Chapter 11 The Formation of Stars

11.1 Making Stars from the Interstellar Medium Star formation/birth is ongoing in our galaxy: e.g. sun is younger than oldest stars; short lived stars exist How does it occur ? youngest stars found near gas clouds somehow: large, low-density, cold clouds of gas become small, high density, hot stars Gravity is Key

11.1 Making stars from the interstellar medium Shock Wave- triggers giant molecular clouds to form stars - this is the astronomical equivalent of a sonic boom Super nova explosions Ignition of very hot stars ionize nearby gas Collision of molecular clouds Spiral pattern of Milky Way Galaxy – spiral arms are shock waves

Giant Molecular Clouds

Shocks Triggering Star Formation

Protostars Still enshrouded in opaque “cocoons”of dust => barely visible in the optical, but bright in the infrared. Protostars= pre-birth state of stars Hydrogen to Helium fusion not yet ignited

ProtostellarDisks Conservation of angular momentum leads to the formation of protostellardisks⌫birth place of planets and moons

Evidence of Star formation Text pages 242-245 Summarize the 4 observational types of evidence

11.2 The source of stellar energy Most stars fuse hydrogen the same way as the sun does, although main sequence stars that are more massive than 1.1. solar masses fuse hydrogen into helium using the CNO cycle.

CNO Cycle

11. 3 Stellar Structure Energy Transport (3 types)

What supports the sun? (and other similar stars) Gravity- strong gravitational pull, pulls atoms towards the center of the sun The pressure from inside the sun, gases that are produced, prevents the sun from shrinking, by pushing the gases outward This gravity-pressure balance is called hydrostatic equilibrium

Inside Stars

11. 4 The Orion Nebula Summarize star formation in the Orion Nebula Text pages 252-254