The Milky Way and Other Galaxies

1. The Milky Way and Other Galaxies Galaxies and the Universe: Part A

2. The Milky Way Galaxy • Our View of the Sky- 2 Key Features • Nearby stars in every direction. • Fuzzy Band of light that stretches across the sky.

3. The Milky Way Galaxy • The dusty path of stars across the sky is our parent galaxy, the Milky Way. • Based on our View • MW has a disk structure, within a faint Galactic Halo (sphere) • Our Sun lies within the disk. • There fatter Galactic Bulge of stars at the center.

4. The Milky Way Galaxy

5. The Milky Way Galaxy • Conclusions dependent on Globular Cluster Density

6. The Milky Way Galaxy • Based on observations, the Milky Way is classified as a Spiral Galaxy • The Disk, Bulge, and Halo are key features • Resembles an “edge-on” view of other spirals like Andromeda

7. The Milky Way Galaxy

8. The Milky Way Galaxy • The Galaxy contains • All types of stars (young/old) • All types of clusters (open/globular) • Nebulae (Emission/DarkDust/Planetary) • Interstellar Matter (Gas and Dus)

10. The Milky Way Galaxy • Rotation- • Most Stars in the Disk rotate in the same direction • Halo stars have largely random orbits • Bulge Stars are between prograde and random

11. The Milky Way Galaxy • Rotation is differential • Orbits faster near the bulge • Slower near the outer rim • Alternating Redshift/Blueshift for internal vsextranal stars.

12. The Milky Way Galaxy • Galactic Spiral Arms- • Key Feature of many galaxies • Theories on spirals aren’t clear • Differential Rotation (discontinued) • Galaxies would wind up and spirals disappear

13. The Milky Way Galaxy • Density Waves (like water waves) • Traveling around the galactic disk, triggers new star formations.

14. The Milky Way Galaxy • Self-Propagating Star Formation • Formation of Stars drives the waves

15. The Milky Way Galaxy • The Mass of the Galaxy and Dark Matter • Study of Rotation allows determination of Mass • Should be more mass than we can see • Majority beyond the Luminous Galaxy • “Dark Halo” • Luminous Galaxy is ~ 30 kpc in across • Dark Matter Extends over 100 kpc across

16. The Milky Way Galaxy • Dark Matter- • Not just unseen in the visible spectrum. • No radiation from any band of the spectrum (radio through gamma) • What is it? • Could just be large numbers of faded Brown/White dwarfs • Could be some as yet undetected Sub-Atomic Particle that pervades the entire Universe

17. The Milky Way Galaxy • Detection? • No experiments successful in detecting “particles” • Gravitational Lensing- for Faint Dwarf Stars

18. The Milky Way Galaxy • The Galactic Center • Very Difficult to see (Gas and Dust in the disk)

19. The Milky Way Galaxy • Infrared and Radio Radiation pass through dust easier. • From these observations get more info about • The stars at the galactic center • Motion around the Potential SMBH

22. The Milky Way Galaxies • Extending Our Distance Scale • Variable Stars (2 types) • RR Lyrae variables (first discovered in Lyra) • Cepheid variables (first discovered in Cepheus) • Pulsating stars tend to have nearly standard luminosities • Gives us a good reference for distance calculations.

23. The Milky Way Galaxy

24. The Milky Way Galaxy

25. Other Galaxies • Hubble’s Classification • Spirals • Barred Spirals • Elipticals • Irregulars

26. Sub- Classes Typically based on size of central bulge.

27. Other Galaxies • Extending the Distance Scale Further • Tulley-Fisher Relation • Galaxy Rotation  Mass • Mass  Luminosity • Luminosity  Distance • Standard Candles- objects with a consistent luminosity • Type I Supernovas

28. “Nearby” Structure • Galactic Structures • Galaxies are not “randomly” distributed • Local Group • 45 Galaxies • Milky Way and Andromeda the Largest • by far.

29. “Nearby” Structure • Galaxy Clusters • Next Largest Grouping • We are in the Virgo Cluster ~ 2500 Galaxies bound by gravity.

30. “Nearby” Structure • Superclusters • Collection of Nearby Clusters • Virgo Supercluster • Over 100 Galaxy Groups and Clusters • Millions of Superclusters in the Observable Universe

34. Cosmic Expansion • Large Scale Motion • You might think it is random and disordered • Within a cluster, galaxy motion is random • Clusters themselves move in an ordered way • Think jar of fireflies • In 1912 it was discovered that all Galaxy clusters are receding from us. • Every Galaxy/Cluster outside our group is Doppler Redshifted • Moving Away

35. Cosmic Expansion • Hubble’s Law • All Galaxies are moving away from us • The further away, the faster they are moving. • The most distant galaxies have increasing Redshifts in their light spectra

36. Redshift

37. Hubble’s Law Plot

38. Cosmic Expansion • Top of the Distance Scale • Spectrum Shift gives Distance • Cosmological Redshift • Using Hubble’s Law we can determine that the most distant objects are receding from us at near 90-95% of the speed of light.

39. Using this scale we can see objects approximately 45-46 Billion Lightyears away.

40. Dark Matter • Dark Matter Revisited • As the masses of individual galaxies are determined by their rotations • 3-10 Times more mass that we can see • The smaller the galaxy the higher the % of unseen mass • Possible Dark Galaxies? • Clusters of galaxies form around dark “Voids” connected by filaments of hot gases • Best Calculations indicate 90% of Matter is “Dark”

42. The Birth of the Universe • Assumptions, The Universe is • Homogeneous- the same everywhere • Isotropic- the same in all directions • Results in the Cosmological Principle • There is no “edge” of the Universe • We are not in the “Center,” there is no “Center”

43. The Birth of the Universe • Hubble’s Law and the Big Bang • Galaxies are moving away from us, • assuming a constant rate • Calculate the time it takes for any galaxy to reach its present location from us. • 14 Billion Years for all any object • Independent of Distance (2x Distance = 2x Speed, same time) • At that time the universe was confined to a single point.

44. The Birth of the Universe • So what’s in the space that the galaxies are moving into? • Galaxies aren’t flying apart into the rest of the universe. • There is no empty space surrounding it. • The Fabric of Space is itself expanding. • Homogeneous and Isotropic

45. The Birth of the Universe

46. The Birth of the Universe • The Cosmological Redshift

47. The Fate of the Universe • Universe is Expanding, will it always? • Possibilities • Expansion will continue, constant • “Big Freeze” everything approaches Absolute 0 • Expansion will slow, stop, and reverse • “Big Crunch” re-collapses into a single point. • “Big Bounce” oscillation, each collapse triggers a new expansion

48. The Fate of the Universe • Expansion will Accelerate • “Big Freeze” again, Absolute 0 • “Big Rip” acceleration increases, all matter will disintegrate into unbound elementary particles. • Universe Will Not End- • Multiverse- our “observable” universe is one part of a larger expanding Universe • Contains other “Universes” • May be expanding or contracting. • No Evidence to support this idea but is Theoretically (Mathematically) possible.

50. The Fate of the Universe • Observations indicate that the expansion is Accelerating • Why is it accelerating? • Two Possibilities • We don’t understand how gravity really works • New Concept called “Dark Energy” Repellant to Gravity To Explain the rate of acceleration we observe, the Universe should be approximately 74% Dark Energy What is it? Still not understood…