Listening to the Sounds of Space-time Kostas Kokkotas ¡ ¡ 13/02/14 Shanghai
Modern Optical Astronomy Hubble Space Telescope OWL VLT 13/02/14 Shanghai
Radio-astronomy 2nd half of the 20th century 13/02/14 Shanghai
Gamma ray Astronomy 13/02/14 Shanghai
X-ray Astronomy Chandra ¡x-‑ray ¡ Newton ¡satellite ¡ 13/02/14 Shanghai
M81 galaxy X-ray: 10 nm UV: 200 nm Visible: 600 nm Radio: 21cm Infrared: 100 mm Radio – HI filter 13/02/14 Shanghai
Neutrino Astronomy Most of our current knowledge of the Universe comes from the observation of photons? Not any more! Neutrinos from Sun & SN1987a 13/02/14 Shanghai Super-Kamiokande Sudbury Neutrino Observatory
A New Window to the Universe Gravitational Waves will provide a new way to view the dynamics of the Universe 13/02/14 Shanghai
Gravitation & Spacetime Curvature π 1 8 G ∇ = π ρ 2 U 4 G − + Λ = R g R g T µ ν µ ν µ ν µ ν 4 2 c ! 2 d x d 2 x µ = ∇ ds 2 ~ f ( g µ ν ) U µ ν = 2 ds g dx dx µ ν 2 dt • Matter dictates the degree of spacetime deformation. • Spacetime curvature dictates the motion of matter. GWs fundamental part of Einstein’s theory 13/02/14 Shanghai
What are Gravitational Waves ⎛ ⎞ π 2 1 d 4 G −∇ µ ν = µ ν 2 h T ⎜ ⎟ Ripples of the spacetime 2 2 4 c dt c ⎝ ⎠ µ ν = η µ ν + µ ν g h They produce tidal deformations on massive bodies 13/02/14 Shanghai
GW primer … Δ = ℓ • Le Length v ngth varia riation tion h ℓ ⎛ ⎞ ⎛ ⎞ h jk ≈ 2 M M Q jk ≈ ε ⋅ !! ⎟ ⋅ • Amplitude plitude ⎜ ⎜ ⎟ ⎝ ⎠ ⎝ ⎠ r r R 5 ⎛ ⎞ L GW = − dE dt = 1 G M ∑ Q ij !!! !!! ≈ Q ij ⎜ ⎟ • Pow ower e r emitte itted d ⎝ ⎠ 5 c 5 R ij 13/02/14 Shanghai
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. • 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 of view, – while • GW detectors cover virtually the entire sky. 13/02/14 Shanghai
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 observations are more like audio than visual • 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. Morale GWs carry information which would be difficult to get by other means. 13/02/14 Shanghai
Uncertainties & Benefits Unc ncerta taintie inties – The ¡strength ¡of ¡the ¡sources ¡ – The ¡rate ¡of ¡occurrence ¡of ¡the ¡various ¡events ¡ its Bene nefits – 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 ¡ 13/02/14 Shanghai
What are we going to learn from the detection of GWs? ü Direct observation of ü Verification of black-holes Einstein’s theory for strong gravitational ü Mass, Radius, Spin and fields Equation of State of Neutron Stars ü Propagation Speed of gravitational waves ! ü “Look” the details of supernovae collapse ü Polarization of gravitational waves ü Unique information about the “moment of ü Unknown sources … ¡ creation” 13/02/14 Shanghai
First verification of GWs PSR 1913+16 Nobel 1993 Hulse & Taylor 13/02/14 Shanghai
Primary GW sour Prim ry GW sources 5 ⎛ ⎞ M L ~ ⎜ ⎟ GW ⎝ R ⎠ ε ⎛ ⎞ ⎛ ⎞ M M ⋅ ⋅ h ~ ⎜ ⎟ ⎜ ⎟ ⎝ r ⎠ ⎝ R ⎠ BH and NS Binaries Supernovae, BH/NS formation Black Holes : M/R=0.5 Neutron Stars : M/R~0.2 White Dwarfs : M/R~10 -4 Spinning neutron stars in X-ray binaries Young Neutron Stars 13/02/14 Shanghai
sources + stoc stocha hastic stic sour (contribute to a noisy background) ü Big Bang, ü early expansion of the Universe, ü cosmic strings, ü unresolved sources... 13/02/14 Shanghai
Low ¡Frequency ¡Sources ¡(eLISA) ¡ Galactic Binaries Galaxy mergers 13/02/14 Shanghai Capture orbits
Information carried by GWs • Frequency 1/2 f ∼ 10 4 Hz → ρ ∼ 10 16 gr/cm 3 ⎛ ⎞ GM ρ 1/2 f ~ ~ ( G ) ⎜ ⎟ dyn 3 ⎝ R ⎠ f ∼ 10 − 4 Hz → ρ ∼ 1gr/cm 3 • Amplitude – Information about the strength and the distance of the source h ~ 1 r • Rate of frequency change ! f / f ~ ( m 1 , m 2 ) • Damping τ ~ M 3 / R 4 • Polarization – Inclination of the symmetry plane of the source – Test of general relativity 13/02/14 Shanghai
Cur urrent R nt Rese search in h in GWs GWs 3 ¡main ¡direc6ons ¡ ¡ ü Understand ¡the ¡physics ¡ Improve ¡the ¡sensi6vity ¡ Data ¡Analysis ¡ of ¡the ¡poten6al ¡sources ¡ & ¡ ü Produce ¡waveforms ¡for ¡ construct ¡new ¡detectors ¡ data ¡analysis ¡ Current detectors 3 rd generation 13/02/14 Shanghai
Gr Gravita vitationa tional W l Wave Spe Spectr trum um Merging Merging super-massive Phase Capture Quantum Fluctuations in the Early Universe Neutron star binary black holes (SMBH) at transitions of black quakes & neutron galactic cores in the holes and magnetars stars and Early compact black Universe stars by holes in SMBH distant galaxies 13/02/14 Shanghai
Acoustic oustic 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 13/02/14 Shanghai
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 13/02/14 Shanghai
Gr Gravita vitationa tional W l Wave D Dete tector tors s s) ¡ (Inte (Interf rferom omete ters)
Gr Gravita vitationa tional W l Wave D Dete tector tors s (Inte (Interf rferom omete ters) s) h = Δ L L h ≈ 10 − 21 ⇒ Δ L ≈ 10 − 16 cm Dista istanc nce fr from om the the Ga Gala lactic tic cente nter d ~ d ~1.5 .5x1 x10 17 17 cm cm Δ d= d= Δ L x d= L x d= 15 15cm cm 13/02/14 Shanghai
Interferometer Projects eLISA ü GEO, LIGO, TAMA & VIRGO taking data ü eLISA is an ESA project (2018?) GEO KAGRA LIGO VIRGO 13/02/14 Shanghai
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 13/02/14 Shanghai
Pulsar ar Timi ming g Array Arrays 13/02/14 Shanghai
Ground interferometers ’ noise budget • Best ¡strain ¡sensi;vity ¡ ¡ – ~3x10 -‑23 ¡ 1/Hz 1/2 ¡ at ¡200 ¡Hz ¡ • Displacement ¡Noise ¡ – Seismic ¡mo;on ¡ – Thermal ¡Noise ¡ – Radia;on ¡Pressure ¡ • Sensing ¡Noise ¡ – Photon ¡Shot ¡Noise ¡ – Residual ¡Gas ¡ 13/02/14 Shanghai
GW network sensitivity Frequency Range of Human Hearing 13/02/14 Shanghai
Gravitational Wave Spectrum… VIR VIRGO Complementary observations, different frequency bands, and different astrophysical sources … 13/02/14 Shanghai
Towards GW Astronomy Present detectors up to ü now tested upper limits Even in the optimistic ü case rate was too low to start GW astronomy LIGO - Virgo Need to improve the ü sensitivity LIGO+ - Virgo+ Increase the sensitivity ü by 10 increase the AdvLIGO - AdvVirgo probed volume by 1000 13/02/14 Shanghai Credit: R.Powell
Illustration of Matched Filtering 13/02/14 Shanghai
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