Stellar Evolution is the process by which a star changes over the course of time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive. Stellar evolution is not studied by observing the life of a single star, since they live for a long time. Instead, astrophysicists come to understand how stars evolve by observing numerous stars at various points in their lifetime, and by simulating stellar structure using computer models.

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The birth of a star

Stars form inside relatively dense concentrations of interstellar gas and dust known as molecular clouds

Molecular clouds are very cold, being just above absolute zero. At this temperature, gases become molecular, meaning that the atoms bind together. Gravity compresses the atoms until the fusion reaction begins.

The phases of a star

What powers a star?

Nuclear fusion powers a star for most of its life. At first, the energy is made by the fusion of hydrogen atoms at the core. Later, once the atoms in the core become helium, is when stars start to grow in size. Once a star has exhausted their nuclear fuel, they usually turn into a white dwarf, neutron star, or black hole.

What determines the stellar remnants?

Their mass. A star with about 1 solar mass makes a white dwarf, while stars in the 10-25 range make a neutron star. Anything above would produce a black hole.

Equations

Mass Luminosity relation

There is a relationship between mass and luminosity. So the more massive main sequence stars are hotter and more luminous than the low-mass main sequence stars.

Hydrostatic Equilibrium

the outward force due to the pressure gradient(a physical quantity that describes which direction and at what rate the pressure changes the most rapidly around a particular location) within the star is exactly balanced by the inward force due to gravity.

Questions

What is the solar mass range for a star to become a neutron star?

What are stars born from?

What powers a star?

Works cited

http://www.astro.princeton.edu/~gk/A403/stellar.pdf

http://www.iucaa.in/~dipankar/ph217/fullstar.pdf

https://www.nasa.gov/audience/forstudents/9-12/features/stellar_evol_feat_912.html