dipartimento the detection of gravitational waves universe ... · the ligo observatories ! adapted...

U

niverse observation through

gravitational waves

the detection of gravitational w

aves.

Fulvio Ricci

Dipartim

ento di Fisica, Università di Rom

a Sapienza

&

INFN

Sezione di Roma

Plan of the talk

1. GW

research motivations

2. Sources 3. Principles of interferom

etric detection 4. W

hat is Virgo 5. LIG

O-Virgo joint observation

6. The discovery 7. 

The start of the GW

astronomy

1. GW

research motivations

2. Sources 3. Principles of interferom

etric detection 4. W

hat is Virgo 5. LIG

O-Virgo joint observation

6. The discovery 7. 

The start of the GW

astronomy

! 

Linearized Einstein eqs. (far from big m

asses) admit w

ave solutions (perturbations to the background geom

etry)

! 

GW

: transverse space-time distortions

propagating at the speed of light,

2 independent polarization

! 

Dynam

ical part of gravity, filling the space

Ripples in the C

osmic S

ea

01

1 w

ith 2 2

22

=! !" #

$ $% &

∂ ∂−

∇⇒

<<+

=µν

µνη

ht

ch

hg

! ! ! ! !" #

$ $ $ $ $% &

−=

+×

×+

−

00

00

00

00

00

00

),

()

(

hh

hh

etz

kzt

iω

h

TG

4

8c Gπ=

Coupling constants

! 

In SN collapse ν w

ithstand 103 interactions before leaving the star,

GW

leave the core undisturbed

! 

Decoupling after Big Bang

– GW

∼ 10-43 s (T ∼ 10

19 GeV)

–  ν ∼ 1 s (T ∼ 1 MeV)

– e.m. ∼ 10

12 s (T ∼ 0.2 eV)

strong e.m

. weak

gravity

0.1 1/137

10-5

10-39

Ideal information carrier,

Universe transparent to G

W all the w

ay back to the Big B

ang!!

GGWW

eemmiissssiioonn:: vveerryy eenneerrggeettiicc eevveennttss bbuutt aallmm

oosstt nnoo iinntteerraaccttiioonn

! 

Luminosity:

! 

Amplitude:

Target G

W am

plitude

42

1

Gh

Qc

rµν

µν=

⋅!!

62

5

55

!" #$% &

!" #$% &

⋅>≈

<=

c vR R

G cQ

Qc G

PS

ijij

ε!!!

!!!Com

pactness C 1 for BH

0.3 for N

S 10

-4 for WD

1059 erg/s

h ~ 10

-21

Target am

plitu

de:

coalescing NS/N

S in the Virgo cluster (r ~10 M

pc)

Efficient sources of GW

must be

compact

and fast

GW

detectors are sensitive to aplitude h : 1/r attenuation!

Plan of the talk

1. GW

research motivations

2.  Sources 3. Principles of interferom

etric detection 4. W

hat is Virgo 5. LIG

O-Virgo joint observation

6. The discovery 7. 

The start of the GW

astronomy

The

The G

ravitational Wave S

pectrum

CB

C

! 

Compact stars (N

S/NS, N

S/BH, BH

/BH)

! 

Inspiral signal accurately predictable

– New

tonian dynamics

– Post-New

tonian corrections (3PN, (v/

c) 11/2) [L.Blanchet et al., 1996] ! 

Recent big progress in merger 3D

sim

ulation [Baker et al 2006, Praetorious 2006]

chirp

[Cam

panelli et al., PR

L, 2006]

Supernovae

! 

Collapse dynamics and w

aveform badly predictable

! 

Estimated rate: several /yr in the VIRG

O cluster, but the efficiency of G

W

emission is strongly m

odel dependent

! 

Simulations suggest E

GW ~

10-6 M

ʘ c2, but N

S kick velocities suggest possible strong asym

metries

GW

emitted

secs

hrs

[Zw

erger, Muller]

More on neutron stars

Relic S

tochastic Background

! 

Imprinting of the early expansion of the universe

! 

Correlation of two interferom

eters needed for detection

Relic neutrinos

CM

BR

R

elic gravitons

Plan of the talk

1. GW

research motivations

2. Sources 3. Principles of interferom

etric detection 4. W

hat is Virgo 5. LIG

O-Virgo joint observation

6. The discovery 7. 

The start of the GW

astronomy

Detection

Need to m

easure: ΔL ~

10-18 m

Target h ~

10-21

(NS

/NS

@V

irgo Cluster)

Great challenge for experim

entalists!

Feasible L ~

103 m

12L

hLΔ

≈

GW

induce space-time

deformation

Measure space-tim

e

Strain using light

Interference fringes

Pout depends also on P

in , λ, L.

ITF sensitive to power and frequency fluctuations, displacem

ent noises, …

4gw

Lh

πφ

λ=

⋅

20

cos(

)out

ingw

PP

φφ

=+

A sim

ple detector

Increasing the optical path

Effe

ctive le

ngth

:

! 

Fabry-Pe

rot cav

ities: am

plify the length-to-phase transduction

! 

High

er fin

esse ="

higher df/dL ! 

Draw

back: works only at

resonance

2'

FL

Lπ

=⋅

! 

Power fluctuations lim

it the phase sensitivity. Ultim

ate power

fluctuations associated to the quantum nature of light

! 

Shot noise (assuming P,λ stable):

! 

L = 100 km, P = 1 kW

!

Lengthen the detector to 100 km.

Increase the light power m

ore than 1 kW.

HO

W?

Optical R

eadout Noise

23

21

310

/H

z

10shot

shot

hh

−

−

≈⋅

≈

!

21

shotshot

ch

PL

Pω

λφ

π=

⇒=

⋅!

!"

"

kWatts pow

er injected!

Interferometer Ecology: recycle the w

asted light!

! 

Peff = Recycling factor ·P

in " 50 x 20 W

= 1 kW

! 

Shot noise reduced by a factor ~ 7

! 

One m

ore cavity to be controlled !

A real detector schem

e

Laser 20 W

Output M

ode Cleaner

3 km long Fabry-Perot cavities:

to lengthen the optical path to 100 km

Input Mode C

leaner

Power recycling m

irror: to increase the light pow

er to 1 kW

Virgo optical schem

e

Free falling test m

asses

ITF

Operation C

onditions

! 

Keep the FP cavities in resonance – M

aximize the phase response

! 

Keep the PR cavity in resonance – M

inimize the shot noise

! 

Keep the output on the dark fringe

– R

educe the dependence on power

fluctuations

Keep the armlength constant w

ithin 10

-12 m !

ACTIVE CO

NTRO

LS NEED

ED!

L OCKING

Interferometer control

Plan of the talk

1. GW

research motivations

2. Sources 3. Principles of interferom

etric detection 4. W

hat is Virgo

5. LIGO

-Virgo joint observation 6. The discovery 7. 

The start of the GW

astronomy

25

! Participated by scientists from

Italy and France (form

er founders of Virgo), The N

etherlands, Poland, Hungary and Spain

THE

VIR

GO

C

OLLA

BO

RATIO

N:

6 European countries

20 labs A

PC

Paris

AR

TEM

IS N

ice E

GO

Cascina

INFN

Firenze-Urbino

INFN

Genova

INFN

Napoli

INFN

Perugia

INFN

Pisa

INFN

Rom

a La Sapienza

INFN

Rom

a Tor Vergata IN

FN Trento-P

adova LA

L Orsay – E

SP

CI P

aris LA

PP A

nnecy LK

B P

aris LM

A Lyon N

IKH

EF A

msterdam

P

OLG

RAW

(Poland)

RA

DB

OU

D U

ni. Nijm

egen R

MK

I Budapest

VALE

NC

IA University

.

Total num

ber 350 mem

bers 68%

Physicists and E

ngineers 16%

Consultants

16% P

hD S

tudents

Ad V

irgo in a nutshell

heavier'mirrors'

(42'kg)'

high'finesse''(≈1000)'larger'beam

'waist'

DC'detec>on'

signal'recycling'

new'IP'

>lt'control'

new'payload'

fused'silica'suspensions'

high'power'SSL'

(200'W)'

Larger central vacuum links

Large cryotraps

28

29

The adV m

irrors

Substrate: SiO2

Mirror: 42 kg, 35 cm

diameter, 20 cm

thick

Beam

Splitter: 50 cm

diameter, 10 cm

thick

Hom

ogenity < 5 x 10-7

Surface uniform

ity< 1 10 -9 m EG

O C

ou

ncil, D

ec 11, 2015

G L

osu

rdo

- Ad

V P

roject L

eader

17

30 T

he payload

The central area

31

Seismic noise attenuation

The vacuum to reduce

the diffusion of the light

Electronic control of the

super attenuator

Superattenuator

Sensors Coil

Drivers

Motors

Sensors

Sensors

Coil

Drivers

Coil

Drivers

Position &

D

ampin

g

Acc. Sens: - 10

-9 m/s 2

-  0 – 100Hz

-  f.s. 1g D

rivers

Plan of the T

alk

1. GW

research motivations

2. Sources 3. Principles of interferom

etric detection 4. W

hat is Virgo 5. LIG

O-V

irgo joint observation 6. The discovery 7. 

The start of the GW

astronomy

The “single m

achine”

MO

U to be signed betw

een LIGO

Scientific Collaboration and Virgo: – Full exchange of data, joint analysis – Coordinate science runs, com

missioning and shutdow

ns – Joint publications

4 detectors to operate as a SSIINN

GGLLEE

MMAA

CCHH

IINNEE

G

reat scientific value added

Triangulation allows to

pin

poin

t the so

urce

The network allow

s to deconvolve detector response and signal w

aveform #

measu

re

signal p

aramete

rs

The benefits of a netw

ork

False alarm

reje

ction

requires coincidence

Longer obse

rvation tim

e, better sk

y cove

rage

The LIG

O O

bservatories

! Adapted from

“The Blue Marble: Land Surface, O

cean Color and Sea Ice” at visibleearth.nasa.gov ! N

ASA Goddard Space Flight Center Im

age by Reto Stöckli (land surface, shallow w

ater, clouds). Enhancements by Robert Sim

mon (ocean color, com

positing, 3D globes, anim

ation). Data

and technical support: MO

DIS Land G

roup; MO

DIS Science D

ata Support Team; M

OD

IS Atmosphere G

roup; MO

DIS O

cean Group Additional data: U

SGS ERO

S Data Center (topography); U

SGS

Terrestrial Remote Sensing Flagstaff Field Center (Antarctica); D

efense Meteorological Satellite Program

(city lights).

LIGO

Hanford O

bservatory (LHO

) H

1 : 4 km arm

s H

2 : 2 km arm

s

LIGO

Livingston Observatory (LLO

) L1 : 4 km

arms

Credit: P.Shaw

an

Plan of the talk

1. GW

research motivations

2. Sources 3. Principles of interferom

etric detection 4. W

hat is Virgo 5. LIG

O-Virgo joint observation

6. The discovery 7. 

The start of the GW

astronomy

H1- H

anford – Washington state

L1- Livingston – Louisiana state

LIGO

upgrade

concluded

The A

dvanced LIGO

dedication cerem

ony w

as held at Hanford on

May 19, 2015

VIR

GO

will end

the upgrade in 2016

strain amplitude evolution in tim

e and frequency

Residual noise after w

aveform

subtraction

35 – 350 Hz bandpassed strain tim

e series

C

ombined S

NR

= 23.6 , F

AR

= 1/203,000 years "

5.1 σ

Param

eter Estim

ation

One of the m

ost energetic astronomical event ever

observed: P

ower em

itted ~~ 220000 MM

//ss E

nergy emitted ~

11004499 JJ ""

33 MM cc

22

50 times brighter of the entire visible universe

How

the signal might look like

This source:

Binary system

Produces this waveform

:

Embedded in this noise

stream:

matched filtering or excess

power

h

Tim

e to coalescence (sec)

Signal (t)SNR

(t)

Assum

ing that the signal is C

BC

like: m

atched filter search

Com

pact Binary C

oalescence: W

aveforms

m1 =

m2 =

10 M

s1,z =

s2,z =

0.99 s1,z =

0.99, s2,z =

-0.99 s

1,z = s

2,z = -0.99

GW

150914 "

Signal/Noise =24

GW

151226 "

Signal/Noise = 13

+

LVT

151012 "Signal/N

oise =9.7

While w

e are not so confident to tag this as a detection, it is m

ore likely to be a gravitational w

ave signal than not

GW151226'

GW150914''''''''

LVT'151012'

Final m

ass 62 times that of the sun

Final m

ass 35 times that of the sun

Final m

ass 21 times that of the sun

Plan of the talk

1. GW

research motivations

2. Sources 3. Principles of interferom

etric detection 4. W

hat is Virgo 5. LIG

O-Virgo joint observation

6. The discovery 7.  The start of the G

W astronom

y

Sky Locations of G

ravitational-wave E

vents G

W150914, G

W151226 and C

andidate LVT

151012

Sky localizations

90% credible areas of about

620 deg

2 GW

150914

1600 deg2 LV

T15012

1000 deg

2 GW

151226

Sim

ulated Sky Locations of O

1 Events and

Candidate Including the V

irgo Interferometer

Sky localizations

90% credible areas of about

10-20 deg

2 GW

150914

1000 deg2 LV

T15012

600 deg

2 GW

151226

LIGO

Livingston

US

A

LIGO

H

anford U

SA

Virgo

Italy

KA

GR

A

Japan

Source Localization of the N

etwork

Credit: S. Fairhurst

How

to improve the

sensitivity W

here and how can w

e reduce further the detector noise?

Seismic

Thermal

Shot H

igh power laser

Better optics

New

optical configuration

QN

D techniques

New

materials

Cryogenic interferometers

Underground detectors

56 Lecce -2013 – F

ulvio R

icci

Conclusion

GW

will help to go beyond E

instein by testing of com

peting theories of gravity

GW

will probe the status of the m

atter in the extreme condition

Deviation from

the prediction of the classical physics can be the clue of a super unification phenom

enon

GW

, predicted by A. E

instein 100 years ago, have been detected directly for the first tim

e

GW