Stars
How are stars formed?
Nebular Theory
Stars are created when a nebula, a cloud of dust and mostly hydrogen and helium gas, collapses and most of the mass is pulled towards the center.
Nebulae collapse when their clouds form clumps that grow until their gravity forces them to collapse.
This matter heats up when it is pulled in and forms the core of a star. As the nebula collapses, it flattens out into a disk shape.
For stars that form solar systems, most of the matter is pulled towards the center to form a sun, and the rest of the matter forms the shape of the solar system.
As planets form and move in the solar system, they often collide with other planets and matter until they find their orbit and location.
Population I and Population II Stars
Population I stars are metal rich and formed in the last 1-2 billion years. In the Milky Way, these stars orbit our galactic center in the same plane. These stars are found throughout the disk of our galaxy, but the most metal heavy ones are located in our galaxy's spiral arms only.
There are two types of stars, the younger Population I, and the older Population II.
Population II stars are metal poor and formed 2-14 billion years ago. These stars orbit out galactic center in extremely tilted elliptical orbits. Population II stars are located farther from the center of our galaxy, and most likely formed during the formation of the Milky Way.
Composition and Classification of Stars
Stars are mostly hydrogen and helium. A star will first burn through its hydrogen, then its helium, then carbon before reaching its iron core. This process is called nuclear burning.
Composition of the Elements a Star
Red Giant: No longer burns through hydrogen, instead burns helium to form carbon
Red Supergiant: The largest amount of volume for a star in the universe, much more luminescent than Red Giants
Blue Giant: Cooler and more luminescent than Red Supergiants
White Dwarf: The core of a star that has burned through it's outer elements, extremely dense
Yellow Dwarf: A main sequence star, meaning it id still burning through its hydrogen
Red Dwarf: The smallest and coolest type of main sequence star, most common star in the Milky Way
Brown Dwarf: A star that never gained enough mass or heat to begin nuclear burning