Interstellar Solid Hydrogen

Lin, Ching Yeh; Gilbert, Andrew T. B.; Walker, Mark A.

doi:10.1088/0004-637x/736/2/91

Cited by 19 publications

(17 citation statements)

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“…He concluded that electrical charging processes stabilize H 2 grain surfaces even at temperatures where, usually, the volatility of H 2 is already very high (10 K). Lin et al (2011) proposed to track H 6 + as a probe for the presence of solid H 2 . Bernstein et al (2013) proposed the presence of contaminated CHIMPs.…”

Section: Astrophysical Implicationsmentioning

confidence: 99%

“…Astronomers have been interested in solid H 2 in the ISM (Lin et al 2011) since the late 1960s . In addition to the few layers adsorbed on water ice mentioned earlier, the presence of solid H 2 was proposed as flakes (Pfenniger & Puy 2003) or as H 2 dust stabilised by an electric field (Walker 2013), forming contaminated H 2 clusters (Bernstein et al 2013).…”

Section: Introductionmentioning

confidence: 99%

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CN radical hydrogenation from solid H₂ reactions, an alternative way of HCN formation in the interstellar medium

Borget

Müller

Grote

et al. 2017

A&A

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Context. Molecular hydrogen (H 2 ) is the most abundant molecule of the interstellar medium (ISM) in gas phase and it has been assumed to exist in solid state or as coating on grains. Aims. Our goal is to show that solid H 2 can act as a hydrogenation agent, reacting with CN radicals to form HCN. Methods. In a H 2 matrix, we studied the hydrogenation of the CN radical generated from the vacuum ultraviolet photolysis (VUVphotolysis) of C 2 N 2 at 3.8 K. We modified the wavelengths and the host gas in order to be sure that CN radicals can abstract H from H 2 molecules. Results. HCN monomers, dimers, and oligomers have been characterised by Fourier transform infrared spectroscopy (FTIR). H 2 CN as well as CN radicals have also been clearly observed during the photolysis performed at 3.8 K.Conclusions. H 2 is a hydrogenation reagent towards CN radicals producing HCN. This type of reaction should be taken into account for the reactivity at low temperature in contaminated H 2 ice macro-particles (CHIMPs), H 2 flakes or in the first sublayers of grains where solid H 2 has accumulated.

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Section: Astrophysical Implicationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

CN radical hydrogenation from solid H₂ reactions, an alternative way of HCN formation in the interstellar medium

Borget

Müller

Grote

et al. 2017

A&A

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“…Detailed models of the cosmic-ray induced chemistry in our clouds would not be easy to construct, despite their simple composition, because of the additional complexities that are introduced by H 2 condensation. We note in particular the following points: ionisation of the condensed H 2 favours the production of H + 6 , rather than H + 3 (which dominates in gas-phase) (Lin, Gilbert and Walker 2011); clusters of H 2 ligands may form around any ions (Duley 1996;Bernstein, Clark and Lynch 2013); electrons and ions that encounter snowflakes will tend to stick on the surface, or in the bulk of the snowflake (Walker 2013); and at present the relevant reaction rates in or on the condensed H 2 are largely unknown.…”

Section: Reconciliation With Mckee's Critiquementioning

confidence: 90%

Cosmic Snow Clouds: Self-gravitating Gas Spheres Manifesting Hydrogen Condensation

Walker

Wardle

2019

ApJ

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We present hydrostatic equilibrium models of spherical, self-gravitating clouds of helium and molecular hydrogen, focusing on the cold, high-density regime where solid-or liquid-hydrogen can form. The resulting structures have masses from 0.1 M down to several ×10 −8 M , and span a broad range of radii: 10 −4 R(AU) 10 7 . Our models are fully convective, but all have a two-zone character with the majority of the mass in a small, condensate-free core, surrounded by a colder envelope where phase equilibrium obtains. Convection in the envelope is unusual in that it is driven by a mean-molecular-weight inversion, rather than by an entropy gradient. In fact the entropy gradient is itself inverted, leading to the surprising result that envelope convection transports heat inwards. In turn that permits the outer layers to maintain steady state temperatures below the cosmic microwave background. Amongst our hydrostatic equilibria we identify thermal equilibria appropriate to the Galaxy, in which radiative cooling from H 2 is balanced by cosmic-ray heating. These equilibria are all thermally unstable, albeit with very long thermal timescales in some cases. The specific luminosities of all our models are very low, and they therefore describe a type of baryonic dark matter. Consequently such clouds are thermally fragile: when placed in a harsh radiation field they will be unable to cool effectively and disruption will ensue as heat input drives a secular expansion. Disrupting clouds should leave trails of gas and H 2 dust in their wake, which might make them easier to detect. Our models may be relevant to the cometary globules in the Helix Nebula, and the G2 cloud orbiting Sgr A*.

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“…There are other direct and indirect ways to detect H 2 , as described in Combes & Pfenniger (1997), but most of them only apply for gaseous H 2 . Lin et al (2011) argue that H + 6 detection would indicate solid H 2 , as this ion is not formed by gas-phase reactions.…”

Section: Introductionmentioning

confidence: 98%

Solid H₂ in the interstellar medium

Füglistaler

Pfenniger

2018

A&A

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Context. Condensation of H 2 in the interstellar medium (ISM) has long been seen as a possibility, either by deposition on dust grains or thanks to a phase transition combined with self-gravity. H 2 condensation might explain the observed low efficiency of star formation and might help to hide baryons in spiral galaxies. Aims. Our aim is to quantify the solid fraction of H 2 in the ISM due to a phase transition including self-gravity for different densities and temperatures in order to use the results in more complex simulations of the ISM as subgrid physics. Methods. We used molecular dynamics simulations of fluids at different temperatures and densities to study the formation of solids. Once the simulations reached a steady state, we calculated the solid mass fraction, energy increase, and timescales. By determining the power laws measured over several orders of magnitude, we extrapolated to lower densities the higher density fluids that can be simulated with current computers. Results. The solid fraction and energy increase of fluids in a phase transition are above 0.1 and do not follow a power law. Fluids out of a phase transition are still forming a small amount of solids due to chance encounters of molecules. The solid mass fraction and energy increase of these fluids are linearly dependent on density and can easily be extrapolated. The timescale is below one second, the condensation can be considered instantaneous.Conclusions. The presence of solid H 2 grains has important dynamic implications on the ISM as they may be the building blocks for larger solid bodies when gravity is included. We provide the solid mass fraction, energy increase, and timescales for high density fluids and extrapolation laws for lower densities.

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Interstellar Solid Hydrogen

Cited by 19 publications

References 82 publications

CN radical hydrogenation from solid H₂ reactions, an alternative way of HCN formation in the interstellar medium

CN radical hydrogenation from solid H₂ reactions, an alternative way of HCN formation in the interstellar medium

Cosmic Snow Clouds: Self-gravitating Gas Spheres Manifesting Hydrogen Condensation

Solid H₂ in the interstellar medium

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Interstellar Solid Hydrogen

Cited by 19 publications

References 82 publications

CN radical hydrogenation from solid H2 reactions, an alternative way of HCN formation in the interstellar medium

CN radical hydrogenation from solid H2 reactions, an alternative way of HCN formation in the interstellar medium

Cosmic Snow Clouds: Self-gravitating Gas Spheres Manifesting Hydrogen Condensation

Solid H2 in the interstellar medium

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Product

Resources

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CN radical hydrogenation from solid H₂ reactions, an alternative way of HCN formation in the interstellar medium

CN radical hydrogenation from solid H₂ reactions, an alternative way of HCN formation in the interstellar medium

Solid H₂ in the interstellar medium