The science potential of gravitational wave observation

1. A.Viceré – INFN Firenze/Urbino The science potential of gravitational wave observation

2. Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze2/34 Coupling constants • In SN collapse n withstand 103 interactions before leaving the star, the gravitational waves instead leave the core undisturbed • Very early GW decoupling after Big Bang • GW ~ 10-43 s (T ~ 1019 GeV) • n ~ 1 s (T ~ 1 MeV) • γ~ 1012 s (T ~ 0.2 eV) GW emission: very energetic events but almost no interaction Ideal information carrier, Universe transparent to GW all the way back to the Big Bang!!

3. Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze3/34 Compactness C 1 for BH 0.3 for NS 10-4 for WD h ~ 10-21 Plausible target GW amplitude • Luminosity: • Amplitude: Efficient sources of GW must be asymmetric, compact and fast GW detectors sensitivity expressed in amplitude h : 1/r attenuation Example target amplitude: coalescing NS/NS in the Virgo cluster (r ~10 Mpc)

4. Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze4/34 Synopsis of sources LONG DURATION SHORT DURATION Signal known Coalescing compact binaries Rotating NS Signal partiallyor unknown Stochastic GW Supernovae

5. Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze5/34 1° generation design sensitivity curves -18 10 1st generation detectors h (Hz-1/2)‏ Pulsars hmax – 1 yr integration LIGO -19 10 Virgo -20 10 Resonant antennas GEO BH-BH Merger Oscillations @ 100 Mpc -21 10 Core Collapse QNM from BH Collisions, @ 10 Mpc QNM from BH Collisions, 100 - 10 Msun, 150 Mpc 1000 - 100 Msun, z=1 BH-BH Inspiral, 100 Mpc NS-NS Merger -22 10 Oscillations @ 100 Mpc BH-BH Inspiral, z = 0.4 -6  NS, =10 , 10 kpc -23 10 NS-NS Inspiral, 300 Mpc -24 10 4 1 10 100 1000 10 Hz Credit: P.Rapagnani

6. Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze6/34 LIGO and Virgo detectors actual sensitivities • LIGO at design sensitivity, Virgo close to it • Both detectors very stable  Science possible

7. Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze7/34 368 days of triple-coincident LIGO data Science Runs So Far • Since end of S5 / VSR1 : • ►Upgrading LIGO 4-km interferometers and Virgo • ►GEO and LIGO 2-km interferometer taking data whenever possible for “AstroWatch” vigil 2002 2003 2004 2005 2006 2007 LIGO: S1 S2 S3 S4 S5 GEO: Virgo: VSR1

8. Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze8/34 1ST GENERATION INTERFEROMETERS CAN DETECT A NS-NS COALESCENCE AS FAR AS VIRGO CLUSTER (15 MPc) 1st generation detection chances LOW EXPECTED EVENT RATE: 0.01-0.1 ev/yr (NS-NS) FIRST DETECTION: POSSIBLE BUT UNLIKELY

9. Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze9/34 Enhanced LIGO/Virgo+ 2009 Virgo/LIGO 108 ly Adv. Virgo/Adv. LIGO 2014 Credit: R.Powell, B.Berger Advanced detectors sensitivity • A factor of 10 in sensitivity  a factor 1000 in volume observed, OR event rate • Advanced LIGO funded, operational in 2014-15 • Advanced Virgo to be approved; with less changes, possibly operational in same years

10. Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze10/34 The Supernovae At the origin of most compact objects Estimated rate: several /yr in the VIRGO cluster; a few / century in our galaxy Integral has measured the gamma emission by Al26 isotope, whose abundance in our galactic centre confirms this rate Latest to explode: Sanduleak, the well known 1987a, in the Magellanic clouds (50 kpc away)

11. Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze11/34 GW emitted Supernovae and GW • Dynamics and waveform from collapse hard to model • A variety of short bursts of GW are predicted. Actual observation will constrain the models • What is clear, is that GW and n emissions are almost simultaneous • Simulations suggest EGW~10-6 Mʘc2, while NS kick velocities suggest possible strong asymmetries. There could be surprises. secs hrs [Zwerger, Muller]

12. Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze12/34 What we know so far about GW and burst events • The most-recent published results use S4 data • LIGO-only search[ Classical and Quantum Gravity 24, 5343 (2007) ] • ►Searched 15.53 days of triple-coincidence data (H1+H2+L1)for short (<1 sec) signals with frequency content in range 64-1600 Hz • ►No event candidates observed • ►Upper limit on rate of detectable events: 0.15 per day (at 90% C.L.) • ►Sensitive to GW energy emission as small as ~10-7 M at 10 kpc,or ~0.25 M at the distance of the Virgo Cluster • LIGO-GEO joint search [ CQG 25, 245008 (2008) ] • First use of fully-coherent network analysis for burst signals • S5 / VSR1 all-sky search is currently under internal review • Factor of ~2 better amplitude sensitivity, and much longer observation time • Doing coherent network analysis using LIGO and Virgo data

13. Targeting SNe and low energy 's • Boost detection confidence • Neutrino and GW expected within a few ms delay • Very tight coincidence can be required • Constrain  mass strongly • 1ms accuracy: m < 1eV constrain

14. Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze14/34 Nobel Prize 1993: Hulse and Taylor Coalescing binaries and PSR1913+16 • Pulsar bound to a “dark companion”, 7 kpc from Earth. • Relativistic clock: vmax/c ~10-3 • GR predicts such a system to loose energy via GW emission: orbital period decrease • Radiative prediction of general relativity verified at 0.2% level

15. Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze15/34 CB signals as probes of compact object dynamics [Campanelli et al., PRL, 2006] • Pairs of compact stars, like PSR1913+16, but close to the final “coalescence” • PBH: Primordial Black Holes (in the galactic halo): M in [0.2, 0.9] • BNS: Binary neutron stars: M in [0.9, 3.0] • BBH: Binary black holes: M in [3, 20] • NS-BH: mixed systems • Inspiral signal accurately predictable • Newtonian dynamics • Post-Newtonian corrections (3PN, (v/c)11/2) [L.Blanchet et al., 1996] • Recent big progress in merger 3D simulation [Baker et al 2006, Praetorious 2006] • Crucial to extract physics, mostly encoded in the merger phase

16. Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze16/34 Coalescing binaries as standard candles The signal instantaneous frequency is linked to the mass parameters of the system The instantaneous GW luminosity is linked to the mass as well Signal at Earth scales down by distance From the multiple observation of the same signals, the signal strength at Earth can be determined, and translated into a distance An alternative method to measure the Hubble constant chirp [Campanelli et al., PRL, 2006]

17. Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze17/34 100 Mpc Binary inspiral searches so far • New result from first year of S5 data • No inspiral signals detected • Using population models,calculated 90% confidencelimits on coalescence rates: • For binary neutron stars:3.8×10–2per year per L10 • For 5+5 M binary black holes:2.8×10–3 • For BH-NS systems:1.9×10–2 • (Slightly tighter limits if BHs are assumed to have no spin) [ Preprint arXiv:0901.0302 ]

18. Coalescing binaries and association with GRB events • Swift now, Fermi (GLAST) keep looking at  rays from GRB • GRB powered by accretion disks on newly formed objects • Neutrino and GW expected within a few ms delay • Short GRB (< 2s) potentially related to BNS, BH-NS • Long GRB (>2s, average 30s) related to (classes of) SNe • Again, boost detection confidence • Provide insight in the fireball mechanism

19. Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze19/34 The GRB 070201 case • Short, hard gamma-ray burst • Leading model for short GRBs: binary merger involving a neutron star • Position (by IPN  triangulation using time of arrival on different gamma satellites) consistent with being in M31 • LIGO Hanford detectors were operating • Searched for inspiral & burst signals • Result from LIGO data analysis:No plausible GW signal found;therefore very unlikely to befrom a binary merger in M31 • [ ApJ 681, 1419 (2008) ] • Hundreds of GRB occurred during the live time of LIGO and Virgo detectors: still under analysis

20. BNS events: can ground detectors see them? • Empirical models • Use observed (4) galactic binary systems coalescing on timescales comparable to Universe age • Infer # of events/Milky Way Equivalent Galaxy • Assume galactic density 0.01 Mpc-3 • Population synthesis models • Use galactic luminosity to deduce star formation rate • Alternatively, use supernova events to calibrate the number of massive stars • Model binary formation and evolution to deduce # of systems coalescing in less than Hubble time

21. Example: range of predictions for BNS in AdV • Wide range of variability • Empirical models uncertains because of the small number of systems observed • Population synthesis models vary because of physical assumptions and uncertainty in parameters • GW observations can constrain stellar evolution models • Each Advanced LIGO or AdV sees a BNS beyond 150 Mpc; will see sufficient events to shed light on stellar evolution models

22. Even more uncertain: binary black holes rates • Until recently, entirely based on models • Evolve populations of stars, based on current knowledge of massive star populations • Only masses < 10 M are simulated • BBH population synthesis very uncertain • Merger rates vary by factors of hundreds • If model A is true, prospects of detection are dim! • However ...

23. An empirical prediction about binary black holes • IC10 X-1 • Binary system in local group (~ 700 kpc)‏ • Includes a BH, m~24 Mo, and a massive Wolf-Rayet star, m~ 35 Mo • Allows to predict a rate (Bulik et al.)‏ • The WR will evolve in BH, without disrupting the binary system • The resulting system should have Mchirp~14Mo • Such systems are detectable by AdV up to 1.1 Gpc ... • Rate for AdV should be ~ 250 /year • Rate for combined Advanced LIGO – AdV ~ 2500/year

24. Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze24/34 Another look at neutron stars • Complicated objects • a solid crust of nuclear matter • an inner core which could be superfluid • Can sustain oscillation modes, whose f0 and Q are related to the structure and the equation of state of the NS matter • A strong magnetic field , O(108 T) • Numerous: 109 NS in the galaxy, 163 known in LIGO/Virgo band

25. Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze25/34 Spinning Neutron Stars • Non-axisymmetric, triaxial rotating NS emit periodic GW at f=2fspin • Signal can be increased by integrating over long times (months)‏ • Doppler correction of Earth motion needed (f/f  10-4) • Makes search more difficult, but • Makes the signal distinguishable from the (many) periodic noises present in the detectors

26. Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze26/34 Crab Searches for Periodic Signalsfrom Known Radio/X-ray Pulsars • Allow data demodulation, correcting for motion of detector • Doppler frequency shift, amplitude modulation from antenna pattern • S5 preliminary results(using first 13 months of data): • Place limits on strain h0and equatorial ellipticity e ► e limits as low as ~10–7 It’s plausible that an ordinary neutron star could sustain an ellipticity as large as ~10–6;Some models allow larger

27. Known pulsars: AdV limits on h • Dots: spin down limits. • Beaten by AdV for about 40 known objects

28. Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze28/34 GW from Soft Gamma Repeaters • SGRs are believed to be magnetars • NS with exceedingly large magnetic fields, O(1011 T) • Occasional flares of soft gamma rays • May be associated with cracking of the crust that excitesvibration f-modes of the neutron star • LIGO searched for GW signals associated with SGR flares • Dec. 2004 “giant” flare of SGR 1806–20 • 190 flares from SGR 1806–20 and SGR 1900+14 during first year of S5 • Placed upper limits on GW signal energy for each flare • [ PRL 101, 211102 (2008) ] • Within the energy range predicted by some models • LIGO also searched for GW signals matching the quasiperiodic oscillations seen in X-rays in the tail of the Dec. 2004 giant flare • Placed upper limits [ PRD 76, 062003 (2007) ]

29. Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze29/34 Stochastic Background of Gravitational Waves • Weak, random gravitational waves should be bathing the Earth • Left over from the early universe, analogous to CMBR ;ordue to overlapping signals from many astrophysical objects / events • Energy density • Characterized by log spectrum • Related to the strain power spectrum • Strain scale

30. Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze30/34 Stochastic background models and constrains LIGO S1, 2 wk data h1002 < 23 PRD (2004) Laser Interferometer Space Antenna - LISA LIGO S3, 2 wk data h1002 < 8 x 10-4PRL (2005)‏ Nucleosynthesis Pulsar Initial LIGO, 1 yr data Expectedh1002 < 2x10-6 Advanced IFOs, 1 yr data Expectedh1002 < 7x10-10 CMB Credit: B.Sathyaprakash 0 -2 -4 (0h1002)‏ Cosmic strings -6 -8 Log Pre-big bang model -10 EW or SUSY Phase transition Inflation -12 Cyclic model Slow-roll -14 -16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 -18 10 Log ( f [Hz])‏

31. Astrophysical backgrounds • A network can locate point sources of random GW signals • Such could be objects of astrophysical interests, for instance very large black holes in active galaxies • A network of three detector sites, like the LIGO – Virgo network, with multiple baselines, allows to map the sky with good resolution

32. Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze32/34 Benefits by a GW detector network LIGO VIRGO False alarm rejection thanks to coincidence Triangulation allowing to pinpoint the source A network allows to deconvolve detector response and regress signal waveform -->measure signal parameters, including source distance for BNS signals Joint operation yields a longer observation time, and a better sky coverage

33. Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze33/34 10-22 10-23 10-24 10-25 Current detectors LISA 3rd generation Credit: B.Sathyaprakash h (1/√Hz)‏ 2008 2015 Adv detectors 2013 2020 0.1mHz 10mHz 1 Hz 100 10k frequency f / binary black hole mass whose freq at merger=f 4x107 4x105 4x103 M 40 0.4

34. Arcetri – February 23rd, 2009 A.Viceré – Università di Urbino & INFN Firenze34/34 The role of new instruments • Better coverage of the frequency spectrum • To fill the gap between LISA and the ground based detectors • Some sources, like coalescing binaries, have much more signal at lower frequencies: for instance LISA can see BBH in the whole universe  requirements on sensitivity are less stringent • Increased number of detectors • To provide a better sky coverage  more events • To improve the detection capabilities  reject background • To reconstruct the signal more accurately  better science