Notes

center of mass: m1r1 = m2r2
v = rw is for small angles only
L = moment of inertia of a rotating body, I = mr^2
the composition of matter in the universe shifts from heavier to lighter particles as the universe expands and cools from the Big Bang.

since dark matter doesn't interact directly with photons it can cause the density enhancements needed for the galaxies and such we see today while allowing for the isotropic CMBR we see. Dark matter will affect normal matter after decoupling.

Some elements will not cause absorption lines for stars because they are not being emitted in the visible part of the spectrum, so just because we don't see them doesn't mean those elements are not in the stars.

Higher pressure means a higher temperature which means particles are colliding more often resulting in different absorption lines being emitted.

wolf-rayett stars are O class stars with broad emissions lines due to the doppler effect

delta (t) * delta (E) = h : heisenberg uncertainty principle relates the average time an atom spends in an energy state, where h is planks constant.

Collisional broadening results in strong spectral lines.

Zeeman effect is from magnetic fields, and causes splitting of lines which appears as the broadening of lines

the strength of an absorption line depends on the column density

synchrotron radiation (or nonthermal radiation) is caused by electron spiraling in a magnetic field and it's highly polarized. Does not depend on Temperature either

spiral arms of the milky way are not material arms

the interstellar medium is not uniformly distributed but is instead in dense areas called interstellar clouds. Neutral ISM means H1 region and ionized ISM means H2 region. Degree of ionization is zero for H1 and 1 for completely ionized H2.

intercloud medium = medium between interstellar clouds that is hotter than the clouds.

H1 = atomic H H2 = molecular clouds. Denser and cooler than H1, exist in the interior of dense clouds (also called dark clouds)
H2 regions = H is completely ionized, surround/are near young hot stars. Ionized by the photons emitted by this star
Dust particles exist in both regions.

magnetic fields exist in the ISM. evidence is shown in dust particles grains being negatively charged

faraday rotation = the rotation of the plane of polarization

H1 regions do not emit visible radiation and are therefore observed through light they absorb from stars

H atoms normally have protons and electrons with opposite spins (b/c its a lower energy level). H atom going from parallel spins to antiparallel spins cause a 21cm photon to be emitted. This is how the level of H is detected

H2 region (emission nebula) = radiating clouds surrounding or near young, hot stars. Emit radiation in all spectral series but we only observe Blamer series from the ground. Photons/particles collide and ionize hydrogen while electrons slow down and form H again. Brightness dependent on background star