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Emission Nebulae * Ultraviolet. photons from hot. stars are absorbed ... Rosette Nebula. Great Orion Nebula. North America Nebula. Trifid Nebula. Hot. Stars. Earth. H ...

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Presentation Transcript
slide1
WHERE

STARS

ARE

BORN

slide2
The Interstellar Medium (ISM)

The space between the stars looks empty . . .

But it’s not!

slide3
Gas

Dust

~ 0.0001 cm

* Mainly hydrogen + helium

* Avg density  1 – 10 atoms/cm3

* 99% of ISM

* Tiny grains (‘smoke’)

* Silicates, carbon, ice (?)

* Avg density  1 grain/million m3

slide7
Rosette Nebula

Emission Nebulae

* Ultraviolet

photons from hot

stars are absorbed

by gas atoms –

cause gas to glow.

slide9
Trifid Nebula

North America Nebula

slide10
Hot

Stars

H atoms

UV

Earth

slide11
UV

Hydrogen atom

Electron ejected

Electron recaptured

Photon emitted

slide12
Red Balmer

emission Line

slide13
Molecules – mainly hydrogen (H2).

Carbon monoxide (CO) in Orion

slide16
Reflection Nebulae

Pleiades

Star Cluster

* Glows due to scattered

(reflected) starlight.

* Dust scatters blue light more efficiently than red light.

slide17
Molecules

abundant

here

Dark Nebulae

slide18
Emission nebula

‘Horsehead’ Nebula

Reflection

nebula

slide20
* Results from collapse of a molecular cloud.
  • Cloud collisions
  • Supernova blast wave
  • Expanding emission nebula
  • Galactic density wave
slide22
Molecular

Cloud

Shrink & heat

Central temp  10 million K:

Hydrogen fusion ignites

‘protostars’

(on main sequence)

slide23
Star birth in the

Eagle Nebula

slide24
Forming star?

Star birth in the

Trifid Nebula

slide26
Bipolar

Flow

Disk

p. 273

slide28
‘Evolutionary tracks’ on the HR diagram:

Time required

for contraction

to main sequence

depends on mass.

pgs. 274-5

slide31
The ‘Pistol’ Star

M > 100 M

Star disrupted

by the pressure

of photons.

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