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In this chapter of the “How Old Is It” video book, we’ll cover stars – second generation stars. We start with giant molecular clouds and what may trigger their collapse into star clusters. We’ll follow their size, density, and temperature as they move from hydrostatic equilibrium to fragments to stars. We’ll then follow the collapse of a fragment capable of creating a star like our Sun. We’ll cover how circumstellar disks around central massive objects are formed. We’ll cover the Protostar phase and examine a few like the ones in the Eagle Nebula and Orion. We’ll cover T-Tauri stars, their properties, and examine several including T Tauri itself, XZ Tauri, and others. We’ll cover how these giant molecular clouds form Open and Globular clusters and how Field Stars like our Sun have left their starting clusters. We’ll follow stars as they start burning hydrogen and migrate to the Main Sequence on the H-R Diagram. We’ll take a deep dive into the hydrogen fusion that powers stars. With a focus on our Sun, we’ll compute proton collision and fusion rates. In order to understand the mass-luminosity relationship better, we’ll cover the Coulomb Barrier and how Tunneling through it works. And finally, we’ll examine what happens to a star once it runs out of hydrogen fuel.
