Probing the Dark Side of the Universe with Gravitational...

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Probing the Dark Side of the Universe with Gravitational Waves

Martin Hendry

Astronomy and Astrophysics Group and Institute for Gravitational ResearchSUPA, Dept of Physics and Astronomy, University of Glasgow, UK

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Outline of talk

• Introduction: what are gravitational waves?

• Astrophysical motivation: possible sources and overview of science case

• GW detection: general principles; noise limitations; and current status (ground-based)

• The advent of GW astronomy: some examples

• Coming attractions (next 5 years) and future developments (next 20 years)

• Case study: cosmology with GW sources

Cambridge, Jan 2010

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Who am I?…

Jim Hough and Ron Drever, 1978

Institute for Gravitational ResearchInstitute for Gravitational Research~50 research staff and students, with activity spanning advanced materials, optics and interferometry, data analysis, for ground-and space-based GW detectors.

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Who am I?…

William Thompson(Lord Kelvin)1824 - 1907

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Who am I?…

“There is nothing new to be discovered in physics now.

All that remains is more and more precise measurement”(1900)

William Thompson(Lord Kelvin)1824 - 1907

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µνµν κTG =

Spacetimecurvature

Matter (and energy)

Gravity in EinsteinGravity in Einstein’’s Universes Universe“The greatest feat of human thinking about nature, the most amazing combination of philosophical penetration, physical intuition and mathematical skill.” Max Born

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Spacetime tells matter how to move, and matter tells spacetimehow to curve

Gravity in EinsteinGravity in Einstein’’s Universes Universe

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Gravitational WavesProduced by violent acceleration of mass in:

neutron star binary coalescencesblack hole formation and interactionscosmic string vibrations in the early universe (?)

and in less violent events:pulsarsbinary stars

Gravitational waves‘ripples in the curvature of spacetime’that carry information about changing gravitational fields – or fluctuating strains in space of amplitude h where:

LLh ∆

=2

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PulsedCompact Binary Coalescences: NS/NS; NS/BH; BH/BHStellar Collapse (asymmetric) to NS or BH

Continuous WavePulsarsLow mass X-ray binaries (e.g. SCO X1)Modes and Instabilities of Neutron Stars

StochasticInflationCosmic Strings

Gravitational Waves: possible sources

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Science goals of the gravitational wave field

Fundamental physics and GR• What are the properties of gravitational waves?• Is general relativity the correct theory of gravity?• Is GR still valid under strong-gravity conditions?• Are Nature’s black holes the black holes of GR?• How does matter behave under extremes of

density and pressure?

Cosmology• What is the history of the accelerating

expansion of the Universe?• Were there phase transitions in the early

Universe?

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Astronomy and astrophysics• How abundant are stellar-mass black holes?• What is the central engine that powers GRBs?• Do intermediate mass black holes exist?• Where and when do massive black holes form

and how are they connected to galaxy formation?• What happens when a massive star collapses?• Do spinning neutron stars emit gravitational waves?• What is the distribution of white dwarf and

neutron star binaries in the galaxy?• How massive can a neutron star be?• What makes a pulsar glitch?• What causes intense flashes of X- and gamma-

ray radiation in magnetars?• What is the star formation history of the Universe?

Science goals of the gravitational wave field

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“Indirect” detection from orbital decay of binary pulsar: Hulse & Taylor

PSR 1913+16

Evidence for gravitational waves

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How can we detect them?Gravitational wave amplitude h ~

LL∆

L + ∆L

LSensing the induced excitations of a large bar is one way to measure this

Field originated with J. Weber looking for the effect of strainsin space on aluminium bars at room temperature

Claim of coincident events between detectors at Argonne Lab and Maryland – subsequently shown to be false

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How can we detect them?

Jim Hough andRon Drever, March 1978

L + ∆L

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32 yrs on - Interferometric ground-based detectors

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laserBeam splitter

Mirror

Observer

It’s all done with mirrors…

Michelson Interferometer

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laser

CONSTRUCTIVE(BRIGHT)

+

DESTRUCTIVE(DARK)

+

path 2

path

1

Michelson Interferometer

It’s all done with mirrors…

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Detecting gravitational waves

GW produces quadrupolar distortion of a ring of test particles

h =2∆L

LDimensionless strain Expect movements of

less than 10-18 m over 4km

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Principal limitations to sensitivity – ground based detectors

Photon shot noise (improves with increasing laser power) and

radiation pressure (becomes worse with increasing laser power)There is an optimum light power which gives the same limitation expected by application of the Heisenberg Uncertainty Principle –the ‘Standard Quantum limit’

Seismic noise (relatively easy to isolate against – use suspended test masses)

Gravitational gradient noise, - particularly important at frequencies below ~10 Hz

Thermal noise – (Brownian motion of test masses and suspensions)

• All point to long arm lengths being desirableLIGO 4km; Virgo 3km; GEO 600m, TAMA 300m

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Ground based Detector Network – audio frequency range

GEO600TAMA, CLIO

LIGO Livingston

LIGO Hanford

4 km2 km

600 m300 m100 m

P. Shawhan, LIGO-G0900080-v1

4 km

VIRGO 3 kmLIGO Livingston

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Sources – the gravitational wave spectrum

Gravity gradient wall

ADVANCED GROUND - BASED DETECTORS

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• After first studies in 1980s, M3 proposal for 4 S/C ESA/NASA collaborative mission

in 1993

• LISA selected as ESA Cornerstone in 1995

• 3 S/C NASA/ESA LISA appears in 1997

• Baseline concept unchanged ever since!

LISA – a joint ESA/NASA Mission to study Black hole physics, and much more, in the frequency range 10-4 Hz -10-1 Hz

LISA: Laser Interferometric Space Antenna

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28Pulsar Timing: nano-Hz search for stochastic background and super-massive black hole coalescences

Australia

Multi-country

Full data sharingNorth America

Courtesy G. Hobbs

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• Gravitational waves distort spacetime as they propagate.

• A periodic gravitational wave passing across the line of sight to a pulsar will produce a periodic variation in the time of arrival (TOA) of pulses.

If the strain along the line-of-sight is h, then the fractional change in the pulse arrival rate due to the gravitational wave just depends on the strain at emission and reception.

Pulsar timing arrays as a probe of GWs

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Real progress in GW astronomy over past few years

Operation of six ground based interferometers (in addition to three cryogenic bar detectors)

Advances in waveform predictions from Numerical Relativity

Significant advances in Space Borne Detectors – LISA and DECIGO

Pulsar Timing coming to the fore

Importance of Multi-messengerAstronomy

Using wider interest in relativity, cosmology and fundamental physics to bring science to schools and the public.

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Current Status 1 -LIGO now at design sensitivity

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Current status 2: the advent of GW astronomy

Initial Science Runs Complete (LIGO, Virgo, GEO 600, TAMA)

Upper Limits set on a range of sources (no detections as yet)

Credit: AEI, CCT, LSU

Coalescing Binary Systems• Neutron stars, low mass black holes, and NS/BS systems

Credit: Chandra X-ray Observatory

‘Bursts’• galactic asymmetric core collapse supernovae• cosmic strings• ???

NASA/WMAP Science Team

Cosmic GW background

• stochastic, incoherent background

• unlikely to detect, but can bound in the 10-10000 Hz range Casey Reed, Penn State

Continuous Sources• Spinning neutron stars

• probe crustal deformations, ‘quarki-ness’

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• Remnant from supernova in year 1054

• Spin frequency νEM = 29.8 Hz

νgw = 2 νEM = 59.6 Hz

• observed luminosity of the Crab nebula

accounts for < 1/2 spin down power

• spin down due to:

• electromagnetic braking

• particle acceleration

• GW emission?

• LIGO S5 result: h < 3.9 x 10-25 GW amplitude ~ 4X below spin down limit• Upper limit on the ellipticity: ε < 2.1 x 10-4

• GW energy upper limit < 6% of radiated energy is in GWs

Example: The Crab Pulsar – Beating the Spin Down Limit

Abbott, et al., “Beating the spin-down limit on gravitational wave emission from the Crab pulsar,” Ap. J. Lett. 683, L45-L49, (2008).

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M31The Andromeda Galaxy

by Matthew T. RussellDate Taken:

10/22/2005 - 11/2/2005

Location:Black Forest, CO

Equipment:RCOS 16" Ritchey-Chretien

Bisque Paramoune MEAstroDon Series I Filters

SBIG STL-11000Mhttp://gallery.rcopticalsystems.com/gallery/m31.jpg

Refs:GCN: http://gcn.gsfc.nasa.gov/gcn3/6103.gcn3

X-ray emission curves (IPN)

Example: GRB070201, Not a Binary Merger in M31

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Example: GRB070201, Not a Binary Merger in M31

Inspiral (matched filter search:

Binary merger in M31 scenario excluded at >99% levelExclusion of merger at larger distances 90%

75%

50%

25%

Inspiral Exclusion Zone

99%

Abbott, et al. “Implications for the Origin of GRB 070201 from LIGO Observations”, Ap. J., 681:1419–1430 (2008).

Burst search:Cannot exclude an SGR in M31

SGR in M31 is the current best explanation for this emission

Upper limit: 8x1050 ergs (4x10-4 MŸc2) (emitted within 100 ms for isotropic emission of energy in GW at M31 distance)

(1<m1<3 Msun)

D. Reitze

Cambridge, Jan 2010

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Example: The Stochastic GW Background, Beating BBN

An isotropic stochastic GW background could come from:Primordial universe (inflation)Incoherent sum of point emitters isotropically distributed over the sky

Energy density:

Log-frequency spectrum:

Strain spectral density:

Published S5/VSR1 result, 95% C.L. limit:

UL consistent with no GW stochastic background (null result)

><= αβαβπ

ρ hhG

cGW

&&32

2

Ω0, LIGO < 6.9 x 10-6

)(ln1)(

fddf GW

critGW

ρρ

=Ω

32

20 )(

103)(

ffHfS GWΩ

=π

Nature, August 20th 2009

Cambridge, Jan 2010

D. Reitze

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Current status 3: coming attractions!

Enhancements to LIGO and Virgo at end of commissioningaimed at a factor of two improvement in sensitivity

meanwhile GEO, LIGO and cryogenic bar detectors have maintained ‘astrowatch’

New science runs recently started (July 7th 2009)

2nd generation detectorsAdvanced LIGO fully funded (10 to 15 x improved sensitivity, operational ~2014)

Advanced Virgo close to approval

GEO-HF conversion starting

For Comparison: Neutron Star Binaries:Initial LIGO (S5): ~15 Mpc → rate ~1/50yrAdv LIGO: ~ 200 Mpc → rate ~ 40/year

Black Hole Binaries (Less Certain):Initial LIGO (S5): ~100 Mpc → rate ~1/100yrAdv LIGO: ~ 1 Gpc → rate ~ 20/year

D. Reitze

Cambridge, Jan 2010

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Need a network of detectors for good source location and improve overall sensitivity

Second Generation NetworkAdvanced LIGO/Advanced Virgo/Geo-HF/LCGT/AIGO

LCGT under review (proposed cryo, underground interferometer in Kamioka mine)

AIGO plans progressing (proposed interferometer in Western Australia)

Future developments – on the ground

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Networking

Sky coverage at >50% maximum sensitivity

L/H+L/L L/H+L/L+V L/H+L/L+V+LCGT

LIGO – Hanford & Livingston LIGO – Hanford & Livingston+ Virgo

LIGO – Hanford & Livingston

+ Virgo + LCGT

Bernard Schutz, AEI

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Third Generation Network — Incorporating Low Frequency Detectors

Third-generation underground facilities are aimed at having excellent sensitivity from ~1 Hz to ~104 Hz.

This will greatly expand the new frontier of gravitational wave astrophysics.

Recently begun:

Three year-long European design study, with EU funding, underway for a 3rd-generation gravitational wave facility, the Einstein Telescope (ET).

Goal: 100 times better sensitivity than first generation instruments.


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Third-generation underground facilities are aimed at having excellent sensitivity from ~1 Hz to ~104 Hz.

This will greatly expand the new frontier of gravitational wave astrophysics.

Recently begun:

Three year-long European design study, with EU funding, underway for a 3rd-generation gravitational wave facility, the Einstein Telescope (ET).

Goal: 100 times better sensitivity than first generation instruments.


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LISA (Laser Interferometer Space Antenna)

10-4 Hz – 10-1 Hz Our first priority for a space based mission

Mission Description– 3 spacecraft in Earth-trailing solar orbit,

separated by 5 x106 km.

– Gravitational waves are detected by measuring change in proper distance between fiducial masses in each spacecraft using laser interferometry

– Partnership between NASA and ESA

– Launch date: soon after 2020?...

Future developments – in space

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Mission Description– 3 spacecraft in Earth-trailing solar orbit,

separated by 5 x106 km.

– Gravitational waves are detected by measuring change in proper distance between fiducial masses in each spacecraft using laser interferometry

– Partnership between NASA and ESA

– Launch date: soon after 2020?...


Cambridge, Jan 2010

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LISA : A Universe Full of Strong Gravitational Wave Sources

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Cosmic backgrounds, superstring bursts?

Massive Black Hole Binary (BHB) inspiral and merger (10s‐100s)

Ultra‐compact binaries(thousands)

Extreme Mass Ratio Inspiral (EMRI) (hundreds)

K. Danzmann


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State of the Universe: September 2009

Some key questions for cosmology:

• What is driving the cosmic acceleration?

• Why is 96% of the Universe ‘strange’ matter and energy?

• Is dark energy = Λ ?

• How, and when, did galaxies evolve?

• Big bang + inflation + gravity = LSS?

What rôle could gravitational waves play in answering these questions?

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Much recent interest in ‘Standard Sirens’:

e.g. SMBHs at cosmological distances, for which DL can in principle be determined to exquisite accuracy.

Inspiral waveform strongly dependent on SMBH masses.

Since amplitude falls off linearly with (luminosity) distance, measured strain determines the distance of the source to high precision.

Holz and Hughes 2005

Long tail due to parameter degeneracies

Gravitational Wave Sources as Cosmological Probes

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What could we do with standard sirens?

• Completely independent, gravitational, calibration of the distance scale and the Hubble parameter

• Useful adjunct to existing constraints from CMBR, BAO,subject to completely different systematic errors.

• High precision probe of

• Extension of beyond the reach of SNIe and BAO.


)(zH

)(zw

Are these goals realistic?...

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Currently three major issues:

• Identification of E-M counterpart

• Impact of weak lensing

• Predicting merger event rates


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Identifying an E-M counterpart:

• GWs are redshifted, just like E-M radiation.Hence we determine (very precisely)

• If our goal is to probe e.g. how varies withwe can assume and break the

degeneracy. (See e.g. Hughes 02, Sesana et al. 07, 08)

)1( z+

zDL −z

• If we want to use sirens to measure , we must observe the E-M counterpart.

For this we need an accurate sky position!

zDL −


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So what exactly can we do with sirens?....

Adapted from Holz & Hughes (2005)


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So what exactly can we do with sirens?....


Adapted from Holz & Hughes (2005)

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GW sources will be (de-)magnified by weak lensing due to LSS.

Same treatment as for SN

[ See e.g. Misner, Thorne & Wheeler; Varvella et al (2004), Takahashi (2006) ].

However, WL has muchgreater impact for sirens,because of their muchsmaller intrinsic scatter.

Weak lensing may also limit identification of E-M counterpart


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But what will the counterpart signatures be, and when would we see them? Much detailed modelling required. See e.g. Kocsis et al (2008)

• Periodic variations in flux during inspiral phase, correlated with variations in potential (c.f. OJ287)

• Viscous dissipation of GW energy released duringcoalescence

• Shocks induced by sudden mass loss during final GW burst

• Shocks induced by a supersonic GW recoil ‘kick’

• Infall of gas onto SMBH merged remnant

Before GW peak

hours / days

days / weeks

months / years

years


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But what will the counterpart signatures be, and when would we see them? Much detailed modelling required. See e.g. Kocsis et al (2008)

• Periodic variations in flux during inspiral phase, correlated with variations in potential (c.f. OJ287)

• Viscous dissipation of GW energy released duringcoalescence

• Shocks induced by sudden mass loss during final GW burst

• Shocks induced by a supersonic GW recoil ‘kick’

• Infall of gas onto SMBH merged remnant

Before GW peak

hours / days

days / weeks

months / years

years


Strong argument for multimessenger approach

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Dalal et al. (2006):Short-duration GRBS, due to NS-NS mergers, will also be observed by ALIGO network.

What could be done from the ground?

First optical observation of a NS-NS merger?

GRB 080503 (Perley et al 2008)

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Dalal et al. (2006):Short-duration GRBS, due to NS-NS mergers, will also be observed by ALIGO network.

Beaming of GRBs (blue curves), aligned with GW emission, could boost GW SNR.

All-sky monitoring of GRBs + 1 year operation of ALIGO network

⇒ H0 to ~2% ?

What could be done from the ground?

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Nissanke et al. (2009):Very thorough treatment.

Considers impact of:

• siren true distance;

• no. of detectors in network;

Identifies strong degeneracy between distance and inclination.

Need E-M observations / beaming assumption to break this?

to 10 – 30% at 600 Mpc (NS-NS); 1400 Mpc (NS-BH).

Competitive with traditional ‘distance ladder’; probe of peculiar velocities?

What can be done from the ground?

LD

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Fit , ,

Looking ahead to the Einstein Telescope…

Sathyaprakash et al. (2009):

~106 NS-NS mergers observed by ET. Assume that E-M counterparts observed for ~1000 GRBs, 0 < z < 2.

Weak lensing De-lensed

Competitive with ‘traditional’methods

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…And even further ahead to BBO…

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Cutler and Holz (2009):

~3 x 105 sirens observed, with unique E-M counterparts, for 0 < z < 5.


BBO schematic

Extremely good angular resolution, even at z = 5!

Robust E-M identification of host galaxy, for determining redshift

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Cutler and Holz (2009):

~3 x 105 sirens observed, with unique E-M counterparts, for 0 < z < 5.


Simulated Hubble diagram, including effects of lensing

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Hubble constant to ~0.1%

w0 to ~1%, wa to ~10%

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Hubble constant to ~0.1%

w0 to ~1%, wa to ~10%All of this lies far ahead, but the key is to work on

development of the science case now

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Opening a new window on the Universe

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Gravitational Waves????

Opening a new window on the Universe

Cambridge, Jan 2010

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