Compare · The Dark Universe

Primordial Black Holes vs Superfluid Dark Matter

Dark Matter Candidates· within family

	Primordial Black Holes Frontier	Superfluid Dark Matter Frontier
Proposed	1974 / 1975	2015
Key figures	Bernard Carr, Stephen Hawking	Lasha Berezhiani, Justin Khoury
In one sentence	Black holes that formed in the first fraction of a second after the Big Bang, from regions where the matter density was unusually high. They gravitate exactly like dark matter would. Strict constraints from microlensing and gravitational waves allow only a sub-fraction of dark matter to be PBHs in most mass windows.	Lasha Berezhiani and Justin Khoury proposed in 2015 a hybrid dark matter framework: a particle that condenses into a superfluid phase in the central regions of galaxies, producing MOND-like phenomenology on galactic scales via phonon excitations, while remaining ordinary cold dark matter on cosmological scales. Berezhiani and Khoury's 2015 and 2016 papers (Phys. Rev. D 92, 103510 and Phys. Lett. B 753, 639) attempt to bridge particle-DM ontology with MOND-style modified-gravity phenomenology in a single framework.
Predictions	Microlensing events: temporary brightening of background stars as a PBH passes in front, with event rate and timescale set by PBH mass and abundance Gravitational wave signals from PBH-PBH binary mergers, especially in mass gaps where stellar evolution predicts no black holes (~3-5 solar masses, ~50-100 solar masses pair-instability gap) CMB and reionization constraints: gas accretion onto PBHs in the early universe would deposit energy, affecting the CMB temperature and reionization history Diffuse gamma-ray background from [[Hawking radiation]] of very-low-mass PBHs (M < 10^14 g) that would have evaporated by now	Galactic rotation curves are explained by phonon excitations in the superfluid phase of dark matter; the framework reproduces the MOND empirical relations on galactic scales Galaxy cluster dynamics are governed by standard CDM (the superfluid phase is destroyed at cluster densities), reproducing the empirical successes of dark matter on large scales Cosmological observables (CMB, large-scale structure) are essentially CDM, since the superfluid phase exists only in dense galaxy interiors Specific predictions for the transition radius between superfluid and normal CDM phases in each galaxy, depending on the central density and the dark-matter particle properties
Where it breaks	Microlensing surveys (OGLE, EROS, Subaru HSC) and dynamical limits exclude PBHs as 100% of dark matter across the asteroid-to-solar-mass range almost everywhere Most LIGO/Virgo events have plausible astrophysical alternative explanations (stellar BH binary formation in dense globular clusters or galactic nuclei) Many formation models require fine-tuned primordial power spectra or specific inflationary features The asteroid-mass window is hard to probe directly: no current microlensing experiment is sensitive at that scale, leaving the most-allowed window also the least-tested	Galaxy cluster constraints (specifically, the Bullet Cluster and related merging-cluster observations) place upper bounds on the dark-matter particle's self-interaction cross-section; the superfluid framework's parameter space is constrained by these observations The framework requires fine-tuning the dark-matter particle's mass and self-interaction parameters to specific ranges that enable superfluid condensation in galaxies but not in clusters; the deep physical motivation for these values is not provided Citation counts for the framework remain below what some researchers consider significant; its current impact is more modest than the bridge-framework ambition suggests Alternative hybrid frameworks (Verlinde Entropic Gravity, modified-inertia variants of MOND) cover similar territory; the choice among bridge frameworks is not currently observationally constrained
Key unresolved problem	The untestable window problem: the only mass range where primordial black holes could still be all the dark matter, roughly asteroid-sized, is exactly the one no current star-brightening (microlensing) survey is sensitive enough to check.	The fine-tuning problem: the particle's mass and interactions must sit in a very narrow range so the dark matter turns into a frictionless superfluid inside galaxies but not in clusters, and there is no deeper reason those exact values should hold.
Reader vote	No votes yet	No votes yet

Primordial Black Holes

1974 / 1975 · Frontier

Superfluid Dark Matter

2015 · Frontier

Proposed

1974 / 1975

2015

Key figures

Bernard Carr, Stephen Hawking

Lasha Berezhiani, Justin Khoury

In one sentence

Black holes that formed in the first fraction of a second after the Big Bang, from regions where the matter density was unusually high. They gravitate exactly like dark matter would. Strict constraints from microlensing and gravitational waves allow only a sub-fraction of dark matter to be PBHs in most mass windows.

Lasha Berezhiani and Justin Khoury proposed in 2015 a hybrid dark matter framework: a particle that condenses into a superfluid phase in the central regions of galaxies, producing MOND-like phenomenology on galactic scales via phonon excitations, while remaining ordinary cold dark matter on cosmological scales. Berezhiani and Khoury's 2015 and 2016 papers (Phys. Rev. D 92, 103510 and Phys. Lett. B 753, 639) attempt to bridge particle-DM ontology with MOND-style modified-gravity phenomenology in a single framework.

Predictions

Microlensing events: temporary brightening of background stars as a PBH passes in front, with event rate and timescale set by PBH mass and abundance
Gravitational wave signals from PBH-PBH binary mergers, especially in mass gaps where stellar evolution predicts no black holes (~3-5 solar masses, ~50-100 solar masses pair-instability gap)
CMB and reionization constraints: gas accretion onto PBHs in the early universe would deposit energy, affecting the CMB temperature and reionization history
Diffuse gamma-ray background from [[Hawking radiation]] of very-low-mass PBHs (M < 10^14 g) that would have evaporated by now

Galactic rotation curves are explained by phonon excitations in the superfluid phase of dark matter; the framework reproduces the MOND empirical relations on galactic scales
Galaxy cluster dynamics are governed by standard CDM (the superfluid phase is destroyed at cluster densities), reproducing the empirical successes of dark matter on large scales
Cosmological observables (CMB, large-scale structure) are essentially CDM, since the superfluid phase exists only in dense galaxy interiors
Specific predictions for the transition radius between superfluid and normal CDM phases in each galaxy, depending on the central density and the dark-matter particle properties

Where it breaks

Microlensing surveys (OGLE, EROS, Subaru HSC) and dynamical limits exclude PBHs as 100% of dark matter across the asteroid-to-solar-mass range almost everywhere
Most LIGO/Virgo events have plausible astrophysical alternative explanations (stellar BH binary formation in dense globular clusters or galactic nuclei)
Many formation models require fine-tuned primordial power spectra or specific inflationary features
The asteroid-mass window is hard to probe directly: no current microlensing experiment is sensitive at that scale, leaving the most-allowed window also the least-tested

Galaxy cluster constraints (specifically, the Bullet Cluster and related merging-cluster observations) place upper bounds on the dark-matter particle's self-interaction cross-section; the superfluid framework's parameter space is constrained by these observations
The framework requires fine-tuning the dark-matter particle's mass and self-interaction parameters to specific ranges that enable superfluid condensation in galaxies but not in clusters; the deep physical motivation for these values is not provided
Citation counts for the framework remain below what some researchers consider significant; its current impact is more modest than the bridge-framework ambition suggests
Alternative hybrid frameworks (Verlinde Entropic Gravity, modified-inertia variants of MOND) cover similar territory; the choice among bridge frameworks is not currently observationally constrained

Key unresolved problem

The untestable window problem: the only mass range where primordial black holes could still be all the dark matter, roughly asteroid-sized, is exactly the one no current star-brightening (microlensing) survey is sensitive enough to check.

The fine-tuning problem: the particle's mass and interactions must sit in a very narrow range so the dark matter turns into a frictionless superfluid inside galaxies but not in clusters, and there is no deeper reason those exact values should hold.

Reader vote

No votes yet