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Strong entry in this series. Seems like Friedrich Bessel was not only the first to use parallax to measure the distance to a star but the first to suspect the presence of a white dwarf (too small for his telescope to detect but large enough to affect the motion of it's twin, Sirius-A).

Chapter 1: White Dwarfs
Bessel's discovery, improved telescopes, estimates of the size, density, etc. of Sirius-B.

Chaper 2: Limits and Explosions
The Chandraskehar limit. This is a boundary on mass. A star that weighs more is too big to collapse to a relatively large and non-dense white dwarf. The mass must collapse the white dwarf. This limit is 1.4 * the weight of the sum, approximately.

Chapter 3: Pulsars and Neutron Stars
Zwicky and Baade speculate on the neutron star, where protons and electrons fuse to form neutrons, and there is no charge to keep matter from collapsing further. A neutron star's surface after it has collapsed is too hot to give off visible light, but it will give off X-rays. Pulsars pulse radio waves, sometimes very fast, but always regularly. Could they be rapidly rotating neutron stars? Seems likely.

Chapter 4: Escape Velocity and Tides
A very short chapter relating escape velocity to tides. Probably the vaguest chapter in the book.

Chapter 5: Total Collapse
Can a star collapse even further than a neutron star? Oppenheimer said yes, and the star only has to be a bit over three times larger than the sun. The Schwarzschild radius is a thing that every massive body has. It's the radius of that body when the escape velocity is exactly the speed of light. The Schwarzschild radius of the earth is about 1 cm.

Chapter 6: Finding Black Holes
Black holes by definition can not be seen. But they can still be discovered by their effects. Some are one component of a double star system. The two stars rotate about each other, but one is clearly massive and yet can not be seen. Invisible, too heavy to be a neutron star, what else could it be but a black hole? Hawking advances the idea of mini black-holes and shows that they could eventually lose their mass.

David Wool's illustrations suit the text well. ( )