In Search Of

Gravity And Gravity Waves

Presented by,

Swati. M. Pujar

BSc IV sem

RLSI Belagavi

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.

What is an electromagnetic Spectrum?

In 1820, Hans Christian Oersted discovered that electric currents (moving electric charges) create magnetic fields.

In 1831, Michael Faraday discovered that varying magnetic fields create electric currents.

In 1864, James Clerk Maxwell put two and two together.

• 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!

Sources of gravitational waves

Inspiral sources:

Neutron Star Binary stars

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

AIGO (opened in 2000) and Wallingup Plain

Livingston, Louisiana Hanford, Washington

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 !!

Thank You