STARS

Stars A star is usually a large ball of gas held together by gravity Stars produce tremendous amounts of energy that shine

Stars Some stars are very old and do not emit any radiation Some stars can be as big as a planet

Energy Production Stars use Nuclear fusion in their cores to produce most of their energy

Nuclear Fusion The combining of nuclei of smaller elements to form the nuclei of larger elements with some mass being converted to energy This process can only occur in extremely high temperatures and pressures

Nuclear Fusion Example Our sun converts hydrogen nuclei to helium nuclei with about 0.07 % of the mass being converted to energy

Luminosity and Temp. Diagram (PAGE 15, ESRT) Luminosity is a measure of how bright a star is in relation to the sun if the stars were all the same distance from the observer

Apparent Brightness What we really see in a star is dependent upon the stars absolute luminosity and distance away from us

Star Types

Main Sequence Make up about 90% of all studied stars Most stars spend a majority of their life as a main sequence star As main sequence stars temperature increases, their luminosity also increases. These stars can range form blue to red in color (ESRT)

Giants Red, Orange, and Yellow in color Easily visible because of their luminosity and how big they are (10 times or more the diameter of the sun) Low temperatures because of how late they are in their evolution

Can be anywhere from 100 to 1000 times the diameter of the sun Super Giants Can be anywhere from 100 to 1000 times the diameter of the sun High luminosity representing the late evolution of the star. Super giants usually explode in a tremendous event called a supernova

Not all white dwarfs are white in color About the size of Earth Not all white dwarfs are white in color Hot on the surface

Black Dwarfs When a white dwarf cools and no longer emits much electromagnetic energy it becomes “dead”

Star Origin and Evolution

Origin Gravity causes gas and dust clouds to clump up, forming larger and larger balls of gas and dust

Origin When the gas and dust start to become big enough (around the size of Jupiter) they have enough gravitational contraction and the result is the beginning of nuclear fusion. Nuclear fusion gives the star enough electromagnetic energy to begin shining and a star is born

Evolution Evolution of a star after they spend most of their lives as a main sequence star depends mostly on the original mass

Main sequence stars expand to become red giants or supergiants. Evolution Main sequence stars expand to become red giants or supergiants.

Evolution Stars with a mass 1.5 times greater than the sun form into supergiants, then rapidly collapse forming a body much smaller than a white dwarf A high mass will form a neutron star An extremely high mass will have a density so high it creates an extreme gravity field, where nothing can escape. This is known as a black hole

Evolution Stars with a mass less than 1.5 times the sun will form into a white dwarf. They use up most of their nuclear fuel while becoming a white dwarf and eventually die to become a black dwarf