The sound of the Universe: The search for Gravitational Waves

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The sound of the UniverseThe search for
Gravitational Waves

• Giovanni Santostasi, Ph. D.
• Baton Rouge Community College,
• Baton Rouge, LA

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Newton and Einsteintheories of Space and
Time Special Relativity Space-Time constant
velocityGeneral Relativity Geometry-Space-Time
acceleration
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Space and Time Unified

• Time and Space are not separated quantities but
  different aspects of a same reality (Space-Time
  continuum)

Relativity of the reference system Absoluteness
of the laws of Physics
Light unifies Space and Time Velocity of Light
c300,000 Km/s 3x108 m/s6.7 x 108 miles/hour
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Equivalence Principlethe fundamental principle
that unifies inertial and gravitational mass

• M_inertialM_gravitational

This simple experimental fact is the essential
basis for Einsteins theory of Gravity General
Relativity
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Acceleration It is not possible to distinguish
between gravity and an uniformly accelerated
system

• Gravity can be simulated by an accelerated system

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The absence of gravity is equivalent to free fall

• The presence of gravity can be neutralized in a
• Reference system in free fall

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The observer in free fall with the elevator
doesnt 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

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Also light can be bent
The other way around If the acceleration is
produced by gravity
As observed by the observer inside the elevator

• 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
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The essential effects of gravity are of tideal
nature

• The difference is that gravity has
• GLOBAL
• Geometric properties
• (locally just undistinguishable from accelerated
  frame)

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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/c4 T
http//www.pbs.org/wgbh/nova/einstein/relativity/a
nimations.html
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Acceleration of Mass creates Gravitational Waves

• The waves travel at the velocity of light
  (3x108m/s) and the waves amplitude goes downs
  with distance

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Gravitational radiation has 2 polarizations and
the energy is emitted mostly in the quadrupole
(football shape distribution of matter required)
Polarization (cross) x

• The wave arrives in the direction perpendicular
  to the circle

Polarization (plus)
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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

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Detectors of Gravitational Waves

• Resonant Bars (LSU)
• Sphere (Rome ?)
• Interferometers
• (LIGO)

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Resonant Bars
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.
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The noise Problem

• Noise is bigger than signal in the current
  detectors (we dont see anything than noise !).
  Noise at h10-20
• Signal maybe at h10-21 or less

• Sources of noise How to control
• Seismic (suspension system)
• Thermal (low temperature)
• Eletronic (SQUID)

Mathemathical tools to extract signal Filtering.
For continuous signals Integration with long
observation times.
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Interferometers
Mirror

• LIGO (USA, Louisiana Washington)
• VIRGO (ITALY, Pisa)
• TAMA (JAPAN)
• GEO 600 (GERMANy, Postdam)
• LISA (NASA-ESA, In space, 2016)

4 km
Vacuum Pipes
Mirror
Laser 10 Watts
Semi-transparent Mirror

• Range of sensitivity on earth 10-1000 Hz
• In space 10-4-1 Hz

Photodetector
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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 (hdeformation/length measured )
• for a star with 3 axis is

They can also wobble if axis of rotation doesnt
coincide with symmetry axis. In this case star
doesnt need to be a football to emit
Gravitational Waves.
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Burst sourcesSupernovae 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 191316
  (Taylor and Hulse 1993 Nobel Prize winners).

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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
  doesnt interact a lot with matter.
• We dont know what to expect but we have some
  vague ideas from other cosmological observations.

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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.