gravity waves
TRANSCRIPT
1) What is a gravity wave?
2) What is an electromagnetic spectrum?
3) Gravity waves versus EM waves
4) Gravity
5) Gravitational-waves
6) Sources of gravitational waves
7) How do we know that GWs exist ?
8) How do we Detect gravitational waves?
9) Conclusion
What is a gravity wave?A gravity wave is a ripple in the curvature of the space time continuum created by the movement of matter
They were predicted in Einstein’s General
Theory of Relativity
GWs are produced by accelerated masses.
In 1820, Hans Christian Oersted discovered that electric currents (moving electric charges) create magnetic fields.
• Oscillating electric fields create oscillating magnetic fields.
• Oscillating magnetic fields create oscillating electric fields.
• Together, electromagnetic waves propagate through empty space at a speed Maxwell calculated to be 3 x 108 meters per second.
In 1886, Heinrich Hertz experimentally demonstrated creation and propagation of electromagnetic waves at the speed of light.
It was eventually realized that:
• Radio
• Microwave
• Infrared Light
• Visible Light
• Ultraviolet Light
• X-Ray Radiation
• Gamma Ray Radiation
are all forms of Electromagnetic Waves.
Gravity waves versus EM waves
EM waves are produced by accelerated charges
EM waves propagatethrough space-time
Typical frequencies of EM waves range from (107 Hz – 1020 Hz).
Waves are easy to detect, but easily blocked
GWs are produced by accelerated masses.
GWs are oscillations of space-time itself.
GW frequencies range from ~ (10-9 Hz – 104 Hz). They are more like sound waves
Waves are hard to detect, but pass undisturbed through anything
Gravity
Einstein’s General theory of relativity :
Gravity is a manifestation of curvature of 4- dimensional (3 space + 1 time) space-time produced by matter
If the curvature is weak, it produces the familiar Newtonian gravity:
F = G M1 M2/r2
Gravitational-waves
When the curvature varies rapidly due to motion of the object(s), curvature ripples are produced. These ripples of the space-time are Gravitational-waves.
Gravitational-waves propagate at the speed of light.
They represent an entirely new spectrum.
Gravity wave detectors are the ears that will
allow us to listen to the sounds of the
universe.
All moving masses change space time around them!
Exploding stars:
Explosion caused by the collapse of an old, burnt-out star produces a burst of gravitational radiation,
Primordial background:
Left over radiation from the beginning of the Universe
Collision of two stellar remnants
Produce a sweeping “chirp” as they spiral together
Stochastic sources Sources that are highly speculative, or not predicted at all!
Could sound like anything
E.g. a possible signal from a folded cosmic string:
How do we know that GWs exist ?
Indirect proof
Hulse-Taylor binary pulsar (Nobel prize 1993)
Steady decrease in orbital separation due to loss of energy through GWs.
How do we detect gravitational waves?
Resonant bars: Selectively amplify distortions that are “tuned” to their natural frequency
First detectors built in the 1960s
Respond only to a narrow frequency range
Laser interferometers: measure relative motions of separate, freely-hanging masses
Masses can be spaced arbitrarily far apart
Respond to all frequencies between 40 and 2000 Hz
Ground based detectors:
LIGO (U.S.A), VIRGO (Italy), GEO (Germany), TAMA (Japan), AURIGA (Australia)
Space-based detectors:
LISA (NASA-ESA)
Laser Interferometer Gravitational Wave Observatory
LIGO
Length of each arm, L = 4 km,
frequency range , f = 10 Hz – 104 Hz
What type of sources can LIGO detect ?
Last stages of inspiral of Binary NS
Mergers of stellar and super-massive black holes
Core-collapse supernovae
Pulsars
Laser Interferometer Space Antenna (LISA)Use onboard lasers to amplify and reflect
beams
5 million km arms respond to very low frequencies (0.0001 to 0.1 Hz)
Sensitive to super-massive black holes
Sources for LISA
• Double White Dwarfs
• White-dwarf black hole
• Supermassive and Intermediate mass black holes
Conclusion:
GWs bring info about objects that can not be seen with EM observations and vice-versa.
This is a radically different field than EM observations.
Measuring a length smaller than proton size is no longer a science fiction !!