Main Sequence Life of Stars

In 1910 the beginnings of the understanding of stellar evolution was attained when a Danish chemist and an American astronomer collaborated in the creation of the Hertzsprung-Russell diagram. This diagram provided a yardstick for measuring stars based on a number of criteria which lead to a number interesting discoveries, including the classification of Main Sequence Stars.

What is a Main Sequence Star?

A Main Sequence star is any star that falls in the widest band on the Hertzsprung-Russell diagram, also referred to as the HRD. The main sequence is the curve of the band on the HRD where most stars fall, thus the name “main sequence.” A second name for a Main Sequence Star, and one easier to say although a bit misleading, is “dwarf star.”

The HRD

The Hertzsprung-Russell diagram plots stars based on a number of criteria, and these criteria are used to determine the size and age of a star. The HRD compares the relative absolute magnitude, luminosity, classification, and effective temperature of the stars. There were a few different diagrams examining these facets at first, some of which are rather difficult to read. In the end there are two types called the HRD; one based on the colour index of the stars, called the colour- magnitude diagram, and the other based on the temperature and luminosity, and thus called the temperature-luminosity diagram. While both are referred to as the HRD, astronomers make the distinction based on how they are conducting their research.

The Life of a Main Sequence Star

Main Sequence stars are not newly- born, nor are they on the way out, strictly speaking. They are in the prime of their life, burning hydrogen fuel and exerting their influence on the objects in their surrounding space. As a star ages it begins to burn up the hydrogen fuel at its core. At such a point it begins to expand and eventually becomes a red giant- definitely off the main sequence. Depending on the initial mass of the star it will either cool and shrink, eventually becoming a white dwarf (and theoretically a black dwarf), or go supernova. After the supernova explosion it will condense and become either a neutron star or a black hole. White dwarfs, neutron stars and black holes are also off the main sequence of the HRD.

The more massive a star is at its birth, the shorter its lifespan. While anything that lasts a million years seems a fairly long time- such as the most massive of stars—the typical age of stars is in the billion year range, from 1 to 10 billion. The least massive of stars (still far more massive than Earth) can last hundreds of billions of years.

Final thoughts

One of the criteria of plotting a star is whether or not it is still producing hydrogen fusion, and most stars are doing so for most of their active life—thus most stars fall in the main sequence of the HRD. One of the problems with the HRD and main sequence classification is that it is a very broad class. It is, in the end, the only ONE way to classify a star.

Related Articles in the 'The Stars' Category...

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• How Far Away are the Stars?
• Pioneer Plaques
• Star Formation
• The Death of Stars
• The Milky Way
• Types of Star
• Using Constellations to Find Other Constellations
• What Are Star Remnants?
• What's Inside a Star