1 / 51

Cosmological Aspects of Nucleosynthesis

Cosmological Aspects of Nucleosynthesis. 1. Comments on the Big Bang Nucleosynthesis (BBN). 2. Observing heavy elements. 3. Heavy-Element Nucleosynthesis beyond the dark age, or Nucleosynthesis in stars. I am not presenting a paper no time for a lecture.

jada
Download Presentation

Cosmological Aspects of Nucleosynthesis

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CosmologicalAspects of Nucleosynthesis 1. Comments on the Big Bang Nucleosynthesis (BBN) 2. Observing heavy elements 3. Heavy-Element Nucleosynthesis beyond the dark age, or Nucleosynthesis in stars I am not presenting a paper no time for a lecture. It remains to try to describe a scenario Mounib El Eid American University of Beirut Department of Physics Sinaia, Romania June 2012

  2. Thermal History of the Universe

  3. Thermal History of the Universe

  4. Why did the density of dark energy became larger the density of matter 5 billion years ago? If the dark energy is due to a cosmological constant, its average mass density remains constant. The consensus model predicts dark-energy dominated universe about 5 billion years ago.

  5. Big Bang Nucleosynthesis (BBN) Argument in favor of BBN 1. The question is: why is approximately one-quarter of the mass of the universe is in the form of helium 2. Cosmic abundance of He too high to be made in stars, since not enough mixing to the surface. 3. Helium survives in the early universe, because the density of the expanding universe becomes too low to burn helium 4. Nuclei of mass number A=5 and 8 are unstable, and this limits the BBN to the light elements: (D,3He, 4He, 6Li, 7Li, 7Be) 5. Under the assumption of homogeneous baryon density the BBN depends on one parameter In other words, is the only parameter, since n is determined by the Micro Wave Background

  6. 1. The Standard Big Bang Nucleosynthesis (SBBN) Occurs in a radiation-dominated universe Assumptions: (1) Standard Particle Physics (2) Cosmological Principle: (Universe isotropic and homogeneous) (3) Geometry described by the Robertson-Walker metric a(t) scale factor absorbs the dynamics (4)Expansion of the Universe described by the Friedmann'sequation =cosmological constant

  7. CRITICAL DENSITY Means: if a galaxy is at 100 Mpc away from us, It will be moving at 7100 km/s Present Hubble constant (WMAP) Cosmological parameter=baryon density/critical density (C)

  8. RESULTS of BBN  Most of the nucleosynthesis took place at about 1.2x109 K. At larger temperature, D would be destroyed by radiation background  4He mass fraction: 0.23 to 0.25 traces of D, 3He, 7Li, 7Be   No nuclei were formed before 10 s because of the deuterium bottleneck See next slide At about 1000 s, T<4x108K, no nucleosynthesis was possible any more. The free neutrons declined and decayed into protons, electrons and antineutrinos.

  9. Simplified network for BBN Deuterium is a bottle neck

  10.  Abundances of D and 3He provide strong constraint on present baryon density, while that of He is remarakably constant Figure Fig. 19.10 Longair  D-abundance very sensitive to the baryon density (B), while that of He almost constant. Reason: He-abundance determined from equilibrium abundance of neutrons and protons. Abundance of D depends on number density of nucleons. D sets upper limit on B observations

  11. Result Even with Baryonic matter cannot close he universe and cannot account for the amount of dark matter Remarkable result of the BBN: 3 neutrino families More than 3 neutrino-families would have contributed to the mass density of ultra-relativistic particles. This would have speeded up the expansion in the radiation-dominated universe. Neutrino would decouple at higher temperature and Helium would have been overproduced. Agreement with elementary particle physics is achieved; 3 neutrino families obtained from the width of the decay spectrum of Z0 boson.

  12. Dark Age A challenge in modern cosmology is to understand how the cosmic dark ages ended.

  13. Timeline of light in the universe WMAP data indicate: Some 400 million years later at z=11 the first stars appeared . They re-ionized the universe, and their light was shifted to infrared wavelength . The oldest light we can see today is the cosmic background radiation . It came from the time 380,000 yrs after Big Bang when the universe became transparent. This light had a redshift of z=1100 and appears in the microwave Galaxies formed more recently and can be seen at visible wavelength. Dark ages: era from recombination (at 380,00 yr) to the first stars at 400 million yr. This dark ages ended when the universe was filled for the first time with light from stars

  14. Using Wien’s law:

  15. 2. Observing heavy elements Talking about galaxies we mean near-field cosmology , while the high red shift universe is associated with the far-field cosmology  Large dispersion in metal abundances [X i/Fe] in particular for the n-capture elements • s-process elements: • Sr, Zr, Ba, Ce, La, Pb • Formed during quiescent phases of stellar evolution: He-burning in AGB stars and massive stars Light s-process • r-process elements: • Sm, Eu, Cd, Tb, Dy, Ho • Cannot be formed during quiescent phases of stellar evolution, but mainly in SNe explosion. Heavy s-process ? r-process elements measured from stellar atmospheres reflect conditions in the progenitor cloud r-process Metallicity

  16. Summary of this part • Observations of nucleosynthetic signatures of metal-poor stars represents a cornerstone of near-field cosmology. • A success in this direction requires improved stellar models, especially of SNe, and nuclear/atomic data and realistic galaxy formation models  The relative r-process and alpha-element abundances for metal-poor stars will constraint the yield for different stellar masses and associated mass cuts in SNe. Here are some thoughts by Freeman and Bland-Hawthorn (2002) • The near-field universe is as important as the far-field universe for understanding galaxy formation and evolution.  Understanding galaxy formation is understanding baryon dissipation within the CDM hierarchy, or understanding the formation of disks.  A great advantage of near-field study is to derive ages and detailed abundances of individual stars within galaxies and the local group.(Gaia sphere)

  17. r-process rich star CS22892-52 show some interesting results A similar case is CS31082-001 (Hill et al. 2002) Sneden eta al: APJ, 591, 936 (2003) Z= 56 Weak r-process Main r=process EMP: [Fe/H]=-3.1 remarkable n-capture elements with Z56 in this metal-poor star match closely solar system r-process pattern Also remarkable Scaled solar r-process distribution does not extend to the lighter n-capture elements below Z=56 For example: Silver (Ag, Z=47) is deficient

  18. Conclusion from previous Figure: It seems that the r-process could be divided like the s-process into 2 components : weak r-process ( so far it is called LEPP=Light Element Primary Process) main r-process (classical r-process) Heavy elements have been also observed in extremely metal-poor stars with [Fe/H]=--5: HE 0107-5420 and HE1327-2326 Both are rich in CNO but very poor in n-capture elements. This is different from the previous cases (CS 22892-052 or CS31082-001) Learn effect Rapid change in nucleosynthesis in the early phase of the Galaxy. It seems: first stars were massive able to produce CNO elements but not the heavy n-capture elements

  19. r-process rich versus r-process poor r-process rich: [Eu/Fe]=+1.6 r-process poor: [Eu/Fe]=-0.5

  20. r-process throughout the Galaxy 16 stars The difference between BD+173248 and HD122563 discussed above is found to be a general behavior as shown in the following Figure: r-process rich flat Nothing here r-process poor No heavy n-capture elements HD122563 References to this Figure: Cowan eta l (2011) preprint

  21. The abundances in HD122563 suggest an incomplete r-process, or let us say an n-capture process with a neutron density between 1020- 1024 cm-3, since the synthesis of the heavy n-capture elements needs 1024 – 1028 cm-3 In the following some results by Kratz et al (2007): r-process rich: [Eu/Fe]=+1.6 Flat Sneden et al. (2003) Honda et al. 2006) Abundances gradually decrease with A r-process poor: [Eu/Fe]=-0.5

  22. Barium Isotopes in extremely meta-poor massive stars Barium Isotopes in the meta-poor subgiant HD 140283 : ( [Fe/H]=-2.6, [Ba/Eu]=-0.66 and [Eu/H]< -2.8 (r-poor) Pure r-process Pure s-process Author f odd Magain (1995) Purley s-process signature Ghallagher et al. (2010) Lambert et al (2002)

  23. Different mixture of odd and even isotopes are produced by the r-process and s-process . In particular, 134Ba and 136Ba are produced only by the s-process due to the shielding by the Xenon isotopes 134Xe 136Xe made by the r-process. Z=56 Shielding Ba Z=54

  24. Conclusions from observations  clear presence of n-capture element in atmospheres of metal-poor stars and globular cluster stars The comparison between r-process rich ([Eu/Fe]> 1.0) and r-process poor ([Eu/Fe] < 1 indicates : abundances of the heavy elements (Ba and above, Z=56) consistent with solar system r-process distribution. This seems to be the main r-process. The distribution of the lighter (Z<56) n-capture elements is not conform to solar pattern. New detection of Pd, Ag, Cd (Z=46, 47,48) suggest a weak r-process not yet identied: LEEP -p process in core collapse SNe High Entropy Wind in core collapse SNe Exotic mixing in late phases of massive EMP stars Do different mass region (Ge, Sr-Zr, Pd-Ag-Cd) require different processes?

  25. 3. Making the Heavy element in Stars Heavy elements beyond copper are formed by 2 neutron-capture processes: r-process s-process 1/2 s for slow, but what is slow? Slow is the n-capture compared to beta-decay r for rapid, but what is rapid? neutron capture compared to beta-decay Standard scenario: Core collapse SNe M >8 Msun. Consistent model not yet available Main component A > 90, AGB stars: (1-8) Msun Main component A < 90, Massive stars, M15 M Sun Primary process: built up from scratch as Taka Kajino emphasized Secondary process: Depends on iron seed-abundance

  26. Basics of the s-process Seed nucleus: Iron Neutron source 13C(,n)16O AGB stars 22Ne(,n) 25Mg Massive Stars Neutron spectrum Maxwell-Boltzmann Distribution (details later) Temperature range (25 – 30) KeV or (1.5 – 3.5) x 108 K Helium Fusion ( 90 – 100) KeV or (1.04-1.16)x 109 K Carbon Fusion Beta-decay much faster, Helium fusion Time scale Comparable time scale: carbon fusion Massive Stars Thermally pulsating stars (AGB stars Where?

  27. Some Details of the s-process ( Ns – curve) The s-process works with thermal neutrons. They undergo elastic scattering in the star’s plasma. The neutrons obey the Maxwell-Boltzmann distribution (MBD): From lab experiments, we know that the neutron-capture cross section varies like: S-wave scattering MBD E0 =most probable energy En E0=kT

  28. Where the s-process?

  29. In AGB Stars Where in HR diagram “Cat Eye” planetary nebula after the AGB phase Asymptotic Giant Branch White dwarf

  30. s and r –processes in Z-N diagram Cd Ag Pd Rh 50 82 126 magic numbers

  31. Cassiopeia A r=process in Supernovae? SPITZER image of Cassiopeia A 10,000 lyr away 15 lyr across The above image is a composite of X-ray, optical, and infrared light exposures that have been digitally combined. The infrared light image was taken by the orbiting Spitzer Space Telescope and was used in the discovery of the light echo. The portion of Cassiopeia A shown spans about 15 light years and lies 10,000 light years away toward the constellation of Cassiopeia.

  32. Log nn=20-22 Log nn=20-24 Log nn=20-26 Log nn=20-28

  33. The world of stars Massive C/O Cores: 64- 133 MSun Explosive oxygen burning Iron core collapse Shock/neutrino driven AGB Planetary Nebula Pair Creation Supernovae Neutron stars Black holes Black holes White Dwarf

  34. The Central Evolution of Stars Iron Disintegration Core collapse supernova Electron-Positron –Creation. Pair Creation supernovae 25 Rapid Electron Capture Core collapse Supernva TEMPERATURE (K) AGB stars White Dwarfs Non-degenerate DENSITY ( g/cm3)

  35. First stars (pop III) If very massive they undergo pair creation supernovae

  36. What is a Pair Instability Supernova (PCSNe)? PCSNe: final state evolution of a very massive stars which develops a very massive carbon-oxygen cores largely supported by radiation pressure Evolution of such cores proceeds toward higher temperature and relatively low density such that electron-positron pairs are created in equilibrium by the radiation field according to Although the mean energy photons is about kT, there are enough photons in the tail of the Planck’s distribution that can create these pairs even at 109 K Temperature-density profile T- profile for a 112 Msun star at time reversal of the collapse. Note that significant part of the core is inside the instability region. Details in: Ober, El Eid & Fricke: A&A , 119, 61 (1983)

  37. Why does <4/3 has a finite range? The decrease of  below 4/3 is a consequence of the new particles which do not immediately add their contribution to the total pressure.. At high densities: >4/3, because the electron becomes more degenerate At high temperatures: >4/3 because the particles become relativistic such that the energy gap for pair creation is no more important

  38. The PCSNe are usually associated with early stars, or Pop III stars Is there any evidence of this unusual supernova type? The observations of the SN 2007bi ( Gal-Yam et al, Nature ,462, 624, 2009) in a dwarf galaxy argue for this with an estimated core mass is about 100 MSun Another object is SN2006gy (Smith et al , ApJ 666, 1116 (2007)) Light curves of super luminous SNe Gal-Yam et al (2009) R-band light curve of SN2007bi. With a peak magnitude of -21.3 mag If this light curve is radioactively driven, > 3 Msun of 56Ni are needed. The slow rise time (70 days) and photospheric velocity of 12,000 km/s indicate an exploding very massive object of about 100 Msunand very high explosion energy > 1052 erg

  39. Implication of the discovery of SN2007 bi  The estimated high core mass is in conflict with the commonly used mass loss rates as a function of metallicity • Regardless the correct description of mass loss, the data indicate that an extremely massive stars (>150 Msun ) are formed in the local universe in a dwarf galaxy with a metallicity • 12+log[O/H]=8.25 (less than 1/10 of the Sun’s metalicity • Can the dwarf galaxies serve as fossil laboratories for studying the earl universe? • Future missions like the • NASA’s James Webb Space telescope • will help to estimate the contribution of these events to the chemical evolution in the early universe.

  40. Nucleosynthesis in PCSNe Updated calculation by Heger & Woosley (2002) yield:  No heavier elements than Zinc, no r-process, no s-process  Mainly products of explosive oxygen burning. Even nuclear charges (Si, S, Ar, Ca,, ...) in almost solar distribution  Element of odd nuclear charges (Na, Al, P, V, Mn,...) are deficient. The explanation of this is because the massive C/O massive evolves almost directly to oxygen burning without creating a neutron excess Production factors of C/O cores of masses 64 to 130 Msun which undergo PCSNe, with different assumption of the exponent of a Salpeter-like IMF

  41. Exotic n-capture scenarios Massive extremely metal-poor stars Zero-age mains sequence shifted to higher effective temperature as Z decreases. This is a consequence of reduced metallicity. Recall that the energy generation via the CN cycle: At T=25x106 K At T=15x106 K Lacking of heavy elements, the star has to contract and heats up to burn hydrogen at high temperature. (2) As consequence of the compactness of the star , it cannot evolve to become red giants. They remain confined to the blue part of the HR diagram, when Z<10-3 . As seen on next page, the hydrogen-burning shell remains convective all the time. El Eid, The , Meyer Space Sci. Rev. , 147, 1-29, 2009 More details are found in :

  42. El Eid, The , Meyer Space Sci. Rev. , 147, 1-29, 2009 Many references there This stays in the blue. Only with significant amount of rotation can such a star evolve to red super giant stage. Even wit rotation, only a small fraction of time is spent in the red part Solar mass star Z=10-3 Z=10-6 Z=0.02 For initial the stars do not evolve to red giant branch.

  43. Solar-like composition Not here Convective hydrogen-burning shell survives

  44. Next exotic scenario: double Shell flash in massive stars Beyond core Helium burning Possible merging of the convective H-burning shell with the He-burning shell Carbon mixed with protons so that the reaction The, El Eid , Meyer: in prep. Is activated as a neutron source

  45. Result after one time step of proton mixing into the helium convective shell. Strong enhancement near Z=38 -48

  46. Another scenario: with ROTATION Pignatari et al. , ApJ, 687, L95, 2008 25 Msun with [Fe/H]=-3, -4 not smaller Basic Scenerio: Neutron source Primary source, since in this scenario Carbon is mixed by rotation to the convective H-burning shell creating 14N which is mixed down to the Helium burning core. In this way an s-process operates near the end of core Helium burning The say they produce nuclei up A=130 Why is the 13C source is not activated??

  47. Final Words  Evolution of early stars linked to nucleosynthesis of heavy elements turns out to be a link to Near-field cosmology (understanding galaxy formation); It is a challenging topic and a revival of the importance of stellar evolution as a fundamental cornerstone of modern Astrophysics  The evolution of the neutron-capture elements traces back the chemical evolution of the galaxy and is bring us back to the dark ages where in order to become more enlightened and remove the darkness of our ignorance

  48. We need his optimism like this star from FC Barcelona (and FC Libya) to get an answer Does this game work? JJ with American muscles

  49. OR am I dreaming He shaved himselfafter he has seen this photo

  50. Final entertainment Nustar http://science.nasa.gov/science-news/science-at-nasa/2012/15jun_nustar/ Why supernova is not happening on computer?

More Related