1. Galaxies GALAXIES AND LARGE SCALE STRUCTURES

2. The light we receive today from the most distance galaxies was emitted long before Earth existed. Even when we take into account their different orientations in space, galaxies do not all looks the same. Hubble’s Galaxy Classification: Four basic types depending on their appearance: spirals, barred spirals, ellipticals, and irregulars.

3. Spirals: - All spirals contain a flattened disk, central bulge and an extended halo. - They are denoted by the letter S and classified as type a, b, or c according to the size of its central bulge. - From Sa to Sc bulge decreases and spiral arms are less tightly bound. - Type Sc contain the most interstellar gas and dust, Sa the least.

4. Andromeda Galaxy

5. M51

6. NGC 2997

13. Barred spirals: presence of an elongated "bar" of stellar and interstellar matter passing through the center and extending beyond the bulge, into the disk. They are designated by the letters SB and are subdivided, like the ordinary spirals, into categories SBa, SBb, and SBc, depending on the size of the bulge.

20. Ellipticals - They have no spiral arms and, no obvious galactic disk. - They often exhibit little internal structure of any kind. - The most circular are designated E0, slightly flattened systems are labeled E1, and so on. E7 the most elongated. Giant ellipticals can range up to a few Mpc across and contain trillions of stars. Dwarf ellipticals may be as small as 1 kpc in diameter and contain fewer than a million stars. Most ellipticals also contain little or no gas and dust and display no evidence of young stars or ongoing star formation. Like the halo of our own Galaxy, ellipticals are made up mostly of old, reddish, low-mass stars with disordered orbits.

22. M84

26. Irregulars: Irregular shape. Rich in interstellar matter and young, blue stars. - The Irr I galaxies often look like misshapen spirals. - The much rarer Irr II galaxies often exhibiting a distinctly explosive or filamentary appearance. Violent events may have occurred within them. - They tend to be smaller than spirals but larger than dwarf ellipticals. - Dwarf Irregular and Dwarf Elliptical make up the vast majority of galaxies.

28. Large Magellanic Cloud

29. M82 or Cigar Galaxy

31. Hubble sequence There is not direct evolutionary connection along the sequence.

32. Expanding the Distance Scale within 1000pc RR Lyrae and Cepheid variables stars are useful to know the distance to the nearest galaxies (up to 25Mpc).

33. Expanding the Distance Scale Tully Fisher relation:For spiral galaxies, the amount of broadening is a direct measure of the rotation speed, and rotation speeds are closely correlated with their luminosities. Up to 200 Mpc

34. Expanding the Distance Scale Supernova Type I explosions: Have remarkably consistent peak luminosity and are very bright (Up to 1000 Mpc)

35. A New Yardstick

36. Galaxy Clusters: a group of galaxies held together by their mutual gravitational attraction.

37. Local Group: 45 galaxies. Only 3 spiral, the rest are dwarf- elliptical or irregular.

38. Virgo cluster: the next large cluster beyond the Local Group. It is at more than 18Mpc from Earth. 2,500 galaxies. 3Mpc across. M86 M87

41. Local Supercluster

42. Hubble’s Law

43. Ursa Major 15,000 150 Corona Borealis 21,600 220 Bootes 39,300 390 61,200 610 Hydra Hubble’s Law IMAGE SPECTRUM Velocity (km/s) Distance (Mpc) BLUE RED Virgo 1,210 12

44. Hubble’s Law - Within a galaxy cluster galaxies move more or less randomly. - On the largest scales, galaxy clusters move in a very ordered way. - They all appear to be receding from the Milky Way at speeds proportional to their distances from us  the Universe is expanding. - This relationship is called Hubble’s law.

45. Hubble’s constant H0 The further the Galaxy is from us the larger the velocity at which it is going away from us  THE UNIVERS IS EXPANDING!! Recessional velocity = H0 x distance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . H0 = 50—80 km/s/Mpc H0 = 70 km/s/Mpc One of the most fundamental quantities of nature - it specifies the rate of expansion of the entire cosmos. Used to measure distances. Distance Ladder

46. Galaxy Masses Ellipticals and spirals contain between 1011 and 1012 solar masses of material. Irregular galaxies about 108 to 1010 times that of the Sun. Dwarf ellipticals and dwarf irregulars can contain 106 or 107 solar masses.

47. Mass for elliptical and irregular galaxies are estimated by observing the orbit in binary systems.

48. Typical cluster masses are 1013—1014 solar masses Dark Matter 90 percent of the universe is composed of dark matter.

49. A stream of matter flowing out. A dark galaxy companion?

50. Large amount of intracluster gas, diffuse intergalactic matter filling the space among galaxies. It is mainly primordial. It is not enough to impact the dark-matter problem.