The modern notion of a black hole has been with us since February 1916, three months after Albert Einstein unveiled his theory of gravity. That’s when the physicist Karl Schwarzschild, in the midst of fighting in the German army during World War I, published a paper with astonishing implications: If enough mass is confined within a perfectly spherical region (bounded by the “Schwarzschild radius”), nothing can escape such an object’s intense gravitational pull, not even light itself. At the center of this sphere lies a singularity where density approaches infinity and known physics goes off the rails.
In the 100-plus years since, physicists and mathematicians have explored the properties of these enigmatic objects from the perspective of both theory and experiment. So it may be surprising to hear that “if you took a region of space with a bunch of matter spread out in it and asked a physicist if that region would collapse to form a black hole, we don’t yet have the tools to answer that question,” said Marcus Khuri, a mathematician at Stony Brook University.
Don’t despair. Khuri and three colleagues — Sven Hirsch at the Institute for Advanced Study, Demetre Kazaras at Duke University, and Yiyue Zhang at the University of California, Irvine — have released a new paper that brings us closer to determining the presence of black holes based solely on the concentration of matter. In addition, their paper proves mathematically that higher-dimensional black holes — those of four, five, six or seven spatial dimensions — can exist, which is not something that could confidently have been said before.