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The Life Cycle of Stars: Chapter 8,
Section 2
What we are going to learn today
about the life cycle of Stars
• The different types of stars
• How to read an H-R diagram
• How stars appear at different stages in their
life cycle on the H-R diagram.
The Beginning and End of Stars
•
The Beginning A star enters the first stage of its life cycle as a
ball of gas and dust. Gravity pulls the gas and dust together,
and hydrogen changes to helium in a processes called nuclear
fusion.
• The End Stars usually lose material slowly, but sometimes
they can lose material in a big explosion. Much of a star’s
material returns to space, where it sometimes forms new
stars..
• How many stars are estimated to
be in our Milky Way Galaxy?
200,000,000,000
Different Types of Stars
• Stars can be classified by their size, mass,
brightness, color, temperature, spectrum, and
age. A star’s classification can change as it ages.
• Main-Sequence Stars After a star forms, it
enters the second and longest stage of its life
cycle known as the main sequence. Energy is
generated in the core as hydrogen atoms fuse
into helium atoms.
• What kind of star is our sun??
Main Sequence Star System:
Alpha Centauri, 25 trillion miles away
Red Giants
• A red giant is a large, reddish (usually main
sequence) star late in its life cycle, or third
stage.
• As the center of the star shrinks, the atmosphere of the star
grows very large and cools to form a red giant or a red
supergiant.
• This is Betelgeuse, a red giant star
in the Milky Way. Who has seen
it through a telescope? In what
Constellation is it located?
Orion Constellation
White Dwarf Stars
• In the final stage of its life cycle, a star that has the same mass
as the sun (main sequence star) or smaller can be classified as
a white dwarf.
• A white dwarf is a small, hot dim star that is the leftover
center of an old star.
• It has no hydrogen left and cannot generate energy any more
by nuclear fusion, but it can shine for billions of years before
cooling completely.
In what constellation is there
a white dwarf in our galaxy?
White Dwarf Stars
White Dwarf : Sirius
Blue Supergiant: Rigel
H-R Diagram: A graph for studying the
stars
• The H-R Diagram (Hertzprung-Russell diagram) is a graph that
shows the relationship between a star’s surface temperature
and its absolute magnitude.
• Reading the H-R Diagram The diagonal pattern on the H-R
diagram where most stars lie, is called the main sequence.
• Where is our sun?
The main sequence
is the location on
the diagram where
most stars lie
H-R Diagram
• How hot is the surface of the sun?
5,000 – 6,000 C or 10,000 F
According to the H-R diagram, what types of stars have very low
temperatures and high absolute magnitudes?
•
A blue stars
•
B red giants
•
C white dwarfs
•
D main sequence stars
When stars get old
• When main sequence stars get old (such as
our sun) they become red giants and then
white dwarfs at the end of their life cycle.
• Massive stars, however, generate much more
energy and also don’t last as long.
• Massive stars may explode with such intensity
that they may become supernovas, neutron
stars, pulsars, or black holes.
• What will our sun probably become in its next
stage?
Supernovas
• A supernova is a gigantic explosion in which a
massive star collapses and throws its outer
layers into space.
• Supernova NGC 6826
Its green gas is almost
half of its mass.
Neutron Star
• After the supernova explosion, the center of the collapsed
star contracts to form a new star. It has been smashed
together so forcefully that all of its particles have become
neutrons.
Pulsars
• When a neutron star is rapidly spinning, it is called PULSAR. It
emits rapid pulses of radio waves and optical energy.
• This is Pulsar B1509. It is spinning so rapidly(7 rotations/sec),
12 miles wide, it creates a hand-shaped nebula
•
Black Holes
• Sometimes the leftovers of a supernova are so massive that
they collapse to form a black hole. A black hole is an object
that is so massive that even light cannot escape its gravity.
• Black Holes are invisible: their extreme gravity can cause light
to stretch ; their spinning can drag the very fabric of space
around with it
Who took these pictures?
• These images were taken from the ALMA
telescope, CHANDRA satellite and the Hubble
Space telescope.
• ALMA is a radio telescope in Chile
• CHANDRA is a satellite launched by NASA in
1999
• The Hubble is an orbiting observatory that
was launched by the Space Shuttle Discovery
in 1990
Let’s see how much you know about
Stars now!
• What are some different types of stars?
• What does an H-R diagram tell us?
• What can main sequence stars (like our sun)
turn into as they get old?
• What are some things massive stars become?