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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
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
White Dwarfs
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
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