Stars, one of the most magnificient structures to look at in the night sky, isn't it ? They twinkle and scintillate glorifying the darkness of the night and leaves many minds wondering about their presence in the cosmos. Let's have a look on the different phases in the lifecycle of a star and try to understand the science behind their properties and features.


1. Star Birth
Stars are formed in enormous, cold and dense clouds, called as Interstellar Clouds. The formation of cloud is only triggered when the cloud is disturbed by some force, like collisions with other similar cloud and shock waves due to other astronomical activities. Due to such disturbances, the cloud becomes unstable, and breaks into several fragments. These Fragments gradually get pulled by their own gravity into a denser formation. This leads to formation of Protostar. This pulls up the material outside into its core, making it denser and more pressurized. The heat and pressure generated in the core of a protostar is proportional to the amount of matter in initial cloud.
When more and more matter gets into the core of the star, it begins to give it a spin around the star. Powerful winds develop, blowing jets of wind outwards called as Spinning Disc. After intense pull of gravity in the core, it becomes extremely hot and the hydrogen atom present in it, which were earlier getting bounced off each other on collision, now merges into helium atom. There is a formation of heat just as hydrogen bomb. The heat so evolved helps the star to glow(shine).
When this additional pressure from the core balances the inward gravitational attraction, the star becomes stable, which at this stage is called a ‘Main Sequence Star’. In the formation of star, not all the matter of the initial gas cloud is used, the leftover matter is gradually converted into other star-orbiting structures. Like Planets, Comets, Asteroids and Moons.

Star-birth Nebulae: Clouds in the cosmos consisting of debris and dust, is called a nebula. These debris the leftover of died stars, who ran out of fuel. This material is recycled and used up for the formation of new stars over a time period. For example, Orion Nebula.

Star Cluster: During the formation of star, many other stars also form from the same gas cloud roughly around at a same time. These formed stars may coexist in the space, either alone (like our Sun) or in a pair (like Alpha Centauri). Example of star cluster is Pleiades Cluster.





2. Star Death
When any star run out of fuel, it dies. The way a star dies depend of the size of the star, gravitational pull, etc.
2.1 Small Star: Stars with less than the half the mass of the Sun, fades away very slowly. They do not use enough gravity to use other elements as fuel, as Hydrogen. As a result, they slowly shrink to become a Black Dwarf.

2.2 Medium Star: Stars (like sun) when have used up the entire hydrogen in its core, the nuclear fusion from its core shifts to its surface and helium fusion begins. When the fusion of helium also ends, it becomes a White Dwarf and its outer layers spread into space as cloud of debris.

2.3 Massive Star: Stars over 8 times more massive than Sun. Near their end, the pressure and temperature in its core becomes so extremely high, that along with hydrogen-helium nuclear process, it can also fuse helium and larger atoms into Oxygen and Carbon, causing it become a Red Super Giant. When this process continues, it converts the helium and hydrogen in the core into Heavier metals like Iron. When the entire turns to iron, it stops generating outward force to resist gravitational pull, and it collapses resulting in Supernova.

2.3.1 After Supernova, the core may get converted into ultra-dense Neutron Stars or even a Black Hole, with unescapable gravitational pull, (out of which, even light cannot escape!)







3. Star Study of Solar System: Sun

Sun is slightly bigger than a medium star, and is almost 1.3 million times of the volume of our earth. It contains 99.8% of the mass of the matter of solar system. Scientists divide the sun’s interior into 3 parts, The Core, Radiative Zones and Convective Zone. By moving towards the core, the gas in it gets denser and at the centre the temperature goes up to 15 million oC. The apparent surface of sun is called Photosphere.
Some common phenomena are:

3.1 Spikes of Gas: Jets of hot gas from the core to the surface, rises all the time on the surface, which may height up to several kilometres. Called as Spicules.

3.2 Solar Flare: A sudden burst of Energy from the surface of sun.

3.3 Mass Ejections: Vast bubbles of superhot gases called as plasma, rises from the surface of sun to millions of kilometres and bursts spreading a blast of charged particles into the solar system. This causes Auroras.



4. Some Star Facts:

HD 140283 or Methuselah is the oldest known star in the universe.

1 spoon material of red giant weighs less than a grain of sand.

1 spoon of material from the core of a neutron star weighs 5 billion tonnes.

1600 light years- the distance from Earth and nearest Black Hole





5. Other Researches and Studies
Chandrashekar’s Limit: In 1928, Indian Astrophysicist S. Chandrashekar found out how big a star could be and still separate itself against its own gravity after it had used up all its fuel. He calculated that a cold star of more than about one and a half times the mass of sun would not be able to support itself against its own gravity. This is known as Chandrashekhar’s Limit