The life cycle of a star
When you look up into the sky at night, you can often see lots of beautiful stars lighting up the universe. But, how do these celestial bodies form, what happens to them in the course of their lives, and how do they die?
Stars form in giant clouds called nebulae (more than one nebula). The nebulae often consist of dust and other basic elements such as hydrogen. In these clouds, the elements with more mass start attracting the elements with less mass, because of gravitational force. However, this process takes an extremely long time as the elements have a very weak gravitational force. As soon as more of these elements pile together, the process speeds up as there now is more mass. However, this may also happen another way when outside forces are helping the dust clouds and elements pile on top of each other. These piles of elements and dust then start collapsing under their gravitational attraction. As the clouds collapse the material in the centre heats up. This then is called a “protostar” as still not a real star. The protostar is hot at its core and is the center of the collapsing cloud that will one day become a beautiful star. Often the cloud splits into two or three blobs, which would explain why most stars are paired or in groups. The blobs continue to collapse and a dense core starts forming. However not all the elements collected will end up burning inside the star. Instead, it might form into a planet or similar. The more mass a protostar collects the more temperature it will release until it can finally take part in the process of nuclear fusion of hydrogen from helium in its core. This process creates enough outflow of energy to make it shine and keep the star from collapsing under its gravitational force.
At this point, the celestial body has reached the main chapter of life and has become a star. A star the size of our sun takes about 50 million years to form and lives for about 10 billion years before it explodes. During the longest part of its life, the star does not do much. It might attract other celestial bodies, like planets, through its gravitational pull, or travel through the galaxy it was born in, but that is about it. At the end of its life time when the star has exhausted its reserves of hydrogen, it will become a red giant. A red giant is a dying star that no longer has enough hydrogen in its core for nuclear reactions. As the core no longer emits the energy that is needed to sustain itself, the core collapses and becomes a lot hotter. Outside of the core, hydrogen is still in stock and therefore nuclear fusion can take place. This causes it to expand and the surface of the star to cool down. A star with the mass of our sun will expand further than the Earth’s orbit, however, this will happen in a few billion years, so no need to worry.
After the star has turned into a red giant, the core will eventually completely collapse. This will cause a huge explosion, sometimes even a supernova. If the star is extremely massive, the core will be crushed with so much force that a black hole is created, an infinitely dense object, whose gravitation nothing can escape. A star the size of our sun or smaller would explode and then form a white dwarf. A white dwarf is a star that starts ejecting its outer layers until only the core is left. This core is dead, but still very hot. White dwarfs are about the size of the Earth, despite containing the mass of a star.
Many things are still a mystery, not only about stars, some questions will never be answered by humanity, as the universe just holds too many secrets.
Source:
“Stars.” NASA, NASA, https://science.nasa.gov/astrophysics/focus-areas/how-do-stars-form-and-evolve.
“What Are Red Giants?” EarthSky, 16 Sept. 2021, https://earthsky.org/astronomy-essentials/what-are-red-giants-definition/.
“National Schools' Observatory.” Red Giant | National Schools' Observatory, https://www.schoolsobservatory.org/learn/astro/stars/cycle/redgiant.
“What Is a Nebula?” Space Center Houston, 24 Mar. 2020, https://spacecenter.org/what-is-a-nebula/.
