White Dwarfs and Degenerate Gases

This video is part of a comprehensive series initially developed for William Paterson University and CUNY Hunter, aimed at supporting online classes and course materials for introductory astronomy. By engaging with all the videos within this series, you will effectively complete a full undergraduate course in astronomy, equipping yourself with the knowledge and skills necessary to navigate the night sky with confidence, learning all the basics and many advanced topics!

White dwarfs and neutron stars are the final stages of stars that are like our sun, but a bit bigger. When stars run out of their special fuel, they change a lot and end up as super-dense objects with unique properties. One of the closest examples is Sirius B, which helps us understand white dwarfs better. A solar-mass star goes through a series of stages before becoming a white dwarf. First, it spends most of its life in the main sequence phase, where it mixes hydrogen into helium in its core and stays the same size. When the hydrogen runs out, the core gets smaller and hotter, and helium starts to mix in too. This makes the outer layers expand and eventually form a planetary nebula. The hot core left behind becomes a white dwarf, and it will slowly cool down and get dimmer as it releases its leftover heat. White dwarfs have some cool features. They’re incredibly dense, sometimes even denser than the atoms in the nucleus of an atom! This is because of something called electron degeneracy pressure. Also, the bigger a white dwarf is, the smaller it is because of the same pressure. When light from a white dwarf escapes, it can be shifted towards the red end of the spectrum, which is called a gravitational redshift. This shows that white dwarfs have super-strong gravity. Most stars live in pairs or groups, and these interactions can create some really amazing things in space. Have you ever wondered about the fascinating world of white dwarfs and neutron stars? These celestial bodies are the remnants of supernova explosions from massive stars and hold some incredible secrets. White dwarfs are like cosmic leftovers, composed mainly of neutrons. Their density is mind-boggling, reaching an astonishing 4 x 10^17 kg/m³! That’s heavier than a ton of bricks compressed into a tiny ball.

0:00 Introduction
0:33 Odd stars on the H-R Diagram
2:02 True Binary Stars
2:46 The motion of the star Sirius across the sky
11:01 The Orbital Motion of Sirius B
14:11 Vital Stats for Sirius B
16:39 Sirius "B" Mass Measured
23:04 The Stellar Graveyard
24:19 Size of a White Dwarf Compared to Earth
25:13 What's a White Dwarf?
26:27 Hydrostatic Equilibrium
27:40 Ideal Gas Law
32:10 Degenerate Gas Law
33:08 The Quantum Regime
42:39 A very simple model of a gas of electrons
47:17 Degeneracy! Electron and Otherwise....
56:31 The Central Pressure of a Star like the Sun
57:59 Massive White Dwarfs are smaller!

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