The life span of a star depends upon its mass. Just like living organisms, stars too undergo a life cycle from birth to growth and finally death. Many of the stars we see now have died a long time ago, and because they are far away from us, it takes time for their light to reach us. Let's have a look at the stages of the life cycle of stars:
1. Giant gas cloud-
A star originates from a large cloud of gas. The temperature in the cloud is low enough for the synthesis of molecules.
Heat energy is produced when gas particles move inside the molecular cloud. Molecular clouds are dense cores with high density. For a low-mass star like the sun, it lasts about 500,000 years. Protostars are warmers and so can be observed by infrared radiations.
Photo credit-universavvy.com 3. T-Tauri phase-
During this stage, a huge amount of energy is released. The star has readied all the mass but is yet not capable of nuclear fusion. This is also called the pre-main sequence stage. It is named so after the T-Tauri a star from the Tauras region.
4. Main sequence-
The star is ready with a temperature capable of nuclear fusion. In this stage hydrogen protons are converted to helium, this is an exothermic reaction and hence lots of energy is released.
5. Red giant-
When the supply of hydrogen is exhausted, a red giant is formed. The surface temperature decreases which gives it a reddish-orange color. As the internal reaction has stopped at the core of the star, it contracts inwards due to gravity at the same time the star expands due to high pressure. Our sun will also turn into a red giant and engulf the nearby planets like mercury and Venus in a few billion years. 6. Fusion of heavier materials-
Helium molecules fuse at the core and once it is over, the core shrinks and begins to fuse carbon. Later, iron is fused which leads to absorption of energy, and the core collapses. Thus, forming supernova.
7. Supernova and planetary nebulae-
Supernova is the last stage of the star cycle in which the star blasts and lots of elements and energy is released. The core forms neutron stars or black holes. The core of stars which are not massive contract and form a white dwarf. Planetary nebulae are expanding objects having ionized gas released from red giants. They usually contain larger proportions of elements such as carbon, nitrogen, and oxygen, and these are recycled into the interstellar medium via these powerful winds called stellar winds