Listening to the Sounds of Space-time Kostas Kokkotas 13/02/14 - - PowerPoint PPT Presentation

Listening to the Sounds

• f Space-time

Kostas Kokkotas

¡

¡

13/02/14 Shanghai

Modern Optical Astronomy

Hubble Space Telescope

VLT OWL

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Radio-astronomy

2nd half of the 20th century

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Gamma ray Astronomy

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X-ray Astronomy

Chandra ¡x-­‑ray ¡

Newton ¡satellite ¡

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M81 galaxy

Radio: 21cm X-ray: 10 nm Radio – HI filter Infrared: 100 mm UV: 200 nm Visible: 600 nm

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Neutrino Astronomy

Sudbury Neutrino Observatory

Not any more! Neutrinos from Sun & SN1987a

Most of our current knowledge of the Universe comes from the observation of photons?

Super-Kamiokande

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A New Window to the Universe

Gravitational Waves will provide a new way to view the dynamics of the Universe

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Gravitation & Spacetime Curvature

2

4 U G π ρ ∇ =

4

1 8 2 G R g R g T c

µν µν µν µν

π − + Λ =

2

ds g dx dx

µ ν µν

=

• Matter dictates the degree of

spacetime deformation.

• Spacetime curvature dictates

the motion of matter.

2 2

d x U dt = ∇ !

GWs fundamental part of Einstein’s theory

d2x µ ds2 ~ f (gµν )

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What are Gravitational Waves

Ripples of the spacetime

They produce tidal deformations

• n massive bodies

2 2 2 2 4

1 4 d G h T c dt c g h

µν µν µν µν µν

π η ⎛ ⎞ −∇ = ⎜ ⎟ ⎝ ⎠ = +

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GW primer …

• Le

Length v ngth varia riation tion

• Amplitude

plitude

• Pow
• wer e

r emitte itted d

h Δ = ℓ ℓ

h jk ≈ 2 r !! Q jk ≈ ε ⋅ M r ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ ⋅ M R ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ LGW = − dE dt = 1 5 G c5 !!! Qij!!! Qij

ij

∑

≈ M R ⎛ ⎝ ⎜ ⎞ ⎠ ⎟

5

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Gravitational vs EM waves

• EM waves are radiated by individual particles,

While

• GWs are due to non-spherical bulk motion of matter.

– The information carried by EM waves is stochastic in nature, while the GWs provide insights into coherent mass currents.

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• The EM waves will have been scattered many times

In contrast,

• GWs interact weakly with matter and arrive at the Earth in

pristine condition.

– Therefore, GWs can be used to probe regions of space that are opaque to EM waves.

• Standard astronomy is based on deep imaging of small fields
• f view,

– while

• GW detectors cover virtually the entire sky.

Gravitational vs EM waves

• EM radiation has a wavelength smaller than the size of the emitter,

while

• the wavelength of a GW is usually larger than the size of the

source.

– Therefore, we cannot use GW data to create an image of the source. GW

• bservations are more like audio than visual

Morale GWs carry information which would be difficult to get by other means.

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• Neutrinos: are more like EM waves than GW in most respects,

except…

§ Propagate through most things like GW, so you can see dense centers § But neutron stars don’t generate so many ν after first few minutes.

Uncertainties & Benefits

Unc ncerta taintie inties

– The ¡strength ¡of ¡the ¡sources ¡ – The ¡rate ¡of ¡occurrence ¡of ¡the ¡various ¡events ¡

Bene nefits its

– Experimental ¡tests ¡of ¡fundamental ¡laws ¡of ¡physics ¡which ¡cannot ¡be ¡tested ¡in ¡ any ¡other ¡way ¡

• The ¡first ¡detec;on ¡of ¡GWs ¡will ¡directly ¡verify ¡their ¡existence ¡

– By ¡comparing ¡the ¡arrival ¡;mes ¡of ¡EM ¡and ¡GW ¡bursts ¡we ¡can ¡measure ¡ ¡their ¡ speed ¡with ¡a ¡frac;onal ¡accuracy ¡~10-­‑11 ¡ – Polariza;on ¡proper;es ¡of ¡the ¡GWs ¡will ¡verify ¡GR ¡predic;on ¡that ¡the ¡waves ¡ are ¡transverse ¡and ¡traceless ¡ – From ¡the ¡waveforms ¡we ¡can ¡directly ¡iden;fy ¡the ¡existence ¡of ¡BHs ¡

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What are we going to learn from the detection of GWs?

ü Direct observation of black-holes ü Mass, Radius, Spin and Equation of State of Neutron Stars ü “Look” the details of supernovae collapse ü Unique information about the “moment of creation” ü Verification of Einstein’s theory for strong gravitational fields ü Propagation Speed of gravitational waves ! ü Polarization of gravitational waves ü Unknown sources… ¡

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First verification of GWs

Nobel 1993 Hulse & Taylor

PSR 1913+16

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Prim Primary GW sour ry GW sources

5

~

GW

M L R ⎛ ⎞ ⎜ ⎟ ⎝ ⎠

~ M M h r R ε ⎛ ⎞ ⎛ ⎞ ⋅ ⋅ ⎜ ⎟ ⎜ ⎟ ⎝ ⎠ ⎝ ⎠

Supernovae, BH/NS formation Young Neutron Stars BH and NS Binaries Spinning neutron stars in X-ray binaries

Black Holes : M/R=0.5 Neutron Stars : M/R~0.2 White Dwarfs : M/R~10-4

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+ stoc

stocha hastic stic sour sources

(contribute to a noisy background)

ü Big Bang, ü early expansion of the Universe, ü cosmic strings, ü unresolved sources...

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Low ¡Frequency ¡Sources ¡(eLISA) ¡

Galaxy mergers Galactic Binaries Capture orbits

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Information carried by GWs

• Frequency
• Amplitude

– Information about the strength and the distance of the source

• Rate of frequency change
• Damping
• Polarization

– Inclination of the symmetry plane of the source – Test of general relativity

f ∼104Hz → ρ ∼1016gr/cm3 f ∼10−4Hz → ρ ∼1gr/cm3

1/2 1/2 3

~ ~ ( )

dyn

GM f G R ρ ⎛ ⎞ ⎜ ⎟ ⎝ ⎠

! f / f ~ (m1,m2)

τ ~ M 3 / R4

h ~ 1 r

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Cur urrent R nt Rese search in h in GWs GWs

3 ¡main ¡direc6ons ¡ ¡

Improve ¡the ¡sensi6vity ¡ & ¡ construct ¡new ¡detectors ¡ Data ¡Analysis ¡ ü Understand ¡the ¡physics ¡

• f ¡the ¡poten6al ¡sources ¡

ü Produce ¡waveforms ¡for ¡ data ¡analysis ¡

Current detectors

3rd generation

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Quantum Fluctuations in the Early Universe Merging super-massive black holes (SMBH) at galactic cores Phase transitions in the Early Universe Capture

• f black

holes and compact stars by SMBH Merging binary neutron stars and black holes in distant galaxies Neutron star quakes & magnetars

Gr

Gravita vitationa tional W l Wave Spe Spectr trum um

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Acoustic

• ustic D

Dete tector tors

ALLEGR LLEGRO - A O - AURIG IGA - EXPL

• EXPLOR

ORER ER - N

• NAUTIL

TILUS

• The “oldest” resonant detector EXPLORER started operations

more than 20 years ago.

• This kind of detector has reached a high level of reliability.
• The duty cycle is greater than 90% .

There will be no continuation on Acoustic Detectors

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Sensitivity of Acoustic Detectors

Narrow band detectors (few tens of Hz) around the bars’ resonant frequency (~900Hz) ü Most suited for short-lived broad-band transient signals ü Operated as a network of detectors, “IGEC”, in 1997-2000 ü Have resumed network analysis in 2005 as “IGEC2” ü THE PROJECTS WILL BE DISCONTINUED

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Gr Gravita vitationa tional W l Wave D Dete tector tors s

(Inte (Interf rferom

• mete

ters) s) ¡

Gr Gravita vitationa tional W l Wave D Dete tector tors s

(Inte (Interf rferom

• mete

ters) s)

h = ΔL L h ≈ 10−21 ⇒ ΔL ≈ 10−16cm

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Dista istanc nce fr from

• m the

the Ga Gala lactic tic cente nter d ~ d ~1.5 .5x1 x1017

17 cm

cm Δd= d=ΔL x d= L x d= 15 15cm cm

Interferometer Projects

LIGO VIRGO GEO eLISA

ü GEO, LIGO, TAMA & VIRGO taking data ü eLISA is an ESA project (2018?)

KAGRA

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Einstein Telescope (ET)

ü Entering the era of routine GW astronomy ü A pan-European project ü Built underground ü 10 km triangle ü Timescale: start 2018 lasting for many decades

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Pulsar ar Timi ming g Array Arrays

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Ground interferometers’ noise budget

• Best ¡strain ¡sensi;vity ¡ ¡

– ~3x10-­‑23 ¡1/Hz1/2 ¡at ¡200 ¡Hz ¡

• Displacement ¡Noise ¡

– Seismic ¡mo;on ¡ – Thermal ¡Noise ¡ – Radia;on ¡Pressure ¡

• Sensing ¡Noise ¡

– Photon ¡Shot ¡Noise ¡ – Residual ¡Gas ¡

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GW network sensitivity

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Frequency Range of Human Hearing

Gravitational Wave Spectrum…

Complementary observations, different frequency bands, and different astrophysical sources…

VIR VIRGO

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Towards GW Astronomy

ü Present detectors up to now tested upper limits ü Even in the optimistic case rate was too low to start GW astronomy ü Need to improve the sensitivity ü Increase the sensitivity by 10 increase the probed volume by 1000

LIGO - Virgo LIGO+ - Virgo+ AdvLIGO - AdvVirgo

Credit: R.Powell 13/02/14 Shanghai

Illustration of Matched Filtering

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events/ year

Virgo/ LIGO Advanced detectors

NS/NS ~0.3 ~100-500 BH/NS ~0.02 ~80 BH/BH ~0.8 ~2000 Total ~1.0 2000

Bina inary Sy ry Syste stems

• The best candidates and most reliable sources for broad

band detectors.

• Three archetypal systems

– Double Neutron Stars (NS/NS) – Neutron Star-Black Hole (NS/BH) – Double Black Holes (BH/BH)

events/ year

Virgo/ LIGO 2007 Advanced Detectors 2015+

ET 2025 NS/NS ~0.02 ~40 millions BH/NS ~0.006 ~10 104 BH/BH ~0.01 ~20 millions Total ~0.04 70 Signal shape very well known

Event rates

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Merging ¡Galaxies ¡

Merging Neutron Stars

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Black-Holes get a Kick

During ¡the ¡final ¡coalescence, ¡or ¡ merger, ¡of ¡ ¡two ¡BHs, ¡a ¡giant ¡burst ¡

• f ¡GWs ¡is ¡emiIed. ¡These ¡waves ¡are ¡

generally ¡emiIed ¡in ¡one ¡preferred ¡ direc6on, ¡the ¡BH ¡is ¡then ¡kicked ¡in ¡ the ¡other ¡direc6on.. ¡ Merging ¡Super-­‑massive ¡BHs ¡can ¡be ¡

• bserved ¡from ¡the ¡edges ¡of ¡the ¡Universe ¡

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The High Frequency Window

• Supernova Core Collapse

– The violent dynamics associated with a supernova core collapse is expected to lead to GW emission through a number of channels

• Rotating Deformed Neutron Stars

– Asymmetries, generated either by strains in the star’s crust or by the magnetic field, are expected to slowly leak rotational energy away from spinning neutron stars.

• Oscillations and Instabilities of NS

– Neutron stars have rich oscillation spectra which, if detected, could allow us to probe the internal composition “GW Asteroseismology”

• Magnetars

– Magnetar flares emit huge amounts of EM radiation, if a small percentage is emitted in GW they can be a promising source. ¡

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Core-collapse Supernova

Supernova core collapse was the primary source of the early GW detectors Rate 1/30yr in a typical galaxy Detection would provide unique insight into SN physics: – optical signal hours after collapse – neutrinos after several seconds – GWs emitted during collapse

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NUMBERS for Core Collapse

• GW burst from core collapse
• GW from convective

boiling…

• GW from the coupling of an

unstable l=1 g-mode in PNS to higher harmonics…

• GWs from QNM oscillations

21 10

10 , 700 kpc h f Hz d

−

≈ !

h ! 10−20 −10−21 10kpc d , f ≈ 600Hz

21 20 10

10 4 10 , 800 1000 kpc h d f Hz

− −

− × ≈ − ! h ! 10−21 − 3×10−20 10kpc d , f ≈ 1− 5kHz

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GWs from Neutron Stars

• Great interest in detecting radiation: physics of

such stars is poorly understood.

• After 40 years we still don’t know what makes

pulsars pulse or glitch.

• Interior properties not understood:

– equation of state, superfluidity, superconductivity, solid core, source of magnetic field.

• May not even be neutron stars: could be

made of strange matter!

• How solid is a neutron star?

Just after supernova (proto-neutron star formation)

Triaxial instabilities, possible fragmentation instability Many kinds of oscillation modes tell us about structure

Later in NS life cycle

Glitches: must excite various modes at some level & emit GW (no direct evidence yet) SGR superflare: some evidence of crust t-modes (torsional) ringing in x-ray signal after Dec. 27, 2004; frequencies sensitive to crust composition, structure & B-field; GW help break degeneracy

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Rotating Neutron Stars

Wobbling neutron star Rotational instabilities “Mountain” on neutron star Accreting neutron star

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Stochastic Sources

n Stochastic backgrounds

n Produced ¡by ¡superposi;on ¡of ¡a ¡number ¡of ¡astrophysical ¡sources ¡or ¡the ¡

energe;c ¡processes ¡in ¡the ¡Early ¡Universe ¡ ¡

n Strength ¡and ¡spectrum ¡of ¡astrophysical ¡backgrounds, ¡produc;on ¡of ¡

early-­‑universe ¡radia;on, ¡rela;on ¡to ¡fundamental ¡physics ¡(string ¡theory, ¡ branes, ¡…) ¡

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2012 - 2018 GWD Network

• slide from INFN roadmap

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The ¡End ¡

… ¡

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