Black Holes

The Event Horizon Telescope captured the first photo of a black hole in 2019

Predicted by Einstein in 1916, these invisible objects can be indirectly seen through their accretion discs and X-ray bursts. Over 40 million trillion black holes may be scattered throughout the universe.

Albert Einstein's equations predicted black holes decades before their discovery

For nearly 50 years, scientists dismissed black holes as implausible oddities, despite solutions to the equations indicating their existence. But the 1970s discovery of intense X-rays from Cygnus X-1 and its massive hidden companion flipped the consensus.

There are likely millions of small black holes lurking undetected near us in space

Because black holes are so hard to spot directly, astronomers rely on models of galaxy and star evolution to estimate their population. A recent study used simulations and galactic data to show that about 1% of all matter in the universe is locked inside black holes.

Black holes form from the collapse of massive stellar cores due to gravity

Over time, less energy is released from the cores of massive stars as heavier elements are created through fusion. Once iron has been fused, energy is consumed rather than created, and runaway collapse creates a dense enough region where the stellar core existed to warp spacetime into a black hole.

The general theory of relativity defines gravity as the curvature of spacetime

The breakthrough that redefined Isaac Newton's picture of gravity came when Albert Einstein realized that freely falling is indistinguishable from weightlessness, leading him to the principle of equivalence between gravity and acceleration. His prediction that gravity bends light was confirmed in 1919 during a solar eclipse.

Cygnus X-1 helped scientists confirm black holes are real and measurable phenomena

The 1964 discovery of Cygnus X-1 provided the first strong candidate, but it took decades—and a famous bet between Stephen Hawking and Kip Thorne—before scientists were certain it was a black hole. Hawking's thumbprinted concession was delivered after breaking into Thorne's office.

The first image of a black hole was captured by creating an Earth-sized virtual observatory from a network of eight radio telescopes.

Sagittarius A* is a massive black hole at the center of our Milky Way galaxy

For years, it was known as a strong source of radio signals, but there wasn't enough data to adequately describe or identify it. Orbital movements of nearby stars would indicate it had 4.6 million times the sun's mass, proving it was a black hole.

There may be as many as four types of black holes, categorized by their mass

Three types are known to exist: stellar mass black holes, supermassive black holes, and intermediate black holes. A fourth type—micro black holes—is theoretical and would have the same mass as Mount Everest in a space the size of an atom.

The event horizon is an inescapable sphere around a black hole singularity

The horizon is often surrounded by an accretion disc of superheated material that orbits the black hole while emitting radiation. Light emitted behind a black hole can be bent around it to create the appearance of a ring of material known as a photon sphere.