The Life Cycle of Stars Stars are born from massive clouds of dust and gas called nebulae . Gravitational attraction causes the nebula to contract, forming a pr...
Stars are born from massive clouds of dust and gas called nebulae. Gravitational attraction causes the nebula to contract, forming a protostar. As the protostar's core heats up, nuclear fusion begins, and a new star is born, fusing hydrogen into helium and releasing vast amounts of energy.
Over billions of years, stars like our Sun exhaust their hydrogen fuel and begin fusing heavier elements like helium and carbon. The star's outer layers expand, forming a red giant. Eventually, the star sheds its outer layers, leaving behind a hot core called a white dwarf.
For stars much larger than the Sun, the final stages are more dramatic. After the red giant phase, these massive stars explode as supernovae, ejecting their outer layers into space. The remnant core may then collapse into an ultra-dense neutron star or, if massive enough, a black hole.
Observational evidence, such as the redshift of galaxies and the Cosmic Microwave Background Radiation (CMBR), supports the Big Bang theory. This theory states that the Universe began as an incredibly hot and dense singularity, rapidly expanding and cooling over billions of years to form the Universe we observe today.
The redshift of galaxies indicates that they are moving away from us, with more distant galaxies receding faster – evidence of the Universe's expansion. The CMBR, a faint background radiation permeating the cosmos, is a relic of the intense heat present in the early Universe.
Concepts like dark matter and dark energy have been proposed to explain observations that cannot be accounted for by the matter and energy we can directly observe.
Our Solar System formed approximately 4.6 billion years ago from a massive, rotating cloud of gas and dust called the solar nebula. Gravitational forces caused the nebula to collapse, forming a central protostar (the Sun) surrounded by a spinning disk of material.
Over time, this disk coalesced into the planets, moons, asteroids, and other objects that make up the Solar System today. The planets orbit the Sun in elliptical paths, held in place by the Sun's gravitational pull, while moons orbit planets in the same way.
Astronomers have discovered exoplanets – planets orbiting stars other than our Sun – using techniques like radial velocity measurements and transit photometry. These discoveries have expanded our understanding of planetary systems and fueled the search for potentially habitable worlds and extraterrestrial life.