AST201H1 Lecture Notes - Protostar, Hydrostatic Equilibrium, Orion Nebula

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Published on 13 Oct 2012
School
UTSG
Department
Astronomy & Astrophysics
Course
AST201H1
Star Formation
Stars do not live forever. They are “born” and they “die”
Depends on its mass
Mass influences the evolution of the star
Where are stars born?
Space between stars is not empty
Interstellar media full of gas and dust
The density of the medium has few particles
The interstellar medium is filled with microscopic dust particles and gas
Dust grains scatter and absorb virtually all visible light that enters a cloud preventing us from
seeing what lies behind it
In infrared we can see past the dust and see that behind dark regions there are lots of stars
Any longer wavelength will go over that dust
Short wavelength ligh will not pass but longer will
Star nurseries
Orion constellation
Orion nebula in visible light
Colours added later and correspond to emission of different spectral lines
In infrared light we see that a very young cluster is embedded in the gas
In such nebulae, we tend to find lots of dark patches, which are places where the gas and dust are
concentrated enough that they block out background light
Sometimes happens spontaneously but most likely triggered by some kind of shockwave or
collision
Often these dark dusty structures are studded with young stars
Where stars are formed
These regions called molecular clouds
Usually these nebular are rich in molecules, often quite complex ones
They are called molecular clouds
If you have dust clouds that block light, then inside thick dust clouds there should be no light at
all
Gravity vs Pressure
Stars and other interstellar material are in a perpetual battle between forces puling in (gravity)
and forces pushing out (pressure)
Gravitational equilibrium
This happens in every star
Also happens in interstellar clouds
Molecular clouds are cold (10-30k)
Cold cloud - > molecules move slowly - > no outward pressure
Pressure decreases because of slow movement
Gravity wins! Clouds begin to contract
Fragmentation of a cloud
This simulation begins with a turbulent cloud containing 50 solar masses of gas
Initial cloud not uniform (greater densities in some area)
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Document Summary

In infrared we can see past the dust and see that behind dark regions there are lots of stars seeing what lies behind it: any longer wavelength will go over that dust. Short wavelength ligh will not pass but longer will. Star nurseries: orion constellation, orion nebula in visible light, colours added later and correspond to emission of different spectral lines. In infrared light we see that a very young cluster is embedded in the gas. If you have dust clouds that block light, then inside thick dust clouds there should be no light at all. Pressure decreases because of slow movement: gravity wins! Fragmentation of a cloud: this simulation begins with a turbulent cloud containing 50 solar masses of gas, initial cloud not uniform (greater densities in some area) If it got a little cooler, the pressure inside would fall and gravity would win ten new star.

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