# Chandrasekhar Limit – Definition & Detailed Explanation – Astronomical Units & Measurements Glossary

## I. What is the Chandrasekhar Limit?

The Chandrasekhar Limit is a critical mass limit that determines the fate of a star. Named after the Indian astrophysicist Subrahmanyan Chandrasekhar, this limit is the maximum mass that a stable white dwarf star can have. Beyond this limit, the force of gravity overwhelms the electron degeneracy pressure that supports the white dwarf against collapse, leading to a catastrophic event known as a supernova.

White dwarf stars are the remnants of low to medium mass stars that have exhausted their nuclear fuel and shed their outer layers to form a dense core. These cores are composed mainly of carbon and oxygen nuclei, which are supported against collapse by the pressure exerted by degenerate electrons. As a white dwarf cools over billions of years, it gradually loses energy and contracts, increasing its density.

## II. How is the Chandrasekhar Limit calculated?

The Chandrasekhar Limit is calculated based on the principles of quantum mechanics and the theory of degenerate matter. According to Chandrasekhar’s work, the limit is approximately 1.4 times the mass of the Sun, or about 2.765 x 10^30 kilograms. This value represents the point at which electron degeneracy pressure can no longer counteract the force of gravity, leading to the collapse of the white dwarf.

The calculation of the Chandrasekhar Limit takes into account the properties of electrons in a degenerate state, where they obey the Pauli exclusion principle. This principle states that no two electrons can occupy the same quantum state, leading to a pressure that resists further compression of the white dwarf. As the mass of the white dwarf increases, the density of electrons also increases, eventually reaching a point where the pressure is no longer sufficient to support the star.

## III. What happens when a star reaches the Chandrasekhar Limit?

When a star reaches the Chandrasekhar Limit, it undergoes a catastrophic collapse known as a Type Ia supernova. This event is triggered by the sudden onset of nuclear fusion in the core of the white dwarf, leading to a runaway thermonuclear explosion that completely destroys the star.

The explosion of a Type Ia supernova releases an immense amount of energy, equivalent to the brightness of billions of stars. This energy is visible across vast distances in space and can outshine entire galaxies for a brief period. The remnants of the supernova, known as a supernova remnant, can be observed as expanding clouds of gas and dust that contain heavy elements synthesized during the explosion.

## IV. What are the implications of the Chandrasekhar Limit in astronomy?

The Chandrasekhar Limit has significant implications for our understanding of stellar evolution and the formation of heavy elements in the universe. Type Ia supernovae are crucial for measuring cosmic distances and studying the expansion of the universe, as they serve as standard candles with known luminosities.

By observing the light curves and spectra of Type Ia supernovae, astronomers can determine the distance to their host galaxies and calculate the rate of cosmic expansion. This information has led to the discovery of dark energy, a mysterious force that accelerates the expansion of the universe and dominates its energy content.

## V. How does the Chandrasekhar Limit relate to white dwarf stars?

White dwarf stars are intimately connected to the Chandrasekhar Limit, as they represent the final stage of evolution for most stars in the universe. As a star exhausts its nuclear fuel and sheds its outer layers, it leaves behind a dense core that eventually cools and contracts to form a white dwarf.

The mass of a white dwarf determines its fate, with stars below the Chandrasekhar Limit evolving into stable white dwarfs that slowly cool over billions of years. However, stars that exceed the limit are destined to undergo a Type Ia supernova, leading to their destruction and the release of heavy elements into the interstellar medium.

## VI. What is the significance of the Chandrasekhar Limit in the study of stellar evolution?

The Chandrasekhar Limit plays a crucial role in the study of stellar evolution and the life cycles of stars. By understanding the mechanisms that govern the stability of white dwarf stars and the conditions that lead to supernova explosions, astronomers can unravel the mysteries of the universe and trace the origins of the elements that make up our world.

The study of the Chandrasekhar Limit has also provided insights into the formation of neutron stars and black holes, which are the remnants of massive stars that undergo supernova explosions. These exotic objects exhibit extreme physical conditions and play a key role in shaping the structure of galaxies and the evolution of the cosmos.

In conclusion, the Chandrasekhar Limit represents a fundamental boundary that defines the fate of stars and the dynamics of the universe. By studying the properties of white dwarf stars and the mechanisms that govern their evolution, astronomers can unlock the secrets of the cosmos and gain a deeper understanding of the forces that shape our world.