1. Stars

4. What is a star?
The objects that heat and light the
planets in a system.
A star is a ball of plasma held together
by its own gravity
– Nuclear reactions occur in stars (H 
He)
– Energy from the nuclear reactions is
released as electromagnetic radiation.

5. Characteristics of Stars

6. Characteristics of Stars

7. Characteristics of Stars
Class Temperature Color
O 20,000- 60,000 K Blue
B 10,000 – 30,000 K Blue-white
A 7,500 – 10,000 K White
F 6,000 – 7,500 K Yellow-white
G 5,000 – 6,000 K Yellow
K 3,500 – 5,000 K Orange
M 2,000 – 3,500 K Red
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9. Hertsprung-Russell Diagram

10. Main Sequence stars
( young stars)
• Main sequence stars are the central band
of stars on the Hertzsprung-Russell
Diagram. These stars' energy comes from
nuclear fusion, as they convert Hydrogen
to Helium. Most stars (about 90%) are
Main Sequence Stars. For these stars, the
hotter they are, the brighter they are. The
sun is a typical Main Sequence star.

11. Main Sequence stars
( young stars)
DWARF STARS
Dwarf stars are relatively small stars, up to 20 times
larger than our sun and up to 20,000 times brighter.
YELLOW DWARF
Yellow dwarfs are small, main sequence stars.
RED DWARF
A red dwarf is a small, cool, very faint, main sequence
star whose surface temperature is under about 4,000 K.
Red dwarfs are the most common type of star. Proxima
Centauri is a red dwarf.

12. Giant and Supergiant Stars
(Old, Large Stars )
• RED GIANT
A red giant is a relatively old star whose diameter
is about 100 times bigger than it was originally,
and had become cooler (the surface temperature
is under 6,500 K). They are frequently orange in
color. It is about 20 times as massive as
the Sun about 14,000 times brighter than the Sun,
and about 600 light-years from Earth. The
appearance of the red giant is from yellow orange
to red, including the spectral types K and M, but
also class S stars and most carbon stars.

13. Giant and Supergiant Stars
(Old, Large Stars )
RED SUPERGIANTS
are supergiant stars (luminosity class I) of spectral
type K or M. They are the largest stars in the universe
in terms of volume. After the hydrogen in a star's core
has fused, stars with more than about 10 solar
masses become red supergiants for the duration of
their helium-fusing phase. These stars have very cool
surface temperatures (3500–4500 K), and enormous
radii. The radius of most red supergiants is between
200 and 800 times that of the Sun. They last 10 to
100 million years and are sometimes found in
clusters. Luminosities can exceed 500,000 times that
of the Sun.

14. Giant and Supergiant Stars
(Old, Large Stars )
• BLUE GIANT
A blue giant is a huge, very hot, blue star. It is a
post-main sequence star that burns helium.
SUPERGIANT
A supergiant is the largest known type of star;
some are almost as large as our entire solar
system. Betelgeuse and Rigel are supergiants.
These stars are rare. When supergiants die they
supernova and become black holes.

15. Virtually Dead Stars
• WHITE DWARF
A white dwarf is a small, very dense, hot star that is
made mostly of carbon. These faint stars are what
remains after a red giant star loses its outer layers.
Their nuclear cores are depleted. They are about
the size of the Earth (but tremendously heavier)!
They will eventually lose their heat and become a
cold, dark black dwarf. Our sun will someday turn
into a white dwarf and then into a black dwarf. the
name white dwarf was coined by Willem
Luyten in 1922.

16. Virtually Dead Stars
• BROWN DWARF
A brown dwarf is a "star" whose mass is
too small to have nuclear fusion occur at
its core (the temperature and pressure at
its core are insufficient for fusion). A brown
dwarf is not very luminous. It is usually
regarded as having a mass between
1028kg and 84 x 1028.

17. Virtually Dead Stars
NEUTRON STAR
A neutron star is a very small, super-dense star
which is composed mostly of tightly-
packed neutrons. It has a thin atmosphere
of hydrogen. It has a diameter of about 5-10 miles
(5-16 km) and a density of roughly 10 15 gm/cm3.
PULSAR
A pulsar is a rapidly spinning neutron star that
emits energy in pulses.

18. SUPERNOVA
in Latin it means NEW. The word supernova was
coined by Walter Baade and Fritz Zwicky in 1931. It
can be triggered in two ways: by the sudden
reignition of nuclear fusion in a degenerate star; or
by the collapse of the core of a massive star. The
explosion expels much or all of a star's material at a
velocity of up to 30,000 km/s (10% of the speed of
light), driving a shock wave into the
surrounding interstellar medium. This shock wave
sweeps up an expanding shell of gas and dust
called a supernova remnant. Furthermore, the
expanding shock waves from supernova explosions
can trigger the formation of new stars.

19. PROTOSTAR
It is a large mass that forms by contraction
out of the gas of a giant molecular cloud in
the interstellar medium. The protostellar
phase is an early stage in the process of
star formation. For a one solar-mass star it
lasts about 100,000 years. It starts with a
core of increased density in a molecular
cloud and ends with the formation of a T
Tauri star, which then develops into
a main sequence star.

20. Life Cycle of Stars

21. http://www.seasky.org/cosmic/sky7a01.html

22. QUESTIONS

23. THANK YOU FOR LISTENING
AND
TO GOD BE THE GLORY!!
ENEGONBAKA9:))