

 2007

– A possible shutdown to fix problems

– Commissioning and noise hunting

– Nominal sensitivity

LISA

Virgo+

 Independent changes

– Same optical layout

– Monolithic suspension

– 50 W laser

– “Short” shutdown

 “Low” cost upgrades

– 1-2 M€

 Installation: early 2008

Virgo Virgo+ (a) Virgo+ (b)

NSNS 12 (31) 46 (114) 22 (56) BHBH 58 (145) 234 (584) 116 (291)

Inspiral Range (Mpc): averaged (optimal orientation )

Advanced Virgo

 Target sensitivity improvement:

–

One order of magnitude compared to Virgo

 Time scale: Shutdown around 2011

 Bigger changes compared to Virgo+:

–

New beam topology:

– Flat beam? Change the beam waist? Signal recycling??

–

Progress on internal thermal noise:

– Material? Coating? Monolithic suspension?

–

Newtonian noise subtraction?

–

…

 But Smaller Changes than Advanced LIGO

–

keep the seismic isolation.

A possible sensitivity

LISA

LISA: How to go to low frequencies

 Space detector to remove the seismic noise

 Low frequencies:

– 10

-1 Hz

 Complementary to ground

based ITF

 Taking data in 2016?

• Spatial interferometer (NASA-ESA)

• 3 satellites, arm length = 5.10

km

Summary

 The Gravitational waves physics is new & exciting

 The detectors sensitivity is improving fast

 Virgo close to start a first Science run

 More progress to come soon…

LISA

LISA Science Goals & Sources

Observational Targets:

• Merging supermassive black holes

• Merging intermediate- mass/seed black holes

• Gravitational captures by supermassive black holes

• Galactic and verification binaries

• Cosmological backgrounds Science Objectives:

• Determine the role of massive black holes in galaxy evolution, including the origin of seed black holes

• Make precision tests of Einstein’s Theory of Relativity

• Determine the population of ultra- compact binaries in the Galaxy

• Probe the physics of the early

universe

LISA Interferometry

 “LISA is essentially a Michelson Interferometer in Space”

 However

– No beam splitter

– No end mirrors

– Arm lengths are not equal

– Arm lengths change continuously

– Light travel time ~17 seconds

– Constellation is rotating and

translating in space

LISA

VIRGO & Lisa – Technical activities

 Linear alignment of Virgo

– Keep mirrors and input beam aligned

 Monolithic suspension of Virgo mirrors

– Reduce thermal noise

 Recycling mirror for Virgo+

– Improve mirror suspension

 Lisa electronics

– Drag-free control readout

Present Virgo noise budget

Control noise

LISA

Developments

 Present developments

–

More modules needed

– Installation of 9

quadrant diode (maybe 10

) – Spares needed

–

New Annecy local oscillator boards, compatible with alignment

– Phase shifters for standard photodiodes

 Possible developments

–

Substitute Si diodes with InGaAs diodes

– Better quantum efficiency – Lower bias voltage

– => higher power capability

 lower noise



Reduction of electronics noise

 Better preamplifier: 5 pA/rtHz -> 1.6 pA/rtHz (?)

 DC signals: pre-amplification / pre-shaping

–

Fast quadrant centering system

– (Napoli is working on that)

– LA noise limits sensibility (especially at low frequencies)

LISA key technology

 Test-mass position sensing:

Capacitive sensing.

 Drag-Free control.

 FEEP micro-Newton thrusters. NIKHEF and SRON develop

ASICS for electronic readout

of all LISA signals

LISA

LISA science: massive black hole mergers

MBH = 0.005M

D. Richstone et al., Nature 395, A14, 1998

But do they merge?

Massive black hole mergers

[Merritt and Ekers, 2002]

 Several observed phenomena may be attributed to MBH

binaries or mergers

– X-shaped radio galaxies (see figure)

– Periodicities in blazar light curves (e.g. OJ 287)

– X-ray binary MBH:

NGC 6240

 See review by Komossa

[astro-ph/0306439]

LISA

EMRI - capture orbits

 Stellar-type black holes (10 M

) sometimes fall into supermassive holes.

 Orbits complicated, can have 10

or more cycles, provide detailed

examination of black-hole geometry.

 Tests of black-hole no-hair theorems, strong-field gravity.

 Filtering the data to find these orbits in a huge parameter space

 Dealing with source confusion

 Challenges:

– Computing the orbits

Typical EMRI event: 10 M

BH

captured by 10

M

BH

Mini-GRAIL: a spherical `bar’ in Leiden

SFERA