- Birth - cold, dark clouds of interstellar gas and dust collapse - PROTOSTAR - IR radiation
- At this stage of evolution (IR emission) the protostar is known as a T Tauri star
Disk of nebular gas forms, jets form, and disk is eventually blown away
Clouds are about 90% hydrogen, 9% helium, less than 1% other (by number of atoms)
Collapse is initiated by SHOCK WAVES from:
- stellar wind of nearby heavy stars (O, B)
- supernova explosion
During collapse, gravitational energy heats globules from a few degrees K to millions Kelvin
Eventually, THERMONUCLEAR FUSION begins (at about 10 million K), and hydrostatic and thermal equilibrium are established
Heaviest stars collapse fastest
- 15 MSUN --> 105 years
- 2 MSUN --> 107 years
- Stars of different masses follow different evolutionary paths
New star formation is associated with
- Open or galactic clusters
- OB associations
- HII regions (HII is ionized hydrogen)
- Stellar association
- Loosely bound group of new-born stars
Nebulae:
- Absorption nebula
- Cloud of gas and dust which obscures more distant light
- Reflection nebula
- Cloud of dust illuminated by stars (bluish)
- Emission nebula
- Glowing from excitation caused by nearby stars
- often found with newborn star clusters
- Main sequence stars begin after the formation stage, on the ZAMS line
- ZAMS = zero-age main sequence
- Brown Dwarf
- If the collapsed mass is less than 0.08 MSUN, it never gets hot enough for thermonuclear fusion --> failed star
End result of the collapse of the star is loosely associated stars in Star Clusters
-
Newborn cluster NGC 3603
-
Pleiades or Seven Sisters
- example of an open cluster
- H-R diagram reveals this is young cluster, less than 100 million years old
Over time, these clustering stars will separate and become isolated stars, like the Sun, or isolated small groups, such as binary star systems
