How To Make a Galaxy

An all-audiences talk explaining the 7 necessary steps that must have happened to create galaxies like we see in the local Universe. (Originally given to an OMSI After Dark audience in September, 2016.)

Transcript

1. HOW TO MAKE A GALAXY Alison Crocker, Reed College
2. HOW TO MAKE A GALAXY SPIRAL ^
3. GOAL A SPIRAL GALAXY We live here!
4. GOAL A SPIRAL GALAXY Disk Spiral arms
5. GOAL A SPIRAL GALAXY Bulge
6. GOAL A SPIRAL GALAXY Supermassive blackhole: Sagittarius A*
7. GOAL A SPIRAL GALAXY Dark Matter ‘Halo’
8. DARK MATTER EASY FOR ASTROPHYSICS! Dark matter: Gravity Electromagnetism Weak Strong Normal matter: Gravity Electromagnetism Weak Strong
9. WHERE DO WE START?
10. WHERE DO WE START? The Early Universe
11. DARK MATTER Density fluctuations. ~0.001% variation
12. DARK MATTER Density fluctuations. ~0.001% variation
13. DARK MATTER Step 1 Choose an overdense region.
14. DARK MATTER Step 2 Turn on gravity! Simulation of dark matter. (Illustris collaboration.) solar masses
15. DARK MATTER Step 2 Turn on gravity! Simulation of dark matter. (Illustris collaboration.)
16. GOAL DARK MATTER HALO ✔
17. NORMAL MATTER Step 3 Wait 380,000 years.
18. NORMAL MATTER Step 3 Wait 380,000 years. Too hot.
19. NORMAL MATTER Step 3 Wait 380,000 years. Too hot. Cool enough! CMB photon
20. NORMAL MATTER Step 4 Let gas fall into your dark matter halo.
21. NORMAL MATTER Step 4 Let gas fall into your dark matter halo. Note: must conserve angular momentum.
22. NORMAL MATTER Step 4 Let gas fall into your dark matter halo. Note: must conserve angular momentum.
23. NORMAL MATTER Step 5 Make stars. Overdense region of gas Star!
24. NORMAL MATTER Step 5 Make stars. Overdense regions of gas Stars
25. NORMAL MATTER Step 5 Make (some) stars. (Self-regulated star formation.)
26. GOAL A SPIRAL GALAXY Disk Spiral arms ✔ ✔
27. GOAL A SPIRAL GALAXY Bulge
28. NORMAL MATTER Step 6 Merge your galaxy. Arp 87. Typical galaxy “family tree”.
29. NORMAL MATTER Step 6 Merge your galaxy. Bulge created!
30. GOAL A SPIRAL GALAXY Bulge Disk Spiral arms ✔ ✔ ✔
31. SUPERMASSIVE BLACKHOLE Step 7 Add a supermassive black hole.
32. SUPERMASSIVE BLACKHOLE Step 7 Add a supermassive black hole… SUPERMASSIVE BLACKHOLE ?
33. 1. Choose over densities 2. Gravity 3. Wait 4. Add gas 5. Form stars 6. Merge 7. Add supermassive blackhole SPIRAL GALAXY
34. Variation: - Choose a small set of small overdensities. - Don’t allow much merging. - Don’t add a supermassive blackhole. IRREGULAR GALAXY
35. Variation: - Choose a larger set of larger overdensities. - Vigorously merge. - Use up or expel all star-forming gas.* ELLIPTICAL GALAXY
36. GOOD LUCK!