preface on blackhole
Answers
These proceedings represent a part of the invited talks that were presented at the symposium. They cover many aspects of black hole physics and astrophysics, regarding stellar-mass, intermediate-mass, and supermassive black holes. Topics range from black hole entropy and the fate of information to supermassive black holes at the centers of galaxies, and from the possibility to produce black holes in collider experiments to the measurements of black hole spins. Since these articles were written by world experts in their respective disciplines, this volume represents an extremely valuable collection for researchers and students alike.
The ST ScI Symposium on Black Holes attempted to capture all the aspects involved in the astrophysics of black holes.
Answer: A black hole is a region of spacetime where gravity is so strong that nothing—no particles or even electromagnetic radiation such as light—can escape from it.[1] The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole.[2][3] The boundary of no escape is called the event horizon. Although it has an enormous effect on the fate and circumstances of an object crossing it, according to general relativity it has no locally detectable features.[4] In many ways, a black hole acts like an ideal black body, as it reflects no light.[5][6] Moreover, quantum field theory in curved spacetime predicts that event horizons emit Hawking radiation, with the same spectrum as a black body of a temperature inversely proportional to its mass. This temperature is on the order of billionths of a kelvin for black holes of stellar mass, making it essentially impossible to observe directly.
Objects whose gravitational fields are too strong for light to escape were first considered in the 18th century by John Michell and Pierre-Simon Laplace.[7] The first modern solution of general relativity that would characterize a black hole was found by Karl Schwarzschild in 1916, and its interpretation as a region of space from which nothing can escape was first published by David Finkelstein in 1958. Black holes were long considered a mathematical curiosity; it was not until the 1960s that theoretical work showed they were a generic prediction of general relativity. The discovery of neutron stars by Jocelyn Bell Burnell in 1967 sparked interest in gravitationally collapsed compact objects as a possible astrophysical reality. The first black hole known as such was Cygnus X-1, identified by several researchers independently in 1971.[8][9]