Transcript Life Cycle of A Star

Lesson Goals

1. Define the terms: Luminosity, Stellar
Classification, Stellar Nebulae, Red
Giant, White Dwarf, Supernova, Neutron
star, and Stellar Black Hole.

2. Describe the life cycle of a star.
Classification of Stars

2 Types of star classification:
luminosity and stellar classification.

Luminosity: the brightness of a star.
○ Sirius A is the brightest star, other than the
sun, at -1.4.
○ The dimmest stars that can be seen with the
naked eye are called 6th magnitude stars.
○ The dimmest stars that can be seen with the
Hubbell telescope are 30th magnitude.

Stars can also be described by their
stellar classification, which is based on
color and temperature.
○ It also lets astronomers know where the star is
at in its life cycle.
Life Cycle of a star

1) The cycle of a star begins with the
formation of a cloud of gas (hydrogen)
and dust called a Stellar Nebula.
○ The gas and dust begin to swirl and clump. As
it clumps, it pulls material into the core.
○ As the star grows, the cloud surrounding the
star is vaporized.
Life Cycle of a star

2) When the core temp reaches about 1
million degrees celsius, the gases
combine and a large amount of energy
is produced over a long period of time.
Life Cycle of a star

3) Eventually most of the core hydrogen
is changed to helium. Then, the helium
begins to change into carbon and the
star begins to expand. As it expands, its
outer layers begin to cool. The star
becomes a Red Giant.
Life Cycle of a star

4) What happens next depends on the mass of the
star: Stars begin to lose their mass due to stellar
winds.
a. Stars the size of the sun and smaller: the
outer layers fall off to leave a nebula, and the core
cools. The core becomes a White Dwarf, giving off heat
as it is stored.
b. Stars three times larger than the sun: The star
becomes a supergiant. These stars may explode,
producing a Supernova.
Life Cycle of a star
5) After most of the mass is lost in the
explosion, what is left behind is a tiny
neutron star.
6) If the star is massive enough, the
neutron star implodes to make a stellar
black hole, where gravity is so strong that
not even light can escape.
 How
long do stars live?
 It depends on the size of the star.
○ Smaller, cooler stars burn their fuel much
more slowly… hence they live longer.
 (20 billion years)
○ Even though they have more fuel,
large/hot stars burn their fuel much more
quickly. Their lives are much shorter.
 (tens of millions of years)
Journal Question

What determines how a star dies?
Explain