scholarly journals Formation of Molecular Hydrogen in Interstellar Space

1965 ◽  
Vol 7 ◽  
pp. 253-257
Author(s):  
H. F. P. Knaap ◽  
C. J. N. Van Den Meijdenberg ◽  
J. J. M. Beenakker ◽  
H. C. Van De Hulst
Keyword(s):  
Interstellar Dust ◽  
Interstellar Space ◽  
Interstellar Gas ◽  
Interstellar Clouds ◽  
Dark Clouds ◽  
Hydrogen Molecules ◽  
Large Factor ◽  
Dust Grain ◽  
Indirect Argument ◽  
Made In

Although Several Attempts at observing the interstellar hydrogen molecules in the ultraviolet or infrared are in preparation (ref. 1), these molecules are still undetected. They may form the most abundant unobserved constituent of the interstellar gas. The strongest indirect argument for the presence of these molecules lies in the fact that the density of atomic hydrogen observed by the 21-cm line goes down in some dark clouds, where the dust density and, presumably, the total gas density goes up by a large factor.Inasmuch as the density in the interstellar clouds is of the order of 10 atoms/cm3 and the temperature is only of the order of 100° K, any formation of molecules by atom-atom collisions is too slow to be of importance. The most eligible process for H2 formation is recombination on the surface of an interstellar dust grain. Rate estimates of this process have been made in various degrees of detail, as reported in references 2 to 4.

scholarly journals Peeling the astronomical onion

2016 ◽  
Vol 18 (46) ◽  
pp. 31930-31935 ◽  
Author(s):  
Alexander Rosu-Finsen ◽  
Demian Marchione ◽  
Tara L. Salter ◽  
James W. Stubbing ◽  
Wendy A. Brown ◽  
...  
Keyword(s):  
Interstellar Dust ◽  
Water Mobility ◽  
Interstellar Gas ◽  
Dust Grain

This work presents a study of water mobility on interstellar dust grain analogues at temperatures as low as 18 K. The work indicates that water forms pure domains rather than covering the entire grain, thereby leaving bare dust grain surfaces available on which other molecules can adsorb as well as themselves providing surfaces for further adsorption from the interstellar gas.

scholarly journals A Historical Review of Star Formation: Observation and Theory

1987 ◽  
Vol 115 ◽  
pp. 57-57
Author(s):  
Kenneth R. Lang
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Interstellar Dust ◽  
Historical Context ◽  
Historical Review ◽  
Interstellar Space ◽  
Giant Molecular Clouds ◽  
Dark Clouds ◽  
T Tauri ◽  
Infrared Stars

We present a historical review of evidence for ongoing star formation in our Galaxy beginning with the discovery that interstellar space is not empty. The discoveries of interstellar dust, interstellar hydrogen and molecular clouds are reviewed. Observational investigations of dark clouds are then traced from the photographs of Edward Emerson Barnard to contemporary studies of their molecular constituents. A historical overview of observational evidence for new-born stars includes T-Tauri stars, young stellar clusters, sequential star birth and infrared stars beginning with Alfred Joy, Merle Walker, Becklin, and Neugebauer, and Adrian Blaauw and continuing to giant molecular clouds and IRAS. Theoretical studies of gravitational collapse and the early stages of stellar evolution are also placed within a historical context.

scholarly journals Detection of interstellar HCS and its metastable isomer HSC: new pieces in the puzzle of sulfur chemistry

2018 ◽  
Vol 611 ◽  
pp. L1 ◽  
Author(s):  
M. Agúndez ◽  
N. Marcelino ◽  
J. Cernicharo ◽  
M. Tafalla
Keyword(s):  
Abundance Ratio ◽  
Recent Model ◽  
Interstellar Space ◽  
Observational Constraints ◽  
Interstellar Clouds ◽  
Sulfur Chemistry ◽  
Dark Clouds ◽  
Oxygen Analog ◽  
Fractional Abundance ◽  
Order Of Magnitude

We present the first identification in interstellar space of the thioformyl radical (HCS) and its metastable isomer HSC. These species were detected toward the molecular cloud L483 through observations carried out with the IRAM 30 m telescope in the λ3 mm band. We derive beam-averaged column densities of 7 × 1012 cm−2 for HCS and 1.8 × 1011 cm−2 for HSC, which translate into fractional abundances relative to H2 of 2 × 10−10 and 6 × 10−12, respectively. Although the amount of sulfur locked by these radicals is low, their detection allows placing interesting constraints on the chemistry of sulfur in dark clouds. Interestingly, the H2CS/HCS abundance ratio is found to be quite low, ~1, in contrast with the oxygen analog case, in which the H2CO/HCO abundance ratio is around 10 in dark clouds. Moreover, the radical HCS is found to be more abundant than its oxygen analog, HCO. The metastable species HOC, the oxygen analog of HSC, has not yet been observed in space. These observational constraints are compared with the outcome of a recent model of the chemistry of sulfur in dark clouds. The model underestimates the fractional abundance of HCS by at least one order of magnitude, overestimates the H2CS/HCS abundance ratio, and does not provide an abundance prediction for the metastable isomer HSC. These observations should prompt a revision of the chemistry of sulfur in interstellar clouds.

scholarly journals Models of the Interstellar Medium

1980 ◽  
Vol 5 ◽  
pp. 301-310 ◽  
Author(s):  
Teije de Jong
Keyword(s):  
Spatial Distribution ◽  
Interstellar Medium ◽  
Interstellar Dust ◽  
Absorption Lines ◽  
Interstellar Space ◽  
Evidence Based ◽  
Interstellar Gas ◽  
Interstellar Dust Grains ◽  
Probable Source ◽  
Photoelectric Threshold

AbstractUp-to-date models of the interstellar medium should account for the existence of at least three phases of the interstellar gas, a hot phase at ˜ 106 K (HICM), a warm phase at ˜ 104 K (WICM) and a cold phase at ≤ 102 K (clouds). Recent observations of interstellar absorption lines are used to derive information about the physical properties and the spatial distribution of these phases. Evidence based on observations of C+ absorption lines indicates that the photoelectric threshold of interstellar dust grains is about 6 eV, much lower than previously thought. If the photoelectric threshold is indeed of this magnitude the WICM can easily be heated to temperatures in the range 6000 to 8000 K by photons of the general interstellar radiation field with λ > 912 Å. The analysis of interstellar CH+ and 0 VI absorption lines suggests that these lines are formed in gas associated with clouds in regions of enhanced pressure that occupy about 10 percent of interstellar space (SN cavities). The CH+ lines are formed in compressed WICM shells around clouds and the 0 VI lines in conductive interfaces between the WICM and the HICM. The velocity characteristics of the observed lines make shock waves a less probable source of the absorbing gases.

scholarly journals Mechanochemical synthesis of aromatic infrared band carriers

2020 ◽  
Vol 637 ◽  
pp. A82
Author(s):  
E. Dartois ◽  
E. Charon ◽  
C. Engrand ◽  
T. Pino ◽  
C. Sandt
Keyword(s):  
Chemical Reactions ◽  
Mechanochemical Synthesis ◽  
Interstellar Dust ◽  
Broad Band ◽  
Structural Evolution ◽  
High Energy ◽  
Dust Particles ◽  
Interstellar Space ◽  
Infrared Band ◽  
Dust Grain

Context. Interstellar space hosts nanometre- to micron-sized dust grains, which are responsible for the reddening of stars in the visible. The carbonaceous-rich component of these grain populations emits in infrared bands that have been observed remotely for decades with telescopes and satellites. They are a key ingredient of Galactic radiative transfer models and astrochemical dust evolution. However, except for C60 and its cation, the precise carriers for most of these bands are still unknown and not well reproduced in the laboratory. Aims. In this work, we aim to show the high-energy mechanochemical synthesis of disordered aromatic and aliphatic analogues provides interstellar relevant dust particles. Methods. The mechanochemical milling of carbon-based solids under a hydrogen atmosphere produces particles with a pertinent spectroscopic match to astrophysical observations of aromatic infrared band (AIB) emission, linked to the so-called astrophysical polycyclic aromatic hydrocarbon hypothesis. The H/C ratio for the analogues that best reproduce these astronomical infrared observations lies in the 5 ± 2% range, potentially setting a constraint on astrophysical models. This value happens to be much lower than diffuse interstellar hydrogenated amorphous carbons, another Galactic dust grain component observed in absorption, and it most probably provides a constraint on the hydrogenation degree of the most aromatic carbonaceous dust grain carriers. A broad band, observed in AIBs, evolving in the 1350–1200 cm−1 (7.4–8.3 μm) range is correlated to the hydrogen content, and thus the structural evolution in the analogues produced. Results. Our results demonstrate that the mechanochemical process, which does not take place in space, can be seen as an experimental reactor to stimulate very local energetic chemical reactions. It introduces bond disorder and hydrogen chemical attachment on the produced defects, with a net effect similar to the interstellar space very localised chemical reactions with solids. From the vantage point of astrophysics, these laboratory interstellar dust analogues will be used to predict dust grain evolution under simulated interstellar conditions, including harsh radiative environments. Such interstellar analogues offer an opportunity to derive a global view on the cycling of matter in other star forming systems.

scholarly journals Chemical Kinetics Simulations of Ice Chemistry on Porous Versus Non-Porous Dust Grains

2021 ◽  
Vol 8 ◽  
Author(s):  
Drew A. Christianson ◽  
Robin T. Garrod
Keyword(s):  
Chemical Kinetics ◽  
Interstellar Dust ◽  
Three Dimensional ◽  
Binding Energies ◽  
Inert Gases ◽  
Chemical Effect ◽  
Dust Grains ◽  
Interstellar Clouds ◽  
Dust Grain ◽  
Grain Surface

The degree of porosity in interstellar dust-grain material is poorly defined, although recent work has suggested that the grains could be highly porous. Aside from influencing the optical properties of the dust, porosity has the potential to affect the chemistry occurring on dust-grain surfaces, via increased surface area, enhanced local binding energies, and the possibility of trapping of molecules within the pores as ice mantles build up on the grains. Through computational kinetics simulations, we investigate how interstellar grain-surface chemistry and ice composition are affected by the porosity of the underlying dust-grain material. Using a simple routine, idealized three-dimensional dust-grains are constructed, atom by atom, with varying degrees of porosity. Diffusive chemistry is then simulated on these surfaces using the off-lattice microscopic Monte Carlo chemical kinetics model, MIMICK, assuming physical conditions appropriate to dark interstellar clouds. On the porous grain surface, the build-up of ice mantles, mostly composed of water, leads to the covering over of the pores, leaving empty pockets. Once the pores are completely covered, the chemical and structural behavior is similar to non-porous grains of the same size. The most prominent chemical effect of the presence of grain porosity is the trapping of molecular hydrogen, formed on the grain surfaces, within the ices and voids inside the grain pores. Trapping of H2 in this way may indicate that other volatiles, such as inert gases not included in these models, could be trapped within dust-grain porous structures when ices begin to form.

scholarly journals Molecule Formation on Grain Surfaces

1971 ◽  
Vol 2 ◽  
pp. 429-431
Author(s):  
E. E. Salpeter
Keyword(s):  
Interstellar Dust ◽  
Adsorption Site ◽  
Sticking Coefficient ◽  
Interstellar Gas ◽  
Molecule Formation ◽  
Recombination Efficiency ◽  
Two Factors ◽  
Time Required ◽  
Dust Grain ◽  
Grain Surface

I will discuss the formation of molecules AB from two atoms or radicals A and B only for cases where the reaction A + B → AB is exothermic. The efficiency of this reaction on the surface of an interstellar dust grain is the product of two factors: (i) the ‘sticking coefficient’ or probability that the first radical hitting the grain surface from the interstellar gas becomes thermalized and sticks to an adsorption site; (ii) the recombination efficiency or probability that the first adsorbed radical will remain adsorbed, rather than evaporating, during the time required for the second radical to hit the grain, be adsorbed and find its partner.

scholarly journals The role of radiolysis in the modelling of C2H4O2 isomers and dimethyl ether in cold dark clouds

2020 ◽  
Vol 500 (3) ◽  
pp. 3414-3424
Author(s):  
Alec Paulive ◽  
Christopher N Shingledecker ◽  
Eric Herbst
Keyword(s):  
Gas Phase ◽  
Dimethyl Ether ◽  
Recent Observation ◽  
Cosmic Ray ◽  
Thermal Method ◽  
Dark Clouds ◽  
Ice Surface ◽  
Dust Grain ◽  
Complex Organic

ABSTRACT Complex organic molecules (COMs) have been detected in a variety of interstellar sources. The abundances of these COMs in warming sources can be explained by syntheses linked to increasing temperatures and densities, allowing quasi-thermal chemical reactions to occur rapidly enough to produce observable amounts of COMs, both in the gas phase, and upon dust grain ice mantles. The COMs produced on grains then become gaseous as the temperature increases sufficiently to allow their thermal desorption. The recent observation of gaseous COMs in cold sources has not been fully explained by these gas-phase and dust grain production routes. Radiolysis chemistry is a possible non-thermal method of producing COMs in cold dark clouds. This new method greatly increases the modelled abundance of selected COMs upon the ice surface and within the ice mantle due to excitation and ionization events from cosmic ray bombardment. We examine the effect of radiolysis on three C2H4O2 isomers – methyl formate (HCOOCH3), glycolaldehyde (HCOCH2OH), and acetic acid (CH3COOH) – and a chemically similar molecule, dimethyl ether (CH3OCH3), in cold dark clouds. We then compare our modelled gaseous abundances with observed abundances in TMC-1, L1689B, and B1-b.

scholarly journals Connecting the Interstellar Gas and Dust Properties in Distant Galaxies Using Quasar Absorption Systems

2015 ◽  
Vol 11 (S315) ◽  
Author(s):  
Monique C. Aller ◽  
Varsha P. Kulkarni ◽  
Donald G. York ◽  
Daniel E. Welty ◽  
Giovanni Vladilo ◽  
...  
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Absorption Feature ◽  
Dust Grains ◽  
Interstellar Gas ◽  
Chemical Enrichment ◽  
Normal Galaxies ◽  
History Of ◽  
Dust Grain ◽  
Grain Properties

AbstractGas and dust grains are fundamental components of the interstellar medium and significantly impact many of the physical processes driving galaxy evolution, such as star-formation, and the heating, cooling, and ionization of the interstellar material. Quasar absorption systems (QASs), which trace intervening galaxies along the sightlines to luminous quasars, provide a valuable tool to directly study the properties of the interstellar gas and dust in distant, normal galaxies. We have established the presence of silicate dust grains in at least some gas-rich QASs, and find that they exist at higher optical depths than expected for diffuse gas in the Milky Way. Differences in the absorption feature shapes additionally suggest variations in the silicate dust grain properties, such as in the level of grain crystallinity, from system-to-system. We present results from a study of the gas and dust properties of QASs with adequate archival IR data to probe the silicate dust grain properties. We discuss our measurements of the strengths of the 10 and 18 μm silicate dust absorption features in the QASs, and constraints on the grain properties (e.g., composition, shape, crystallinity) based on fitted silicate profile templates. We investigate correlations between silicate dust abundance, reddening, and gas metallicity, which will yield valuable insights into the history of star formation and chemical enrichment in galaxies.

scholarly journals DIBs, Interstellar Dust, and Extinction

2013 ◽  
Vol 9 (S297) ◽  
pp. 147-152 ◽  
Author(s):  
G. C. Clayton
Keyword(s):  
Interstellar Medium ◽  
Interstellar Dust ◽  
Dust Grains ◽  
Weak Correlation ◽  
Interstellar Clouds ◽  
The Galaxy ◽  
The Relationship

AbstractThe relationship between DIBs and dust is still unknown. The correlation between reddening and DIB strength means that the DIBs are mixed in with the dust and gas in interstellar clouds. The DIBs are relatively stronger in the diffuse interstellar medium than in dense clouds. There is only a weak correlation between the DIBs and the UV extinction parameters including the 2175 Å bump strength and the far-UV rise. In addition, the bump dust grains are sometimes polarized, while the DIBs are not. However, observations of DIBs in the SMC show that when the 2175 Å bump is weak or missing so are the DIBs. Two of the four sightlines that deviate strongly from the CCM UV extinction in the Galaxy show weak DIBs.

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