Fuzzy cold dark matter is a hypothetical form of
cold dark matter
In cosmology and physics, cold dark matter (CDM) is a hypothetical type of dark matter. According to the current standard model of cosmology, Lambda-CDM model, approximately 27% of the universe is dark matter and 68% is dark energy, with only a sm ...
proposed to solve the
cuspy halo problem
The cuspy halo problem (also known as the core-cusp problem) is a discrepancy between the inferred dark matter density profiles of low-mass galaxies and the density profiles predicted by cosmological N-body simulations. Nearly all simulations form ...
. It would consist of extremely light
scalar particles with masses on the order of
eV; so a
Compton wavelength
The Compton wavelength is a quantum mechanical property of a particle, defined as the wavelength of a photon whose energy is the same as the rest energy of that particle (see mass–energy equivalence). It was introduced by Arthur Compton in 1 ...
on the order of 1
light year
A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distance, astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by t ...
. Fuzzy cold dark matter halos in dwarf galaxies would manifest wave behavior on astrophysical scales, and the cusps would be avoided through the
Heisenberg uncertainty principle
The uncertainty principle, also known as Heisenberg's indeterminacy principle, is a fundamental concept in quantum mechanics. It states that there is a limit to the precision with which certain pairs of physical properties, such as position a ...
.
The wave behavior leads to interference patterns, spherical
soliton
In mathematics and physics, a soliton is a nonlinear, self-reinforcing, localized wave packet that is , in that it preserves its shape while propagating freely, at constant velocity, and recovers it even after collisions with other such local ...
cores in
dark matter halo
In modern models of physical cosmology, a dark matter halo is a basic unit of cosmological structure. It is a hypothetical region that has decoupled from cosmic expansion and contains gravitationally bound matter.
A single dark matter halo ma ...
centers,
and cylindrical soliton-like cores in dark matter cosmic web filaments.
Fuzzy cold dark matter is a limit of
scalar field dark matter without self-interaction.
Fuzzy cold dark matter is sometimes called wave DM, or simply fuzzy dark matter (FDM).
It is governed by the
Schrödinger–Poisson equation.
Fuzzy dark matter models are the simplest class of the ultralight dark matter models; the only free parameter is the particle mass. (In "ultralight dark matter models", the dark matter of a galaxy
condenses
Condensation is the change of the state of matter from the gas phase into the liquid phase, and is the reverse of vaporization. The word most often refers to the water cycle. It can also be defined as the change in the state of water vapor ...
into a
superfluid
Superfluidity is the characteristic property of a fluid with zero viscosity which therefore flows without any loss of kinetic energy. When stirred, a superfluid forms vortex, vortices that continue to rotate indefinitely. Superfluidity occurs ...
. This requirement greatly constrains the particle mass; for example, the QCD (
Peccei–Quinn)
axion
An axion () is a hypothetical elementary particle originally theorized in 1978 independently by Frank Wilczek and Steven Weinberg as the Goldstone boson of Peccei–Quinn theory, which had been proposed in 1977 to solve the strong CP problem ...
is considered too heavy to condense.) A second approach, where FDM is modified to have simple self-interaction, has been suggested with theories such as self-interacting fuzzy dark matter (SIFDM), repulsive DM, scalar field DM, and fluid dark matter. A third approach, called the "DM superfluid model", focuses on the empirical data for a large-scale
MOND
Modified Newtonian dynamics (MOND) is a theory that proposes a modification of Newton's laws to account for observed properties of galaxies. Modifying Newton's law of gravity results in modified gravity, while modifying Newton's second law resul ...
relation, and then works backwards to determine what types of complicated self-interactions would best produce such a distribution.
New research (2023) has uncovered evidence that fuzzy dark matter, specifically ultralight axions, may better fit gravitational lens data than
WIMP
WiMP is a music streaming service available on mobile devices, tablets, network players and computers. WiMP, standing for "Wireless Music Player," was a music streaming service that emphasized high-quality audio. WiMP offered music and podcast ...
dark matter.
Notes
Dark matter
Hypotheses in physics
{{physical-cosmology-stub