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Acknowledgement
I would like to express my gratitude towards my Physics
Teacher Mrs. A. Mukhopadhyaya and our Principle Mr. D. A.
Luke who gave me a wonderful opportunity to gain
knowledge by doing this wonderful project on “Gravitational
Waves”. This project enabled me to come across many new
things which gave me a new experience and greatly increased
my knowledge.
Secondly I would like to thanks my parents who helped me
in completing this project by providing me with all the
necessary things and support required to complete this
project. They also helped me a lot in finalizing this project
within the limited time frame.
I greatly thankful to all of the people who were involved in
completing this project.
Lastly I would like to thank God who kept me well and gave
me enough wisdom to complete this knowledgeable project.
INTRODUCTION
Albert Einstein
Einstein first postulated the existence of gravitational waves in 1916 as a consequence of his theory of General Relativity, but no direct detection of such waves has been made yet. The best evidence thus far for their existence is due to the work of 1993 Nobel laureates Joseph Taylor and Russell Hulse. They observed, in 1974, two neutron stars orbiting faster and faster around each other, exactly what would be expected if the binary neutron star was losing energy in the form of emitted gravitational waves. The predicted rate of orbital acceleration caused by gravitational radiation emission according to general relativity was verified observationally, with high precision. Cosmic gravitational waves, upon arriving on earth, are much weaker than the corresponding electromagnetic waves. The reason is that strong gravitational waves are emitted by very massive compact sources undergoing very violent dynamics. These kinds of sources are not very common and so the corresponding gravitational waves come from large astronomical distances. On the other hand, the waves thus produced propagate essentially unscathed through space, without being scattered or absorbed from intervening matter.
It all started with Einstein’s theory of general relativity which predicted the existence of “Gravitational Waves” in space time.
Einstein’s theory stated that objects cause the fabric of space-time around them to curve. Moving objects should therefore create ripples in space- time.
It predicted that the more massive the object, the larger the gravitational waves it would create.
Since then, many astronomers have studied pulsar radio-emissions (pulsars are neutron stars that emit beams of radio waves) and found similar effects, further confirming the existence of gravitational waves. But these confirmations had always come indirectly or mathematically and not through direct contact.
While the processes that generate gravitational waves can be extremely violent and destructive, by the time the waves reach Earth they are thousands of billions of times smaller! In fact, by the time gravitational waves from LIGO's first detection reached us, the amount of space-time wobbling they generated was a 1000 times smaller than the nucleus of an atom!
Mirrors at the ends of each arm
form a long “resonant cavity,” in which laser light of a precise wavelength bounces back and forth, resonating just as sound of a specific pitch rings in an organ pipe. Where the arms meet, the two beams can overlap. If they have traveled different distances along the arms, their waves will wind up out of step and interfere with each other. That will cause some of the light to warble out through an exit called a dark port in synchrony with undulations of the wave. From the interference, researchers can compare the relative lengths of the two arms to within 1/10,000 the width of a proton — enough sensitivity to see a passing gravitational wave as it stretches the arms
All of this changed on September 14, 2015, when Laser Interferometer Gravitational-wave Observatory (LIGO) physically sensed the undulations in space-time caused by gravitational waves generated by two colliding black holes 1.3 billion light-years away. LIGO's discovery will go down in history as one of humanity's greatest scientific achievements.
Artist's Impression of a Binary Pulsar
LIGO watches for a minuscule stretching of space with what amounts to ultraprecise rulers: two L-shaped contraptions called interferometers with arms 4 kilometers long.
The LIGO facility in Livingston, Louisiana
by different amounts. To spot such tiny displacements, however, scientists must damp out vibrations such as the rumble of seismic waves, the thrum of traffic, and the crashing of waves on distant coastlines.
Why are these waves so hard to detect?
By the time gravitational waves reach us from the distant events that spawn them; they distort space-time by an utterly minuscule amount. The distortion is many times smaller than the width of a proton, one of the particles in an atom’s nucleus. Measuring such minute changes in length is pretty much impossible for most instruments.
Why should we care about these things?
Since LIGO’s first detection, we’ve gained unexpected insight into the cosmos. That’s because gravitational waves are a new way of “seeing” what happens in space: We can now detect events that would otherwise leave little to no observable light, like black hole collisions. And with this latest detection, astronomers were able to combine gravitational waves with more traditional ways of seeing the universe, helping to untangle mysteries about the dense, dead objects known as neutron stars.
Using the Swope and Magellan telescopes in Chile, astronomers recorded the neutron star explosion as it suddenly appeared as a bright spot in visible light and then faded. After about seven days, the spot was no longer detected in visible wavelengths.
Properties of Gravitational Waves
Energy, momentum, and angular momentum
Water waves, sound waves, and electromagnetic waves are able to carry energy, momentum, and angular momentum and by doing so they carry those away from the source. Gravitational waves perform the same function. Thus, for example, a binary system loses angular momentum as the two orbiting objects spiral towards each other — the angular momentum is radiated away by gravitational waves.
The waves can also carry off linear momentum, a possibility that has some interesting implications for astrophysics.^ After two supermassive black holes coalesce, emission of linear momentum can produce a "kick" with amplitude as large as 4000 km/s. This is fast enough to eject the coalesced black hole completely from its host galaxy. Even if the kick is too small to eject the black hole completely, it can remove it temporarily from the nucleus of the galaxy, after which it will oscillate about the center, eventually coming to rest. A kicked black hole can also carry a star cluster with it, forming a hyper- compact stellar system. Or it may carry gas, allowing the recoiling black hole to appear temporarily as a "naked quasar ”. The quasar SDSS J092712.65+294344.0 is thought to contain a recoiling supermassive black hole
Redshifting
Like electromagnetic waves, gravitational waves should exhibit shifting of wavelength and frequency due to the relative velocities of the source and observer (the Doppler Effect), but also due to distortions of space-time, such as cosmic expansion. This is the case even though gravity itself is a cause of distortions of space-time. Redshifting of gravitational waves is different from redshifting due to gravity (gravitational redshift).
Quantum gravity, wave-particle aspects, and graviton
In the framework of quantum field theory, the graviton is the name given to a hypothetical elementary particle speculated to be the force carrier that mediates gravity. However the graviton is not yet proven to exist and no scientific model yet exists that successfully reconciles general relativity, which describes gravity, and the Standard Model, which describes all other fundamental forces. Attempts, such as quantum gravity, have been made, but are not yet accepted.
If such a particle exists, it is expected to be massless (because the gravitational force appears to have unlimited range) and must be a spin-2 boson. It can be shown that any massless spin-2 field would give rise to a force indistinguishable from gravitation, because a massless spin-2 field must couple to (interact with) the stress – energy tensor in the same way that the gravitational field does; therefore if a massless spin-2 particle were ever discovered, it would be likely to be the graviton without further distinction from other massless spin- particles. Such a discovery would unite quantum theory with gravity
Significance for study of the early universe
Due to the weakness of the coupling of gravity to matter, gravitational waves experience very little absorption or scattering, even as they travel over astronomical distances. In particular, gravitational waves are expected to be unaffected by the opacity of the very early universe. In these early phases, space had not yet become "transparent", so observations based upon light, radio waves, and other electromagnetic radiation that far back into time are limited or unavailable. Therefore, gravitational waves are expected in principle to have the potential to provide a wealth of observational data about the very early universe.
The first detection of gravitational waves was a very important event in science. Before this, just about everything we knew about the universe came from studying waves of light. Now we have a new way to learn about the universe — by studying waves of gravity.
Gravitational waves will help us learn many new things about our universe. We may also learn more about gravity itself!
The current study is looking at gravitational waves were theorized about a hundred years ago by Einstein (not the dog), but it took two black holes colliding 1.3 billion years ago for us to finally confirm their existence. A gravitational wave is a wave through space-time (the fabric of the universe) this means that space and time can be bent which means time travel / teleportation is half-possible, it is also a guaranteed Nobel Prize to LIGO team. Throughout history, humans have mainly relied on different forms of light to observe the universe. Today, we are on the edge of a new frontier in astronomy: gravitational wave astronomy. Gravitational waves carry information on the motions of objects in the universe. Since the universe was transparent to gravity moments after the Big Bang and long before light, gravitational waves will allow us to observe further back into the history of the universe than ever before. And since gravitational waves are not absorbed or reflected by the matter in the rest of the universe, we will be able to see them in the form in which they were created. Moreover, we will effectively be able to "see through" objects between Earth and the gravitational wave source. Most importantly, gravitational waves hold the potential of the unknown. Every time humans have opened new "eyes" on the universe, we have discovered something unexpected that revolutionized how we saw the universe and our place within it. Today, with the United States' gravitational wave detector (LIGO) and its international partners, we are preparing to see the universe with a new set of eyes that do not depend on light.
All the information of the above project is taken from the following sources:
www.sciencemag.org www.ligo.caltech.edu www.nationalgeographic.com spaceplace.nasa.gov
en.wikipedia.org www.researchgate.net
