What are Gravitational Waves?
In a recent announcement that electrified the world of astronomy, Scientist from Laser Interferometer Gravitational- wave Observatory (LIGO) revealed that they had detected gravitational waves, the ripples in the fabric of space-time that Albert Einstein predicted a century ago. Some scientists likened the breakthrough to the moment Galileo took up a telescope to look at the planets.
What are Gravitational Waves?
First proposed in 1916 by Albert Einstein, gravitational waves are ripples in space and time that are produced when whole black holes collide and stars explode. Through these waves scientists hope to gain valuable insight into the universe because these waves experience no barriers, unlike electromagnetic waves such as radio waves, visible light, infrared light, X-rays, and gamma rays. Black holes, do not emit light, radio waves and the like, but can be studied via gravitational waves. Unlike seismic waves, however, gravitational waves can travel in empty space — and they do so at the speed of light.
Gravitational Waves, first theorised by Einstein in 1916 as part of his theory of general relativity, are extraordinarily faint ripples in space-time, the hard- to-fathom fourth dimension that combines time with the familiar up, down, left and right. When massive but compact objects like black holes or neutron stars collide, they send gravity ripples across the universe.
Scientists found indirect proof of the existence of gravitational waves in the 1970’s – computations that showed they ever so slightly changed the orbits of two colliding stars- and the work was honoured as part of the 1993 Nobel Prize in Physics. But recent announcement was a direct detection of gravitational waves.
In 1979, the National Science Foundation decided to give money to the California Institute of Technology and Massachusetts Institute of Technology to come up with a ways to detect the waves.
Ripples in space-time, a bit like ripples on a pond that propagate out at the speed of light. Throw something really big into the stillness of space – like two black holes colliding, or two pulsars merging – and gravitational waves created by the event should spread not just across the galaxy, but ultimately through all of space-time.
Rippling out from a super- massive collision, for example between two black holes, gravity waves could be detected through the stretching and contracting of space and time.
Gravitational waves are distortions or ‘ripples’ in the fabric of space-time caused by some of the most violent and energetic processes in the Universe. Einstein’s mathematics showed that massive accelerating objects (such as neutron stars or black holes orbiting each other) would disrupt space-time in such a way that ‘waves’ of distorted space would radiate from the source. Furthermore, these ripples would travel at the speed of light through the Universe, carrying with them information about their cataclysmic origins, as well as invaluable clues to the nature of gravity itself.
The strongest gravitational waves are produced by catastrophic events such as colliding black holes, the collapse of stellar cores (supernovae), coalescing neutron stars or white dwarf stars, the slightly wobbly rotation of neutron stars that are not perfect spheres, and the remnants of gravitational radiation created by the birth of the Universe itself.
Sources and Types of Gravitational Waves
Any object with mass that accelerates (which in science means changes position at a variable rate, and includes spinning and orbiting objects) produces gravitational waves, including humans and cars and airplanes etc. But the gravitational waves made by us here on Earth are much too small to detect. In fact, it isn’t even remotely possible to build a machine that can spin an object fast enough to produce a detectible gravitational wave.
Since we can’t generate detectable gravitational waves on Earth, the only way to study them is to look to the places in the Universe where they are generated by nature. The Universe is filled with incredibly massive objects that undergo rapid accelerations (things like black holes, neutron stars, and stars at the ends of their lives). In order to understand the types of gravitational waves these objects may produce, LIGO scientists have defined four categories of gravitational waves, each with a unique “fingerprint” or characteristic vibration signature that the interferometers can sense and that researchers will look for in LIGO’s data. These categories are: Continuous Gravitational Waves, Compact Binary In spiral Gravitational Waves, Stochastic Gravitational Waves, and Burst Gravitational Waves. Each of these kinds of gravitational wave generators is described below.
Continuous Gravitational Waves
Continuous gravitational waves are produced by a single spinning massive object, like an extremely dense star called a neutron star. Any bumps or imperfections in the spherical shape of this star will generate gravitational waves as the star spins. If the spin rate of the star stays constant, so too do the properties of the gravitational waves it emits. That is, the gravitational wave is continuously the same frequency and amplitude.
Compact Binary in spiral Gravitational Waves
The next class of gravitational waves is called Compact Binary In spiral. Compact binary in spiral gravitational waves are produced by orbiting pairs of massive and dense (hence “compact”) objects like white dwarf stars, black holes and neutron stars. There are three kinds of “compact binary” systems in this category of gravitational wave generators include Binary Black Hole (black hole-black hole)or BBH, Binary Neutron Star (neutron star-neutron star) or BNS, Neutron Star-Black Hole Binary (NSBH)
Each binary pair creates a characteristic series of gravitational waves, but the mechanism of wave-generation is the same across all three. It’s called, “In spiral”.
In spiral occurs over millennia as binary pairs of these dense compact objects revolve around each other. With each revolution, they emit gravitational waves. These waves carry away some of the system’s orbital energy meaning that the objects in the system lose some of the energy they need to maintain the distance between them. Each revolution removes a little more energy so that over eons, the objects inch closer and closer together. Unfortunately, moving closer means orbiting faster, which means emitting more gravitational waves, which causes the pair to lose more orbital energy, move ever closer, orbit faster, lose more energy, move closer, orbit faster etc.
Compact Binary In spiral Gravitational waves are characteristically short in duration (several seconds to less than a second long) and increase in frequency as the stars orbit ever-faster. The expected gravitational wave signals from merger of neutron stars and black holes have been modeled into audible signals based on the frequencies of the gravitational waves as they would arrive at LIGO’s detectors
Stochastic Gravitational Waves
Astronomers predict that there are so few significant sources of Continuous or Binary In spiral gravitational waves in the Universe that we don’t worry about the possibility of more than one passing by Earth at the same time (potentially producing confusing signals in the detectors).There are many small gravitational waves coming from all over the Universe that all combine together. These small waves from every direction make up what we call a “Stochastic Signal”, so called because the word, ‘stochastic’ means, having a random pattern that may be analyzed statistically but may not be predicted precisely. These will be the smallest (i.e. quietest) and most difficult gravitational waves to detect, but it is possible that at least part of this stochastic signal may originate from the Big Bang.
Burst Gravitational Waves
Burst gravitational waves are truly a search for the unexpected—both because we’ve never detected them directly before, and because there are still so many unknowns that we really don’t know what to expect or what we might find. Sometimes we don’t know enough about the conditions and physics of a system to be able to predict how the gravitational waves from that source will appear. We also expect to find gravitational waves from systems we never knew about before. Searching for burst gravitational waves is an exercise in being utterly open-minded. For these kinds of gravitational waves, scientists must maintain an ability to recognize when a noticeable pattern of signals arrives, even when such a signal has not been predicted or modeled before.
Significance of Gravitational Waves
As vibrations in the fabric of space-time, gravitational waves are often compared to sound, and have even been converted into sound snippets. Gravitational-wave telescopes allow scientist to ‘hear’ phenomena at the same time as light- based telescopes ‘see’ them.
The discovery of these gravitational waves, created by violent collisions in the universe, it opens the door to a new ways of observing the cosmos. These waves are sound track of cosmos. Gravitational waves provide a completely new way at looking at the Universe. The ability to detect them has the potential to revolutionize astronomy. This discovery is the first detection of a black hole binary system and the first observation of black holes merging. These waves are a ripple in the invisible fabric of the universe, called the space-time continuum.
Gravitational waves give us another way to observe space. So detecting these waves would give us a new insight into the cosmic events that produced them.
Gravitational waves could also help physicists understand the fundamental laws of the universe. Finding them would prove that theory—and could also help us figure out where it goes astray. This will lead to a more accurate, more all- encompassing model, and perhaps point the way toward a theory of everything.
Gravitational waves are important in telling about the early universe. The cosmic microwave background gives us a snapshot of the universe about 380,000 years after the start of the universe. Looking very closely at the cosmic microwave background there are structure of the universe. These patterns in the cosmic microwave background were caused by very tiny random perturbations from the time when the universe expanded rapidly, known as inflation.
Inflation should also generate gravitational waves. These waves affect polarisation of the cosmic microwave background. Measuring the strength of the polarisation due to gravitational waves gives us a ballpark figure of the amount of energy involved at the time of inflation and helps pin down when inflation occurred.
These waves are the confirmation of a cornerstone theory of the standard picture of cosmology. This theory, called inflation, says that during the first moments of its existence, the Universe underwent a brief period of exponential expansion.
The waves are the confirmation of a cornerstone theory of the standard picture of cosmology. This theory, called inflation, Because inflation is a quantum phenomenon and gravitational waves are part of classical physics, gravitational waves establish a link between the two, and could be the first evidence that gravity has a quantum nature just like the other forces of nature
Role of Indian Scientists
Indian scientist played a crucial role, including in data analysis, in the path braking project for the detection of gravitational waves. Several institutions, including Institute of Plasma Research (IPR) Gandhinagar, Inter University Centre for Astronomy and Astrophysics (IUCAA), Pune, and Raja Ramanna Centre for Advanced Technology (RRCAT), Indore were involved in the research.
