Interstellar Carbon Dust

Studies of interstellar dust have currently drawn more attentions.It remains fully understanding to dust composition,size and morphology.Benefited by the improvement of detection method,especially in infrared band,dust mode has improved and the understanding of interstellar dust has been deeper than previously known.In this paper,we focus on the interstellar carbon dust,especially for the study of interstellar graphite,and explore the relationship between the spectrum features of carbonaceous dust and results of astrophysical observations.Carbon is the fourth most abundant element in the Universe,and is a major component of interstellar grains whose infrared absorption and emission spectra provide a powerful diagnosis of the physical and chemical conditions of astrophysical regions where the dust is found.Carbonaceous dust materials such as graphite,nanodiamonds,polycyclic aromatic hydrocarbon molecules?PAHs?,fullerene,and hydrogenated amorphous carbon are ubiquitously present in the interstellar space and are the most promising candidate carriers of the unidentified 2175 A extinction bump,the unidentified infrared emission bands,and the mysterious diffuse interstellar bands.Currently,fullerene,graphite and carbon nanotube become the new hot issue in interstellar physics and chemistry.Interstellar graphite is the important intermediate product of the formation of fullerene.With the silicate-graphite-PAHs dust model,we figure out the upper limit abundance of graphene to be?5 ppm is sufficient to match the DIRBE,FIRAS and IRTS isometrically.We bear out theoretically the existence of nanometer scale graphene in interstellar space,which enriches the species of carbon dust.We also study more deeply than previously study in the conjecture of interstellar geographer.Meanwhile,the spectra of many carbon nanotubes fall in the visible spectra region.We search for the characteristic IR features of C₂₄ at?6.6,9.8,20 ?m toward Sgr B2,a high-mass star formation region,and find a candidate target toward R.A.?J2000?=267°.05855 and Decl.?J2000?=-28°.01479 in Sgr B2 whose Spitzer/IRS spectra exhibit three bands peaking at ? 6.637,9.853 and 20.050 ?m which appear to be coincident with that of C₂₄.Possible features of C₆₀are also seen in this region.The candidate region is in a warm dust environment heated by massive stars or star clusters,associated with a WISE spot?a tracer of star-formation activity?,close to the HII region candidate IRAS 17450-2759,and is surrounded by seven young stellar object candidates within?5',suggesting that the creati on and/or excitation of C₂₄ could be related to star formation activities.Carbon nano tubes present strong electron transition in optical and near infrared band,which coincides with the optical property of diffuse interstellar band?DIB?carriers.It will conduce to identify the DIB carriers to explore optical features of carbon nanotubes.Carbon nanotubes?CNTs,hereafter?could form through rolling up from graphene sheet.In this work,we attempt to calculate the absorption cross section of the smallest CNT-?5,0?CNT based on the discrete dipole approximation approach?DDSCAT?.The result shows that the peak absorption cross section would shift toward the red end with increasing tube length.When the tube length contains 23 carbons,a?2.9 ?m characteristic peak of the absorption cross section changes to be incredibly high.The peak value decreases with increasing number of dipoles.In addition,the increasing number of dipoles results in the peak absorption cross section shifting toward the blue end.The feature at?0.3 and?0.9 ?m may be useful to calculate the upper limit abundance of CNTs.