Search for gravitational waves

Search for gravitational waves

Jo van den Brand

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 transparent for GWs, all

the way back to the Big Bang

Gravitational waves `squeeze’ space: small effects

Proper distance between x

and x

+dx

Plane GW propagating in z-direction Define

Wave equation

Gravitational waves

L

h  L

 2

GW

time L- L L+ L

 Predicted by general relativity

 GW = space-time metric wave

–

Distance variation

–

Strain amplitude h:

 GW produced by mass acceleration

–

d = source distance

–

Q = quadrupole moment dt d

Q d c

h 2 G 1

2 2

 4

 Small coupling factor → astrophysical sources

1 1 2

10

s kg

m

s J L

 10

/

L=20 m, d = 2 m, 27 rad/s

J E

Hz

m

25

10

10

 





Earth-sun: 313 W

Evidence for gravitational waves

 PSR 1913+16

–

R. Hulse, J. Taylor (1974)

–

Binary pulsar (T = 7.75 hr)

–

1 pulsar (17 rev/s) → get the orbital parameters

–

Orbital period decreases

– Energy loss due to GW emission (~3 x 10

W) – Good agreement with GR

– Inspiral lifetime about 300 Myears (3.5 m/yr)

– Expected strain, h~10

m

GW source: coalescing binary

 End of the life of compact binary systems

–

Neutron stars, systems have been observed

 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 tests

–

Standard candles: get the distance from the waveform

– Coincidence with short gamma ray burst?

Two body problem in general relativity

 Collision of two black holes

 Numerical solution of Einstein equations required

 Problem solution started 40 years ago (1963 Hahn &

Lindquist, IBM 7090)

 Wave forms critical for

gravitational wave detectors

 A PetaFLOPS-class grand

challenge

Numerical relativity

First merger of three black holes simulated on a supercomputer ScienceDaily (Apr. 12, 2008)

Manuela Campanelli, Carlos Lousto and Yosef Zlochower—Rochester Institute of Technology Center for Computational Relativity and Gravitation

Triple quasar (10.8 Gly) S. G. Djorgovski et al., Caltech, EPFL (Jan. 2007)

ly m

m m

L m

L  1   ( 10

) /( 10

)  10

 1

 

km m

m m

L m

L  10

  ( 10

) /( 10

)  10

 10



Interferometric detectors: an international dream

GEO600 (British-German) Hanover, Germany

LIGO (USA)

Hanford, WA and Livingston, LA

TAMA300 (Japan) Mitaka

VIRGO (French-Italian) Cascina, Italy

AIGO (Australia),

Wallingup Plain, 85km north of Perth

Virgo: science case



First (?) direct observation of gravity waves



Better understanding of gravity

– GW produced 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??



Pushing interferometer techniques to their limits

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

Beam splitter LASER

Light Detection

Virgo: CNRS+INFN

(

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

+ NIKHEF joined 2007

First science run: May – September 2007

Interferometer Concept

As a wave passes, the arm lengths

change in different

ways….

…causing the interference pattern

to change at the

photodiode Suspended

Masses

Laser 20 W

Input Mode Cleaner (144 m)

Power Recycling

3 km long Fabry-Perot Cavities

Output Mode Cleaner (4 cm)

Input mode cleaner

 Mode cleaner cavity: filters

laser noise, select TEM00

mode

Installation in IMC end tower

Each switch has been tested in open and closed position.

The mirror and RM are moved 55 mm for- and backwards.

Eric Hennes

Nikhef: redesign and replace dihedron

Optronica Marinebedrijf Den Helder

Zorg dat je erbij komt…

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

+ Han Voet

Linear alignment setup

 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

–

CPU issues

GW source: pulsars

 

 



 



 



 



 



 



 



 



2

2 45

27

10 200

10 10 10

3 

Hz f cm

g I r

h kpc

f (Hz) N

LIGO: <10% of energy in GW

Crab pulsar

Periodic Sources – all sky search – Roma / NIKHEF

• Doppler shifts

• Frequency modulation: due to Earth’s motion

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

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

• Note the daily variations

• After FFT: energy not in a single bin, so the SNR is highly reduced

• Bin in galactic coordinates

• Re-sampling

• Short FFTs

• Hough maps

ALL SKY SEARCH

enormous computing challenge

(Sipho van der Putten, Henk Jan Bulten, Sander Klous)

GWs from binaries

 Frequency changes a lot due to Doppler: df/f~10

Hulse-Taylor:

_

Towards Detector

V 

Grid-based analysis

Extension of LIGO – Virgo CW analysis

Calibration systems for LISA

Virgo sensitivity compared to LIGO and GEO600

May 2

Inspiral range 6.5 Mpc

The horizon (best orientation) for a binary system

of two 10 solar mass black holes is 63 Mpc

Discovery potential first event

 Hypothesis:

–

Finesse = 150 (now : 50)

–

Same losses & power recycling as today

 Horizon (Virgo+)

–

BNS: 150 Mpc (optimal orientation)

–

BBH: 750 Mpc (optimal orientation)

 BNS Rates: (most likely and 95% interval)

–

Initial Virgo (30Mpc) 1/100yr (1/500 -1/25 yr)

–

Enhanced LIGO (60Mpc) 1/10yr (1/50- 1/2.5yr)

–

Virgo+ limit (150Mpc) 1.2/yr (1/4yr-5/yr)

–

Advanced detectors (350Mpc) 40/yr (8-160/yr)

Kalogera et al; astro-ph/0312101; Model 6

 BBH and other sources rates are more difficult to predict

LIGO and VIRGO: scientific evolution

 At present hundreds of galaxies in range for 1.4 M

NS-NS binaries

 Enhanced program

–

In 2009 about 10 times more galaxies in range

 Advanced detectors

–

About 1000 times more galaxies in range

–

In 2014 expect 1 signal per day or week

–

Start of gravitational astrophysics

–

Numerical relativity will

provide templates for

interpreting signals

Advanced Virgo: vacuum – cryo links

6885 985

Gas load from mirror 10^-4 mbar l/s

mbar

Element number Start pressure

Intermediate Final pressure Pressure

LN2 GN2

Beam vacuum Isolation vacuum

LN2 Fixed 300 K

3.2 mm/m

3.2 mm/m

Reinforce rib

Forces

Vacuum + super isolation Tie rod

Advanced Virgo: vacuum – cryo links

Advanced Virgo: superattenuator

FEA:

Frans Mul

Corijn

Other activities in GW program

 Einstein Telescope – conceptual design study

–

Approved in May 2008

–

Funded for 3 years

–

Nikhef responsible for Working Group 1 on site selection

Design Study Proposal approved by EU within FP7

Large part of the European GW community involved EGO, INFN, MPI, CNRS, NIKHEF, Univ. Birmingham, Cardiff, Glasgow

28

GRB050509B

3^RD GENERATION INTERFEROMETER

2^ND

GENERATION 1^ST GENERATION

Credit G.Cagnoli

NS - NS INSPIRAL RANGE

Virgo

LOI to ESA – LISA analysis Nikhef, VU, RUN and SRON

Netherlands: Bulten/Nelemans

Beyond Einstein is the umbrella program for a series of

NASA/ESA missions linked by powerful new technologies and common science goals to answer the questions:

Gravitational Waves Can Escape from Earliest Moments of the Big

Bang

Inflation

(Big Bang plus 10^-34 Seconds)

Big Bang plus 300,000 Years

gravitational waves

Big Bang plus 14 Billion Years

light

Now

What powered the Big Bang?

Is Einstein’s theory still right in these conditions of

extreme gravity? Or is new physics awaiting us?

Chandra - Each point of x-ray light is a Black Hole!

What happens at the edge of a Black Hole?

Dark energy and matter interact through gravity

We do not know what 95%

of the universe is made of!

What is the mysterious Dark Energy pulling the Universe apart?

September 6, 2007: Committee on NASA's Einstein Program: An Architecture for Implementation, National Research Council

Finding 4. LISA is an extraordinarily original and technically bold mission concept. LISA will open up an entirely new way of observing the universe, with immense potential to enlarge our understanding of physics and astronomy in unforeseen ways.

LISA, in the committee’s view, should be the flagship mission of a long-term program addressing Beyond Einstein goals.

Finding 8. The present NASA Beyond Einstein funding wedge alone is inadequate to develop any candidate Beyond Einstein mission on its nominal schedule. However, both JDEM and LISA could be carried out with the currently forecasted NASA

contribution if DOE's contribution that benefits JDEM is taken into account and if LISA's development schedule is extended and funding from ESA is assumed.

Summary

 Gravitational wave physics

–

Component of our Astroparticle Physics initiative

–

Exciting new physics program

– Important questions are addressed

– Program with a long-term scientific perspective

 VIRGO

–

Sensitivity is improving fast

–

First science run underway

–

Data sharing and analysis between LIGO and Virgo

 NIKHEF commitment

–

Modest at this moment

–

Expand to FOM research program in 2009 / 2010