Download formation1

Proto-stars with tails. The tails point away
from Trapezium.
Debris disk around young star
Stellar Wind and Radiation
pressure
• Stellar wind is comprised of charged particles
which are shot out of a star and move with very
high speeds out into space
• When stellar wind particles hit gas outside the
star, it causes the gas move rapidly away from
the star.
• Radiation (light) being emitted by stars can also
effect material outside of a star. When dust
absorbs the light, dust particles respond by
moving away from the star.
Proto-planetary Survivors
New star in the vicinity of a high mass O-star.
The same effect occurs with comets and our
Sun
Comets
• Comets form far outside of the normal solar system.
They sometimes fall in and pass close to the and then
move back out into the depths of the solar system.
• They have a composition that is the same as the gas
cloud (the solar nebula) that the Sun formed out of.
• They are mostly frozen water, frozen carbon dioxide,
dust and small rocks.
• Their typical size is about the size of Lexington.
• Radius ~ 10 miles.
• When a comet approaches the Sun the
volatile compounds (water, CO2) begin to
evaporate.
• Jets of gas knock off dusty particles as
well.
• As the comet approaches the Sun it starts
to grow a tail. Often times two distinct
tails. One composed of gas molecules
and one composed of dust.
Halley’s comet and gas jets
Gas tail
Dust tail
When the comet goes around and then
leaves the Sun, will it look like this….
• 1)
Or this?
• 2)
Please make your selection...
1. Choice One
2. Choice Two
It’s this one
• 2)
• In the vacuum of space the only thing
pushing on the tail is the solar wind and
the light coming from the Sun. The tail
has to always point away from the Sun,
regardless of how the comet moving.
Star pushing back with
its own, weaker wind
Direction of
intense light
and stellar
wind from
high mass
stars
Eagle Nebula (M 16)
Self-sustained star formation
• Very massive O-type stars and drive away all
the gas and dust near them. When the material
collides with other gas and dust in the molecular
cloud, the gas and dust becomes compressed
and new star formation begins.
• This is why most star forming regions have stars
forming, and nearby a cluster of stars with hot Ostars that are driving the new formation.
Perseus Double Cluster
• This is also why, not all of the star forming
regions in a galaxy are found in the spiral
arms. Some are in between the spiral
arms. Because of self-sustained star
formation.
M 51 The Whirlpool Galaxy
Triggers to star formation
• Over density of gas and dust in spiral arms can
initiate star formation in a molecular cloud.
• It is also possible for two molecular clouds to
collide and set off star formation. This happens
when galaxies collide.
• Once star formation is initiated in a molecular
cloud it is possible to continue the process
through self-sustained star
– Either from Hot O and B type stars
– Or from supernova explosions
Cloud-cloud collisions
Cloud-cloud collisions
Cloud-cloud collisions
The spiral arms in a galaxy are density waves.
These waves are nearly stationary. They do not
move like the stars, gas and dust do. The sun for
instance orbits the galaxy at 220 km/s. Since the
spiral arms are barely moving, the Sun passes in
and out of spiral arms several times each orbit.
Gas clouds also orbit at the same speed as the
Sun. But when gas clouds pass through the spiral
arms they become compressed.
The spiral arms in galaxies are star forming
factories.
M 51 The Whirlpool Galaxy
Spiral Density waves initiate star
formation
A molecular cloud passing through the
Sagittarius spiral arm
A molecular cloud passing through the
Sagittarius spiral arm
Spiral arm
Gas outflows
from super
supernova or
O/B star winds
Initiation of
star formation
• It takes the Sun about 250 million years to
orbit the Galaxy once. (250,000,000 years)
• The Sun formed about 5 billion years ago.
• That’s 5,000,000,000 years ago.
• How many times has the Sun orbited the
Galaxy?
How many times has the Sun orbited the
Galaxy?
60
30
1.
2.
3.
4.
2 times
20 times
200 times
It has made one
orbit yet
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• 5 billion years/250 million years for each
orbit.
• 5,000,000,000/250,000,000
• Or 500/25 = 20 times.
• The Sun has orbited the Galaxy about 20
times since it formed.
• It takes the Sun about 250 million years to
orbit the Galaxy once.
• The circumference of the orbit is about
200,000 light years. Let just call it 250,000
light years. (for ease of calculation)
• If an O-star forms that has the same orbit
as the Sun but has a total lifetime of 1
million years.
• How far does this star make it from the
spot that it formed?
How far does the O-star move in its orbit
before it dies?
60
30
1.
2.
3.
4.
1 light year
100 light years
1000 light years
250 million light
years (one complete
orbit)
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• If it takes 250 million years to go around
the Galaxy once, then the O-star will only
make it 1/250 the way around.
• IF the circumference is 250,000 light
years, then it will travel 250,000 ly/250.
• Distance from the spot of origin is 1,000
light years. Then it dies.
Supernova triggered star
formation
• The largest mass stars, form, use up their
fuel and die in an enormous explosion
before they ever move away from their
formation site.
• The shock waves from the explosion helps
to compress the molecular cloud in which
they formed and set off new star
formation.
Supernova bubble
Supernova bubble
Molecular
cloud
Bubble moving
outward from
supernova
Star formation in a compressed cloud
• A region of the molecular cloud becomes dense.
• This pocket of over density is much bigger than
a single star.
• This over dense region is not uniform, but has
within it other, smaller regions of high density.
• As the over density begins to be drawn together
by gravity, it fragments into smaller pockets of
gas which go on to form individual stars.
• The result is a star cluster. The more massive
pockets from massive stars, the less massive
form smaller stars, like the Sun
Spinning stars and disks
• As material falls into a newly forming star it
begins to spin rapidly.
• This is due to another conservation law. It
is the conservation of angular momentum.
• Angular momentum is similar to regular
momentum in a straight line. Angular
momentum is just the momentum that
keeps things spinning.
Angular momentum is constant
• L = mass X velocity X radius
• Where L is angular momentum and it is
constant in a system.
• L = mvr
• Let’s examine this by first holding the
mass, m, constant.
L = mvr So, what happens if the radius
decreases?
30
30
1. The velocity will
increase
2. The velocity will
decrease
3. The velocity will stay
the same
4. L will decrease
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• If the radius were to decrease, then the
velocity has to increase. Causing the
object to speed up its rotation.
• L = mvr and L is constant. So if r gets
smaller and m is constant, there is no
choice but for v to increase in such a way
as to keep mvr constant.