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Big Bang Nucleosynthesis Alexander Knebe (Universidad Autonoma De Madrid) Big Bang Nucleosynthesis

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Big Bang Nucleosynthesis Alexander Knebe (Universidad Autonoma De Madrid) Big Bang Nucleosynthesis Big Bang Nucleosynthesis Alexander Knebe (Universidad Autonoma de Madrid) Big Bang Nucleosynthesis ! introduction ! particle physics ! cosmology ! big bang nucleosynthesis Big Bang Nucleosynthesis ! introduction ! particle physics ! cosmology ! big bang nucleosynthesis Big Bang Nucleosynthesis introduction where do all the elements come from? Big Bang Nucleosynthesis introduction where do all the elements come from? stellar fusion reactions!? (stellar evolution work in 1920/30’s…) Big Bang Nucleosynthesis introduction ! stellar fusion… • cannot account for observed 4He abundance Big Bang Nucleosynthesis introduction ! stellar fusion… • cannot account for observed 4He abundance → if MW were to “shine” for 1010 years, it would generate* 4% 4He *(Burbidge, 1958, PASP, 70, 83) Big Bang Nucleosynthesis introduction ! stellar fusion… • cannot account for observed 4He abundance → if MW were to “shine” for 1010 years, it would generate 4% 4He vs. 24% 4He as observed! 0.35 HII regions 0.30 0.25 0.20 0.15 Izotov & Thuan fit & Turner,& arxiv:9903300, Fig.4) Helium Mass Fraction 0.10 Izotov & Thuan data Other data 0.05 Nollett 0.00 (Burles, 0 100 200 106 times O/H Ratio (“metalicity” = indicator of stellar processing) Big Bang Nucleosynthesis introduction ! stellar fusion… • cannot account for observed 4He abundance • cannot create D* but only burn it: fusion reactions in the sun are consuming D faster than generating it *D=2H=p+n Big Bang Nucleosynthesis introduction ! stellar fusion… • cannot account for observed 4He abundance • cannot create D but only burn it: fusion reactions in the sun are consuming D faster than generating it …but we do observe D Turner,& arxiv:9903300, Fig.2) in the interstellar medium: Nollett (Burles, Big Bang Nucleosynthesis introduction ! stellar fusion… • cannot account for observed 4He abundance • cannot create D but only burn it ’s existence… fusion events otherGyrs thanof stellarthe Universe must have happened during the ca. 13.7 Big Bang Nucleosynthesis introduction ! cosmological considerations • z = 0 (today): TCMB = 2.73K -31 3 rb = 5 x 10 g/cm Big Bang Nucleosynthesis introduction ! cosmological considerations • z = 0 (today): TCMB = 2.73K -31 3 rb = 5 x 10 g/cm • z ≈ 1010 (t≈1sec.): 10 TCMB ≈ 10 K 3 rb ≈ 80 g/cm Big Bang Nucleosynthesis introduction ! cosmological considerations • z = 0 (today): TCMB = 2.73K -31 3 rb = 5 x 10 g/cm • z ≈ 1010 (t≈1sec.): 10 TCMB ≈ 10 K 3 rb ≈ 80 g/cm sufficient for nuclear fusion! Big Bang Nucleosynthesis introduction ! cosmological considerations • z = 0 (today): TCMB = 2.73K -31 3 rb = 5 x 10 g/cm • z ≈ 1010 (t≈1sec.): 10 TCMB ≈ 10 K 3 rb ≈ 80 g/cm sufficient for nuclear fusion " “Big Bang Nucleosynthesis” !? Big Bang Nucleosynthesis introduction ! BBN: Alpher, Bethe & Gamow (1948) “The Origin of Chemical Elements” PH VSICAL REVIEW VOLUME 73, NUM HER 7 AP RI L 1, 1948 We may remark at first that the building-up process was . : etters to t.ze 'a.itor apparently completed when the temperature of the neutron gas was still rather high, since otherwise the observed ~ ~ ~ UBLICA TION of brief reports of important discoveries abundances would have been strongly affected by the ~ ~ in physics may be secured by addressing them to this resonances in the region of the slow neutrons. According to ~ ~ 2 department. The closing date for this department is five ueeks Hughes, the neutron capture cross sections of various elements (for neutron energies of about 1 Mev) increase prior to the date ofissue. ¹ proof a@ill be sent to the authors. The Board of Editors does not hold itself responsible for the exponentially with atomic number halfway up the periodic opinions expressed by the correspondents. Communications system, remaining approximately constant for heavier should not exceed 600 words in length. elements. Using these cross sections, one finds by integrating Eqs. (1)as shown in Fig. 1 that the relative abundances of various nuclear species decrease rapidly for the lighter elements and remain approximately constant for the ele- The Origin of Chemical Elements ments heavier than silver. In order to fit the calculated R. A. ALPHER+ curve with the observed abundances' it is necessary to Applied Physics Laboratory, The Johns Hopkins Un&rersity, assume thy integral of p„dt during the building-up period is Silver Spring, Maryland equal to 5 X104 sec./cm'. AND g On the other hand, according to the relativistic theory of H. BETHE Cornell University, Ithaca, %em York the expanding universe4 the density dependence on time is given by p —10'/t~. Since the integral of this expression G. GAMow diverges at t =0, it is necessary to assume that the building- The George Washington University, 8'ashington, D. C. up process began at a certain time to, satisfying the February 18, 1948 relation: S pointed out by one of us, ' various nuclear species (10'jt')dt =5X 104, (2) A must have originated not as the result of an equilib- J&0 rium corresponding to a certain temperature and density, but rather as a consequence of a continuous building-up which gives us to=20 sec. and p0=2.5)&105 g sec./cm'. This process arrested by a rapid expansion and cooling of the result may have two meanings: (a) for the higher densities primordial matter. According to this picture, we must existing prior to that time the temperature of the neutron imagine the early stage of matter as a highly compressed gas was so high that no aggregation was taking place, (b) neutron gas (overheated neutral nuclear Quid) which the density of the universe never exceeded the value 10' /cm' started decaying into protons and electrons when the gas 2.5 )& g sec. which can possibly be understood if we pressure fell down as the result of universal expansion. The radiative capture of the still remaining neutrons by the newly formed protons must have led first to the formation of deuterium nuclei, and the subsequent neutron captures resulted in the building up of heavier and heavier nuclei. It must be remembered that, due to the comparatively short time allowed for this procgss, ' the building up of heavier nuclei must have proceeded just above the upper fringe of the stable elements (short-lived Fermi elements), and the present frequency distribution of various atomic species was attained only somewhat later as the result of adjust- ment of their electric charges by P-decay. Thus the observed slope of the abundance curve must not be related to the temperature of the original neutron gas, but rather to the time period permitted by the expan- CAt ClMlKO sion process. Also, the individual abundances of various nuclear species must depend not so much on their intrinsic stabilities (mass defects) as on the values of their neutron capture cross sections. The equations governing such a -2 building-up process apparently can be written in the form: lsd — n; —;n;) i=1,2, " 238 =f(t)(;, '0 /50 BO where n; and a;. are the relative numbers and capture cross Fio. 1. sections for the nuclei of atomic weight i, and where f(t) is a Log of relative abundance factor characterizing the decrease of the density with time. Atomic weight 803 Big Bang Nucleosynthesis introduction ! BBN: Alpher, Bethe & Gamow (1948) “The Origin of Chemical Elements” PH VSICAL REVIEW VOLUME 73, NUM HER 7 AP RI L 1, 1948 We may remark at first that the building-up process was . : etters to t.ze 'a.itor apparently completed when the temperature of the neutron gas was still rather high, since otherwise the observed ~ ~ ~ UBLICA TION of brief reports of important discoveries abundances would have been strongly affected by the ~ ~ in physics may be secured by addressing them to this resonances in the region of the slow neutrons. According to ~ ~ 2 department. The closing date for this department is five ueeks Hughes, the neutron capture cross sections of various elements (for neutron energies of about 1 Mev) increase prior to the date ofissue. ¹ proof a@ill be sent to the authors. The Board of Editors does not hold itself responsible for the exponentially with atomic number halfway up the periodic opinions expressed by the correspondents. Communications system, remaining approximately constant for heavier should not exceed 600 words in length. elements. Using these cross sections, one finds by integrating Eqs. (1)as shown in Fig. 1 that the relative abundances of various nuclear species decrease rapidly for the lighter elements and remain approximately constant for the ele- The Origin of Chemical Elements ments heavier than silver. In order to fit the calculated R. A. ALPHER+ curve with the observed abundances' it is necessary to Applied Physics Laboratory, The Johns Hopkins Un&rersity, assume thy integral of p„dt during the building-up period is Silver Spring, Maryland equal to 5 X104 sec./cm'. AND g On the other hand, according to the relativistic theory of H. BETHE Cornell University, Ithaca, %em York the expanding universe4 the density dependence on time is given by p —10'/t~. Since the integral of this expression G. GAMow diverges at t =0, it is necessary to assume that the building- The George Washington University, 8'ashington, D. C. up process began at a certain time to, satisfying the February 18, 1948 relation: S pointed out by one of us, ' various nuclear species (10'jt')dt =5X 104, (2) A must have originated not as the result of an equilib- J&0 rium corresponding to a certain temperature and density, but rather as a consequence of a continuous building-up which gives us to=20 sec. and p0=2.5)&105 g sec./cm'. This process arrested by a rapid expansion and cooling of the result may have two meanings: (a) for the higher densities primordial matter.
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