Life Cycle of a Star

• Stars are formed in clouds of gas and dust, known as nebulae.
• Nuclear reactions at the centre (or core) of stars provide enough energy to make them shine brightly for many years.
• The exact lifetime of a star depends very much on its size.
• Very large, massive stars burn their fuel much faster than smaller stars and may only last a few hundred thousand years.
• Smaller stars, however, will last for several billion years, because they burn their fuel much more slowly.
• 

Death of stars

• Eventually, however, the hydrogen fuel that powers the nuclear reactions within stars will begin to run out, and they will enter the final phases of their lifetime.
• Over time, they will expand, cool and change colour to become red giants. The path they follow beyond that depends on the mass of the star.
• Small stars, like the Sun, will pass through a planetary nebula phase to become a white dwarf, which eventually cools down over time and stops glowing to become a so-called “black dwarf”.
• Massive stars, on the other hand, will experience a most energetic and violent end, which will see their remains scattered about the cosmos in an enormous explosion, called a supernova.
• Once the dust clears, the only thing remaining will be a very dense star known as a neutron star, these can often be rapidly spinning and are known as pulsars.
• If the star which explodes is especially large, it can even form a black hole.

Why in News?

A forty-year-old puzzle regarding the production of lithium in stars has been solved by Indian researchers.

Unusual lithium rich stars  

• Stars, as per known mechanisms of evolution, actually destroy lithium as they evolve into red giants. 
• Planets were known to have more lithium than their stars — as is the case with the Earth-Sun pair.
• However, leading to a contradiction, some stars were found that were lithium-rich.

New findings

• When stars grow beyond their Red Giant stage into what is known as the Red Clump stage, they produce lithium in what is known as a Helium Flash and this is what enriches them with lithium.
• This is the first study to demonstrate that lithium abundance enhancement among low mass giant stars is common.
• Until now, it was believed that only about 1% of giants are lithium rich.
• Secondly, the team has shown that as the star evolves beyond the Red Giant stage, and before it reaches the Red Clump stage, there is a helium flash which produces an abundance of lithium.