black hole

History

The idea of an object from which light cannot escape dates back to the 18th century (John Michell and Pierre-Simon Laplace). However, modern understanding began with solutions to Einstein's equations found by Karl Schwarzschild in 1916 — he obtained an exact solution for a spherically symmetric black hole. The term 'black hole' was coined by John Wheeler in 1967. In the 1970s, Stephen Hawking showed that black holes can emit energy (Hawking radiation), and Jacob Bekenstein linked them to entropy.

How it works

Imagine spacetime as a stretched rubber sheet. A massive body presses a dent into it, and a black hole is such a deep funnel that even light rays slide inward and cannot get out. Everything that crosses the event horizon falls toward the center — the singularity, where density is infinite. This analogy illustrates how gravity bends the path of light and matter.

History

The idea of an object from which light cannot escape dates back to the 18th century (John Michell and Pierre-Simon Laplace). However, modern understanding began with solutions to Einstein's equations found by Karl Schwarzschild in 1916 — he obtained an exact solution for a spherically symmetric black hole. The term 'black hole' was coined by John Wheeler in 1967. In the 1970s, Stephen Hawking showed that black holes can emit energy (Hawking radiation), and Jacob Bekenstein linked them to entropy.

How it works

Imagine spacetime as a stretched rubber sheet. A massive body presses a dent into it, and a black hole is such a deep funnel that even light rays slide inward and cannot get out. Everything that crosses the event horizon falls toward the center — the singularity, where density is infinite. This analogy illustrates how gravity bends the path of light and matter.

History

In 1783, John Michell suggested the existence of 'dark stars', and in 1796 Pierre-Simon Laplace independently put forward a similar idea. In 1916, Karl Schwarzschild found the first exact solution to Einstein's equations for a point mass, describing a static black hole. A few decades later, in the 1960s, Roy Kerr obtained the solution for rotating objects. Jacob Bekenstein in 1972 proposed that a black hole possesses entropy proportional to the horizon area, which Stephen Hawking confirmed in 1974 by discovering quantum-mechanical radiation. Also crucial were the works of Roger Penrose and John Wheeler, who cemented the concept of a black hole in astrophysics.

How it works

A black hole is described by the metric of the corresponding solution to Einstein's equations. The gravitational field is so strong that no material particle or electromagnetic radiation can leave it after crossing the event horizon. According to the second law of black hole thermodynamics, the event horizon area never decreases, which is analogous to entropy. Hawking radiation arises from quantum vacuum fluctuations: near the horizon, particle-antiparticle pairs are created, one of which may fall into the hole while the other escapes to infinity, carrying away energy and reducing mass. Also at work are Newton's law of universal gravitation for distant effects and the constant speed of light principle, which defines the horizon boundary.

Open problems & fun facts

The information paradox: is information about matter falling into a black hole preserved?; The nature of the singularity and quantum gravity: what is at the center of a black hole?; Formation of supermassive black holes in the early universe; The connection between black hole entropy and the holographic principle

💡 Black holes can merge, generating powerful gravitational waves that have been detected on Earth since 2015. The largest known black hole, TON 618, has a mass of about 66 billion Suns. And the information paradox in black holes still boggles the minds of physicists.