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The Sun, like other stars, is a huge spherical object made of hydrogen and helium. Its diameter reaches 1.400.000 km, or 109 times the Earth’s diameter; but is 4 times less dense than the Earth due to its composition. The Sun is not only made of the glowing gas that we see with a telescope.
This book is divided into two parts: stellar interiors and stellar atmospheres. While the division between the two is fairly arbitrary, it is a traditional division separating regimes where different axioms apply. A similar distinction exists between the continuum and lines of a stellar spectrum.
One of our goals in this class is to be able to describe not just the observ-able, exterior properties of a star, but to understand all the layers of these cosmic onions — from the observable properties of their outermost layers to the physics that occurs in their cores.
The different transport mechanisms of high-mass, intermediate-mass and low-mass stars. Different layers of the stars transport heat up and outwards in different ways, primarily convection and radiative transfer, but thermal conduction is important in white dwarfs.
Many of stars’ properties — how long they live, what color they appear, how they die — are largely determined by how massive they are. The study of stellar structure and evolution is dedicated to understanding how stars change over their lifetimes, including the processes that shape them on the inside.
This guide illustrates in a general way how stars of different masses evolve and whether the final remnant will be a white dwarf, neutron star, or black hole. Stellar evolution gets even more complicated when the star has a nearby companion.
There is an order in the properties of stars! ⚫ Most of the stars lie on the “main sequence”: massive stars are hot and have high power (top left), while the small stars have lower masses, are cold and have low power (bottom right) ⚫ The giant stars lie on the top-right part of the diagram, while the white dwarfs are on the bottom-left
