Stephen Hawking made several groundbreaking discoveries in theoretical physics, particularly related to black holes and cosmology:

• He discovered the concept of the event horizon of a black hole, which is the boundary beyond which nothing can escape the black hole's gravitational pull

• Hawking proved the area theorem, stating that the area of a black hole's event horizon can never decrease, linking black holes to thermodynamics

• In 1974, he proposed that black holes are not completely black but emit radiation due to quantum effects near the event horizon, now known as Hawking radiation. This means black holes can lose mass and eventually evaporate

• Together with Roger Penrose, Hawking showed that the universe must have begun from a singularity, an infinitely small point, supporting the Big Bang theory

• He predicted the existence of mini black holes formed shortly after the Big Bang, which would have been very hot and evaporated quickly

• Hawking formulated a thermodynamic theory of black holes, including the Bekenstein-Hawking entropy formula, linking black hole physics with quantum mechanics and thermodynamics

• He contributed to the idea that the universe might have no boundaries in space-time, meaning time and space as we know them began with the Big Bang and have no prior boundary

These discoveries revolutionized our understanding of black holes, quantum mechanics, and the origins of the universe, bridging gaps between general relativity and quantum theory