1. A new view of the Universe VI Fred Watson April 2005

4. COSMOLOGY The study of the origin and evolution of the Universe as a whole…

5. What we need is more money for cosmology One will see what one can do Three microbes in Edinburgh…

6. Professor Malcolm Longair: “We are witnessing the dawn of a new realm of precision cosmology…” August 2000 Better described as “industrial-strength” cosmology because it is very robust… The robustness comes from advances in astronomical technology and theoretical physics in recent years…

7. Two kinds of observational cosmology… Near-field cosmology –History of nearby objects, e.g. stars, galaxies Far-field cosmology –Studies of the most distant objects: galaxies, quasars, gamma-ray bursters etc. –Studies of gravitational lensing, the cosmic microwave background, etc. Both kinds tell us about the evolution of the Universe

8. The Nearby Universe

9. Tools of the trade Astronomers don’t use light years. (You can’t measure a light year.) Astronomers use parsecs. (Not to be confused with parsnips.)

10. What’s a parsec? Earth Earth 6 months later Star appears to move against background Sun 1 arcsecond 1 parsec = 3.27 light-years 1 parsec

11. Galaxies … Basic building-blocks of the Universe If this was our Galaxy, we’d be here Around 100,000,000,000 stars Lots of gas and dust (in spirals) Around 100,000 l.y. across (or 30 kiloparsecs)

12. Edge-on view of a spiral galaxy… The gungy brown stuff is dust, which limits the view from the inside

13. The Eagle Nebula—stellar birthplace In galaxies, stars are born…

14. The Vela supernova remnant …and die

15. The Expanding Universe

16. The Hubble Deep Field—a core-sample of the Universe Most of these galaxies have look-back times measured in billions of years… But how do we know it’s expanding?

17. Tools of the trade Telescopes can be used as celestial speedometers for galaxies. Astronomers record and measure the spectra of the galaxies.

19. Blue end Red end A spectrum (Not to be confused with a plectrum)

20. Spectra of about 100 galaxies arranged in order of increasing velocity Blue end Red end

21. Hubble’s Law (1929) “The speed of recession of a galaxy, v, is proportional to its distance, d, from the observer.” v = H 0 d The constant of proportionality, H 0 is called the Hubble constant, and is in units of km/s per megaparsec. (1 Mpc = 3.27 million l.y.) Accepted value today is H 0  75 km/s/Mpc.

22. But what does “redshift” mean…? We now know the Hubble law comes about because space itself is expanding, stretching the wavelength of light moving through it. Rather than calculating a galaxy’s velocity, astronomers simply measure the fractional shift of its spectrum towards the red resulting from the expansion (  / emitted ). This is called the redshift, z

23. Tools of the trade The Really Useful Quantity 1/(1 + z) tells us how big the Universe was when the light was emitted. R emitted / R now = 1/(1 + z) E.g., for a galaxy with z = 1, the Universe was half its present size when it emitted its light.

24. An Einstein Ring ( B0047-2808) … z foreground = 0.485; z background = 3.595

25. The Age of the Universe

26. How old is the Universe? In 1927, Georges Lemaître realised that Hubble’s Law means the Universe itself is expanding. He extrapolated back in time to when all the galaxies were at a single point. The age of the Universe is then given by the “Hubble time” = 1/H 0 If H 0 = 75 km/s/Mpc, the Hubble time is 13 billion years.

27. 13 billion years The Universe today Origin of the Universe Lemaître’s Picture: Defining quantity: Hubble constant, H 0 (uniform expansion) Problem: it only works if the Universe is completely empty.

28. About 9 billion years The Universe today Origin of the Universe Refined Model (1970s): Defining quantities: Hubble constant, H 0 (current expansion) cosmic density parameter,  Problem: the Universe is younger than most of its contents.

29. Dark matter and the composition of the Universe

30. ~13 billion years The Universe today Origin of the Universe Current Model: Defining quantities: Hubble constant, H 0 (current expansion) cosmic density of all matter,  m cosmic density of ordinary matter,  b dark energy (cosmological constant,  ) (evidence from distant supernovae, etc.)

31. Age of the Universe

32. Mapping the Universe

34. Survey Regions Pie-slice directions in the 2dF Galaxy Redshift Survey

35. The distribution of galaxies allows us to measure the“clumpiness” of the Universe

36. Then, of course, there are the quasars… Spectra of 11,000 quasars from the 2dF survey arranged in order of distance

37. The biggest survey to date—but it still shows us only 0.1% of the Universe… Quasars are also clumpy.

38. The hot Big Bang

39. The Hot Big Bang model Modern equivalent of Lemaître’s picture. It postulates a hot Big Bang—a unique event in which not only the matter in the Universe was created, but space and time as well… Three vital pieces of evidence support it: the expansion of the Universe; the relative abundances of light elements; the cosmic microwave background radiation.

40. What’s the cosmic microwave background radiation? Faint background glow in the millimetre wavelength region of the radio spectrum. Almost perfectly uniform in all directions. It is the echo of the Big Bang fireball itself. We’re seeing back in time to a moment 300,000 years after the Big Bang when the Universe ceased to glow with brilliant white light— and became transparent…

41. Applause You Applause Silence You R R = 330 metres after 1 second; R = 660 metres after 2 seconds, etc. i.e., R increases at the speed of sound.

42. Cosmic microwave background radiation Why don’t we see a brilliant white back- ground in every direction? The radiation has been redshifted by the expansion of the Universe. The light waves have been s-t-r-e-t-c-h-e-d by about 1000 times to become longer wave- length microwaves. Thus, z CMBR  1000. The CMBR is easily the most ancient fossil remnant we can see…

43. COBE all-sky map showing 1-in-10 5 temperature fluctuations The hot-spots are the seeds of the structure we see in the Universe today

44. What does the CMBR tell us about the Big Bang? The rippling in the CMBR (due to acoustic oscillations in the fireball) closely matches the clumpiness seen in the redshift surveys. It is the “baby face” of today’s Universe The radiation is very smooth—fluctuations in the early fireball must have been ironed out by an exceedingly short period of inflation. The rippling can tell us much, much more about both the Big Bang and the evolution of the Universe—hence NASA’s WMAP…

45. Wilkinson Microwave Anisotropy Probe Launched 30.6.2001

46. Not such a bad effort for a bunch of microbes… In summary…

47. Observing first-generation galaxies with the James Webb Space Telescope

48. There’s nothing wrong with a Dish – as long as it’s not lamb casserole…