AST Lec 11: Life Cycles of the Sun

What are the 3 components of molecular clouds?

Mixtures of gas and dust: ¾ Hydrogen, ¼ Helium, and traces of other elements, including Carbon dust.

What is sub-milimeter light?

Light from molecular clouds that is very long wavelengths because the cloud is cold. It is invisible.

If an object is very very cold…

It will emit invisible, very long wavelength sub-mm light.

What 2 steps are needed to see sub-milimeter light?

1) a sub-mm-sensitive telescope and camera, 2) to get out of the atmosphere, which blocks sub-mm light.

Describe the general relationship of pressure, temperature, and density.

As pressure increases, so does temperature and density.

If a gas has a high temperature…

The gas particles will always be moving fast.

Describe how a Molecular Cloud becomes a Protostar.

Places in a molecular cloud that are more dense will exert a gravitational pull on surrounding material.

This core gets increasingly denser and hotter.

Describe how a Protostar becomes a Main Sequence Star.

When the protostar becomes hot and dense enough, fusion begins to convert Hydrogen into Helium in the core. The star separates into Core, where fusion takes place, Radiative Zone of hot plasma, and Convection Zone where hot plasma rises.

Describe how a Main Sequence Star becomes Red Giant.

As the MSS’s core continues to undergo fusion, the Hydrogen content decreases and Helium content increases.

Eventually, the Hydrogen runs out and fusion stops. The Helium core begins to cool and collapse, until this is stopped by Degeneracy Pressure.

The pressure and temperature of this core is not enough for Helium fusion. Instead it exerts a strong force of gravity on the H/He gas above, where fusion starts again.

Describe how a Red Giant becomes a White Dwarf.

The dense Helium core of a Red Giant exerts a strong gravitational pull on the gases above, where fusion is happening.

The energy produced by this makes the star puff up massively.

Eventually the pressure and temp in the Helium core causes Helium fusion to convert it into Carbon and Oxygen. When the Helium runs out, the Carbon core collapses.

Above that, Helium fusion begins, and in a shell above that Hydrogen fusion begins.The massive energy from these shells blows off the envelope, creating a temporary planetary nebula and cooling Carbon and Oxygen core.

The envelope of a Red Giant grows because…

Fusion in the Hydrogen shell produces much more energy because the pressure is much larger, causing the gas in the envelope to expand.