The Origin of the Elements and the Evolution of the Composition of the Cosmos

1. The Origin of the Elements and the Evolution of the Composition of the Cosmos Jim Truran Astronomy and Astrophysics Enrico Fermi Institute University of Chicago and Argonne National Laboratory Lectures in Nuclear Chemistry Associated Colleges of the Chicago Area November 4th , 2008

2. Cosmic Nucleosynthesis Perspective • The Universe emerged from the Big Bang with a composition consisting of hydrogen, deuterium, helium, 3He, and 7Li. • The first stars and galaxies were born with this “primordial” composition. The “Big Bang” Star Formation in Orion

3. Cosmic Nucleosynthesis Perspective • The heavy elements with which we are familiar - from carbon and oxygen, to iron, .. to uranium - are the products of nuclear processes occurring in stars and supernovae.

4. Cosmic Nucleosynthesis Perspective Courtesy: Jason Tumlinson History of the Universe?

5. Cosmic Nucleosynthesis Perspective Picture Credit: Hubble (HST) • This history of the composition of our Galaxy (and the Cosmos) is written in the compositions of its stars and gas. Picture Credit: Hubble (HST) Halo Star Formation in the Large Magellanic Cloud Disk • Stars are formed in gas clouds in galaxies. The Sombrero Galaxy: M104

6. Cosmic Nucleosynthesis Perspective • Stars are formed from gas, powered by nuclear energy, and produce heavy elements. • Mass ejected from stars and supernovae is returned to the gas, from which the next generation(s) of stars will be born. (A cycle of enrichment.) • Successive stellar generations produce stars of higher initial metal contents. Courtesy:Carla Frohlich Pleiades (HST) Orion’s Belt (HST)

7. Cosmic Nucleosynthesis Perspective • The heavy element content of the Universe at any point in its history reflects the integrated nucleosynthesis contributions from earlier stellar generations. • The composition of our Solar System (born 4.6 billion years ago) was determined by the nuclear processes that took place in stars during the prior 9 billion years of Galactic history. Palomar: Crab Nebula HST: Nova Pyxidis

8. “We are Star Stuff.” (Cosmos: Carl Sagan) Elemental Composition of the Human Body Element Symbol Percentage(by mass) Site of Origin Oxygen O 65.0 Supernovae Carbon C 18.5 Red Giants Hydrogen H 9.5 Big Bang Nitrogen N 3.3 Red Giants Calcium Ca 1.5 Supernovae Phosphorus P 1.0 Supernovae

9. Stellar Stability: the Need for Nuclear Energy • Stars are ‘born’ in dense clouds of gas in galaxies. • Contraction of a ‘proto-star’ heats the interior to the point at which the pressure is sufficient to counter gravity. Horsehead Nebula in Orion: HST Since the star continues to radiate energy as it contracts, we must identify a sufficient energy source. Figure Credit: Carla Frohlich

10. Stellar Stability: the Need for Nuclear Energy • Prior to the discovery of the nature of stellar energy input from nuclear processes, it was not possible to understand an age of the earth of more than a billion years (inferred from diverse geological studies of rock strata and of rates of sedimentation). • In the absence of an energy source other than gravity, a star of the Sun’s luminosity would be able to survive only approximately 20 million years. • The currently accepted age of the Earth (and therefore of the Sun and Solar System) is 4.6 billion years. • How can we understand this apparent discrepancy?

11. Nuclear Energetics and Element Synthesis in Stars • The contraction of a star to high temperatures allows nuclear processes to occur in the interior. • In our Sun, at a temperature of 15 million degrees Kelvin, energy is released in the nuclear “burning” of hydrogen to helium. (Four protons are transformed into one helium {4He} nucleus.) Figure Credits: Carla Frohlich

12. Nuclear Energetics and Element Synthesis in Stars • It is critical to note the extremely low rate at which the “proton-proton” reaction p + p 2H + + +  proceeds in the Sun’s core. Only about one proton-proton collision in one million-billion-billion-billion yields the formation of deuterium. • The slow rate of the p + p reaction has made possible the evolution of life on Earth. The lifetime of the Sun is ~ 12 billion years. Stars more massive than the Sun have shorter lifetimes: e.g.~ 20 million years for 10 solar mass.

13. Nuclear Energetics and Element Synthesis in Stars • The binding energy per nucleon (protons+neutrons) provides a measure of nuclear stability. • 56Fe is the most stable nucleus having the maximum binding energy per nucleon. • Fusion reactions starting with H and He, occurring in stellar interiors, continue to provide energy to power the star up to 56Fe. • Heavy nuclei like thorium (232Th) and uranium (238U) release energy when they break up (decay) by fission. fusion Maximum Stability fission 56Fe

14. Nuclear Energetics and Element Synthesis in Stars • The progress of nuclear burning in stars is temperature dependent. • Stars of mass less than 10 solar masses do not become hot enough to burn carbon: they end their lives as planetary nebulae and leave carbon-oxygen white dwarf remnants. • Stars of mass greater than 10 solar masses burn to iron leaving a shell-like structure of elements between carbon and iron, viz: Figure Credits: Carla Frohlich

15. Significance of Supernovae Supernovae - both Type Ia and Type II - are spectacular events: • They release ≈ 1051 ergs of light and kinetic energy. • They enrich the Galaxy in “heavy” elements (more massive than helium) to levels of order 2 percent (Solar Abundance). • Supernovae of Type II leave condensed remnants - neutron stars and black holes. • Supernovae SNe Ia are probes of the distance scale and provide constraints on the expansion and the geometry of the Universe and the nature of dark energy. SNe 1994D High-Z Supernova Search Team, HST SNe 1987A

16. Historical Supernovae in our Galaxy SN 1054  Crab Nebula Chaco Canyon Petroglyph • The expected rate in the Milky Way is about 1 every 50 years,with SNe II being roughly 3 times more frequent than SNe Ia.

17. Type II Supernovae: Theory • “Standard model” (Hoyle & Fowler 1960): • SNe II are the product of the evolution of massive stars 10 < M < 100 M • Evolution to criticality: • A succession of nuclear burning stages yield a layered compositional structure and a core dominated by 56Fe. • Collapse of the 56Fe core yields a neutron star. • The gravitational energy is released in the form of neutrinos, which interact with the overlying matter and drive explosion. • Nucleosynthesis contributions: elements from oxygen to iron and neutron capture products from krypton through uranium and thorium. Courtesy Mike Guidry: guidry@utk.edu SNe1054: Crab Nebula SNe1987A Hubble Image

18. Cas A Supernova Remnant red: iron rich blue: silicon/sulfur rich Chandra X-ray Observatory

19. SN 1987A in the Large Magellanic Cloud An Exciting Recent Supernova Event 30 Doradus subsequent to explosion of SN 1987A 30 Doradus Nebula prior to explosion of SN 1987A

20. SN 1987A in the Large Magellanic Cloud A likely supernova candidate for the next millenium: Betelgeuse Courtesy: Ernst Rehm, ANL

21. Type Ia Supernovae: Theory • “Standard model:” (Hoyle & Fowler 1960): • SNe Ia are thermonuclear explosions of carbon-oxygen white dwarf stars. • Evolution to criticality: • Accretion from a binary companion leads to growth of the white dwarf to a critical mass (1.4 solar masses). • Complete incineration and disruption occurs in ~ two seconds. (No compact remnant.)

22. Discovery of a SNe Ia? One evening when I was contemplating as usual the celestial vault, whose aspect was so familiar to me, I saw, with inexpressible astonishment, near the zenith, in Cassiopeia, a radiant star of extraordinary magnitude. Struck with surprise, I could Hardly believe my eyes. Tycho Brahe, November 1572 “Stella Nova” (1573), discovery chart Tycho, SAO, Chandra

23. Kepler’s Supernova 1604

24. Significance of Type Ia Supernovae SNe Ia and Cosmology Doggett and Branch (1985) In 1998, SNe Ia played a major role in the “science breakthrough of the year:” Using SNe Ia as distance indicators, astronomers found evidence for an accelerating cosmic expansion. • The Phillips relation identifies a correlation between the peak brightness and the rate of decline (brighter SNe Ia decline more slowly) which yields an effective “standard candle.”

25. Hubble’s Law: Then and Now (Hubble 1929)

26. The Standard Model for SNe Ia • Progenitor: White dwarf in a binary system • Growth to the Chandrasekhar limit by mass transfer

27. GCD 3D Simulations Jordan et al. (2007)

28. Heavy Element Synthesis and the Age of the Universe Uranium Thorium

29. r-Process Synthesis and Stellar Ages r-process in supernovae • Observations confirm the rapid neutron capture process dominates at the lowest metallicities (in the oldest stars). (Truran et al. 2002)

30. Nuclear Radioactive Dating of Halo Stars • A knowledge of the abundances of both uranium and thorium in a star allows an age determination. • For the halo star CS31082-0018 (Cayrel et al. 2001), this gives an age of 12.5 +/- 3 billion years. An early halo star.

31. Probing Early Nucleosynthesis Astronomers are uniquely able to travel backward in time. • The farther we see across the Universe, the farther back in time we can explore. The fact that the speed of light is finite allows astronomers to probe the early star formation and nucleosynthesis history of the Universe and its composition as a function of time, using: • Studies of old stars - analysis of the “fossil” record • Studies of gas clouds at - high red shift using both Quasars and Gamma Ray Sources as probes

32. Cosmic Nucleosynthesis Perspective Courtesy: Jason Tumlinson History of the Universe?

33. Abundances when Fe/H < 1/10,000 its Solar Value Frebel et al. (2005) • The abundances in the two most “iron-deficient” stars known differ distinctly from abundances in the Sun.

34. Abundances in a Galaxy at Redshift z=2.6 (Prochaska 2005)

35. QSO (background) near galaxy (foreground) Galaxy,J1042, z=0.03; QSO z=2.66 (Don York 2008)

36. Gamma Ray Burst: GRB050820A A Gamma Ray Burst at Redshift z= 2.615 (Hsian Wen Chen 2008)

37. Hubble Deep Field Viewing the Distant Universe

38. Look-back Times versus Redshift (Ho= 65 km s-1 Mpc-1; baryons= 0.022 h-2; M = 0.3; =0.7; cosmos= 14.5 Gyr)

39. The Origin of the Elements Thank you for your attention.