The primary factor determining how a star evolves is its mass as it reaches the main sequence. The following is a brief outline tracing the evolution of a low-mass and a high-mass star. Stars are born out of the gravitational collapse of cool, dense molecular clouds.
The overall lifespan of a star is determined by its mass. Since stars spend roughly 90% of their lives burning hydrogen into helium on the main sequence (MS), their 'main sequence lifetime' is also determined by their mass.
By compiling data on many pairs of stars, we know that the luminosity of a star on the main sequence increases rapidly with mass: larger masses imply higher luminosities because higher mass stars have higher central temperatures and hence convert H to He faster.
The primary factor driving stellar evolution is the star's mass. Stars form from the gravitational collapse of cool, dense molecular clouds.Feb 2, 2016
A star's mass is the most important factor in determining its life cycle.
Mass is the most important stellar property. This is because a star's life is a continuous fight against gravity, and gravity is directly related to mass. The more massive a star is, the stronger its gravity.
The higher temperatures mean that the nuclear reactions occur at a much greater rate in massive stars. They thus use up their fuel much quicker than lower mass stars. This is analogous to the situation with many chemical reactions, the higher the temperature the faster the reaction rate.
Why? The mass of a star determines both its surface temperature and its luminosity. A star's mass is how much fuel it has and its luminosity is what determines how fast the star consumes its fuel. Therefore, the higher the mass, the higher the luminosity and consumption rate which decreases its lifespan.
Characteristics used to classify stars include color, temperature, size, composition, and brightness. Stars vary in their chemical composition.
Stars form inside relatively dense concentrations of interstellar gas and dust known as molecular clouds. These regions are extremely cold (temperature about 10 to 20K, just above absolute zero). At these temperatures, gases become molecular meaning that atoms bind together.
Greater gravity compresses the gas, making it denser and hotter, so the outward pressure increases. In any given layer of a star, there is a balance between the thermal pressure (outward) and the weight of the material above pressing downward (inward). This balance is called hydrostatic equilibrium.Jun 6, 2019
How do astronomers test the theory of stellar evolution? Astronomers compare their comprehensive theory which ties together atomic and nuclear physics, electromagnetism, thermodynamics and gravitation with their painstaking observations of stars and star clusters which offer a look at all types of stars.