Galaxy Clusters and Superclusters

1. Galaxy Clusters and Superclusters • galaxies come in clusters of 10-1000 galaxies: gravitationally bound, impacts formation • clusters usually part of superclusters which reflect distribution of matter in early Universe Formax Cluster 60 MLY from us PHYS 162

2. Local Cluster = “Local Group” spiral: MW, Andromeda(M31), M33 elliptical: NGC205, M32, NGC185, NGC147 irregular: LMC, SMC, NGC 6822, IC 1613 PHYS 162

3. Superclustersof GalaxiesNOT uniform(dark matter…later) PHYS 162

4. Milky Way Galaxy • Milky Way – spiral galaxy - flattened disk 150,000 LY in diameter with about 200 billion stars • we sit in a gas/dust “arm” - active star formation - absorbs visible light • study using IR/radio/gamma or by looking at other galaxies PHYS 162

5. Milky Way Structure • Nucleus • Disk • Halo PHYS 162

6. Galaxy Nucleus • Nucleus - high density of stars - little gas or dust; limited new stars • very active star formation in past - many black holes - super massive BH at center >1,000,000 Mass(Sun) PHYS 162

7. Galactic Center measure motion over time  get mass in center (like Kepler) PHYS 162

8. Milky Way Galaxy - Disk and Halo Stars • In Disk - lots of bright, young stars - lots of gas and dust - stars abundant in heavy elements (Type I)  earlier generations formed heavy elements • active star formation • in Halo - mostly old red stars - no gas/dust - no heavy elements (just H and He) (Type II) • no current star formation PHYS 162

9. Globular Clusters  Halo Stars M10: 85 LY across, 16,000 LY from Earth PHYS 162

10. Size and Shape of Galaxy • measure distances to globular clusters • outside plane of galaxy  not obscured by gas and dust (done early in 20th century) • tell where center of galaxy is • shape of early Galaxy Center of Galaxy sun Visible stars Glob cluster PHYS 162

11. Spiral Arm Formation where stars are being formed in spiral arms “moves” over time as gas/dust is compressed by stars in other regions PHYS 162

12. 21 cm line in H (like MRI) – Doppler Shifts As radio penetrates through gas/dust can use to map out Milky Way PHYS 162

13. Radio Maps of Galaxy use Doppler shift to get velocity of different regions, identify different arms PHYS 162

14. Masses of Galaxies Measure mass by: • motion within a galaxy • motion of different galaxies about each other • gravitational lensing • Gives - most mass isn’t in stars and “normal” matter  DARK MATTER PHYS 162

15. Mass of Galaxy PHYS 162

16. Differential Rotation of Galaxy PHYS 162

17. Mass of Milky Way • Sun is 30,000 light years from center (2,000,000,000 AU); period of 200,000,000 years • same as for planets: Dist3 / Period2 = M (inside)giving 200 billion mass(Sun) inside the Sun’s radius • repeat for 150,000 LY  >1000 billion Mass(Sun) for Galaxy mass inside that distance PHYS 162

18. Differential Rotation of Galaxy PHYS 162

19. Mass of Galaxies • mass doesn’t match observed amount of matter • unseen “dark matter” unknown composition • extends beyond visible part of Milky Way • observed in other Galaxies (1959) PHYS 162

20. Visible and Dark Matter • “visible” matter - star, gas, dust, neutron star, black hole • “dark” matter - not understood - - cooled down white dwarves or black holes leftover from early universe (MACHO study) NO - new physics - neutrinos having enough mass, new particles (WIMPS) YES?? • more than 75% of mass is not understood - Dark Matter mystery  possible new physics like Supersymmetry (NIU’s Steve Martin) PHYS 162

21. MACHOs vs WIMPS • Massive Astrophysical Compact Halo Objects - MACHOs - not new physics – look for by gravitational lensing • Weakly Interacting Massive Particles – WIMPs - new subatomic particles - look for in high energy experiments at CERN and Fermilab or in ultra cold experiments in deep underground mines (will be in movie) PHYS 162

22. MACHO search PHYS 162

23. Other Dark Matter Observations • look at velocities of individual galaxies in a cluster about each other  missing mass first observed by Fritz Zwicky in the 1930s (Caltech; he also introduced name “supernova”) • look at gravitation lensing by a nearby galaxy of a more distant galaxy (many including NIU students Donna Kubik and Matt Weisner. see their theses at www.physics.niu.edu/physics/academic/grad/theses1.shtml) PHYS 162

24. Gravitational Lensing by Galaxies PHYS 162

25. Donna Kubik Thesis NIU students work with Fermilab astrophysicists. Use Sloan Digital Sky Survey data to find “Einstein” ring candidates. Then use better telescope to improve image. Size of ring tells mass in closer galaxy  amount of dark matter PHYS 162

26. Composition of the Universe 95% not understood Graphics courtesy: NASA PHYS 162

27. Galaxy Formation • Rotating gas cloud about 13 billion years ago - local concentrations give first stars • Cloud collapses due to gravity large rotation  spiral small rotation  elliptical near other big galaxy  irregular • Often interacting with other galaxies • Gas/Dust/Star formation persist in spiral and irregular PHYS 162

28. Milky Way Formation old stars in halo give shape early in formation PHYS 162

29. Elliptical vs Spiral Galaxy Formation if less initial rotation easier for early star formation prior to collapse into disk PHYS 162

30. Elliptical vs Spiral Galaxy Formation elliptical galaxies tend to have older stars PHYS 162

31. Colliding and Merging Galaxies galaxies pull on each other by gravity  orbits  interact  can merge happens over billions of years PHYS 162

32. Colliding and Merging Galaxies smaller galaxies often consumed by the larger galaxy nicadd.niu.edu/~hedin/162/andromeda.mov M31-M33 PHYS 162