Formation of Micron-sized Presolar Graphite Grains in Low-energy Supernova Ejecta
Abstract
Presolar graphite grains with supernova isotopic signatures provide direct evidence that large graphite grains formed in supernova ejecta. However, theoretical calculations of dust formation in supernovae have typically predicted graphite grains smaller than 0.1 μm, leaving unclear the physical conditions required to form those grains with radii of order 1 μm. We systematically investigate graphite nucleation and growth in expanding supernova ejecta by varying the explosion energy, ejecta mass, initial ejecta radius, and ejected 56Ni mass. We use a simplified one-zone model that follows the temperature and density evolution including adiabatic cooling, radiative cooling, and heating by radioactive nickel. We show that the final graphite grain size is mainly determined by the product of the mass density of atomic carbon available for grain growth and the local cooling timescale, both evaluated at a reference temperature of 2000 K. Our models show that graphite growth is favored by lower explosion energy, larger ejecta mass, and smaller initial ejecta radius, which keep the gas denser near the graphite-condensation temperature. When radioactive heating and radiative cooling are included, explosions with Eexp∼1050 erg and MNi≲10−3 M⊙ can form $1−10\,μ{\rm m}$ graphite grains in the ejected helium layer or carbon-oxygen core, whereas Eexp∼1051 erg models do not. These results suggest that micron-sized presolar supernova graphite preferentially forms in faint-supernova-like explosions with low explosion energies, little ejected nickel, and helium layer or carbon-oxygen core ejecta.
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BibTeX
@misc{shinoda2026formation,
title = {{Formation of Micron-sized Presolar Graphite Grains in Low-energy Supernova Ejecta}},
author = {Kengo Shinoda and Ryo Tazaki and Takato Tokuno and Yudai Suwa},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.41948},
eprint = {2610.41948},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.41948},
}
RIS
TY - UNPB
TI - Formation of Micron-sized Presolar Graphite Grains in Low-energy Supernova Ejecta
AU - Kengo Shinoda
AU - Ryo Tazaki
AU - Takato Tokuno
AU - Yudai Suwa
PY - 2026
DA - 2026/10/30
PB - arXiv
DO - 10.48550/arxiv.2610.41948
UR - https://arxiv.org/abs/2610.41948
AB - Presolar graphite grains with supernova isotopic signatures provide direct evidence that large graphite grains formed in supernova ejecta. However, theoretical calculations of dust formation in supernovae have typically predicted graphite grains smaller than 0.1 μm, leaving unclear the physical conditions required to form those grains with radii of order 1 μm. We systematically investigate graphite nucleation and growth in expanding supernova ejecta by varying the explosion energy, ejecta mass, initial ejecta radius, and ejected ^56Ni mass. We use a simplified one-zone model that follows the temperature and density evolution including adiabatic cooling, radiative cooling, and heating by radioactive nickel. We show that the final graphite grain size is mainly determined by the product of the mass density of atomic carbon available for grain growth and the local cooling timescale, both evaluated at a reference temperature of 2000 K. Our models show that graphite growth is favored by lower explosion energy, larger ejecta mass, and smaller initial ejecta radius, which keep the gas denser near the graphite-condensation temperature. When radioactive heating and radiative cooling are included, explosions with E_exp∼10^50 erg and M_Ni≲10^−3 M_⊙ can form $1−10\,μ{\rm m}$ graphite grains in the ejected helium layer or carbon-oxygen core, whereas E_exp∼10^51 erg models do not. These results suggest that micron-sized presolar supernova graphite preferentially forms in faint-supernova-like explosions with low explosion energies, little ejected nickel, and helium layer or carbon-oxygen core ejecta.
ER -