Ronald Westra University Maastricht

1. Introduction to Astrophysics Part 2 Our Amazing Universe Ronald Westra University Maastricht

3. 1. Gravity Revisited

5. At large distances only the force of universal gravity counts

6. All movements are defined by: Gravitation and Kinetic Energy

7. Example 1a: two-body system

8. Example 2a: Formation of solar system from accretion disk This animation begins with a collapsing interstellar cloud of gas and dust. Most of the material becomes part of the young Sun, but some debris forms a disk. Within this disk form the planets, moons, comets, asteroids, and meteoroids. Note that this process is repeated on a smaller scale in the outer solar system, where miniature disks form around the Jovian planets. Within the Orion Nebula—a giant cloud of gas and dust some 1500 light-years from Earth—new stars, and perhaps new planets, are being formed. The final closeup is a young star surrounded by a dark disk of material within which planets may be forming. (HST images).

9. Example 2a: Observations of stellar motions near the central supermassive black hole of our Galaxy

10. Example 2b: Observed stellar motions in the centre of our galaxy M82 suggest a supermasive black hole

11. Example 3a: Computer animation of two colliding galaxies The Merger of Two Disk Galaxies This supercomputer simulation shows the collision and merger of two disk-shaped galaxies. Stars in the disk of each galaxy are colored blue, while stars in their central bulges are shown in yellow. Red indicates dark matter that surrounds each galaxy. The total elapsed time for this simulation is one billion years.

12. Example 3b: Computer animation of six colliding galaxies This supercomputer simulation shows six galaxies merging to form a single giant galaxy. Toward the end of the simulation a large galaxy forms that "devours" other, smaller galaxies, a process called galactic cannibalism. (In ordinary galactic mergers, galaxies of about the same size are involved.) Galactic cannibalism may explain how giant elliptical galaxies form near the centers of rich clusters of galaxies, where galactic collisions are frequent.

13. Computer animation of an active galaxy (Quasar) based on a HST picture

14. Animation of the two opposit jets of a Quasar

15. 2. Exotic Matter !!!

16. The Enigmatic Dark Matter * 90% of all matter is missing !!! * Brown Dwarfs? ... no * Old Pulsars? ... no * Black holes? ... no * MACHO's? ... no * WIMP's? ... ??? * neutrino mass? ... no * Cosmical constant? ... ??? * Gravitation adapted? ... ???

17. Galactic Rotation Curve

18. Supermassive Black Holes in Galactic Centres

19. The centre of our Galaxy: Sagitarius A*

21. 3. History of the Universe

22. Is the Universe Infinite and static? * Olbers Paradox * Newton: Infinite uniformely distributed mass

23. Hubble's Law of Redshift * Galaxies move aways from each other (Slipher&Hubble) * Velocity proportional to distance (Hubble) *Proportionality: Ho ~ 70 km/s/Mpc

25. Hubble's Law implies an Expanding Universe Heliocentric position or Newtonian relativity ?

26. Einstein's General Theory of Relativity The laws of physics must be of such nature that they apply to systems of reference in any kind of motion

28. GTR Equivalence principle gravity --> accelarated motion --> noninertial frames --> curved spacetime

29. GTR Equivalence principle gravity --> accelarated motion --> noninertial frames --> curved spacetime

30. Curved Spacetime

31. The Big Bang Theory Hubble's Law implies that the entire universe started at one moment and in one point at 1/H0 ~ 14 billion yrs ago

32. The Big Bang Theory Physics can reconstruct the history of the universe up to the Planck-time ~ 1.35 .10-34 sec Before that time QM and RT contradict

33. Models for the Evolution of the Universe • 2D-Analogy: inflation of a baloon • All points move apart a la Hubble • There is no centre of the universe • Space itself expands

34. Critical Density of the Universe Critical density : crit = 2.10-27 kg/m3  = /crit

35. Models for the evolution of the Universe

36. Models for the evolution of the Universe

37. The Early Universe Up to 300,000 yrs Hot and opaque Matter and radiation coupled

38. Some fine day 300,000 yrs after the BB ... Universe cooled by expansion: matter and radiation become suddenly decoupled Universe becomes transparant This is the oldest radiation and the farthest we can possibly see

39. Models for the evolution of the Universe

40. Cosmic Background Radiation This radiation is the Cosmic Background Radiation (CBR) Because of subsequent expansion the the universe this is now cooled to ~ 2.7 Kelvin Since january 2003 a entire map of the CBR is available

41. CBR Isotropy Problem Isotrope 1:10,000

42. Universe is flat and isotrope Newest measurements indicate that space is almost flat and isotrope Solution: inflation theory Short after Plancktime space grew during about 10-24 seconds a factor 1050

43. Accelarating Universe and Anti-gravity Newest measurements also indicate that redshift grows stronger than Hubble’s law The expansion is accelerating !!! Possible solution: reintroduction of Cosmological Constant ? What would Einstein say ???

44. Models for the evolution of the Universe

45. Models for the evolution of the Universe

46. Models for the evolution of the Universe

47. The Fate of the Universe Big Crunch : not likely Big Sleep : 1036 yrs from now only low-energy radiation

48. Models for the evolution of the Universe

49. Is the Universe part of an infinite Multiverse ??? ...

50. ... only when physics becomes metaphysics ...