This talks about stars- from how they are formed to the death of a star, from the nebula to the black hole.

1. Astronomy
(Life of Stars)
by Merlin Raphael
Page 1

2. The Universe
Scientists believe the universe
began in a “big bang”, about
13,700 million years ago. The
universe continues to expand
today. The evidence for the
“big bang” theory includes the
existence of a microwave
background radiation and red
shift. The universe contains
extremely dense objects and
may consist mostly of dark
matter that cannot be seen.
Stars do not remain the same-
they change as they age.
Page 2

3. The Origin of Stars
Nebula: A large cloud of gas
(helium and hydrogen) and dust
which forms into a star.
Dust and gas particles exert a
gravitational force on each other
which keeps pulling them closer
together.
As the particles pull closer together
the temperature increases.
At 10,000,000o C fusion takes
place and energy radiates outward
through the condensing ball of gas.
Page 3

4. -Cloud Collapse -
occurs deep in cloud
-“EGGS” (Evaporating
Gaseous Globules) :
Dense regions forming new
stars - surrounding gas &
dust “eaten into” by strong
stellar winds, UV photons &
ionization fronts.
Page 4

5. The Star
A star is a luminous globe of
gas producing its own heat
and light by nuclear
reactions. They are born
from nebulae and consist
mostly of hydrogen and
helium gas. Surface
temperatures range from
2000°C to above 30,000°C,
and the corresponding
colours from red to blue-
white.
Page 5

6. Red Giants
After hydrogen is exhausted
in core, energy released
from nuclear fusion counter-
acts inward force of gravity.
-Core collapses,
•Kinetic energy of collapse
is converted into heat.
•This heat expands the
outer layers.
-There is an increase in
temperature and pressure
during the collapse.
Page 6

7. Planetary Nebula
Planetary nebulae are the
outer layers of the star that
are lost when it changes
from a red giant to a white
dwarf.
After helium is exhausted,
the core collapses and the
outer layer of the star is
expelled. The outer
atmosphere is ionized by
the hot remaining core.
Page 7

8. White Dwarf
White dwarfs are the
shrunken remains of normal
stars whose nuclear
supplies have been used
up. They consist of
degenerate matter with a
very high density due to
gravitational effects.
A white dwarf cools and
fades over several billion
years.
Page 8

9. Supernova
This is the explosive death of a
star. It often results in the star
obtaining the brightness of 100
million suns for a short time.
Type1- These occur in binary
star systems in which gas from
one star falls onto a white
dwarf, causing it to explode.
Type2- These occur in
massive stars, which suffer
runaway internal nuclear
reactions at the end of their
lives.
Page 9

10. Neutron Stars
These stars are composed
mainly of neutrons and are
produced when a supernova
explodes, forcing the protons
and electrons to combine to
produce a neutron star. It is
very dense. Typical stars have
a mass of 3 times the sun, but
a diameter of only 20km. If its
mass is any greater, it will
shrink further to become a
black hole.
Page 10

11. Black Holes
These are believed to form
from massive stars at the end
of their lifetime. The
gravitational pull in a black
hole is so great, nothing can
escape from it- not even light.
The density of matter in a
black hole cannot be
measured. Black holes distort
the space around them, and
can often suck neighboring
matter into them, including
stars.
Page 11

12. Page 12