Sound Bytes: nanocones from space |
star smoke | red giant onion cores | graphene rain | early days of life's
atoms We suspect this is the first close look at naturally-occuring unlayered but solidified graphene (hexagonal carbon nets, layers of which make up the graphite in pencils). This unlayered graphene is found in the center of carbon spheres (about the size of a human blood cell) which were extracted from the Australian meteorite Murchison. Each sphere contains atoms manufactured in the red giant star* from which it began its journey to earth. In addition to providing information about precipitation processes (e.g. storms) in the atmosphere of red giants, such unlayered graphene may comprise much of the carbon in the interstellar medium, and be part of the history of carbon atoms in life-forms as well. Man-made counterparts of this material include bulk assemblies of single graphene-sheet carbon molecules like fullerines, single-walled carbon nanotubes, and single-walled carbon nanohorns. The selective laboratory production of the latter was only recently reported, in a paper whose data suggested a possible role for liquid carbon in the efficient formation of such structures. Since carbon has a higher melting temperature than any other solid known, an intriguing possibility not yet carefully considered is that the cores condensed as droplets of liquid carbon, where they were allowed to cool in the star's atmosphere less quickly than they might cool on earth, before being coated with graphite and ejected by radiation pressure into the interstellar medium. /pf 2002oct02
* Incidentally, isotopic studies indicate that this meteorite contains intact particles from stars formed at wide-ranging times during our ten billion year old Milky Way's first five billion years. Odds are therefore that the atoms inside you, the reader, have similarly wide-ranging origins even if they were long ago separated from ``sibling atoms'' which made the trip with them here from the star in which their nuclei were assembled from smaller parts.
Headings: circumstellar matter | dust,extinction |
meteors,meteoroids | molecular processes | stars:carbon | stars:mass loss"The core structure of pre-solar graphite onions" Ap. J. Lett. 578(2) (2002) L153-156 by P. Fraundorf and Martin Wackenhut, 20 Oct 2002 (c) American Astronomical Society (posted with permission)
pfmw.onioncores eprint PDF (prior to revision clarifying the astrophysical context)
BiBTeX reference:
@article{pfmw.onioncores,
author = "P. Fraundorf and Martin Wackenhut",
title = "The core structure of pre-solar graphite onions",
journal = "Astrophysical Journal Letters",
volume = "578",
number = "2",
pages = "L153-L156",
year = "2002",
eprint = "arXiv:astro-ph/0110585"}
HRTEM of unlayered graphene from the atmosphere of red giants
P. Fraundorf and N. Hunton
Physics and Astronomy and Center for Molecular Electronics
University of Missouri-StL, St. Louis MO 63121
A paper to be published in the 20 October 2002 issue of ApJ Letters [1] discusses electron phase contrast imaging of an unlayered graphene phase which makes up the core of a subset of micron-sized "presolar" graphite-rimmed spheres. By "presolar", we mean particles extracted from meteorite dissolution residues (in this case the carbonaceous chondrite Murchison which fell in Australia in 1967) that show isotopic evidence of formation in the neighborhood of other stars prior to the origin of our solar system. The paper suggests that single graphene sheet defects in the onion cores (e.g. cyclopentane loops) may be observable edge-on by high-resolution electron microscopy (HRTEM) via the conical deformation that they cause to the graphene sheet in which they reside. This could allow better evaluation of models for their formation. Since much of the mass-loss from carbon-rich red giants might be in even smaller interstellar particles (too small to make it into meteorites during the early days of our solar system), a significant amount of interstellar carbon may be in this form.
Here we review these observations, and discuss the relevance of this natural source for unlayered graphene in context of recent laboratory developments, particularly on the efficient bulk manufacture of single-walled carbon nano-horns [2]. Prospects will be discussed (hopefully with group participation) for a possible role in both cases of a carbon liquid phase, for astrophysical simulations of condensation in stellar atmospheres, for discovery and/or preparation of terrestrial analogs, and for future imaging, diffraction, spectroscopy and decomposition studies of this extraterrestrial graphene.
Section: Astronomy Education/Frontiers in Astronomy
(Invited)
Since 1980 extraterrestrial bodies directly involved in
the night sky's appearance have been identified on earth. These include
particles from the dust cloud around our sun, collected in the earth's
stratosphere
** cf. Analysis of Interplanetary Dust, AIP Conf. Proc. 310 (eds. Zolensky, Wilson, Rietmeijer & Flynn, Amer. Inst. of Physics, NY, 1994); J. P. Bradley, S. A. Sandford and R. M. Walker, Interplanetary dust particles, in Meteorites and the Early Solar System (eds. J. F. Kerridge and M. S. Matthews), U. Ariz. Press, Tucson AZ, 861-895 (1988); D. E. Brownlee, Cosmic Dust: Collection and Research. Ann. Rev. Earth Planet. Sci. 13 (1985) 147-173; P. Fraundorf, D. E. Brownlee and R. M. Walker, Laboratory studies of interplanetary dust, in Comets (ed. L. Wilkening), U. Ariz. Press, Tucson AZ, 383-409 (1982).
*** cf. Astrophysical Implications of the Laboratory Study of Presolar Materials, AIP Conf. Proc. 402, (eds. Bernatowicz and Zinner, Amer. Inst. of Physics, NY, 1997); Zinner E., Interstellar grains from primitive meteorites: New constraints on nucleosynthesis theory and stellar evolution models, in Nuclei in the Cosmos III, (ed. M. Busso, R. Gallino and C. M. Raiteri), AIP, New York, 567-579 (1995). See also the current (Dec '97) Physics Today article on Ancient Stardust in the Laboratory, by T. Bernatowicz and R. M. Walker.
Examine unlayered graphene grown in digito on our Live3D models page.
Parody of "Twinkle, twinkle, little star" adapted from the August 2001 Physics Today, but whose replacement of diamond with "gem carbonaceous" might be construed as a clue to the presence of stardust in carbonaceous chondrites (by an unknown author):
A cartoon from colleages at Johnson Space Center, prepared after reports of the first closeup look at interplanetary dust particles collected in the earth's stratosphere. Was this penned by Pogo cartoonist Walt Kelly?
John Dryden (1631-1700) offered this possible inspiration toward further work on tiny dark objects that have traversed (intact) the soundless aeons of interstellar space: