1. Irn Bru from the Stars (or, the stellar creation of the heavy elements) Dr. Lyndsay Fletcher University of Glasgow

3. Formation of the light elements - primordial nucleosynthesis

4. The hot Big Bang Time

5. After nucleosynthesis, the universe contains 1 neutron for every 10 protons (ie hydrogen nuclei). Neutrons and some of the protons collide at high energy forming deuterium, helium, and a little lithium. But the universe is cooling rapidly, so collision energy decreases and no heavier elements can be formed.

6. Formation of the heavy elements -stellar nucleosynthesis

7. How were the first stars formed? We don’t know, as we can’t look back in time that far. However, we think that they formed about 400 million years after the big bang, and later clustered into the first galaxies image: Robert Hurt, Caltech

8. Part of the Hubble ‘Deep Field’: Galaxies in the distant universe ~ 4 billion yrs after the big bang image: R. Williams, STScI

9. a globular cluster The “Sombrero” Galaxy (M104) (somewhat bigger than the Milky Way)

12. Molecular cloud in Orion - a star-forming region protostellar cloud

15. A cloud of gas and dust in space…

16. …may be perturbed by external pressures..

17. e.g. by a shock wave from a supernova

18. M81 M82 Or by a collision with another galaxy

19. Visible light image Visible plus infrared light – showing star formation regions

20. Star’s own self- gravity takes over, making it contract

21. It breaks up into smaller clouds

22. “Thackeray’s Globules”

23. Each smaller blob continues to shrink and is probably rotating slowly

27. Star forming region in Orion

28. The Sun: Surface temperature 6000 o C Core temperature 15,000,000 K nuclear reactor

29. Core nuclear Fusion E = mc 2

30. Hot, massive stars Cool, less massive stars The Hertzsprung-Russell Diagram brightness temperature

31. What happens when the hydrogen fuel runs out?

32. Star core contracts, and outer layers swell to become a red giant If the star is massive enough, helium burning might start in the core, producing carbon

33. - Core He burning - Shell H burning outer layers swell up and drift off into space The fate of a solar-mass star

34. This stage is called a planetary nebula

35. The nebula is mostly hydrogen, helium, plus some carbon and oxygen

36. White dwarfs: earth-sized stellar relics

37. 2,000,000,000 km 1000 km Shell burning in a > 4 solar mass star supergiant phase

39. After iron, no more energy is available from fusion Fusion stops, and the star’s core collapses – until the density is so high that protons and electrons are forced together into neutrons

40. 300 km Stellar core ‘solidifies’ into neutron lattice. Enormous quantities of neutrinos stream outwards. Both of these cause the collapsing layers above the core to ‘bounce’ outwards, forming a shock front. The whole process takes about 1s

41. Formation of elements heavier than iron In the colossal densities and temperatures in the shock, free neutrons can get close enough to heavy nuclei to be captured. But too many extra neutrons produces an unstable nucleus. Beta decay changes a neutron into a proton.

42. Supernova 1987a

43. The Crab Nebula in Taurus The blast wave from a star which exploded as a supernova 950 years ago

44. Stellar remains – a neutron star the diameter of the West End, spinning 33 times per second

45. The Cosmic Cycle: Supernova remnants return gas, dust, and both light and heavy elements to the interstellar medium So, the next round of stellar formation can take place - there have been at least 2 stellar generations here before us!