Time evolution of simple molecules during proto-star collapse

Abstract

We study the formation and evolution of several molecules in a collapsing interstellar cloud using a reasonably large reaction network containing more then four hundred atomic and molecular species. We employ a time dependent, spherically symmetric, hydrodynamics code to follow the hydrodynamic and chemical evolution of the collapsing cloud. The flow is assumed to be self-gravitating. We use two models to study the hydrodynamic evolution: in the first model, we inject matter into an initially low density 2 Das et al.region and in the second model, we start with a constant density cloud and let it collapse due to self-gravity. We study the evolution of the central core for both the cases. We include the grain chemistry to compute the formation of molecular hydrogen and carried out the effect of gas and grain chemistry at each time step. We follow the collapse for more than 1014 s (about 3 million years) and present the time evolution of the globally averaged abundances of various simple but biologically important molecules, such as glycine, alanine etc. We compare our results with those obtained from observations found that for lighter molecules the agreement is generally very good. For complex molecules we tend to under predict the abundances. This indicates that other pathways could be present to form these molecules or more accurate reaction rates were needed.

Hydro-chemical study of the evolution of interstellar pre-biotic molecules during the collapse of molecular clouds

“…In the present paper, for the sake of simplicity, we assume the density distribution as described in Das et al, (2008a) and Das et al, (2010). A spherically symmetric self-gravitating interstellar cloud was considered in order to mimic the physical behavior during the star formation.…”

Deuterium enrichment of the interstellar medium

“…So deuterium chemistry is extremely important for tracing dynamic properties of a cloud. Aikawa et al (2005), Das et al (2008b), and Das et al (2013b) already discussed how dynamic parameters of a cloud affect its chemical composition. Over the last two decades, several attempts were made to differentiate evolutionary stages of protostars.…”

Monte Carlo simulation to investigate the formation of molecular hydrogen and its deuterated forms

“…Simpler molecules are formed primarily on grain surfaces and then desorbed to the gas phase (Gould and Salpeter, 1963). The importance of grain chemistry has previously been described in the literature (Hasegawa et al, 1992;Chakrabarti et al, 2006a,b;Cuppen and Herbst, 2007;Das et al, 2008aDas et al, ,b, 2010Das et al, , 2013aDas and Chakrabarti, 2011;Majumdar et al, 2012Majumdar et al, , 2013Das et al, 2015;Sivaraman et al, 2014). Even without explicit grain chemistry, effective rates have occasionally been used in studying the formation of bio-molecules (Chakrabarti and Chakrabarti, 2000a,b) For large grains or high accretion rates, the rate equation method (Biham et al, 2001) can be used to explain the abundances of surface species.…”

“…The second set corresponds to experimental values obtained for amorphous carbon grains (Katz et al, 1999), and the third set is the same as that used by LBH. The binding energies for deuterated species are calculated using the following scaling relations: Following Hasegawa et al (1992) and Das et al (2008a) and the references therein, we consider E d ðxÞ ¼ 0:3 E b ðxÞ for H 2 ; HD and D 2 molecules. In the case of set 3, the desorption energy for H 2 was not available.…”