330 likes | 438 Views
WHERE STARS ARE BORN. The Interstellar Medium (ISM). The space between the stars looks empty . . . But it’s not!. Gas. Dust. ~ 0.0001 cm. * Mainly hydrogen + helium * Avg density 1 – 10 atoms/cm 3 * 99% of ISM. * Tiny grains (‘smoke’). * Silicates, carbon, ice (?)
E N D
WHERE STARS ARE BORN
The Interstellar Medium (ISM) The space between the stars looks empty . . . But it’s not!
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
‘Whirlpool’ Galaxy
Rosette Nebula Emission Nebulae * Ultraviolet photons from hot stars are absorbed by gas atoms – cause gas to glow.
Trifid Nebula North America Nebula
Hot Stars H atoms UV Earth
UV Hydrogen atom Electron ejected Electron recaptured Photon emitted
Red Balmer emission Line
Molecules – mainly hydrogen (H2). Carbon monoxide (CO) in Orion
Reflection Nebulae Pleiades Star Cluster * Glows due to scattered (reflected) starlight. * Dust scatters blue light more efficiently than red light.
Molecules abundant here Dark Nebulae
Emission nebula ‘Horsehead’ Nebula Reflection nebula
* Results from collapse of a molecular cloud. • Cloud collisions • Supernova blast wave • Expanding emission nebula • Galactic density wave
Molecular Cloud Shrink & heat Central temp 10 million K: Hydrogen fusion ignites ‘protostars’ (on main sequence)
Star birth in the Eagle Nebula
Forming star? Star birth in the Trifid Nebula
* Accretion disk may form around young stars . . . Bipolar Flow
Bipolar Flow Disk p. 273
‘Evolutionary tracks’ on the HR diagram: Time required for contraction to main sequence depends on mass. pgs. 274-5
Protostar mass < 0.08 M: No hydrogen ignition: ‘Brown Dwarf’
The ‘Pistol’ Star M > 100 M Star disrupted by the pressure of photons.