The Birth and Death of Stars Stars are born from massive clouds of gas and dust called nebulae . Gravity causes these nebulae to contract, and their increased d...
Stars are born from massive clouds of gas and dust called nebulae. Gravity causes these nebulae to contract, and their increased density and temperature initiate nuclear fusion reactions at the core, marking the birth of a new star.
During their lifetimes, stars fuse lighter elements like hydrogen and helium into heavier ones through nuclear fusion, releasing tremendous amounts of energy. The specific life cycle of a star depends on its mass:
According to the widely accepted Big Bang theory, the universe began as an incredibly hot and dense singular state around 13.8 billion years ago and has been expanding ever since. This expansion is evidenced by the redshift observed in the light from distant galaxies, which indicates they are moving away from us.
The cosmic microwave background radiation (CMBR) is a remnant of the intense heat and radiation that filled the early universe, providing further evidence for the Big Bang theory.
Our Solar System formed around 4.6 billion years ago from a giant molecular cloud of gas and dust. Gravitational forces caused this cloud to collapse, forming a central protostar (the Sun) and a rotating disk of material that eventually coalesced into planets, moons, asteroids, and other celestial bodies.
Planets and satellites orbit around larger celestial bodies due to the balance between gravitational forces and their orbital velocities. This principle is essential for understanding the motion of objects in the Solar System, as well as the orbits of exoplanets (planets orbiting other stars) discovered in recent decades.
Problem: The Earth orbits the Sun at an average distance of 1.496 x 10^11 m. Calculate the orbital period of the Earth, given that the mass of the Sun is 1.989 x 10^30 kg and the gravitational constant G = 6.67 x 10^-11 N·m²/kg².
Solution: