Galaxy evolution

Dr Andrew Conway

Observations to be explained

Colour-magnitude diagram

Colour-magnitude diagram

Source: Joshua Schroeder CC BY-SA 3.0

Colour-magnitude interpretation

Jeans mass

Top-down or bottom-up?

Dark matter

Dark matter - unseen gas clouds?

We know the Universe is full of gas clouds of mainly H and some He. Could dark matter be such clouds, perhaps spread very thinly (low density) throughout the galaxy so they're hard to see? The arguments against are many, including:

Dark matter - MACHOs

Could the mass be hidden in many massive but compact objects, such as white dwarfs, neutron stars and black holes? Referred to as MAssive Compact Halo Objects (MACHOs).

Dark matter - however improbable!

"You will not apply my precept," he said, shaking his head. "How often have I said to you that when you have eliminated the impossible, whatever remains, however improbable, must be the truth? We know that he did not come through the door, the window, or the chimney. We also know that he could not have been concealed in the room, as there is no concealment possible. When, then, did he come?"

Sherlock Holmes in The Sign of the Four, Chapter 6. (1890)

Non-baryonic matter


Dark matter - hot or cold

Cold Dark Matter (CDM) refers to dark matter that has speeds much less than the speed of light.

Hot Dark Matter (HDM) refers to dark matter that moves close to the speed of light, such as the neutrino.

Disk formation

Elliptical galaxies and central bulges

Galaxy interactions

Antenna galaxies - NGC 4038 and 4039

Antennae galaxies

Source: NASA Public Domain

NGC 4038 and 4039 - Hubble

Antennae galaxies HST

Source: ESA/Hubble CC BY-SA 3.0

Galaxy interactions - simulations

Try running the simulation on the galaxy crash website to produce the following from the two disk galaxies (that start with no spiral):