What is the end result of a low mass star?
The end result of a low mass star is a white dwarf.
When a low mass star, like our Sun, exhausts its nuclear fuel (hydrogen and then helium) in its core, it undergoes certain stages of stellar evolution. The first stage is the red giant phase, where the star swells up and increases in size as hydrogen fusion moves to a shell surrounding the core, causing the outer layers to expand.
Eventually, the red giant undergoes a process called planetary nebula formation. During this stage, the outer layers of the star are ejected into space, leaving behind a dense core called a white dwarf. This occurs due to the instability and pulsation of the helium and hydrogen shells, leading to a series of thermal pulses pushing the outer layers of the star away.
A white dwarf is the final stage of evolution for a low mass star. It is incredibly dense, with the mass of the star compressed into a volume roughly the size of the Earth. It no longer undergoes fusion and generates energy, so it gradually cools down and fades away over billions of years.
The end result of a low mass star is typically a white dwarf. Here are the step-by-step stages of a low mass star's life cycle leading to the formation of a white dwarf:
1. Stellar Birth: A low mass star begins its life as a cloud of gas and dust called a nebula. Gravitational forces cause the nebula to collapse, forming a protostar.
2. Main Sequence: The protostar continues to contract and heat up until it reaches the temperature and pressure necessary for nuclear fusion to occur. This marks the star's entry into the main sequence phase, where it spends most of its lifespan.
3. Hydrogen Burning: Throughout its main sequence phase, the star fuses hydrogen into helium in its core through the process of nuclear fusion. This fusion process releases an enormous amount of energy and sustains the star.
4. Red Giant: After about 10 billion years, the hydrogen fuel in the core begins to deplete. As a result, the star expands and becomes a red giant. During this phase, the star starts burning hydrogen in a shell around the core, while the core contracts due to gravitational forces.
5. Helium Flash: As the core contracts, the temperature and pressure increase significantly. Eventually, the core becomes hot enough to ignite helium fusion, resulting in a sudden and violent event known as the helium flash. This stabilizes the star for a while.
6. Planetary Nebula: While burning helium in the core, the outer layers of the red giant become unstable and are expelled, forming a shell of gas known as a planetary nebula. This process exposes the core, which now becomes a white dwarf.
7. White Dwarf: The remaining core, composed mostly of carbon and oxygen, forms a highly dense and hot object known as a white dwarf. It is approximately the size of Earth, but its mass is comparable to that of the Sun. A white dwarf no longer undergoes fusion and gradually cools down over billions of years until it becomes dark and inert, ultimately becoming a "black dwarf."
Note: It's important to mention that more massive stars go through different stages and may end their lives as neutron stars or black holes instead of white dwarfs.
The end result of a low mass star, such as our Sun, is a white dwarf. To understand why, let's explore the life cycle of a low mass star.
1. Main Sequence: A low mass star starts its life in the main sequence phase, where nuclear fusion occurs in its core. During this phase, hydrogen nuclei combine to form helium, releasing energy and balancing out the inward gravitational force.
2. Red Giant: As the hydrogen in the core gets depleted, the core contracts while the outer shell of the star expands, causing the star to become a red giant. In this phase, the star fuses helium into heavier elements like carbon and oxygen, through a process called helium burning.
3. Planetary Nebula: Eventually, the outer layers of the red giant are expelled into space, forming a shell of gas and dust called a planetary nebula. This happens because the star's core starts to contract, generating intense stellar winds that blow its outer layers away.
4. White Dwarf: After the planetary nebula dissipates, all that remains is the hot and dense core, which is known as a white dwarf. The white dwarf is composed mainly of carbon and oxygen, and it no longer undergoes nuclear fusion. Without the heat generated by fusion, the star gradually cools off and dims, becoming a dim white dwarf over a very long time.
So, the end result of a low mass star is a white dwarf—a dense, compact star that gradually cools down over billions of years.