Black Holes

A black hole is the simplest object in the universe, defined entirely by three numbers: mass, electric charge, and angular momentum. It is also, by every measure that matters, the strangest. Inside the event horizon, the geometry of spacetime is so warped that time itself behaves as a spatial dimension. No information escapes. No light returns. And yet, slowly and inevitably, every black hole evaporates.

The mathematics of black holes was worked out by Karl Schwarzschild in 1916, weeks after Einstein published general relativity and while Schwarzschild was dying of an autoimmune disease on the Russian front. For nearly fifty years afterward, most physicists assumed the singularity he had described was a mathematical artifact rather than a physical object. It is not. The Event Horizon Telescope has now imaged the photon ring around two of them, M87* and Sagittarius A*, and the predictions of general relativity hold to better than five percent.

What follows is what we currently know, and what we are still arguing about. How does a black hole die? Stephen Hawking proved in 1974 that an event horizon must radiate a faint thermal spectrum, slowly losing mass until the entire object evaporates. In 2025, a laboratory in Israel observed the analog of that radiation in a system of ultracold atoms, the first direct confirmation. What lives inside the singularity? Possibly another universe: a one-page 1972 paper by Raj Kumar Pathria proposed that our entire observable cosmos sits inside the event horizon of a larger one, and the idea has matured into a serious branch of theoretical cosmology. And how do black holes form in the first place? The collapsing cores of massive stars, the same supernovae we now observe in real time, with polarized spectra revealing the shape of the blast.

The articles below cover each of these threads, with sources traced back to peer-reviewed papers in Nature, Physical Review Letters, and the Astrophysical Journal. They can be read in any order.