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STARS
A Life and Death Production
Nebula
A very large diffuse mass of interstellar
dust and gas (mostly Hydrogen).
This material starts to collapse in on itself
due to gravitational forces.
Eventually enough material gathers
together to form a gas clump called a
protostar.
Examples of Star Forming Nebula
Cone Nebula
Eagle Nebula
Protostar
As a gas clump collapses, it heats up
because the gas particles collide more
often and it starts to spin
(counterclockwise)
The gas clump forms a disk with the
protostar in the center. Extra material in
the disk may form planets.
Protostars in Infrared Light
Visible Light
Infrared Light
Dust clouds block visible light whereas infrared light
can pass through the dust clouds and be seen as
bright spots where new stars are forming.
Nuclear Fusion
When enough material collapses the
temperature and pressure can build
until nuclear fusion starts in the core.
4 H  He
The star settles down to spend about
90% of its life as a main sequence star.
Main Sequence Stars
Depending on the size of the protostar a small or
medium sized star may be created such as our sun.
Small sized stars may last for 100 billion years.
Medium sized stars may last for 10 billion years.
Large stars (10 times the mass of our sun) use their
hydrogen fuel faster and may only last a few million
years. However they are 5000 times brighter than
our sun.
Extremely large stars (30 times the mass of our sun)
may only last for one million years and are extremely
bright (and are very rare).
Old Age
Eventually all the H2 is converted to He
and the nuclear reactions stop.
Gravity causes the core to shrink.
As the layers collapse, fusion may start
again using Helium as the fuel and the
outside layers puff out to form a RED
GIANT.
Main Sequence Star
When our Sun expands and becomes a red
giant, Mercury, Venus and possibly Earth will
be swallowed up by the Sun.
If Earth is not swallowed up, the Sun will heat
the Earth's surface so that the oceans will boil
and the atmosphere will evaporate away.
Final Farewell
When the core fuel runs out again, the
outer layers are ejected and a
planetary nebula forms.
Supernova
The largest stars shed their layers in a
massive explosion called a Supernova.
The end result is also a planetary nebula.
Supernova are so bright that they can outshine
an entire galaxy for a period of time.
Planetary Nebula from a
Supernova
Supernova 1987A
In February 1987, a supernova exploded in a
nearby galaxy. It was the first supernova to
be clearly visible to the unaided eye in over
400 years.
AFTER
BEFORE
Supernova 1987a
Remnants
Death
What remains after the outer layers of a
star are blown off depends on the mass
of the core .
1. Small and medium stars will shrink
down to a white dwarf.
2. Large stars form a neutron star.
3.The largest of the large will collapse to
a point called a black hole.
White Dwarf
The last stage of a small to medium sized star.
After losing its outer layers of gas as a planetary
nebula the rest of the star collapes to about an
Earth-sized object and will remain hot enough
so that it appears as white light.
These celestial objects are extremely dense
(a lot of matter in a very small volume).
Neutron Star
The last stage of a large sized star (10 solar
masses).
After losing its outer layers of gas as a planetary
nebula the rest of the star collapes to about
10 to 20 km in size and is even more dense
than a white dwarf.
One teaspoonful of a neutron star weighs
about 2 billion tons.
Black Hole
The last stage of a very large sized star (30
solar masses).
This collapsed core is so dense that not
even light can escape it’s gravitational pull!
It may only be a few kilometers in size.
http://imagine.gsfc.nasa.gov/docs/science/know_l2/black_holes.html
Star Colour
The colour of a star is dependent on its temperature.
The order of colours from hottest to coolest is:
Blue
Bluish-white
White
Yellowish-white
Yellow (our sun)
Orange
Red
Star Brightness
The brightness of a star as we see it from Earth
is dependent on two things:
1. How big/hot the star is.
2. How far away the star is.
Magnitude
The brightness of stars are split into six
categories of magnitudes.
The brightest stars are called first-magnitude
and the faintest stars visible with the unaided
eye are called sixth magnitude.
The rest of the stars are ranked in between.
Apparent Magnitude
This is the brightness of a star as it
appears to someone looking at the night
sky.
This is not an indication of how bright
the star actually is since the observed
brightness is affected by how far away
the star is.
Brightness is affected
by distance
If two stars of equal size
and brightness were
observed, the closer of the
two stars would appear
brighter to us and the
further star would appear
dimmer.
Absolute Magnitude
This discrepancy in measuring the
brightness of stars led to a new
measurement called absolute
magnitude.
This is an actual measurement of the
brightness of a star if it were located
3.26 light years from Earth (1 parsec).
An example of Absolute
Magnitude
Stars as they actually
appear in the sky.
The same stars as they
would appear if they were all
3.26 light years from Earth.