I'd known next to nothing about neutron stars the day the puppeteer picked me up. Now I was an expert. And I still had no idea what was waiting for me when I got down there.

All the matter you're ever likely to meet will be normal matter, composed of a nucleus of protons and neutrons surrounded by electrons in quantum energy states. In the heart of any star there is a second kind of matter, for there the tremendous pressure is enough to smash the electron shells. The result is degenerate matter nuclei forced together by pressure and gravity but held apart by the mutual repulsion of the more or less continuous electron «gas» around them. The tight circumstances may create a third type of matter.

Given: a burned-out white dwarf with a mass greater than 1.44 times the mass of the sun — Chandrasekhar's Limit, named for an Indian-American astronomer of the 1900s. In such a mass the electron pressure alone would not be able to hold the electrons back from the nuclei. Electrons would be forced against protons — to make neutrons. In one blazing explosion most of the star would change from a compressed mass of degenerate matter to a closely packed lump of neutrons: neutronium, theoretically the densest matter possible in this universe. Most of the remaining normal and degenerate matter would be blown away by the liberated heat.

For two weeks the star would give off X rays as its core temperature dropped from five billion degrees Kelvin to five hundred million. After that it would be a light-emitting body perhaps ten to twelve miles across: the next best thing to invisible. It was not strange that BVS-1 was the first neutron star ever found.