1. Gravitational Wave Astronomy --The Dawn has Arrived!-- 1 Misao Sasaki Yukawa Institute for Theoretical Physics Kyoto University APCTP 25 March, 2016

2.  APCTP has been very active in promoting gravitational wave physics 2 Congratulations on 20 th Anniversary! [2014.11.28-11.29] The 50th Workshop on Gravitation and Numerical Relativity [2014.05.16-05.17] The 48th Workshop on Gravitation and Numerical Relativity [2014.02.17-02.21] 2014 AP School and Workshop on Gravitation and Cosmology (APCTP-NCTS-YITP Joint Program) [2013.11.29-11.30] The 47th Workshop on Gravitation and Numerical Relativity [2013.08.03-08.10] 2013 International School on Numerical Relativity and Gravitational Waves [2013.04.26-04.27] The 45th Workshop on Gravitation and Numerical Relativity [2013.02.19-02.22] APCTP-NCTS-YITP Joint School and Workshop on Gravitation and Cosmology [2012.12.07-12.08] The 44th Workshop on Gravitation and Numerical Relativity [2012.10.12-10.13] The 43rd Workshop on Gravitation and Numerical Relativity [2012.03.30] The 42nd Workshop on Gravitation and Numerical Relativity [2012.03.01-03.04] 2012 Asia Pacific School/Workshop on Cosmology and Gravitation [2011.12.17-12.22] Xth International Conference on Gravitation, Astrophysics and Cosmology(ICGAC10) …. Search result from previous activities (~ 2014) at APCTP webpage 2

3.  GWs are ripples of spacetime propagating at speed of light, whose existence was predicted by Einstein in 1916 (so this year is 100 th anniversary of GW!)  When a system undergoes dynamical motion, with its quadrupole moment varying in time, GWs are generated.  In contrast to EM waves, whose nature is dipolar (s=1), GWs are quadrupolar (s=2) in nature (~ oscillating tidal force). 3 What are Gravitational Waves? dipole radiation quadruple radiation 3

4. 4 GWs from NS/BH Binary https://www.gravity.phy.syr.edu/~satya/Publication-IMR_comparison/ http://www.jpl.nasa.gov/ NS=Neutron Star BH=Black Hole Accurate detection of the waveforms will tell us a lot about physics in strong gravity/beyond nuclear density 4

5. 5 Indirect Evidence from NS binary PSR B1913+16/Hulse-Taylor binary 1993 Nobel Prize in Physics Best test of GR until last month PSR J0737-3039 Kranmer et al. ‘06 6-parameter fit 5

6.  On 11 February (EST), LIGO announced the first direct detection of gravitational waves.  The waves were from a binary black hole (BH) merger, with each BH of about 6 First Direct Detection of GW! 30 solar mass at 400 Mpc (~1 Billion lyr) from earth. 1 solar mass =10 33 g  It was only two days after LIGO started its operation Very Lucky! 6

7.  LIGO=Laser Interferometric Gravitational wave Observatory 7 What is LIGO? Each arm is 4km long. LIGO can detect the GW amplitude of ~ 10 -21 Washington Louisiana nucleon size ~ 10 -13 cm 3000km 3000km = 10 ms 7

8. 8 Observed Signal inspiral merging BH ring-down 8

9. 9 Where did the GWs come from? GWs cam from 1.3 billion light-years away, most likely in the direction of the Magellanic Clouds, two satellite galaxies of our Galaxy. N.B. Magellanic Clounds are only about 0.2 million lyr away from our Galaxy Large Magellanic Cloud Small Magellanic Cloud

10.  Dawn of GW astronomy/astrophysics has arrived! GWs will be used as a tool to explore the Unknown Universe  Already from the LIGO result, we infer that there are unexpectedly many binary BHs of 10-100 solar mass: 10 Implications  They may constitute a non-negligible fraction of Dark Matter  Their existence has made us reconsider the stellar population synthesis  Detected GWs will give us various tests of GR and/or modified gravity theories at strong field  The LIGO result is perfectly consistent with GR predictions  The first evidence of BH ring-down=existence of event horizon 10

11. 11 Future Network of GW Observatories VIRGO will be ready soon (by this summer?) KAGRA will start operation by 2018 (iKAGRA has just started!) LIGO-India has been recently approved by Indian gov. 11

12. 12 iKAGRA today!

13. 13 KAGRA KAmioka GRAvitational wave detector In Japanese it is pronounced as Kagura, which means “God Music” （神 楽） Previously called LCGT Large Cryogenic Gravitational wave Telescope Arm length 3km Cooled to 20K Super-Kamiokande KAGRA APCTP http://gwcenter.icrr.u-tokyo.ac.jp/en/

14. 14 http://lisa.nasa.gov/ Deci-hertz Interferometer Gravitational wave Observatory Laser Interferometer Space Antenna Space-based Future Projects DECIGO: 1,000 km launched by ~2030? target freq: ~ 0.1 Hz LISA: 5,000,000 km launched by ~2034? target freq: ~10 -3 Hz Arm Length 14

15. 15 Multi-frequency GW Astronomy Pulsar Timing Array Spaced-based Ground-based http://rhcole.com/apps/GWplotter/ 15

16. Cosmological GW Background  scalar field(s) produce density fluctuations -> CMB temp+E-mode fluctuations Inflation enhances vacuum fluctuations to macroscopic scales E-mode (even parity) B-mode (odd parity) = cannot be produced from density fluctuations  Spacetime (GW) fluctuations -> CMB temp+E-mode+B-mode fluct’ns B-mode polarization temperature fluct’ns http://www.skyandtelescope.com/ Source: Harvard-Smithsonian Center for Astrophysics 16

17. 17 Lite (light) Satellite for the studies of B-mode polarization and Inflation from cosmic background Radiation Detection Experimental Probe of Inflationary Cosmology B-mode Space-based Projects LiteBIRD (~ 2025) http://litebird.jp/eng/ LiteBIRD EPIC (~2030?) http://arxiv.org/abs/0906.1188 : tensor-to-scalar ratio http://arxiv.org/abs/0811.3911v1 17

18. 18 GW Spectrum from Inflation Direct detection by GW observatories http://arxiv.org/abs/1206.2109 18

19.  LIGO detection of GWs marked the 1 st milestone in GW astronomy/astrophysics. The Dawn has arrived!  Future GW detector network will accelerate progress in GW astronomy/astrophysics.  Multi-frequency GW astronomy/astrophysics is arriving soon.  Search for primordial GWs from inflation will continue. Summary GWs will become an essential tool for exploring the Physics of the Unknown Universe LIGO result is perfectly consistent with GR with 1 st direct evidence of BH. It also indicates the need for a new theory of stellar population synthesis. 19