Components of our Universe Stars and Galaxies Light

Components of our Universe Stars and Galaxies

Light Year • Astronomers measure distances to objects beyond the solar system using a larger distance of unit the light year. • A light year is the distance light travels in one year.

Big Bang Theory • According to the big bang theory, the universe began from one point billions of years ago and has been expanding ever since.

Star • A star is a large ball of gas held together by gravity with a core so hot that nuclear fusion occurs.

Life Cycle of a Star: • Stars formed deep inside clouds of gas and dust called a nebula (plural nebulae). • Gravity causes the densest parts to collapse forming regions call Protostars. Over thousands of years, the energy produced by the protostars heats the gas and dust surrounding them. • Eventually, the surrounding gas and dust blows away and the protostar becomes visible as a star.

Life Cycle of a Star: • A star becomes a main sequence star as soon as it begins to fuse hydrogen into helium in the core. • When a star's hydrogen supply is nearly gone, the star moves off the main sequence. Massive stars become red giants, then larger red giants.

Death of a Star: • Average mass stars- After helium in their core is gone, the star casts off their gases exposing their cores. The core becomes a white dwarf, a hot, dense, slowly cooling sphere of carbon.

Death of a Star • More Massive Starsbecome red supergiants. The red supergiant explodes into something called a super nova. • The supernova can then form a neutron star which is a dense core of neutrons that remain after the supernova.

Hurtzsprung-Russell Diagram • Stars can be classified by their temperature, color, and mass. • The Hertzsprung-Russell diagram, or HR diagram, is a graph that plots luminosity versus temperature of stars.

Galaxies • Galaxies are huge collections of stars. • There are three major types of galaxies: spiral, elliptical, and irregular. • Spiral galaxies look like flat discs with spiral arms and bulges in their center core.

Galaxies • Elliptical galaxies are more rounded, like a football or egg. • Galaxies that appear neither spiral nor elliptical are classified as irregular because they do not have a definite shape.