Bibliographic record
Abstract
Elements heavier than Helium are expected to sink quickly on white dwarf atmospheres, yet are observed on 25-50 per cent of white dwarfs, indicating that these stars are accreting material from their planetary systems. First, the scenario of an Oort cloud polluting white dwarfs is studied. The dynamics of Oort cloud comets around white dwarfs with the effects of Galactic tide and a massive companion, either stellar or planetary, is characterised through numerical and analytic methods. A fast, direct N-body simulation including these dynamical effects is developed, which can simulate a large number of comets to resolve the rate of comets entering a white dwarf’s Roche limit over one gigayear. Through simulations, pollution rates by Oort cloud objects onto white dwarfs with and without planetary companions are found to broadly produce observed pollution rates. Second, an upgrade to the adaptive timestep criterion of IAS15, a numerical integrator, is presented to improve N-body simulation efficiency. Third, the impact rate between interstellar objects and neutron stars is considered to explain another phenomenon — fast radio bursts. Various observational predictions of this radiation emission are discussed. Fourth, the evolution of cometary volatiles as a Sun-like star evolves post-main sequence is studied. The volatile budget in Solar system long-period comet reservoirs are simulated, along with debris discs at various distances for exoplanetary systems. A coupled stellar-dynamical-thermal-mass evolution model is developed to resolve comets on the most eccentric orbits around a highly luminous star. We find that debris discs at different distances retain volatiles and hypervolatiles at varying fractions, depending on distance and object sizes, though all show signs of volatile depletion. This finding supports observations that many white dwarfs are polluted with rocky materials. This thesis seeks to explain phenomena around compact objects and consider how observations can probe small bodies across the Universe.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".