FORM 2 CHAPTER 11 STAR AND GALAXIES note

CHAPTER 11

STARS AND GALAXIES
IN THE UNIVERSE

11.1 STARS AND GALAXIES IN THE
UNIVERSE

 A galaxy is a set of bodies consisting of millions of stars
with gas and dust particles.

 3 types of galaxies:
a) Elliptical galaxies
b) Spiral galaxies
c) Irregular galaxies

 Our solar system is situated in the Milky way galaxy.



The Milky Way

 The MilkyWay is a medium large spiral galaxy.
 Our solar system is located at the edge of one of the

spiral arms of the MilkyWay.
 The MilkyWay consists of approximately 200 billion

stars and the Sun is one of it.

The Milky ways

 The milky ways is the name of our galaxy.
 It has a spiral shape and contains about 200 billion

stars.
 Our Sun is one of the stars in the milky way.
 Our solar System consist of eight planets, and

their moon orbiting around the Sun.

The birth of a star

1. A star is born from nebula.
2. Nebula is a large cloud made up of dust and gases

such as helium and hydrogen.
3. Gravity pulled the dust and gases in a nebulae

together to form a globe.
4. The globe of gas shrink and compress due to strong

gravitational force, becomes very dense and forms a
core.
5. The core shrinks and becomes dense continuously
due to increasing strength of the gravitational force.

6. When the core became hot and dense enough,
nuclear reaction started.

7. Hydrogen gas turns into helium.

8. A huge amount of heat and light energy is
released.

9. The core will shine and a star is formed
(protostar).

10.This new star continues to expand and becomes
either an average star like the Sun or a massive
star.

The Death of Stars

1. A star will die once the hydrogen gas in its core is
used up for its nuclear reaction.

2. Then the core would begin to contract and its outer
parts expand to become red giant stars.

3. The remains of the core can form a neutron star or
a black hole depending upon the mass of the
original star.

4.If the star is average star, the red giant star would
change into white dwarf star.

5. If the star is large star, a red giant star would expand
to become a super giant star then explode (known as
supernova) producing a neutron star.

6. If the star is super-large star, a black hole is formed.

7. Black hole is a region which has strong gravitational
attraction and suck all matters into it including light.

The life cycle of a star

The Various Types of Stars

Some Of The Ways That Stars Differ From Each
Other



1. Stars have different sizes :
➢Really big ones → supergiant stars
➢Big stars → giant stars
➢Really small ones → dwarf stars

2. The brightness of the stars depends on :
✓ Size
✓ Distance
✓ Surface temperature
Sirius and Rigel (the brightest stars in the sky).

FOUR MAIN GROUPS OF STARS

Name Characteristics

White dwarf Dim, compact stars

Neuron stars Very dense, small stars

giants Large stars.Their diameters are
Supergiants 10 to 100 times that of the Sun

Even larger than giants.

The universe

 The universe consists of billions of galaxies, stars,
planets, particles and all the objects in outer space.

 Relative size comparison between Earth and the
universe:

Earth → Solar system → The Milky Way→ A group
of galaxies → A cluster of galaxies → Universe

END OF
CHAPTER