The Life Cycle of a Star

When we look out at the sky at night and see the stars, we often ponder about life and philosophy. However, we do not commonly think about these astronomical phenomena themselves. Stars have a life cycle, like anything else. Surprisingly, there are nine stages in the course of their existence. In the following paragraphs, a detailed explanation of each step of a star’s life will be given.

In the nebula

A star originates in a nebula—a large, cold cloud of gas and dust. According to NASA, “Over time, the hydrogen gas in the nebula is pulled together by gravity and it begins to spin” (“The Life Cycles of Stars: How Supernovae Are Formed”). The stages continue based on temperature as the nebula warms up.

Protostar

This is when the gas clump starts to collapse. According to Swinburne University, “These clumps initially contain ~0.01 solar masses of material, but increase in mass as surrounding material is accumulated through accretion. The temperature of the material also increases while the area over which it is spread decreases as gravitational contraction continues, forming a more stellar-like object in the process. During this time, and up until hydrogen burning begins and it joins the main sequence, the object is known as a protostar” (“Protostar”). This stage can last for millions of years.

T Tauri

Believe it or not, a star is still young at this stage. As stated by Britannica, “They represent an early stage in stellar evolution, having only recently been formed by the rapid gravitational condensation of interstellar gas and dust. These young stars are relatively unstable, though contracting more slowly than before, and will remain in that condition until their interior temperatures become high enough to support thermonuclear reactions for energy generation” (Britannica, The Editors of Encyclopaedia). As a side note, about 500 such stars have been observed so far.

Main sequence

When the temperature of a star reaches 150,000,000 degrees Fahrenheit, nuclear fusion takes place (nuclei combine to create a larger mass). At this point, the cloud will glow with brightness, become smaller, and stabilize. This stage can go on for billions of years (“The Life Cycles of Stars: How Supernovae Are Formed”).

Red giant

One can say that at this stage, the star is dying. It is when the process of nuclear fusion stops, and gravity presses on the star, making it more compact. From this action, temperatures go up to where helium can fuse with carbon (Redd, Nola Taylor).

Core fusion

Once the temperature reaches levels that allow fusion (light and heavy) to happen again, core fusion begins. This process releases a lot of energy, and the star becomes bigger and stable (“The Life Cycles of Stars: How Supernovae Are Formed”).

Red giant, again

The star becomes a red giant through its fusion, size, and stability. The process of interchanging between the core fusion stage and the step of being a red giant can occur several times (Redd, Nola Taylor).

Supernova

This is an explosion of a star. According to NASA, there are two ways a supernova can happen: when a star acquires too much matter from a nearby star, and when nuclear fusion stops and its mass goes into its core, which makes it so heavy that it cannot sustain its own gravitational force (May, Sandra).

Remnant

This is what is left behind from the explosion. The remnants of a star can trigger the future formation of stars, can bring heat to interstellar gas, and it becomes the main source for heavy elements (Mathis, John S.).

The life cycle of a star is fascinating: it begins in a cloud of gas and dust known as a nebula; transforms into a protostar with gravitational contraction; gradually shifts to being more compact and increases in temperature as a T Tauri; changes to being stable and bright as a main sequence star; starts to die as a red giant; releases more energy again with core fusion; becomes a red giant again; explodes as a supernova under its own gravity; and finally becomes precious remnants that enrich the universe.