A Brief Introduction to Stars

Stars are something we all know and see, glittering in the night sky above. Most people, however are content to just admire their beauty. These stars have their own fascinating physics and chemistry behind them. There are a lot of fascinating information which not many people are aware of. This article will attempt to give some basic information about stars to facilitate a greater interest in them.

What exactly are stars and how are they ‘born’

Stars are luminous spheroidal celestial objects made up of plasma. They are held together by their own gravity. They may be found singularly or in groups known as constellations. Stars are born in star nurseries called nebula. Nebula are nothings but clouds of gas and dust. Star formation begins due to instability in the gravity within molecular clouds. This gravitational instability soon causes the nebula cloud / clouds to collapse under its own gravitational force. The density of the region also increases. The gravitational energy gets converted into heat which causes a rise in temperature. After a certain period, the collapsed nebula cloud reaches the hydrostatic equilibrium condition. Hydrostatic equilibrium is the condition where and external force (like gravity) of an object either fluid or plastic in nature gets balanced by a pressure-gradient force. This gives rise to a protostar, which then evolves into a star.

Stars are comprised of gases, mainly hydrogen and helium. The structure of a star comprises of its core where various nuclear reactions take place, a conduction zone which carries energy outwards from the core, a convection zone which transfers gases of extremely high temperatures to the surface, and the surface of the star. The heat generated by these nuclear reactions is what makes the stars shine.

The types of stars

Red Giants

Red giants are stars which have run out of hydrogen from their core. As an alternative way, they start to use hydrogen present outside the core, which causes it to swell and puff up. After the hydrogen totally gets over, it starts burning up other gases which may cause it to grow into yellow or blue supergiants and hypergiants.

Betelguese, a red giant seen from a telescope
Betelguese, a red giant seen from a telescope

White Dwarfs

White Dwarfs are dying stars. They are formed from stars which has used up all of its available gas. It then collapses to form a small planet-sized star with only a white-hot and extremely dense core.

Sirius B, a white dwarf seen from a telescope
Sirius B, a white dwarf seen from a telescope

Neutron Stars

If a star roughly 5 times or more the size of our sun dies, it does not become a white dwarf. Instead, it undergoes a supernova explosion. Supernova explosions are very bright and powerful enough that it could be seen with the naked eye even on Earth despite the star being 168, 000 light years away (SN 1987A). The intense force of the gravity produced in the collapse causes the protons and electrons to merge forming a star made purely of neutrons, giving these stars the name ‘neutron stars’. However more massively sized stars, roughly 8 times the sun, instead collapse to form not neutron stars, but black holes, a region of space with gravity so extremely powerful that even light cannot escape it.  

Illustration of neutron star
Illustration of neutron star
Image of a black hole courtesy NASA
Image of a black hole courtesy NASA