A protostar is a collection of interstellar gas that has collapsed down from a giant molecular cloud. The protostar phase lasts 100,00 years. Pressure and gravity begin to increase over time and eventually, the protostar collapses into itself.
T Tauri Star is a stage of the formation and evolution of a star that occurs right before it becomes a main sequence star. They don’t have enough pressure and temperature at their cores to produce nuclear fusion. They are larger than main sequence stars and exist for about 100 million years.
A main sequence star is a common type of star in the universe. They vary in size, brightness, and mass, but they all share one thing in common: converting hydrogen into helium in their cores and releasing tremendous amounts of energy. Main sequence stars maintain their spherical forms through a process known as hydrostatic equilibrium. Gravity is pulling the star inwards, and the light pressure from the fusion reaction is pushing outwards.
A main sequence star becomes a red giant when it has exhausted all the hydrogen supply in its core. Fusion stops because it can no longer generate an outward pressure to counter inward pressure pulling it together. A shell of hydrogen around the core starts to ignite and continue the life of the star. This process causes the star to increase to upwards of 100 times its original size. When the hydrogen shell is fully exhausted, the star will then ignite further shells of helium and other elements to prolong its life. The entire phase only lasts a few hundred million years and then the star becomes a white dwarf.
A white dwarf occurs when a star has completely exhausted the hydrogen in its core and loses the ability to force higher elements into fusion reaction. A white dwarf still shines despite not having an interior fusion reaction. When a star enters the white dwarf state, it cools until it reaches the background temperature of the Universe. This process takes billions of years.
Red dwarf stars are the most common kind of stars in the Universe. These are like main sequence stars but the mass is so low that they are cooler. Red dwarf stars conserve their fuel for much longer than main sequence stars. Astronomers estimate that red dwarfs can burn for up to 10 trillion years.
If a star is between 1.35 to 2.1 times the mass of the Sun, it doesn’t become a white dwarf when it dies. Instead, the star dies through a process called supernova. The remaining core is what is known as a neutron star. A neutron star received its name because it is a star composed entirely of neutrons. The intense gravity of the neutron star crushes protons and electrons together to become neutrons. Stars that are more massive than 2.1 times the mass of the Sun will become black holes after a supernova.
Supergiant stars are the largest stars in the Universe. They have dozens of times the mass of the Sun. Their large size comes with a fatal disadvantage – they die fast. They consume hydrogen at an increased rate and supernova within a few million years. The largest known star is called VY Canis Majoris and it is so large that if it were in place of our Sun, it would stretch from the Sun’s position to Saturn.