Comet P/Shoemaker-Levy 9 Collision with Jupiter: A Model of G-Site Dust Composition     

Daryl H. Wallis  N.C. Wickramasinghe 《Astrophysics and Space Science》1997,254(1):25-35

Scattering models of aerosol particles at the G-impact site (18 July1994) are presented for a number of likely compositional candidates. Two differing dust particle population distribution functions are taken, along with varying aerosol cloud densities, leading to differing optical depths. A number of models including graphite, amorphous carbon, astrophysical silicate, water ice and a number of organic compounds are discussed, but no single material provides a fully satisfactory fit to the published observations. A porous silicate/graphite composite is found to provide a good fit to the spectral data. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

The extinction of starlight revisited     

N. C. Wickramasinghe  B. Jazbi  F. Hoyle 《Astrophysics and Space Science》1991,186(1):67-80

The rigorous Kerker-Matijevi formulae for light scattering by co-axial double cylinders are used to calculate the extinction properties of hollow organic grains. A size distribution of such particles together with iron whiskers of radii 0.01 m, silica spheres of radius 0.03 m and free aromatic molecular clusters comprised of 50–100 atoms yield excellent agreement with data on the extinction of starlight. The mass ratios of silica to organics and of iron to organics are in good accord with cosmic abundance constraints.  相似文献   

Far-infrared contribution to interstellar extinction from graphite whiskers     

N. C. Wickramasinghe  Daryl H. Wallis 《Astrophysics and Space Science》1996,240(1):157-160

A mass contribution of graphite whiskers as small as 0.1% to the population of interstellar grains could dramatically change their far-infrared extinction properties. With varying mass fractions of graphite whiskers, and for different size parameters, the infrared extinction could vary from a ^-2 dependence to ⁰, consistent with the requirements of some astronomical observations.  相似文献   

Biofluorescence and the extended red emission in astrophysical sources     

F. Hoyle  N. C. Wickramasinghe 《Astrophysics and Space Science》1996,235(2):343-347

A broad emission band over the wavelength range 6000–7500 Å in submicron dust in the galaxy and in M82 can be explained by fluorescence phenomena in low-temperature chloroplasts and bacterial pigments. Alternative explanations do not appear to be promising.  相似文献   

On the nature of interstellar grains     

F. Hoyle  C. Wickramasinghe 《Astrophysics and Space Science》1979,66(1):77-90

Data on interstellar extinction are interpreted to imply an identification of interstellar grains with naturally freeze-dried bacteria and algae. The total mass of such bacterial and algal cells in the galaxy is enormous, 10⁴⁰ g. The identification is based on Mie scattering calculations for an experimentally determined size distribution of bacteria. Agreement between our model calculations and astronomical data is remarkably precise over the wavelength intervals µ^–1 < ;^–2 < 1.94µ^–1 and 2.5µ^–1 < ;^–1 < 3.0 ;^–1. Over the more restricted waveband 4000–5000 Å an excess interstellar absorption is found which is in uncannily close agreement with the absorption properties of phytoplankton pigments. The strongest of the diffuse interstellar bands are provisionally assingned to carotenoid-chlorophyll pigment complexes such as exist in algae and pigmented bacteria. The 2200 Å interstellar absorption feature could be due to degraded cellulose strands which form spherical graphitic particles, but could equally well be due to protein-lipid-nucleic acid complexes in bacteria and viruses. Interstellar extinction at wavelengths <1800 Å could be due to scattering by virus particles.  相似文献   

The identification of the 3μ spectral feature in galactic infrared sources     

F. Hoyle  C. Wickramasinghe 《Astrophysics and Space Science》1980,68(2):499-503

We show that a 3 extinction feature in galactic infrared sources cannot be due to water-ice grains. Infrared spectra with a resolution of /=0.015 are in remarkably close agreement with the 2.5–4 extinction properties calculated for bacterial grains.  相似文献   

Polyoxymethylene co-polymers on grains     

A. Cooke  N. C. Wickramasinghe 《Astrophysics and Space Science》1977,50(1):43-53

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 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 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 emission feature in many sources. Theoretically computed band profiles of the 10 -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 10 in the 8–12 feature of the infrared source OH 231.8+4.2 may be a signature of POM grains; likewise, a persistent 3.3 emission feature in many different types of infrared source could be attributed to the CH stretching mode in formaldehyde co-polymer grains.  相似文献   

Effects of suprathermal grains     

S. P. Tarafdar  N. C. Wickramasinghe 《Astrophysics and Space Science》1976,39(1):19-30

Grains ejected from stars at velocities of 10⁷ cm s^–1 and/or grains accelerated by the pressure of starlight in the intercloud medium to velocities in the range 2×10⁶–10⁷ cm s^–1 are slowed to velocities of about 2×10⁵ cm s^–1 in a typical interstellar cloud. The interaction of fast grains with gas atoms as they are slowed in clouds could provide (a) the dominant heat source for interstellar clouds; (b) sites for molecule formation; and (c) a mechanism of providing a pressure balance between clouds and the intercloud medium.Paper presented at the Symposium on Solid State Astrophysics, held at the University College, Cardiff, Wales, between 9–12 July, 1974.  相似文献   

The infrared excess from the white dwarf star G29-38: A brown dwarf of dust?     

N. C. Wickramasinghe  F. Hoyle  S. Al-Mufti 《Astrophysics and Space Science》1988,143(1):193-197

The recently-observed infrared excess from the white dwarf star G29-38 is shown to be better fitted by a model involving organic dust grains, than one involving a brown-dwarf companion star.  相似文献   

Diatoms on earth,comets, europa and in interstellar space     

Hoover  Richard B.  Hoyle  Fred  Wickramasinghe  N. C.  Hoover  Miriam J.  Al-Mufti  S. 《Earth, Moon, and Planets》1986,35(1):19-45

There exists a close correspondence between the measured infrared properties of diatoms and the infrared spectrum of interstellar dust as observed in the Trapezium nebula and toward the galactic center source GC-IRS 7. Diatoms and bacteria also exhibit an absorbance peak near 2200 », which is found to agree with the observed ultraviolet absorbance properties of interstellar grains. We review the observational data and consider the known properties of diatoms and bacteria. It is suggested that these characteristics are consistent with the concept of a cosmic microbiological system in which these or similar microorganisms might exist on comets, Europa and in interstellar space.  相似文献