Space Physics: Big Bang

Life Cycles of Stars

Stars are formed from massive clouds of dust and gas, known as nebulae, in a process triggered by disturbances such as a nearby supernova.
Dense pockets within the nebula begin to collapse under the force of gravity, forming a protostar.
As the gravitational energy increases, it heats the protostar, leading to nuclear fusion of hydrogen atoms. This is the point at which a protostar becomes a main sequence star.
How a star develops further depends on its mass: average-sized stars like our Sun become red giants, while larger stars become supergiants.
Red giants eventually eject their outer layer of dust and gas, leaving behind a white dwarf star and a surrounding planetary nebula.
Over billions of years, white dwarfs cool to become black dwarfs.
Large supergiants can explode, after fusion ends, in a supernova, forming neutron stars or black holes.
Elements heavier than iron, such as gold or uranium, are made during such explosions.

The Universe: Structure and Evolution

The universe is a vast, expanding space filled with everything that exists — galaxies, stars, planets, dark matter, etc.
The structure of the universe on the largest scale is the cosmic web; a network of interconnected filaments of galaxies interspersed with enormous voids.
Galaxies are huge collections of stars, typically containing billions of stars, as well as dust, gas, and dark matter, held together by gravity.
Our Milky Way galaxy is one among billions in the universe, and it is part of a collection of local galaxies known as the Local Group.
Evidence for the expansion of the universe comes from the observed redshift of light from distant galaxies.

The Big Bang and the Age of the Universe

The Big Bang Theory proposes that the universe started from a hot, dense point around 13.8 billion years ago, and has been expanding ever since.
The observed red-shift of distant galaxies and the detection of *Cosmic Microwave Background Radiation (CMBR)** supports this theory.
CMBR is the leftover heat from the Big Bang and it fills the universe, further evidence of the universe’s origin.
The age of the universe may be estimated from observing distant galaxies and calculating how long the light has taken to reach us.
Current scientific understanding estimates the universe to be approximately 13.8 billion years old.