Download Name Date ______ Per _____ Doc ____ Lives of Stars WS Each

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Lives of Stars WS
Each star is born, goes through its life cycle, and dies. Astronomers can’t watch a single
star for billions of years so they study many stars in different stages of their lives and see how
they differ from one another.
A nebula is a large amount of gas and dust spread out in a huge volume. Gravity pulls
some of the gas and dust together. This contracting matter is then called a protostar. A protostar
is the earliest stage of a star’s life. A star is born when the contracting gas and dust becomes so
hot that nuclear fusion starts. During nuclear fusion, atomic nuclei of low atomic number
elements fuse to form a heavier nucleus of a larger element. Energy is released as a result.
How long a star lives depends on how much mass it has. Small stars use their fuel more
slowly than large stars, so they have much longer lives. When a star begins to run out of
hydrogen fuel, the star becomes a red giant. When a star runs out of fuel, it becomes a white
dwarf, a neutron star, a pulsar, or a black hole.
When small-mass or medium-mass stars use up their fuel, their outer layers expand. At
this stage they are called red giants. Eventually, the outer parts grow bigger and drift off into
space. The blue-white hot core of the star that is left behind is a white dwarf. Eventually, a white
dwarf loses its energy and becomes a black dwarf.
A dying giant or supergiant star can suddenly explode. The explosion is called a
supernova. After the star explodes, some of the material left behind forms a neutron star. A
neutron star is smaller and denser than a white dwarf. If the star emits pulses of radio waves, it is
called a pulsar, which is short for pulsating radio sources, instead of a neutron star.
The most massive stars become black holes when they die. After a large-mass star
explodes, a large amount of mass may remain. The gravity of the mass is so strong that gas is
pulled inward, pulling more gas into a smaller and smaller space. Eventually, the gravity
becomes so strong that nothing can escape, not even light!
Astronomers have discovered objects that are very bright but are also very far away.
These distant bring objects look almost like stars and were given the name quasi-stellar objects,
or quasars. Quasars are galaxies with giant black holes at their centers. More recently,
astronomers have determined that every galaxy probably has a black hole at its center.
1. red giant or supergiant
2. where fusion begins
3. part of a nebula
4. the stage our Sun is in
5. white dwarf, neutron star, or black hole
6. How long a star lives and what it becomes at the end of its life depends on
7. pulsar
8. white dwarf
a. exerts such a strong gravitational pull that no radiation
can escape
b. a huge cloud of gas and dust in space
9. nebula
c. what an average-sized star becomes at the end of its life
10. protostar
d. the earliest stage of a star’s life
11. supernova
e. emits pulses of radio waves
12. neutron star
f. shines brightly in the center of a galaxy
13. black hole
g. formed from leftover material after a giant star explodes
14. quasar
h. an explosion that occurs at the end of a giant star’s life
15. At which stage is a star
most stable?
Why?
16. Which has the greatest
density?
How do you know?
18. Neutron stars that emit
pulses of radio waves are
called
19. Which types of stars are “invisible”?
And
20. If you looked at the sky and a supernova occurred, why would you NOT see it?