Birth of a Star: Nebulae: Practice Problem Solutions

1. A cloud of gas and dust between the stars. A molecular cloud is a very cold, dense nebula where atoms have joined into molecules, mostly hydrogen.

2. A shock wave (for example from a nearby supernova), collisions between clouds, or a slow build-up of mass can compress a region until gravity wins.

3. A young star still collapsing, glowing from the heat of compression. No, it is not fusing hydrogen yet.

4. The cloud was rotating; as it shrinks it spins faster and flattens into a disk (conservation of angular momentum).

5. About 10 million kelvins.

6. An object with less than about 8% of the Sun's mass that cannot sustain hydrogen fusion; it is between a planet and a star.

7. Any two of: Orion Nebula, Eagle Nebula (Pillars of Creation), Carina Nebula.