Download protostars low mass stars intermediatemass stars red giant planetary

Stars form inside relatively dense concentrations of interstellar gas and dust known as ​
molecular clouds​
. Very cold temperatures bind molecules together & cause density to increase. When density is high enough, stars form! PROTOSTARS ...begin to form when an area of the molecular cloud collapses under its own weight, becoming denser & gaining its own gravity ­­ this process takes ~10 million years. The protostar begins to undergo ​
accretion​
(accumulate more matter in the form of solids and gases) and after a few million years, begins thermonuclear fusion. A ​
stellar wind​
(flow of charged particles from a star) begins, which stops more matter accumulating. This means that the star’s mass is now stable and will not change. Its mass determines which path it will follow. LOW MASS STARS Thermonuclear fusion will not occur in a protostar with a mass less than 8% of our sun’s mass. It becomes a ​
brown dwarf​
, which is basically a failed star. Brown dwarfs have a mass greater than a gas giant planet, but are too small for fusion to begin. They will fade & cool to become black dwarfs. INTERMEDIATE­MASS STARS Briefly goes through the T­Tauri stage in a few years.Stay in the ​
main sequence (middle age) for ~ 10 billion years. Energy continues to be generated as the star converts hydrogen into helium. Not many changes occur during the main sequence, as stars are very stable at this point. Changes only begin when the star begins to run out of hydrogen in its core and the rate of fusion decreases. RED GIANT When an intermediate­mass star leaves the main sequence as it runs out of hydrogen, the shell of gases around the star begin to expand and cool, causing a reddish glow.This is where the term ​
red giant comes from. These stars are very bright because of their larger surface area. The core becomes very compressed (not much larger than Earth) and begins fusing helium into carbon. This stage will last about 100 million years. PLANETARY NEBULA Fusion stops after helium atoms have been fused into heavier elements, and the star is no longer producing energy. The star’s outer layers of gas are ejected and drift through space. The shell of gas around a dying star is a ​
planetary nebula​
, even though it has nothing to do with planets. This stage will last only a few thousand years. WHITE DWARF As the planetary nebula disperses, a white dwarf is formed when gravity causes the remaining star matter to collapse in on itself. These are very hot and dense and can burn for billions of years, but are dim and become fainter as they cool. LARGER / MASSIVE STARS Briefly goes through the T­Tauri stage in a few years. These have a much shorter life cycle than intermediate­mass stars, as massive stars only stay in the ​
main sequence​
(middle age) for ~ 10 million years. Energy continues to be generated as the star converts hydrogen into helium. Not many changes occur during the main sequence, as stars are very stable at this point. Changes only begin when the star begins to run out of hydrogen in its core and the rate of fusion decreases. RED SUPERGIANT Usually at least 100x larger than our sun. Goes through the same process of expansion and helium fusion as a red giant. SUPERNOVA After the supergiant stage, an enormous amount of gravitational force causes the stars to contract and produce high pressure that causes nuclear fusion to fuse carbon into oxygen, magnesium, and silicon. This continues until the core is all iron. Then, the core collapses under its own gravity & releases tremendous amounts of energy. NEBULA A ​
nebula ​
is the cloud resulting from a supernova. This consists of the expanding ejected layers of the star, and can result in a black hole, a neutron star, or new stars. NEUTRON STAR BLACK HOLE Small & dense ball If the core of a star of neutrons. These is over 3x the mass are very faint, rotate of our sun, a black quickly, & may be hole will form due to pulsars​
(stars that the star’s massive emit radio waves). gravity. Nothing, not even light, escapes!