M. E. Caplan
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View article: MESA-QUEST: Tracing the formation of direct collapse black hole seeds via quasi-stars
MESA-QUEST: Tracing the formation of direct collapse black hole seeds via quasi-stars Open
The origin of the first supermassive black holes (SMBHs) observed at redshifts $z\geq 9$ remains one of the most challenging open questions in astrophysics. Their rapid emergence suggests that massive ``heavy seeds'' must have formed early…
View article: The Sun’s Dark Core: Helioseismic and Neutrino Flux Constraints on a Compact Solar Center
The Sun’s Dark Core: Helioseismic and Neutrino Flux Constraints on a Compact Solar Center Open
As dark matter appears to comprise most of the Galactic mass, some of it may accumulate in the cores of stars, thereby making the Sun a laboratory for constraining various dark matter theories. We consider the effects on the solar structur…
View article: MESA-QUEST: Modeling Quasi-stars in MESA
MESA-QUEST: Modeling Quasi-stars in MESA Open
Supermassive black hole formation remains an unsolved problem. Quasi-stars have been suggested as a viable heavy-seeding mechanism. In this work, we implement methods for modeling quasi-stars previously used with the Cambridge STARS code i…
View article: New Molecular Dynamics Methods for Simulating Neutron Star Crusts with Superfluid Vortices
New Molecular Dynamics Methods for Simulating Neutron Star Crusts with Superfluid Vortices Open
Superfluid vortices in neutron star crusts are thought to be pinned to the lattice of nuclei in the crust. The unpinning of superfluid vortices in spin glitches therefore motivates us to study the vortex-crust interaction explicitly with m…
View article: No Evidence of Anomalous Diffusion in Yukawa Crystals
No Evidence of Anomalous Diffusion in Yukawa Crystals Open
Diffusion in Yukawa crystals is stochastic due to the thermally activated formation of vacancy-interstitial pairs, which have poor statistics in simulations. This makes it difficult to argue if Yukawa crystals exhibit normal diffusion, or …
View article: The Sun's Dark Core: Helioseismic and neutrino flux constraints on a compact solar center
The Sun's Dark Core: Helioseismic and neutrino flux constraints on a compact solar center Open
As dark matter appears to comprise most of the Galactic mass, some of it may accumulate in the cores of stars, thereby making the Sun a laboratory for constraining various dark matter theories. We consider the effects on the solar structur…
View article: No Evidence of Anomalous Diffusion in Yukawa Crystals
No Evidence of Anomalous Diffusion in Yukawa Crystals Open
Diffusion in Yukawa crystals is stochastic due to the thermally activated formation of vacancy-interstitial pairs, which have poor statistics in simulations. This makes it difficult to argue if Yukawa crystals exhibit normal diffusion, or …
View article: Possible constraints on asteroid-mass primordial black holes from Solar system cratering
Possible constraints on asteroid-mass primordial black holes from Solar system cratering Open
Due to their novel cratering mechanism, primordial black holes (PBHs) in the asteroid mass window of about $10^{17}$ to $10^{19}$ g can produce surface features on Solar system bodies that are distinguishable from traditional impact crater…
View article: Formation of Sub-Chandrasekhar-mass Black Holes and Red Stragglers via Hawking Stars in Ultrafaint Dwarf Galaxies
Formation of Sub-Chandrasekhar-mass Black Holes and Red Stragglers via Hawking Stars in Ultrafaint Dwarf Galaxies Open
Primordial black holes (PBHs) in the asteroid mass window from 10 −16 M ⊙ to 10 −10 M ⊙ are currently a popular dark matter candidate. If they exist, some stars would capture them upon formation, and they would slowly accrete the star over…
View article: Universal Diffusion in Coulomb Crystals
Universal Diffusion in Coulomb Crystals Open
Diffusion coefficients for crystallized Coulomb plasmas are essential microphysics input for modeling white dwarf cores and neutron star crusts but are poorly understood. In this work we present a model for diffusion in Coulomb crystals. W…
View article: Formation of Sub-Chandrasekhar Mass Black Holes and Red Stragglers via Hawking Stars in Ultra-Faint Dwarf Galaxies
Formation of Sub-Chandrasekhar Mass Black Holes and Red Stragglers via Hawking Stars in Ultra-Faint Dwarf Galaxies Open
Presently, primordial black holes (PBHs) in the asteroid-mass window from $10^{-16}$ M$_\odot$ to $10^{-10}$ M$_\odot$ are a popular dark matter candidate. If they exist, some stars would capture them upon formation, and they would slowly …
View article: Is there a black hole in the center of the Sun?
Is there a black hole in the center of the Sun? Open
There is probably not a black hole in the center of the Sun. Despite this detail, our goal in this work to convince the reader that this question is interesting and that work studying stars with central black holes is well motivated. If pr…
View article: Is there a black hole in the center of the Sun?
Is there a black hole in the center of the Sun? Open
There is probably not a black hole in the center of the sun. Despite this detail, our goal in this work to convince the reader that this question is interesting and that work studying stars with central black holes is well motivated. If pr…
View article: Diffusion Coefficients of <sup>56</sup>Fe in C–O and O–Ne White Dwarfs
Diffusion Coefficients of <sup>56</sup>Fe in C–O and O–Ne White Dwarfs Open
The diffusion coefficients of neutron rich nuclei in crystallizing white dwarf (WD) stars are essential microphysics input for modeling the evolution of the composition profile. Recently, molecular dynamics simulations have been used to co…
View article: Diffusion Coefficients of $^{56}$Fe in C-O and O-Ne White Dwarfs
Diffusion Coefficients of $^{56}$Fe in C-O and O-Ne White Dwarfs Open
The diffusion coefficients of neutron rich nuclei in crystallizing white dwarf (WD) stars are essential microphysics input for modeling the evolution of the composition profile. Recently, molecular dynamics simulations have been used to co…
View article: Distillation of <sup>56</sup>Fe in Ultramassive O–Ne White Dwarfs
Distillation of <sup>56</sup>Fe in Ultramassive O–Ne White Dwarfs Open
When white dwarfs freeze, the plasma mixtures inside them undergo separation processes that can produce radical changes in the composition profile of the star. The abundance of neutron-rich elements, such as 22 Ne or 56 Fe, determines whet…
View article: Distillation of $^{56}$Fe in Ultramassive O-Ne White Dwarfs
Distillation of $^{56}$Fe in Ultramassive O-Ne White Dwarfs Open
When white dwarfs freeze the plasma mixtures inside them undergo separation processes which can produce radical changes in the composition profile of the star. The abundance of neutron rich elements, such as $^{22}$Ne or $^{56}$Fe, determi…
View article: Horizons: nuclear astrophysics in the 2020s and beyond
Horizons: nuclear astrophysics in the 2020s and beyond Open
Nuclear astrophysics is a field at the intersection of nuclear physics and astrophysics, which seeks to understand the nuclear engines of astronomical objects and the origin of the chemical elements. This white paper summarizes progress an…
View article: Nuclear fission reaction simulations in compact stars
Nuclear fission reaction simulations in compact stars Open
Type-Ia supernovas are powerful stellar explosions that provide important distance indicators in cosmology. Recently, we proposed a new Type-Ia supernova mechanism that involves a nuclear fission chain-reaction in an isolated white dwarf […
View article: Accurate diffusion coefficients for dense white dwarf plasma mixtures
Accurate diffusion coefficients for dense white dwarf plasma mixtures Open
Diffusion coefficients are essential microphysics inputs for modelling white dwarf evolution, as they impact phase separation at crystallization and sedimentary heat sources. Present schemes for computing diffusion coefficients are accurat…
View article: Nuclear fission reaction simulations in compact stars
Nuclear fission reaction simulations in compact stars Open
Type-Ia supernovae (SN Ia) are powerful stellar explosions that provide important distance indicators in cosmology. Recently, we proposed a new SN Ia mechanism that involves a nuclear fission chain-reaction in an isolated white dwarf [PRL …
View article: Cooling Delays from Iron Sedimentation and Iron Inner Cores in White Dwarfs
Cooling Delays from Iron Sedimentation and Iron Inner Cores in White Dwarfs Open
Do white dwarfs have inner cores made of iron? Neutron-rich nuclei like 56 Fe experience a net gravitational force and sediment toward the core. Using new phase diagrams and molecular dynamics simulations, we show that 56 Fe should separat…
View article: Nuclear fission chain reaction in cooling white dwarf stars
Nuclear fission chain reaction in cooling white dwarf stars Open
The first solids that form as a white dwarf (WD) starts to crystallize are expected to be greatly enriched in actinides. Previously [PRL 126, 1311010] we found that these solids might support a nuclear fission chain reaction that could ign…
View article: Crater morphology of primordial black hole impacts
Crater morphology of primordial black hole impacts Open
In this work, we propose a novel campaign for constraining relativistically compact massive compact halo object (MACHO) dark matter, such as primordial black holes (PBHs), using the Moon as a detector. PBHs of about 1019 to 1022 g may be s…
View article: Thermal fluctuations in nuclear pasta
Thermal fluctuations in nuclear pasta Open
Despite their astrophysical relevance, nuclear pasta phases are relatively\nunstudied at high temperatures. We present molecular dynamics simulations of\nsymmetric nuclear matter with several topologies of `lasagna' at a range of\ntemperat…
View article: Precise diffusion coefficients for white dwarf astrophysics
Precise diffusion coefficients for white dwarf astrophysics Open
Observations of Galactic white dwarfs with Gaia have allowed for unprecedented modelling of white dwarf cooling, resolving core crystallization, and sedimentary heating from neutron-rich nuclei. These cooling sequences are sensitive to the…
View article: Actinide Crystallization and Fission Reactions in Cooling White Dwarf Stars
Actinide Crystallization and Fission Reactions in Cooling White Dwarf Stars Open
The first solids that form as a cooling white dwarf (WD) starts to crystallize are expected to be greatly enriched in actinides. This is because the melting points of WD matter scale as Z^{5/3} and actinides have the largest charge Z. We e…
View article: Fast neutrino cooling of nuclear pasta in neutron stars: Molecular dynamics simulations
Fast neutrino cooling of nuclear pasta in neutron stars: Molecular dynamics simulations Open
The direct Urca process of rapid neutrino emission can occur in nonuniform nuclear pasta phases that are expected in the inner crusts of neutron stars. Here, the periodic potential for a nucleon in nuclear pasta allows momentum conservatio…
View article: Black dwarf supernova in the far future
Black dwarf supernova in the far future Open
In the far future, long after star formation has ceased, the universe will be populated by sparse degenerate remnants, mostly white dwarfs, though their ultimate fate is an open question. These white dwarfs will cool and freeze solid into …
View article: Structure of multicomponent Coulomb crystals
Structure of multicomponent Coulomb crystals Open
Coulomb plasmas crystallize in a number of physical systems, such as dusty plasmas, neutron star crusts, and white dwarf cores. The crystal structure of the one-component and binary plasma has received significant attention in the literatu…