Formation of GEMS from shock-accelerated crystalline dust in Superbubbles
Interplanetary dust particles (IDPs) contain enigmatic sub-micron components called GEMS (Glass with Embedded Metal and Sulfides). The compositions and structures of GEMS indicate that they have been processed by exposure to ionizing radiation but details of the actual irradiation environment(s) have remained elusive. Here we propose a mechanism and astrophysical site for GEMS formation that explains for the first time the following key properties of GEMS; they are stoichiometrically enriched in oxygen and systematically depleted in S, Mg, Ca and Fe (relative to solar abundances), most have normal (solar) oxygen isotopic compositions, they exhibit a strikingly narrow size distribution (0.1-0.5 {micro}m diameter), and some of them contain ''relict'' crystals within their silicate glass matrices. We show that the compositions, size distribution, and survival of relict crystals are inconsistent with amorphization by particles accelerated by diffusive shock acceleration. Instead, we propose that GEMS are formed from crystalline grains that condense in stellar outflows from massive stars in OB associations, are accelerated in encounters with frequent supernova shocks inside the associated superbubble, and are implanted with atoms from the hot gas in the SB interior. We thus reverse the usual roles of target and projectile. Rather than being bombarded at rest by energetic ions, grains are accelerated and bombarded by a nearly monovelocity beam of atoms as viewed in their rest frame. Meyer, Drury and Ellison have proposed that galactic cosmic rays originate from ions sputtered from such accelerated dust grains. We suggest that GEMS are surviving members of a population of fast grains that constitute the long-sought source material for galactic cosmic rays. Thus, representatives of the GCR source material may have been awaiting discovery in cosmic dust labs for the last thirty years.
- Research Organization:
- Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 15015145
- Report Number(s):
- UCRL-JRNL-209128; TRN: US0501556
- Journal Information:
- The Astrophysical Journal, Vol. 617; Other Information: Journal publication date December 20, 2004; PDF-FILE: 29 ; SIZE: 0.4 MBYTES; PBD: 8 Dec 2004
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
74 ATOMIC AND MOLECULAR PHYSICS
99 GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE
ACCELERATION
ATOMS
COSMIC DUST
DISTRIBUTION
DUSTS
GLASS
IONIZING RADIATIONS
IRRADIATION
MATRICES
OXYGEN
SILICATES
STARS
SULFIDES
TAIL IONS
TARGETS