Gravitational Force:

Gravity is the fundamental force of life. It is the basis that holds us to earth, the moon and regulates the motion of stars, galaxies and other celestial objects in the galaxy and universe. It is a force which affects each and every particle in the universe and helps in holding these tiny particles cohesively to give the world its structural formation.

Newton’s Law of Universal Gravitation: 

Envision a universe where apples do not drop from trees, and the moon does not hover perfectly around the earth. This was the world before Sir Isaac Newton, a scientist who introduced people to the laws of gravity through the Law of Universal Gravitation. He put forward that each particle in the universe tends to attract every particle in the universe with a force that is equal to the sum of the products of their masses and inversely as the square of the distance between their centers. This was a very basic yet impactful formula that changed the view toward the universe, F = G(m1m2)/r².

Celestial Bodies: 

Cosmic objects are the stars, planets, moons, asteroid, comets, and galaxies that exist in the universe. They are connected by gravity, and they move around in a dance that is controlled by this force.

Influence of Gravity on Celestial Bodies: 

• Orbiting Bodies

Kepler’s Laws of Planetary Motion:

Picture the sky as a vast clock which has parts, such as planets that orbit the sun perfectly. This is the general form of Kepler’s laws, the smooth motions that govern the motions of planets.

Kepler’s First Law: 

The planets move in elliptical orbits around the Sun with the Sun at one of the foci of the ellipse. This means that the orbits of these objects are not circular but rather oval-shaped.

Kepler’s Second Law: 

The line joining a planet to the Sun describes equal areas in space in equal times. They indicate that a planet revolves faster if it is closer to the star than if it is far away from it.

Kepler’s Third Law: 

The square of the time it takes a planet to go round the Sun is equal to the cube of the average distance between the planet and the Sun. This law states that there is a direct proportion between the size of the orbit and the time it takes a planet to make one revolution.

These laws which were found out by careful observation of heavenly objects formed the basis of appreciating the complex motion of planets. However, it was Newton, who gave the theoretical background as to why these laws are constant.

Centripetal Force:

Consider an object such as a ball suspended from a string which is on the head of an individual. The string acts as a force which enforces the ball to move inwards and not to go off straight. This inward force is referred to as centripetal force.

In the cosmos, gravity can be considered as the string as it attracts any two objects towards the central mass and is the centripetal force that keeps planets in their orbits around stars, moons around planets, and stars within galaxies.

Orbital Velocity:

The rate of rotation of a celestial body depends on the relationship between momentum which a Celestial body has the tendency to maintain a straight path towards the center of mass and Gravity.

Stronger Gravity: 

This means that the higher the force of attraction, the greater the speed that must be used for any object that is orbiting to avoid getting pulled in towards the center.

Greater Distance: 

The further the body is from the central mass, the less the gravitational attraction, and hence the slower it must travel to remain in a circular path.

Imagine a planet revolving close to a star. It feels a strong gravitational pull and must move quickly to avoid falling in. A planet far from its star feels a weaker pull and can move more leisurely. 

Orbital Shapes:

It is important not to assume that orbits are perfect circles or oval shaped. It is, in fact, the path of an object based on the initial speed and direction in which the object is launched.

Circular Orbit: 

Circular orbit is the closest possible orbit whereby the orbiting body has the optimum velocity to sustain a fixed distance from the central mass.

Elliptical Orbit: 

The kind of orbit that is frequently used is an elliptical orbit. This is when the velocity of the orbiting body is not parallel to that of the path of the central mass, thus causing it to expand and contract in cyclic nature.

Parabolic Orbit: 

Parabolic orbit is one in which the orbiting body has sufficient energy to overcome the force of attraction of the central mass but it lies in a parabolic path.

Hyperbolic Orbit: 

A hyperbolic orbit is one where the orbiting body possesses sufficient energy to become free from the mass’s gravitational force and moves in a hyperbolic fashion.

Gravity determines whether the orbit will be open or closed and therefore whether the celestial body will stay with the central mass or be lost out into the universe.

Examples:

Earth around the Sun: 

The Earth moves in an elliptical fashion around the Sun with different seasons experienced due to distances from the Sun.

Moon around Earth: 

The Moon also moves about the Earth in an elliptical motion and the tides of the Sea fluctuate based on the strength of gravitational force exerted on the different geographical locations of the Earth.

These examples demonstrate the complex interactions between gravity and motion into orbits determining the celestial ballet in the solar system.

• Tidal Forces

The force of gravity is not equal for every part of an object. As a point approaches a big object, the pull becomes greater. The presence of a variation in the force of gravity gives rise to tidal forces.

Differential Gravity:

For instance, consider an arbitrary object such as a large rubber ball that is being dragged by another large body. Due to the force of gravity, the side of the rubber ball touching the massive object will experience a greater force of attraction than the side which is least in contact with the object. This variation in gravity from one part of the object to the other is called differential gravity.

Now to illustrate, let us consider Earth and the Moon. The one side of the earth, where the moon is, has a stronger force than the side where the moon is not. This difference in pull stretches the Earth slightly, forming water bulges on the two sides of the Earth.

Tidal Bulges:

These bulges of water are referred to as tidal bulges. Thus with the movement of the earth, the tidal bulge also moves in and out thereby creating the two tides. When a tidal bulge coincides with the Moon or the Sun, high tides are formed. While low tides form when the tidal bulge is at the other side of the Earth.

The Sun also has a tidal force on earth although this has a weaker pull compared to that of the moon since the sun is way much farther. When the Sun and the Moon are in-phase, then both pull in the same direction, causing very high tides that are referred to as spring tides. When the two are perpendicular the forces reduce each other hence leading to smaller tides referred to as neap tides.

Tidal Locking:

Tides caused by the Moon are regular because its rotation period is conjugated with the orbital one. This means that the same side of the moon always turns towards the earth. This occurrence is referred to as tidal locking due to the tidal forces at play.

When the Moon is in orbit around the Earth, direct Earth gravitation applies a torque to the Moon that causes it to slow down as it rotates. Due to this torque, the moon’s rotation slowly adjusts to take as long as its orbit around the earth.

It is important to note that tidal locking is not limited to the Moon-Earth system only. It is also important to note that most moons in the solar system are synchronously rotating with their host planets. It is also possible to have this between planets and stars.

Tidal Disruption:

Tide forces can grow quite intense in the proximity of large objects including black holes. These extreme tidal forces tend to pull objects apart – a phenomenon termed tidal disruption.

Suppose a star is orbiting a black hole and the distance between them decreases. The black hole gravitation will affect the star by pulling it with greater force on the side that is closer to the black hole rather than the farther side. This differential gravity can actually tear apart the star and the result is known as a tidal disruption event.

• Gravitational Interactions

Gravity is a natural and unchanging force that defines the behavior of objects in space.

Gravitational Attraction:

According to Newton, any two bodies in the universe will experience a force of attraction that is inversely proportional to square of distance between the two bodies, and directly proportional to the product of the masses.

This implies that the larger the objects, the larger the force of attraction between those objects. On the other hand, the closer the objects are, the stronger the force is and the farther apart they are, the weaker it becomes.

Collisions:

Gravitation can force astronomical objects to merge together, thereby resulting in the creation of new objects or the annihilation of others.

Planet Formation: Initially, gravitation force accumulated particles of dust and gasses and compressed them to form planetesimals. These planetesimals evolved through accretion, coming together in pairs or groups to become planets.

Supernovae: The core of massive stars undergoes gravitational collapse which results to supernova explosion that emits large amount of energy and synthesizes heavy elements.

Galaxy Mergers: Gravitation can result into merging of galaxies and formation of greater galaxies from smaller ones.

Gravitational Lensing:

Gravity bends light and this results in what is known as the lensing effect, whereby images of distant objects appear to be distorted.

Suppose there is a large body, for instance, a galaxy cluster located in between the Earth and a remote galaxy. Since light is attracted by gravity, the light coming from the distant galaxy will be bent by the gravity of the galaxy cluster therefore the distant galaxy will seem distorted or will seem to have several images. This process is referred to as gravitational lensing.

Gravitational Waves:

Gravity is not only a force that pulls objects together. It also produces disturbance in space-time fabric which is known as gravity waves. These waves are produced when two large objects meet, for instance, when two black holes merge.

Although, gravitational waves were predicted by the general theory of relativity by Einstein, its perception was first made in the year 2015 by LIGO Laser Interferometer Gravitational-Wave Observatory. The discovery of gravitational waves paved the way into capturing an event that was not clearly noticeable before.

• Gravity and Stellar Evolution

Gravity is responsible for the creation, growth and eventual demise of stars. This force is the key that dictates their future and their final lot in life.

Star Formation:

Think of a cloud of dust and gas, floating in the darkness of the space. In this cosmic cloud, gravity starts to be an artist and convokes the particles, begins to gather them into one place, gradually pulling them together. Because gravity causes the cloud to become more and more compressed, material within the cloud becomes so hot that elements combine to start nuclear fusion. This is the beginning of a star.

Stellar Equilibrium:

When a star starts burning, there is an equilibrium between the force of gravity acting inwards and the pressure of the nuclear fusion reactions occurring within the core of the star. Gravity constantly tries to merge the star while, on the other hand, the process of fusion act against the force of gravity by pushing the star outwards. The accumulation or distribution of these forces in a star, called the hydrostatic equilibrium prevents the star from collapsing for billions of years.

Stellar Evolution:

Stellar life can therefore be said to be dynamic in that it has various phases, and its evolution is a continuous process. It transforms sequentially due to gravity and nuclear fusion processes. As the star advances in its life cycle, the hydrogen reserves at its core begin to diminish. This leads to a reduction in the outward pressure hence the core is compressed by the force of gravity.

This contraction increases the temperature and pressure and causes elements such as helium to undergo fusion. This process leads to the expansion of the star and makes it a red giant star.

This leads to evolution of the star through the acquisition of new layers, gravity and nuclear fusion which makes the star to increase in size, temperature and luminosity. It is found that the history of stellar evolution is determined by the initial mass of stars.

 Supernovae and Neutron Stars:

Stars larger than the Sun undergo spectacular explosions at the end of their lives known as supernovae. When a huge star runs out of nuclear fuel in its core, it suddenly contracts under the force of gravity and explodes.

This causes an explosion that sends the star’s outer parts flying out into space and creating a very bright supernova. The core, however, compresses to an incredibly dense object referred to as the neutron star in which protons and electrons embrace to form neutrons.

Neutron stars are extremely compact objects with mass of the star in them but the size only a few miles. They possess strong fields and frequently spin rapidly, which results in radiation beams that can be detected as pulsars.

Sometimes the center of a huge star shrinks down to a density so high that even light cannot get away from it, forming a black hole.

Role of Gravity in the Universe 

Galaxy Formation and Evolution: 

Gravity is the builder of galaxies, pulling together huge clouds of gas and dust, sculpting the spiral lanes, ellipticals, and irregular patterns of these galactic cities. The interactions of stars within a galaxy result in a complex motion that holds them together and keeps the galaxy together.

Dark Matter and Gravity: 

There is something in the universe which is unknown, and it is called dark matter. It does not shine in any way, but its gravity is an undeniable force. Dark matter constitutes a significant fraction of the total mass in the universe. It plays an essential role in capturing and linking galaxies together while determines the distribution of distribution of galaxies depending on the type of clusters. This is a very interesting mystery and awareness of it is indispensable to explain the development of the universe.

The Expanding Universe: 

The expansion of the universe is considered to be one of the most fascinating discoveries in cosmology. Galaxies are getting away from each other and space between them is also expanding. This expansion is driven by unknown force, which is referred to as ‘dark energy,’ that works against gravity. In simple terms it is a fight between two universal powers and the outcome of this fight is the creation of the universe.

Conclusion

Gravity is the cosmic force that binds the heavens and earth, subatomic particles and galaxies, and everything else that exists in the universe. It explains the movement of planets, produces tides, is responsible for the development of stars and galaxies, and impacts the universe’s expansion.

Well, the concept of gravity, as we know it today, is by no means complete. Some of the key concepts, such as dark matter and dark energy, are still a subject of research to this day and the science behind gravity is still developing constantly. Exploring gravity as a force is a process of discovery, and the future promises new discoveries of this force as well.

FAQs

Q1. How does gravity affect the evolution of stars?

A: Gravity control is very important in the formation, existence, and destruction of stars. It combines the gas and dust to make stars, and it also maintains stability of stars by counteracting the outward pressure from nuclear fusion. 

Q2. How does gravity affect the orbits of planets?

A: Gravity makes planets orbit stars in elliptical orbits. The gravity of the star holds the planet in place, or, in other words, it does not let it to escape into the depths of space.

Q3. Why do some planets have more moons?

A: In general, the number of moons a planet has depends on its size, or mass, and its gravity. Larger planets have more gravity which enables them to retain more moons than the relatively small ones.

Q4. Describe the affect of gravity on tides?

A: The force of gravity from the Moon affects the Earth’s water bodies and causes it to accumulate on the side of the Earth facing the moon and the side that is diametrically opposite to this. These bulges are known as tidal bulges and are responsible for the movement of tides up and down.

Q5. How does gravity influence the expansion of the universe?

A: Gravity helps to counteract the influence of the big-bang effect and the expansion of the universe. It can be noted that the more the mass is present in the universe the bigger the forces of attraction, hence a slower expansion.