The sound of the Universe: The search for Gravitational Waves

1. The sound of the Universe:The search for Gravitational Waves Giovanni Santostasi, Ph. D. Baton Rouge Community College, Baton Rouge, LA

2. Newtonand Einstein:theories of Space and Time Special Relativity = Space-Time constant velocityGeneral Relativity = Geometry-Space-Timeacceleration

3. Space and Time Unified Relativity of the reference system “Absoluteness” of the laws of Physics Time and Space are not separated quantities but different aspects of a same reality (Space-Time continuum) Light unifies Space and Time Velocity of Light c=300,000 Km/s =3x10^8 m/s=6.7 x 10^8 miles/hour

4. Equivalence Principle:the fundamental principle that unifies inertial and gravitational mass M_inertial=M_gravitational This simple experimental fact is the essential basis for Einstein’s theory of Gravity: General Relativity

5. Acceleration It is not possible to distinguish between gravity and an uniformly accelerated system Gravity can be simulated by an accelerated system

6. The absence of gravity is equivalent to free fall The presence of gravity can be neutralized in a Reference system in free fall

7. The observer in free fall with the elevator doesn’t see any change in the vertical position of the sphere In the meanwhile the observer on the ground sees an horizontal and vertical change in position and interprets the motion as a “curved” path

8. The other way around If the acceleration is produced by gravity As observed by the observer inside the elevator Also light can be bent Gravity = curvature in the Fabric of Space-Time As observed by external observer if acceleration is produced by rocket this is what it will be observed

9. The essential effects of gravity are of tideal nature The difference is that gravity has GLOBAL Geometric properties (locally just undistinguishable from accelerated frame)

10. Curvature of Space Time caused by the sun This is a quasi-static situation for what concerns space-time Matter tells space-time how to curve; the curvature “tells” to matter how to move Einstein ‘s Equation G= 8pG/c^4 T http://www.pbs.org/wgbh/nova/einstein/relativity/animations.html

11. Acceleration of Mass creates Gravitational Waves The waves travel at the velocity of light (3x10^8m/s) and the waves’ amplitude goes downs with distance

12. Polarization (cross) x Gravitational radiation has 2 polarizations and the energy is emitted mostly in the quadrupole (“football shape distribution of matter required”) The wave arrives in the direction perpendicular to the circle Polarization (plus) +

13. Sources of gravitational waves Supenovae Neutron Stars that rotate (or wobble in space) Coalescent Binary Systems of Black Holes and/or Neutron Stars Cosmic Background caused by the Big Bang

14. Detectors of Gravitational Waves Resonant Bars (LSU) Sphere (Rome ?) Interferometers (LIGO)

15. Cylindrical Bars, typically made of alluminum (about 1 ton. ). They work on the principle of resonance, they are tuned at about 1000 Hz, the resonant frequency of neutron stars . The wave interacts with the bar and the motion is transmitted to a sophisticated “microphone” that transform the mechanical motion into an electrical impulse: this is our signal. Resonant Bars

16. Sources of noise: How to control • Seismic (suspension system) • Thermal (low temperature) • Eletronic (SQUID) The noise Problem Mathemathical tools to extract signal: Filtering. For continuous signals: Integration with long observation times. Noise is bigger than signal in the current detectors (we don’t see anything than noise !). Noise at h=10^-20 Signal maybe at h=10^-21 or less

17. Mirror • LIGO (USA, Louisiana & Washington) • VIRGO (ITALY, Pisa) • TAMA (JAPAN) • GEO 600 (GERMANy, Postdam) • LISA (NASA-ESA, In space, 2016) 4 km Vacuum Pipes Interferometers Mirror Range of sensitivity on earth 10-1000 Hz In space 10^-4-1 Hz Laser 10 Watts Semi-transparent Mirror Photodetector

18. Neutron stars Continuous sources. They rotate up to frequencies of 1000 Hz. To emit GW they have to be tri-axial (football shaped). The strain (h=deformation/length measured ) for a star with 3 axis is: They can also wobble: if axis of rotation doesn’t coincide with symmetry axis. In this case star doesn’t need to be a football to emit Gravitational Waves.

19. Burst sources:Supernovae and Coalescent Systems Explosion of Supernovae have to be asymmetric to radiate gravitationally. The neutron star that is left over after the explosion vibrate violently (~1000 Hz) • Coalescent Systems: compact objects as black holes and neutrons stars. Binary Systems are very “football shape” like. They emit Gravity Waves so they loose energy. The system is inspiraling until it collides (in time scales of millions of years). Indirect evidence of GW: pulsar 1913+16 (Taylor and Hulse: 1993 Nobel Prize winners).

20. Cosmic Background The most ancient evidence of the birth of the Universe. Electromagnetic Background300,000 years after the Big Bang (a young baby, 0.7 day old). Gravitational Background is a “polaroid” of the birth of the Universe (as it was born !) Gravity doesn’t interact a lot with matter. We don’t know what to expect but we have some vague ideas from other cosmological observations.

21. Conclusion: What can we learn from Gravitational Waves? Another, fundamental confirmation of General Relativity (Viva Einstein !) New window on the Universe. Radiation very different from EM and particles. Bulk Motion of mass. GW do not interact well with matter. We can probe very high density region of the universe as neutron stars and the core of black holes. Birth Cry of the Universe.