Origin and Evolution of Stars - Chandrashekhar Limit

Each galaxy in the universe includes billions of stars, and there are an endless number of them. The most basic components of galaxies are stars. Nebulae, or molecular clouds, are collapsing gas and dust clouds that are the precursors to stars. Deep within these clouds, turbulence creates knots with enough mass for the gas and dust to fall under its own gravitational pull. Stars are known as protostars when they are in their early stages of formation. The star then moves on to the following stage of growth, known as main sequence star. These protostars reach an equilibrium over the course of millions of years and develop into what is known as a main-sequence star.

A star's mass determines the stages it will go through and how long each stage will persist. Small stars grow more slowly than heavy stars. Heavy stars have shorter lives than typical stars because, while having more hydrogen available for nuclear reactions, their rate of fuel consumption is substantially higher.

A star is powered by nuclear fusion over the majority of its life. The main-sequence star's core produces the initial energy through the fusion of hydrogen atoms. Later, stars like the Sun start to fuse hydrogen around a spherical shell surrounding the core as the majority of atoms at the core turn into helium. Nuclear processes can stop if a star burns through all of the hydrogen fuel that makes up its core. The core starts to shrink as a result of its own gravity. As a result, more hydrogen enters a region with the right temperature and pressure for fusion to restart in the shell around the core. A star is referred to as a "red giant" during this period. This allows the star to progressively increase in size as it moves from the subgiant stage to the red-giant phase.

A star undergoes a second, maturing process that requires millions of years for it to mature from the start of the collapse. A star the size of our sun takes roughly 50 million years to reach maturity and will remain there for nearly 10 billion years. The sun's mass may make up as little as 10% of the tiniest stars, known as red dwarfs, while the sun's mass may make up as much as 100 times the size of the largest stars, known as hypergiants.

A nuclear fusion explosion takes place during the red giant or hyper giant stage, turning the dwarf into a nova or supernova. Following this, the stars progress through one of the three stages of death—black dwarf, neutron star, or black hole—depending on their size.

Small stars like the sun - if the remaining mass after the Novae explosion is within 1.44 times that of the solar mass, the star will become a white dwarf and will eventually go extinct in the form of a black dwarf.

Medium-sized stars will become neutron stars if, following a supernova explosion, their remaining masses fall between the range of 1.44 to 3 times those of the sun.

Larger stars will turn into black holes if, following a supernova explosion, the leftover mass is greater than 3 times that of the sun.

The maximum mass of a white dwarf star or the mass at which a star will eventually collapse into a neutron star or a black hole was described by Indian astronomer Subrahmanyan Chandrasekhar. In 1983, he revealed that this mass amounted to roughly 1.44 solar masses. Chandrashekhar received the Physics Noble Prize for his research on the evolution of stars.