gravitational waves: how are they different?

Gravitational Waves (Working group 6)

resonant mass detectors:Visco

current generation terrestrial interferometers: Frolov, Brady

next generation terrestrial interferometers:Adhikari, Owen

“science fiction” terrestrial interferometers: Mavalvala

Bruce Allen, UWM

8/31/06 WG6 summary, TEV II 2

Gravitational waves:How are they different?

Gravitational wavesGravitational waves• Couple to mass 4-current

• Produced by coherent motions of high density or curvature

• Wavelengths > source size, like sound waves (no pictures)

• Propagate through everything, so you see dense centers

Electromagnetic wavesElectromagnetic waves• Couple to electric 4-current

• Incoherent superposition of many microscopic emitters

• Wavelengths source size, can make pictures

• Stopped by matter, so “beauty is skin deep”

8/31/06 WG6 summary, TEV II 3

Science Goals• Direct verification of two dramatic predictions of Einstein’s

general relativity: gravitational waves & black holes

• Physics & Astronomy– Detailed tests of properties of gravitational waves including

speed, polarization, graviton mass, .....

– Probe strong field gravity near black holes & in early universe

– Probe the neutron star equation of state

– Performing routine astronomical observations

• A new window on the Universe

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• Compact binary inspiral: “chirp”

• Supernovae / Mergers: “burst”

• Spinning NS: “continuous”

• Cosmic Background: “stochastic”

GW Sources 50-1000 Hz

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Present performance of resonant mass detectors

Massimo Visco

INAF –IFSI Roma INFN – Sez. Roma Tor Vergata

International Gravitational Events Collaboration

ALLEGRO– AURIGA – ROG (EXPLORER-NAUTILUS)

• The “oldest” resonant detector EXPLORER started operations about 16 years ago.

• This kind of detector has reached a high level of realibilty.

• The duty factor is greater than 90% .

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A DIRECTIONAL 4-ANTENNAE A DIRECTIONAL 4-ANTENNAE OBSERVATORY OBSERVATORY

• The four antennas are sensitive to the same region of the sky

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SENSITIVITY OF PRESENT DETECTORSSENSITIVITY OF PRESENT DETECTORS

8/31/06 WG6 summary, TEV II 9

TRIPLE COINCIDENCE DISTRIBUTION TRIPLE COINCIDENCE DISTRIBUTION AU-EX-NA (PRELIMINARY)AU-EX-NA (PRELIMINARY)

NO DETECTIONSNO DETECTIONS

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2012 - 2018 NETWORK2012 - 2018 NETWORK

- slide from INFN roadmap

8/31/06 WG6 summary, TEV II 11

Status of LIGO

Valera Frolov

LIGO Lab

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LIGO Observatories

Livingston, LA (L1 4km)

Hanford, WA (H1 4km, H2 2km)- Interferometers are aligned to be as close to parallel to each other as possible

- Observing signals in coincidence increases the detection confidence

- Determine source location on the sky, propagation speed and polarization of the gravity wave

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Time Line

NowInauguration

1999 2000 2001 2002 20033 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4

First Lock Full Lock all IFO

10-17 10-18 10-20 10-21

2004 20051 2 3 4 1 2 3 4 1 2 3 4

2006

First Science Data

S1 S4Science

S2 RunsS3 S5

10-224K strain noise at 150 Hz [Hz-1/2]

2006

HEPI at LLO

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NS-NS Inspiral Range Improvement

Time progression since the start of S5

Design Goal

Commissioningbreaks

Stuck ITMY opticat LLO

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Triple Coincidence Accumulation

100%

~ 45%

~ 61%

Expect to collect one year of triple coincidence data by summer-fall 2007

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LIGO Observational Results

Patrick Brady

U. Wisconsin - Milwaukee

8/31/06 WG6 summary, TEV II 17

Bursts

• Supernovae: Neutron star birth, tumbling and/or convection

• Cosmic strings, black hole mergers, .....

• Coincident EM observations• Surprises!

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Detection Efficiency• Evaluate efficiency by adding simulated GW bursts

to the data.– Example waveform

Central

Frequency

De

tec

tio

n E

ffic

ien

cy

S4

● S5 sensitivity: minimum detectable in band energy in GW

– EGW

> 1 M⊙ @ 75 Mpc

– EGW

> 0.05 M⊙ @ 15 Mpc (Virgo cluster)

8/31/06 WG6 summary, TEV II 19

S2

S1

S4 projected

Excluded 90% CL

S5 projected

Ra

te L

imit

(e

ve

nts

/da

y)

Upper Limits• No GW bursts detected

through S4 – set limit on rate vs signal

strength.

Lower amplitude limits

from lower detector

noise

Lower rate

limits from

longer

observation

times

8/31/06 WG6 summary, TEV II 20

Stochastic Background• Big bang & early universe• Background of gravitational

wave bursts• Unresolved background of

contemporary sources

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

WMAP

8/31/06 WG6 summary, TEV II 21-16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8

-14

-12

-10

-8

-6

-4

-2

0

Log (f [Hz])

Lo

g(

0)

-18 10

Inflation

Slow-roll

Cosmic strings

Pre-big bang

model EW or SUSY

Phase transition

Cyclic model

CMB

Pulsar

Timing

BB Nucleo-

synthesis

Initial LIGO, 1 yr data

Expected Sensitivity

~ 4x10-6

Advanced LIGO, 1 yr data

Expected Sensitivity

~ 1x10-9

LIGO S1: Ω0 < 44

PRD 69 122004 (2004)

LIGO S3: Ω0 < 8.4x10-4

PRL 95 221101 (2005)

Predictions and Limits

H0 = 72 km/s/Mpc

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– Black holes & neutron stars– Inspiral and merger– Probe internal structure,

populations, & spacetime geometry

Compact Binaries

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S5 Search

Image: R. Powell

binary black hole

horizon distance

• 3 months of S5 analyzed

• Horizon distance versus mass for BBHAverage over run

130Mpc

1 sigma variation

binary neutron star

horizon distance

8/31/06 WG6 summary, TEV II 24

• Spinning neutron stars– Isolated neutron stars with

mountains or wobbles– Low-mass x-ray binaries– Probe internal structure and

populations

Astrophysical sources of gravitational waves

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Known pulsarsS5 preliminary

• 32 known isolated, 44 in binaries, 30 in globular clusters

Lowest ellipticity upper limit:

PSR J2124-3358

(fgw = 405.6Hz, r = 0.25kpc)

ellipticity = 4.0x10-7

Frequency (Hz)

Gra

vita

tiona

l-wav

e am

plitu

de

~2x10-25

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Einstein@Home• Public distributed

computing project• All-sky, all-frequency

search is computationally limited

To participate, sign up at

http://www.physics2005.org

● S3 results:– No evidence of pulsars

● S4 search– Post-processing underway

8/31/06 WG6 summary, TEV II 27

Next Generation Interferometers

Rana Adhikari

Caltech

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The next several years

Between now and AdvLIGO, there is some time to improve…1)~Few years of hardware improvements + 1 ½ year of observations. Factor of ~2.5 in noise, factor of ~10 in event rate.1)3-6 interferometers running in coincidence !

S5 S6

4Q‘05

4Q‘06

4Q‘07

4Q‘08

4Q‘10

4Q‘09

Adv

LIGO~2 years

8/31/06 WG6 summary, TEV II 29

Increased Power + Enhanced ReadoutLower Thermal

Noise Estimate

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180 W LASER,MODULATION SYSTEM

40 KG FUSED SILICA TEST

MASSES

PRM Power Recycling MirrorBS Beam SplitterITM Input Test MassETM End Test MassSRM Signal Recycling MirrorPD Photodiode

Advanced LIGO Design Features

ACTIVE SEISMIC

ISOLATION

FUSED SILICA, MULTIPLE

PENDULUM SUSPENSION

8/31/06 WG6 summary, TEV II 31

Advanced LIGO

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What can gravitational waves tell us about neutron stars?

Ben Owen

PSU

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Periodic signals:Pulsar emission mechanism

• Pulse profiles in different EM bands illuminate mechanism

• Profiles show (phase) timing noise, mostly in young pulsars

• GW won’t show interesting pulse profiles (only lowest harmonic detectable)

• Will be able to test if GW signal has timing noise or not

• Tells us how magnetosphere is coupled to dense interior (Does B-field structure go all the way in? Just crust? …)

8/31/06 WG6 summary, TEV II 34

Periodic signals:How solid is a neutron star?

• NS definitely have (thin) solid crust (known from pulsar glitches)

• Normal nuclear crusts can only produce ellipticity < few 10-7

• If “?” is solid quark matter, whole star could be solid, < few 10-4

• If “?” is quark-baryon mixture or meson condensate, half of core could be solid, < 10-5

• High ellipticity measurement means exotic state of matter

• Low ellipticity is inconclusive: strain, buried B-field…

8/31/06 WG6 summary, TEV II 35

Burst signals:Supernova core collapse

• Burst from collapse and bounce

• Poorly modeled: different groups predict different waveforms, agree that there is no supernova explosion….

• Long GRBs: knowing time & location helps GW searches

• GRB/GW/neutrino relative delays could shed light on explosion mechanism

• If GW & signals are both short, result is a black hole

8/31/06 WG6 summary, TEV II 36

Path to sub-quantum-noise limited gravitational wave

interferometers

Nergis Mavalvala

MIT

8/31/06 WG6 summary, TEV II 37

Optical Noise• Shot Noise

– Uncertainty in number of photons detected

– Higher circulating power Pbs low optical losses

– Frequency dependence light (GW signal) storage time in the interferometer

• Radiation Pressure Noise– Photons impart momentum to cavity mirrors

Fluctuations in number of photons – Lower power, Pbs

– Frequency dependence response of mass to forces

1( )

bs

h fP

∝

2 4( ) bsPh f

M f∝Optimal input power depends

on frequency

8/31/06 WG6 summary, TEV II 38

A Quantum Limited Interferometer

LIGO I

Ad LIGO

Seism

ic

Suspension

thermal

Test mass thermal

QuantumInput laser power > 100 W

Circulating power > 0.5 MW

Mirror mass40 kg

8/31/06 WG6 summary, TEV II 39

Squeezed input vacuum state in Michelson Interferometer

X+

X

X+

XX+

X

X+

X

• Consider GW signal in the phase quadrature– Not true for all

interferometer configurations

– Detuned signal recycled interferometer GW signal in both quadratures

• Orient squeezed state to reduce noise in phase quadrature

Laser

8/31/06 WG6 summary, TEV II 40

Squeezed vacuum states for GW detectors

• Requirements – Squeezing at low frequencies (within GW band)– Frequency-dependent squeeze angle– Increased levels of squeezing– Long-term stable operation

• Generation methods – Non-linear optical media ((2) and (3) non-linearites)

crystal-based squeezing– Radiation pressure effects in interferometers

ponderomotive squeezing

8/31/06 WG6 summary, TEV II 41

Squeezed Vacuum

8/31/06 WG6 summary, TEV II 42

Noise budget

8/31/06 WG6 summary, TEV II 43

Conclusions• Resonant bar detectors are operating in a stable mode but at low

sensitivity compared with…• LIGO is currently carrying out a science run at design sensitivity.• Searches for all major categories of sources are underway and will

at least set upper limits.• Detections are possible!• Enhancements in ~ 3 years will increase the reach by a factor of 3• An upgrade (Advanced LIGO) is planned early next decade• Detections are ‘guaranteed’• Quantum non-demolition techniques needed to beat quantum limits

(squeezed light)