Black Holes
Black holes are regions of space where gravity is so intense that nothing, not even light, can escape, formed typically from the collapse of massive stars at the end of their life cycles.
Black holes were first theoretically predicted as a consequence of Einstein's theory of general relativity, though it took decades for scientists to accept that such extreme objects could actually exist in nature.
A black hole's boundary, known as the event horizon, marks the point beyond which nothing can escape its gravitational pull, and supermassive black holes, millions or billions of times the mass of the Sun, are now understood to exist at the centers of most galaxies, including our own Milky Way.
In 2019, the Event Horizon Telescope collaboration captured the first-ever direct image of a black hole, located in the galaxy M87, providing groundbreaking visual confirmation of these previously only theoretical objects.