Can one explain the recently discovered quasars as objects thrown from exploding nebulae? Are pulsars rapidly rotating neutron stars, so dense that a thimbleful of their matter would weigh more than ten million tons? or could a star collapse into a 'black hole' in space, leaving no trace other than an intensely strong gravitational field? These are some of the perplexing questions now facing cosmologists. How such questions relate to modern theories of the universe is the main theme of this book. The author prepares the ground for his central discussion with a historical survey of relevant scientific developments from earliest times, and concludes with some thoughts on the intractable problem of reconciling the worlds of the astronomer and nuclear physicist in a single comprehensive theory.