A black hole is a region in space where the gravitational pull is so intense that nothing, not even light, can escape from it. Here are some key aspects of black holes:

1. Formation: Black holes are formed when massive stars exhaust their nuclear fuel and undergo gravitational collapse. If the remaining core of the star is sufficiently massive (typically more than about three times the mass of the Sun), it will collapse into a black hole.
2. Event Horizon: The boundary around a black hole beyond which nothing can escape is called the event horizon. Once something crosses the event horizon, it cannot return and becomes part of the black hole.
3. Singularity: At the center of a black hole lies the singularity, a point of infinite density where the laws of physics as we currently understand them break down. The singularity contains all the mass of the black hole.
4. Types of Black Holes:
   • Stellar-Mass Black Holes: These black holes are formed from the collapse of individual stars and typically have masses ranging from about 3 to 20 times that of the Sun.
   • Supermassive Black Holes: Found at the centers of galaxies, these black holes have masses ranging from millions to billions of solar masses. Their formation is still a topic of active research.
   • Intermediate-Mass Black Holes: These are black holes with masses between stellar-mass and supermassive black holes, a few hundred to a few thousand solar masses.
   • Primordial Black Holes: Hypothetical black holes that could have formed in the early universe due to high-density fluctuations.
5. Detection: Black holes cannot be observed directly because light cannot escape them. Instead, they are detected by their effects on nearby matter and radiation. For example:
   • Accretion Disks: Matter falling into a black hole forms an accretion disk, which heats up and emits X-rays and other radiation.
   • Gravitational Waves: Mergers of black holes produce ripples in spacetime known as gravitational waves, which can be detected by observatories like LIGO and Virgo.
   • Gravitational Lensing: Black holes can bend light from objects behind them due to their strong gravitational fields, a phenomenon known as gravitational lensing.
6. Hawking Radiation: Proposed by physicist Stephen Hawking, this theoretical process suggests that black holes can emit radiation due to quantum effects near the event horizon. This radiation could cause black holes to lose mass and eventually evaporate over extremely long timescales.