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Birth of Stars
Astronomy
The solar
system
Galaxies
The Universe
The Birth of a Star
1. Stars begin as diffuse clouds of
dust in deep space
2. By chance areas with more dust
form, and the increased
gravitational attraction begins to
pull more and more dust in
3. The cloud starts to collapse around
the original concentration of matter,
and pressure and temperature in
the center increases.
4. Plasma forms as electrons are torn
from protons
5. Nuclei come together and fuse –
forming hydrogen
1. Energy increases pressure in
the outer layer, balancing
against the force of gravity –
and the star gains stability
Energy from the stars
• 4 protons
helium + energy (+
leftover particles)
• The process
provides the
energy we see
radiating from
stars, and is self
perpetuating
A Star is Born
• Energy from fusion
pours out from the
core, setting up a
pressure in the
surrounding gas that
balances out the force
of gravity
• The star becomes
stabilized
1. As the contraction starts,
the rotation speed
increases – like a skater
who pulls her arms in while
spinning
2. If nothing slow the rotation
down, the speed will
increase until the star is
torn apart
3. One way that rotational
energy is diminished is by
the star splitting into a
double star system
4. Another rout is for the star
to spin off material in the
act of forming planets
Twin stars or Planets?
• Most stars tend to take the twin star
approach
• This is one way that planets are thought
to form – it is not the only way
Stellar
Lifetimes
• The larger the sun, the greater the
gravitational force, and the more
energy is used in stabilizing the inward
trend.
• Every star must eventually burn all of
its hydrogen
• The larger the star, the shorter the
lifetime
The hydrogen in the outer layers is pulled inward by the gravity – it begins to
fuse with the helium ultimately forming carbon. In the process the star expands
greatly forming a red star
White Dwarf: Diamonds in the sky
• When the core has
reached the point where
they cannot be further
compressed, and the star
is stabilized by the
upward pressure of
electrons
• This star is called a white
dwarf. It no longer
produces energy by
fusion – but continues to
glow as it cools off.
• Stars up to 8 times the
size of our star will
become white dwarfs
• If the star is very large,
it burns through the
hydrogen quickly; helium
fuses to make carbon,
and as the helium is
exhausted the collapse
of the core generates
enough energy to fuse
the carbon forming iron.
• Eventually the star
collapses, as the
electrons are trapped
inside the core, forming
neutrons – thus a
neutron star, or
alternatively a black hole
is formed.
Neutron Stars
& Black Holes
Hertz sprung-Russell Diagram
•
The Main Sequence of a star's life is
the period of time that begins after the
star is "born" starts burning on its own,
and the time that the star starts dying
•
The hotter a star burns, the more
quickly it uses up the helium that fuels
the nuclear furnace at its center.
•
Cooler red stars burn their fuel much
more slowly. As a result, they can
remain on the main sequence for
many of billions of years before they
begin to die.
The Planets of the Solar System
• Planets are categorized according to
composition and size. There are two
main categories of planets:
– small rocky planets (Mercury, Venus,
Earth, Mars, and Pluto)
– gas giants (Jupiter, Saturn, Uranus,
and Neptune)
The Relative Size of the Planets
in the Solar System
My very educated mother just sat up near Pluto
Rocky Planets
Mercury,
Venus,
Earth,
Mars,
Pluto
• They are made up mostly
of rock and metal.
• They are very heavy.
• They move slowly in
space.
• They have no rings and
few moons (if any).
• They have a diameter of
less than 13,000 km
Characteristics of
Gas Giants
Jupiter
Saturn
Uranus
Neptune
• They are made up mostly
of gases (primarily
hydrogen & helium).
• They are very light for
their size.
• They move quickly in
space.
• They have rings and
many moons.
• They have a diameter of
less than 48,000 km
Galaxies
• Stars are gathered
into clumps called
galaxies
• Our solar system is
part of the Milky
Way
• Our galaxy is only
one among billions
links
• Essential for teachers Earth and space
science
• (select Session 8. Order out of Chaos:
Our Solar System )