LIFE CYCLE OF A STAR

LIFE CYCLE OF A STAR

Don’t get confused by the name of the post. It is true, a star also has a life cycle. In stars there are also stages of generation, some scientists believe that our Sun is the second-generation star. Now come back to the topic, the life span of a star ranges from billions to trillions of years. This cycle starts from a nebula (a giant cloud of dust and gas), space dust is not like the dust that we find around us rather it contains a fraction of micro grains of carbon or silicates, present in interstellar. Different stars have a different life span as the life span of a star depends on its mass. Massive star has a shorter life span than a smaller one (Massive star burns its fuel, in its core, faster than a small one).

For an overview just give a glance on following image;

The life cycle of a star

Well! As we all know hydrogen is the lightest element, now let start from it. In nebula, the molecules of hydrogen gas are pulled together by gravity and the nebula is begun to spin. As it spins the temperature is begun to increase, due to a rise in temperature nuclear fusion (i.e. Hydrogen fusion) starts, this stage can be called a protostar (A contracting mass of gas). Protostar represents an early stage in the formation of a star. The cloud starts glowing and contracts and becomes stable, now it is called as the main sequence star and will remain shining in this stage from billions to trillions of years, this is the current stage of our Sun. As time passes the hydrogen atoms convert into helium atoms by nuclear fusion.

Now ably we can say that the source of heat and energy for a star is nuclear fusion reactions. Considerably it will be right that stars are the Universe’s factories. Stars can generate more heavy elements like carbon, nitrogen, or iron from chemical (nuclear fusion) reactions. When the supply of hydrogen runs out, so there is no more source of heat and energy. As the gravitational pull of a star is balanced by inner created heat pressure so when there is no more heat the core of the star becomes unstable and contracts. This phenomenon is known as gravitational collapse. The core of the star is run out of hydrogen while still there is some hydrogen in the outer shell of the star that causes expansion of the outer shell and it is called the red giant phase. The red giant is not a monster, the reason behind this name is its color and size. Its red color represents it is cooler than the main sequence star and it is giant because of the expansion of the outer shell.

This is a point where the twist comes. Every star has a similar story to the red giant phase but after this destiny changes. We know, stars can be distinguished from each other based on their size, moreover, it is the mass of the star that signifies the endpoint of stellar evolution (The process that shows how stages change in the life cycle of the star). For a low mass star after the collapse of the core and expansion of the outer layer (briefly, red giant phase), a planetary nebula is formed and the core is converted into a white dwarf that will become a black dwarf after exhausting its whole heat. The Massive star (that should be ten times or more than the size of our Sun) ends up in a more mysterious ridge. A massive star undergoes an explosion after the red giant phase, this powerful and luminous stellar explosion is termed as a supernova. After the supernova explosion, if the size of remnants ranges from Chandrasekhar limit (1.4 times the solar mass) to about three times the mass of the Sun, this supernova turns out to be a neutron star. While if remnants’ size is more than three times the solar mass, gravity will overcome the nuclear forces. As gravity dominates, a curious result comes out. Blackhole 🕳 comes into existence after swallowing the core of the star due to its gravity.

Furthermore, like every cycle, the stars can procreate its next generation. Some researchers believe that the next generation of a star can come into existence if eventually a white dwarf will come near a black hole and the black hole tries to swallow it and overcomes the gravity of a white dwarf that will result into an explosion which again produces a cloud of star, nebula. It will be the doorway for next-generation stars. In reality, it will take trillions of years, more than the age of our Earth, to exhibit.

Reference:

americanboard.org (The credit of the image goes to American board.)