Stars are a fundamental part of the universe, providing sources of light and gravity for the formation of solar systems. Like humans, stars undergo a life cycle of birth and death, spanning millions or billions of years. Read more to learn about a life of a star!
Star Formation
Stars form from cosmic clouds of dust and gas named nebulae. Over time, gravity will pull a nebula into itself, and as it collapses, it will begin to heat itself at the center- this is a protostar. It will become the hot core of the star, reaching up to 15 million degrees. Once the protostar reaches this temperature, nuclear reactions in which hydrogen fuses to form helium can start. This process called nuclear fission provides an outflow of energy that stabilizes the star and gives its glow.
Main Sequence Star
Once the star can sustain nuclear fission, it is now considered a main-sequence star. Stars will spend about 90% of their life in this stage. The lifetime of a star depends on the star’s mass. Smaller stars will last longer than larger stars. Smaller stars burn slower and last for billions of years when compared to larger stars who must burn more to sustain their size.
Red Giant
Eventually, the star will run out of hydrogen at its core to fuse into helium, and nuclear fission will cease. The star’s core will collapse onto itself, causing the star to expand in size. The surface will cool down and shine less bright, transforming the star into a red giant. If large enough, a star could become a red supergiant. In these types of stars, fission of heavier elements like carbon and iron could occur within the star’s core. Eventually, all stars in the red giant phase will become unstable, and begin to dissolve their outer layers into clouds of dust or gases.
Stars and Their Fates
Stars can die off in multiple ways, depending on their masses:
White dwarfs: Stars similar in size to the Sun will continue to shed their outer layers, called the planetary nebula until only the core is left. This is known as a white dwarf. It will continue to cool down over billions of years into a black dwarf once it has lost all of its glow.
Supernova: For larger stars, their ending is more dramatic than the peaceful end of smaller stars. In red supergiants, the presence of iron in the core makes it incredibly unstable and will collapse into itself in less than a second. This concentrates the mass of the star within a small area, and spikes temperatures to over 100 billion degrees. A repulsive force then recoils all the mass with high energy in an event called a supernova.
What is left after a supernova depends. Electrons can be fused with protons to form neutrons within the star’s core under extreme pressures in red supergiants. If the core remains after the supernova explosion, it will remain a neutron star, an extremely dense star. However, if the mass of the star was too large, the neutron core will not survive the collapse and the star instead becomes a black hole.
The remains of dust and gases from dying stars can eventually be recycled and begin the process of forming a new star.
Thanks for reading!
Written by Kaylee Barrera
Sources:
“Scientific Background for Life Cycle of Stars.” CERES Project, btc.montana.edu/ceres/html/lifecycle/starsbackground.htm. Accessed 9 Feb. 2021.
“Stars | Science Mission Directorate.” NASA Science, science.nasa.gov/astrophysics/focus-areas/how-do-stars-form-and-evolve. Accessed 9 Feb. 2021.
“The Life Cycles of Stars.” Imagine the Universe, imagine.gsfc.nasa.gov/educators/lifecycles/LC_main3.html. Accessed 9 Feb. 2021.
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