Science 101 Universal

At its core, gravity is the attractive force that exists between all objects with mass. This force is what keeps planets in orbit around stars, holds galaxies together, and causes objects to fall to the ground on Earth. It was first mathematically described by Sir Isaac Newton in the 17th century, who formulated the law of universal gravitation. According to Newton, every mass exerts an attractive force on every other mass, with the force being directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.

The event horizon of a black hole is one of the most captivating and enigmatic concepts in astrophysics. It represents the boundary surrounding a black hole, beyond which no information or matter can escape the gravitational pull. This invisible surface marks a point of no return, where the escape velocity exceeds the speed of light. The event horizon, therefore, creates a stark divide between the observable universe and the hidden singularity at the black hole's core. Understanding the event horizon is crucial for grasping the fundamental nature of black holes and the limits of our observable universe.

Its gravity holds the Solar System together, influencing the orbits of planets, moons, comets, and asteroids. This stellar giant is primarily composed of hydrogen and helium, undergoing nuclear fusion in its core, where hydrogen atoms combine to form helium, releasing a tremendous amount of energy. This process is the source of the Sun's light and heat, essential for life on Earth.

Predicted by Albert Einstein in 1916 as a consequence of his General Theory of Relativity, these waves propagate at the speed of light, carrying with them information about their cataclysmic origins and about the nature of gravity. Unlike electromagnetic waves, which travel through space, gravitational waves actually travel through spacetime itself, making them a unique messenger in the realm of astrophysics.

According to this theory, the universe began from an extremely dense and hot state approximately 13.8 billion years ago and has been expanding ever since. This initial explosion not only created the majority of matter but also the physical laws that govern our cosmos.



Initially, the universe was in a state of extreme heat and density. Within the first few moments, it began expanding rapidly—a phase known as cosmic inflation. This expansion helped to smooth out any irregularities or anisotropies in the nascent universe, laying the groundwork for a more uniform distribution of energy and matter. As the universe expanded, it also began to cool, allowing for the formation of subatomic particles, and later simple atoms.

It was formed approximately 4.6 billion years ago from the gravitational collapse of a region within a large molecular cloud most commonly found in the Milky Way galaxy. Over millions of years, the collapsing material formed a spinning disk, with the Sun coalescing at its center, growing hot and dense enough to initiate nuclear fusion.