Nonparametric inference of neutron star composition, equation of state, and maximum mass with GW170817
Bibliographic record
Abstract
The detection of GW170817 in gravitational waves provides unprecedented constraints on the equation of state (EOS) of the ultradense matter within the cores of neutron stars (NSs). We extend the nonparametric analysis first introduced by Landry and Essick (2019), and confirm that GW170817 favors soft EOSs. We infer macroscopic observables for a canonical $1.4\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ NS, including the tidal deformability ${\mathrm{\ensuremath{\Lambda}}}_{1.4}={211}_{\ensuremath{-}137}^{+312}$ $({491}_{\ensuremath{-}181}^{+216})$ and radius ${R}_{1.4}=10.8{6}_{\ensuremath{-}1.42}^{+2.04}$ $({12.51}_{\ensuremath{-}0.88}^{+1.00})\text{ }\mathrm{km}$, as well as the maximum mass for nonrotating NSs ${M}_{\mathrm{max}}=2.06{4}_{\ensuremath{-}0.134}^{+0.260}$ $({2.017}_{\ensuremath{-}0.087}^{+0.238})\text{ }{M}_{\ensuremath{\bigodot}}$, with nonparametric priors loosely (tightly) constrained to resemble candidate EOSs from the literature. Furthermore, we find weak evidence that GW170817 involved at least one NS based on gravitational-wave data alone (${B}_{\mathrm{BBH}}^{\mathrm{NS}}=3.3\ifmmode\pm\else\textpm\fi{}1.4$), consistent with the observation of electromagnetic counterparts. We also investigate GW170817's implications for the maximum spin frequency of millisecond pulsars, and find that the fastest known pulsar is spinning at more than 50% of its breakup frequency at 90% confidence. We additionally find modest evidence in favor of quark matter within NSs, and GW170817 favors the presence of at least one disconnected hybrid star branch in the mass-radius relation over a single stable branch by a factor of 2. Assuming there are multiple stable branches, we find a suggestive posterior preference for a sharp softening around nuclear density followed by stiffening around twice nuclear density, consistent with a strong first-order phase transition. While the statistical evidence in favor of new physics within NS cores remains tenuous with GW170817 alone, these tantalizing hints reemphasize the promise of gravitational waves for constraining the supranuclear EOS.
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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 | 0.004 | 0.015 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| 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".