THE CHEMISTRY OF POPULATION III SUPERNOVA EJECTA. I. FORMATION OF MOLECULES IN THE EARLY UNIVERSE

Journal Article · Sun Sep 20 00:00:00 EDT 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/703/1/642· OSTI ID:21371982

Cherchneff, Isabelle ^[1]; Dwek, Eli ^[2]

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1. Departement Physik, Universitaet Basel, CH-4056 Basel (Switzerland)
2. Observational Cosmology Laboratory, Code 665, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

We study the formation and destruction of molecules in the ejecta of Population III supernovae (SNe) using a chemical kinetic approach to follow the evolution of molecular abundances from day 100 to day 1000 after explosion. The chemical species included in the study range from simple diatomic molecules to more complex dust precursor species. All relevant molecule formation and destruction processes that are unique to the SN environment are considered. Our work focuses on zero-metallicity progenitors with masses of 20, 170, and 270 M{sub sun}, and we study the effect of different levels of heavy element mixing and the inward diffusion of hydrogen and helium on the ejecta chemistry. We show that the ejecta chemistry does not reach a steady state within the relevant timespan ({approx}3 yr) for molecule formation, thus invalidating previous results relying on this assumption. The primary species formed in the harsh SN environment are O{sub 2}, CO, SiS, and SO. The SiO, formed as early as 200 days after explosion, is rapidly depleted by the formation of silica molecular precursors in the ejecta. The rapid conversion of CO to C{sub 2} and its thermal fractionation at temperatures above 5000 K allow for the formation of carbon chains in the oxygen-rich zone of the unmixed models, providing an important pathway for the formation of carbon dust in hot environments where the C/O ratio is less than 1. We show that the fully mixed ejecta of a 170 M{sub sun} progenitor synthesizes 11.3 M{sub sun} of molecules, whereas 20 M{sub sun} and 270 M{sub sun} progenitors produce 0.78 M{sub sun} and 3.2 M{sub sun} of molecules, respectively. The admixing of 10% of hydrogen into the fully mixed ejecta of the 170 M{sub sun} progenitor increases its molecular yield to {approx}47 M{sub sun}. The unmixed ejecta of a 170 M{sub sun} progenitor SN without hydrogen penetration synthesizes {approx}37 M{sub sun} of molecules, whereas its 20 M{sub sun} counterpart produces {approx}1.2 M {sub sun}. This smaller efficiency at forming molecules is due to the large fraction of He{sup +} in the outer mass zone of the ejecta. Finally, we discuss the cosmological implication of molecule formation by Pop III SNe in the early universe.

• OSTI ID: 21371982
• Journal Information: Astrophysical Journal, Vol. 703, Issue 1; Other Information: DOI: 10.1088/0004-637X/703/1/642; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ABUNDANCE
CARBON
CARBON MONOXIDE
DUSTS
EXPLOSIONS
HELIUM
HELIUM IONS
HYDROGEN
MASS
OXYGEN
SILICON OXIDES
STEADY-STATE CONDITIONS
SUPERNOVAE
UNIVERSE
BINARY STARS
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
CHARGED PARTICLES
ELEMENTS
ERUPTIVE VARIABLE STARS
FLUIDS
GASES
IONS
NONMETALS
OXIDES
OXYGEN COMPOUNDS
RARE GASES
SILICON COMPOUNDS
STARS
VARIABLE STARS