How gravitational waves are formed?
Any object with heavy mass that accelerates ( means changes position at a variable rate of time, and includes spinning or orbiting objects) produces gravitational waves.
This includes humans, cars, musical instruments, and airplanes, etc. but the gravitational waves made by these sources on Earth are much too small to detect.
How gravitational waves are formed? | Overview
So we cannot generate detectable gravitational waves on Earth, the only way to study the gravitational waves in the Universe where they are generated by nature process.
The Universe is filled with incredibly heavy massive objects that undergo rapid accelerations due to a large amount of energy
LIGO scientists have introduced four categories of gravitational waves based on what causes them.
These categories are following below
Types of gravitational waves
- Continuous Gravitational Waves
- Compact Binary Inspiral Gravitational Waves
- Stochastic Gravitational Waves
- Burst Gravitational Waves
Each waves type generates unique prints or characteristic vibrational signals that LIGO’s interferometers can sense by LIGO’s data.
These types are described in more detail below.
Artist’s depiction of a super denser and compact neutron star.
The continuous gravitational waves are produced by a spinning of single massive object, like a neutron star.
Any cracks on the surface in the spherical shape of this star will generate gravitational waves as it spins.
The gravitational waves emit If the spin rate of the star remains constant.
That’s gravitational waves are continuously the same frequency and amplitude.
That’s why these are called “Continuous Gravitational Waves”.
Scientists have created simulations of what an arriving continuous gravitational wave would produce a sound like if the signal LIGO detected was converted into a sound.
Compact Binary Inspiral Gravitational Waves
The next type is the Compact Binary Inspiral.
Compact binary inspiral gravitational waves are produced by orbiting pairs of massive and denser (“compact”) objects like white dwarf stars, neutron stars, and black holes.
There are three subclasses of “compact binary” systems in this category by which the gravitational wave generators:
- Binary Neutron Star
- Binary Black Hole
- Neutron Star-Black Hole Binary
Each binary pair creates a unique characteristic series of gravitational waves, but the mechanism of wave-generation is the same across all three; it’s called, “inspiral”.
Inspiral occurs over millions of years as pairs of these heavy and dense compact objects orbiting around each other.
As they orbit, they emit gravitational waves in the form of radiations, by which some of the system’s orbital energy removes.
Over eons, the objects inch, come closer together.
Unfortunately, moving closer causes them to orbit each other move faster, which emit stronger gravitational waves,
which causes them to lose more orbital energy in the form of radiation, inch ever closer, orbit faster, lose more energy, move closer, orbit faster… etc.
The stars are now destroyed, inescapably locked in a runaway accelerating spiraling embrace.
Imagine that the skater’s outstretched fists are neutron stars, black holes, and the skater’s body is the force of gravity attracting them with each other together.
As the spinning skater pulls them toward their body (as the object’s orbit closer and closer), they spin faster and faster.
Unlike the skater, however, the pairs of stars, pulsars stars or black holes cannot halt their rotation.
The process of emitting gravitational waves and orbiting closing or closer sets off an unstoppable sequence of events that can only end with the two objects colliding with each other,
generating one of the Universe’s big violent explosions.
Colliding black holes produce characteristically short gravitational waves on the order of fractions of a very short time,
whereas neutron stars generate signals several times longer than black holes.
In both cases, the signal frequency increases rapidly as the objects spiral into each other, orbiting more-faster.
LIGO has detected both merging black holes and neutron stars, and the differences in their signals quite the same.
LIGO’s detect first merging black hole merger that produced a signal just two-tenths of a second long.
This signal was converted into an audible sound we call a “chirp”.
On the other end, the merging neutron star that LIGO detected in August 2017 generated a signal that was seen in LIGO’s detectors for over 100 seconds.
These two examples of actual gravitational waves illustrate how different systems of merging objects generate completely unique signals in the interferometers.
Shorter signals mean the object has more massive, like black holes, were involved; longer signals suggest that objects have low mass, like neutron stars.
Stochastic Gravitational Waves
Astronomers predicted that there are few sources of continuous gravitational waves or binary inspiral gravitational waves in the Universe that LIGO doesn’t worry about the possibility of more than one passing by Earth at a time (producing confusing signals in the detectors).
However, we assume that many small gravitational waves are passing from all over the Universe at a time and that they are mixed together at random.
These small waves from in every direction make up what is called Stochastic Signal.
The word, ‘stochastic’ means having a random pattern means no proper direction that may be analyzed statistically but not predicted precisely.
These will be the smallest and more difficult gravitational waves to detect, but it is possible that at least part of this signal may originate from the Big Bang.
Burst Gravitational Waves
The burst gravitational wave is truly a search for the unexpected because we have yet to detect them,
and because there are still so many phenomena that are unknowns, we really don’t know what to expect!
For example, sometimes we don’t know enough about the physics of a source to predict how the gravitational waves from that source will appear.
We expect to detect gravitational waves from the source we never knew about before. To search for these types of gravitational waves,
we cannot assume that they will have well-defined properties and characteristics like those of continuous and compact binary inspiral waves.
This means we cannot restrict our analyses to searching only for the signals of gravitational waves that scientists have predicted.