The most fascinating phenomena in the Universe, black holes and spacetime singularities, occur at the end of a massive star’s life cycle when it has exhausted its internal nuclear fuel and collapses under its own gravity. A star that was millions of kilometers in size shrinks to a pinprick smaller than the dot on an ‘i’. According to Einstein gravity, a collapsing massive star must give rise to a spacetime singularity, which is an extreme region where densities, temperatures, and other physical quantities take arbitrarily large values. The singularity either is covered within an event horizon, ... More

The most fascinating phenomena in the Universe, black holes and spacetime singularities, occur at the end of a massive star’s life cycle when it has exhausted its internal nuclear fuel and collapses under its own gravity. A star that was millions of kilometers in size shrinks to a pinprick smaller than the dot on an ‘i’. According to Einstein gravity, a collapsing massive star must give rise to a spacetime singularity, which is an extreme region where densities, temperatures, and other physical quantities take arbitrarily large values. The singularity either is covered within an event horizon, thus giving rise to a black hole, or is a naked singularity visible to observers faraway in the Universe. This book discusses here recent results and developments on gravitational collapse and the possible observational implications when naked singularities occur. A star’s final fate in terms of a black hole or visible singularity depends on the star’s internal structure and the way it collapses. In the case of a naked singularity, we would be able to witness the workings of quantum gravity effects in the Cosmos, which may help us formulate a quantum theory of gravity, a long cherished dream of physicists. The exciting possibility considered here is that collapsing massive stars and the resulting singularities may provide a cosmic laboratory where we could test the unification possibilities for the basic forces of nature. Black holes and singularities also offer us the opportunity to observe ultra-high energy astrophysical phenomena, such as gamma rays bursts, quasars, and jets from the centers of galaxies.