A black hole is an astronomical object with an extremely strong gravitational pull, so strong that nothing—not even light—can escape from it, making it invisible in direct observation. The boundary around a black hole where the escape velocity exceeds the speed of light is called the event horizon. This boundary marks the point beyond which nothing can return once it crosses into the black hole. Black holes form mainly in two known types:
- Stellar-mass black holes: These form when massive stars—much larger than our Sun—run out of nuclear fuel and collapse under their own gravity after a supernova explosion. The core collapses into a tiny, incredibly dense point called a singularity, with the black hole's size being just a few kilometers across.
- Supermassive black holes: These contain millions to billions of times the mass of the Sun and are typically found at the centers of most galaxies, including our Milky Way. They play a crucial role in the formation and evolution of galaxies, though their precise origins remain one of astronomy's biggest mysteries.
Black holes can grow by pulling in matter from their surroundings, including gas, dust, stars, and even other black holes. We detect black holes by observing the effects of their gravity on nearby matter, such as stars orbiting them, or the light emitted by hot gases as they spiral inward. Another detection method involves measuring gravitational waves from merging black holes. Black holes are not "holes" as the name suggests, but rather regions in space filled with highly concentrated mass, warping space and time around them profoundly. The first direct image of a black hole was captured in 2019 by the Event Horizon Telescope, showing a dark silhouette against the bright glowing matter orbiting it. In summary, black holes are dense cosmic objects with gravity so intense that they trap everything within a defined boundary, influencing galaxies and serving as natural laboratories for testing fundamental physics.
