By Ryan and Mike

How stars are formed There are two main models of star formation. Gravitational collapse is a process when molecular clumps that are way heavier than the Sun put each other into gaseous cores, which then collapse to make other stars. Competitive accretion, is a whole other process: stars are born as small looking like seeds that grow by accreting material from nearby clouds of gas and, sometimes, colliding with each other.

Low mass – High Mass stars The life cycle of a low mass star (left oval) and a high mass star (right oval). Since Low Mass stars are smaller than High mass stars obviously they usually last longer because they don’t burn fuel as fast as a High Mass star does. Low Mass stars burn less fuel because its rate of fusion is slow. But as for the High Mass star, when it’s a Red Giant it will burn much more fuel because of its size and its faster rate of fusion.

Lifecycle of The Star (Act1) Nebula - A Nebula is a cloud of gas & dust that usually starts off as the beginning of a star. The clouds and gas start clumping together forming a star Small Proto Star - Brown Dwarfs are too small to create enough heat to start fusion, so they are called “Failed Stars” Main Sequence - The Protostar gains enough mass to begin fusion all main sequence stars fuse Hydrogen Red Giant - Small to medium main sequence star runs out of hydrogen & begins fusing helium Planetary Nebula - A Red Giant completely stops fusing & the outer layers of the star are driven away White Dwarf - The left over core of a star. May only be the size of the earth but has a mass of ½ of the sun - A White Dwarf cools off over trillions of years until it no longer emits light and turns into a Black Dwarf.

Lifecycle of a Star (Act2) Nebula Protostar Red Super Giant - Star runs out of Hydrogen & begins fusing helium, carbon, oxygen, etc SuperNova - Fusion stops, the star collapses & creates a huge explosion Neutron Star - Dense star left over after super nova. Only 5 to 15 miles in diameter but have a mass times that of the sun Black Hole - Stars with masses of 25 to 50 times of the sun form black holes after a super nova. The leftover core of the star is so dense.

Lifecycle Definitions. -Supernova- A supernova is a catastrophic death of a star, Also followed by a huge stellar explosion. When a star collapses there is a chemical reaction which makes the center of the star to implode. When this happens the surroundings of the star are blown out into the surrounding space, and a neutron star is left in the middle. -Black Dwarf- A Black Dwarf is the ending of the star. It usually doesn’t shine any light because it has fully cooled down. There are no Black Dwarfs that were reported by astronomers because of they’re either to dark to spot out in the universe, or because the star hasn’t been cooled down which takes almost a Trillion Years. It will be a long time before we start seeing Black Dwarfs in the Universe. -Black Hole- A black hole is when in a certain part in space the pull of gravity is so strong that almost nothing can escape it. Not even the speed of light can escape it. If you actually were to be sucked into a Black Hole then you would be squashed because of the infinetely dense point. -Brown Dwarf- A brown dwarf is intermediate in mass between a star and a planet. Brown Dwarfs are usually known as failed stars because they are not big enough to fuse hydrogen in their cores. -HYDROGEN FUSION --HYDROGEN FUSION - IN BASIC HYDROGEN FUSION CYCLE, FOUR HYDROGEN NUCLEI (PROTONS) COME TOGETHER TO MAKE A HEILUM NUCLEAUS. THIS IS THE SIMPLE VERSION OF THE STORY. THERE ARE ACTUALLY ELECTRONS, NEUTRINOS AND PHOTONS INVOLVED THAT MAKE THE FUSION OF HYDROGEN INTO HELIUM POSSIBLE.