20 - Forming disks inside halos

We expect a halo is made up of about ___ baryonic matter (by mass), mostly in H and He.

1/6

What is Radioactive cooling?

The process by which hot gas emits light. It begins by atoms moving around which collide, kicking an electron to a higher energy level. After some time, the electron falls back to a lower energy level, releasing a photon

Baryonic matter can interact with ____ whereas dark matter cannot.

Light

The only possibility is that the energy of the photon comes from the motion of the atoms, such that atoms ____ ____.

Slow down

The only thing keeping the matter suspended against gravity is its velocity. Taking that away, the atoms ___ towards the _____.

Fall, centre

Denser gas inside ______ _____ is able to cool fast enough to fall into the centre.

Cooling radius

The collisions of the baryons result in the halo losing all its _________ support, so that it can only hold itself up with the 3% _________ support.

Dispersion, rotational

Gas falling to the centre has some small net ________, counteracting gravity in the plane of rotation, resulting in a ____ structure.

Rotation, disk

What are spiral arms of halos made of?

Density waves, causing stars and gas to pile up, making them bright

When halos merge, the galaxies within them merge, destroying the _____ structure, resulting in an _______ form.

Spiral, elliptical

________ are classified by roundness, _____ are classified by number and tightness of spiral arms, and _______ are oddballs, like mergers and starbursts (rare).

Ellipticals, spirals, irregulars

Ellipticals are ___ and ____.

Red, dead

Spirals are ____ and _____________.

Blue, star-forming