Evolution and ecology of influenza A viruses.

Cosmochemistry of the rare earth elements: meteorite studies.

▪ Abstract At luminosities above 1011 , infrared galaxies become the dominant population of extragalactic objects in the local Universe (z ≲ 0.3), being more numerous than optically selected starburst and Seyfert galaxies and quasi-stellar objects at comparable bolometric luminosity. The trigger for the intense infrared emission appears to be the strong interaction/merger of molecular gas-rich spirals, and the bulk of the infrared luminosity for all but the most luminous objects is due to dust heating from an intense starburst within giant molecular clouds. At the highest luminosities (Lir > 1012 ), nearly all objects appear to be advanced mergers powered by a mixture of circumnuclear starburst and active galactic nucleus energy sources, both of which are fueled by an enormous concentration of molecular gas that has been funneled into the merger nucleus. These ultraluminous infrared galaxies may represent an important stage in the formation of quasi-stellar objects and powerful radio galaxies. They may al...

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Luminous infrared galaxies

We construct size distributions for carbonaceous and silicate grain populations in different regions of the Milky Way, LMC, and SMC. The size distributions include sufficient very small carbonaceous grains (including polycyclic aromatic hydrocarbon molecules) to account for the observed infrared and microwave emission from the diffuse interstellar medium. Our distributions reproduce the observed extinction of starlight, which varies depending on the interstellar environment through which the light travels. As shown by Cardelli, Clayton, and Mathis in 1989, these variations can be roughly parameterized by the ratio of visual extinction to reddening, RV. We adopt a fairly simple functional form for the size distribution, characterized by several parameters. We tabulate these parameters for various combinations of values for RV and bC, the C abundance in very small grains. We also find size distributions for the line of sight to HD 210121 and for sight lines in the LMC and SMC. For several size distributions, we evaluate the albedo and scattering asymmetry parameter and present model extinction curves extending beyond the Lyman limit.

https://iopscience.iop.org/article/10.1086/318651/pdf

Dust Grain-Size Distributions and Extinction in the Milky Way, Large Magellanic Cloud, and Small Magellanic Cloud

▪ Abstract This review surveys the observed properties of interstellar dust grains: the wavelength-dependent extinction of starlight, including absorption features, from UV to infrared; optical lum...

https://www.ifa.hawaii.edu/users/reipurth/reviews/draine.pdf

Interstellar dust grains

Astronomical data at infrared wavelengths point decisively to an organic composition of interstellar grains.

Organic grains in space

Conditions prevalent in dense molecular clouds are shown to favour the polymerization of H2CO molecules and the deposition of formaldehyde co-polymer mantles, with typical radii ∼10−5 cm, on smaller refractory grains. If a significant fraction of such co-polymer coated grains are expelled with systematic gas flows into the general interstellar medium, these moderately refractory grains may be responsible for the bulk of interstellar extinction and polarization at optical wavelengths. Mie calculations for a mixture consisting of iron, graphite and POM particles are presented as an example where POM grains of radii 0.15 μ dominate the extinction at optical wavelengths, providing a satisfactory overall fit to a range of extinction data. A size distribution of POM needles with a ‘mean’ radius 0.15 μ also provides good agreement with data on interstellar linear as well as circular polarization. Suitably end-capped and stabilized co-polymer-coated grains, with either silicate or graphite cores, may survive at temperatures ∼450 K under interstellar ambient conditions and be responsible for the 10 μ emission feature in many sources. Theoretically computed band profiles of the 10 μ-feature in POM coated grains, in general, provide better agreement with observations than most types of silicate grains considered so far. We also note that an unexplained dip at λ≃10 μ in the 8–12 μ feature of the infrared source OH 231.8+4.2 may be a signature of POM grains; likewise, a persistent 3.3 μ emission feature in many different types of infrared source could be attributed to the CH stretching mode in formaldehyde co-polymer grains.

Polyoxymethylene co-polymers on grains

The data on the far-ultraviolet extinction of starlight in our galaxy and in external galaxies is interpreted in terms of the widespread occurrence of organic particles of optical refractive index 1.4 and radii less than or equal to 20~nm. Such particles are candidates for nanobacteria such as recently been found in abundance on the Earth.

A Cosmic Prevalence of Nanobacteria

Medical science is not accustomed to turning to the skies for warnings of pandemics although this is precisely what our distant ancestors throughout history were prone to do. The Sun clearly plays an important role in all aspects of our lives. For instance, there have been many claims that the occurrence of pandemic influenza and other viral outbreaks is correlated with the well-known 11-year sunspot cycle 1–3 although the precise mechanism for such a causative connection had remained unclear.

Space Weather and Pandemic Warnings

It is shown that the 10–13 μ band observed in the spectra of some carbon stars could arise from simple hydrocarbon molecules, especially of the type C n H 2n . These molecules could be present in circumstellar dust shells which are responsible for the 1000 K black-body excess observed for these stars, and the emission band is produced by collisional excitation.

N. C. Wickramasinghe

Papers

Organic grains in space

Polyoxymethylene co-polymers on grains

A Cosmic Prevalence of Nanobacteria

Space Weather and Pandemic Warnings

Hydrocarbon molecules in carbon stars