Gravity: From Planetary Orbits to Black Holes

Gravity is the invisible force that pulls objects towards the center of planets and stars. It keeps planets in their orbits around the sun and determines our weight based on the mass of the planet. Understanding gravity helps us explore how planets behave and even detect cosmic events like black holes colliding.

Exploring Gravity: From Earth to Black Holes and Beyond

Understanding Gravity 

• • Definition: Gravity is the force by which a planet or other body draws objects toward its center. 
  • Role of Gravity in Planetary Orbits: The force of gravity keeps all of the planets in orbit around the sun.
  • Relationship Between Mass and Gravity: Objects with more mass have more gravity. 

• Gravity also gets weaker with distance. 

• • So, the closer objects are to each other, the stronger their gravitational pull is.

Relation between Gravity, Mass and weight

Effect of Mass on Weight: Earth’s gravity comes from all its mass. All its mass makes a combined gravitational pull on all the mass in your body. That’s what gives you weight.

• If you were on a planet with less mass than Earth, you would weigh less than you do here.

• Variations in Earth’s Gravity: Gravity isn’t the same everywhere on Earth. Gravity is slightly stronger over places with more mass underground than over places with less mass.
• NASA’s Measurement Mission: NASA uses two spacecraft to measure these variations in Earth’s gravity. 
  • These spacecraft are part of the Gravity Recovery and Climate Experiment (GRACE) mission.

Gravity and Black Hole

Formation: A black hole is an object in space that is formed after the death of a star (core runs out of fuel) and is so dense and has strong gravity that no matter or light can escape its gravity pull.

• Characteristics: Because no light can escape, it is black and invisible.
  • Black holes pack so much mass into such a small volume that their gravity is strong enough to keep anything,even light, from escaping.
• Singularity: The point where all that mass is trapped is called a singularity. It may be infinitely small, but its influence is enormous.[UPSC 2017]
• Black holes are divided into three types: Stellar black holes (also known as unicorns), Supermassive black holes, and Intermediate-mass black holes.

Gravitational Waves [Upsc 2019]

History of Gravitational Waves: Gravitational waves were first proposed by Albert Einstein, 100 years ago as part of the Theory of Relativity.

• • Detection by LIGO: In 2016, scientists at Laser Interferometer Gravitational- wave Observatory (LIGO) first detected the gravitational waves.
  • Origins of GWs: GWs are ripples in space-time that move at the speed of light and are created by some of the Universe’s most furious and intense processes.
    • They hold information about their cataclysmic origins, as well as crucial insights regarding gravity’s nature.

• Formation of GWs:

• • Things move at extremely high speeds,
  • When a star explodes asymmetrically (known as a supernova),
  • When two large stars orbit one other, and
  • When two black holes orbit each other and join.

Gravitational Lensing

Einstein’s Prediction: One of the most remarkable predictions of Einstein’s theory of general relativity is that gravity bends light.

• Eclipse Observation: That effect was first demonstrated during a total solar eclipse in 1919, when the positions of stars near the Sun were observed to be slightly shifted from their usual positions.
• Gravitational Lensing Definition: Gravitational lensing occurs when two objects are nearly perfectly aligned along the line of sight.
• Effects: The gravitational field of the nearer object bends the light of the background object and produces several effects, including multiple imaging and magnification of the brightness.
• Applications: Gravitational lensing can provide information on the expansion rate and geometry of the Universe and about the distribution of mass in the Universe, particularly dark matter.

LIGO- India – InDIGO

Overview: LIGO-India project is an Indian Initiative in Gravitational wave observations, expected to be completed by 2025.

• Objective of the Project: It aims to move one advanced LIGO detector from Hanford to Maharashtra (Hingoli district), India.
• Piloting Departments: The project is piloted by the Dept. of Atomic Energy (DAE) and Dept. of Science and Tech (DST).

Conclusion

Gravity is not just a force on Earth but a fundamental aspect of the universe. From holding planets in orbit to revealing the secrets of black holes and even bending light, gravity shapes our understanding of space and time. 

• With ongoing missions like LIGO and advancements in technology, we continue to unlock new insights into the mysteries of the cosmos through the study of gravity.

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