Astrophysics

Is Dark Matter Really Matter?

Jun-Qian Jiang, Arman Shafieloo

Featured August 8, 2026

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Simply

By letting both dark matter and dark energy properties change, the study finds that dark matter might have a tiny pressure, challenging the standard model and showing how these 'dark' components are deeply linked.

In depth

The study challenges the standard cosmological model's assumptions that dark matter is pressureless (

w_{D M} = 0

) and dark energy is a cosmological constant (

w_{D E} = - 1

). By jointly varying these equations of state using DESI DR2, DES supernovae, and CMB data, the authors find that both standard values are disfavored at approximately

2 σ

. This suggests a degeneracy where a positive

w_{D M}

can compensate for a dark energy equation of state

w_{D E} > - 1

, potentially reinterpreting observed phantom crossing preferences.

Key Takeaways

1
When the equations of state for dark matter ( $w_{D M}$ ) and dark energy ( $w_{D E}$ ) are varied simultaneously, both standard $Λ$ CDM values ( $w_{D M} = 0$ , $w_{D E} = - 1$ ) are disfavored at approximately $2 σ$ .
2
The apparent preference for phantom crossing in dark energy models can be absorbed by allowing a non-zero $w_{D M}$ , suggesting a degeneracy between the dark matter and dark energy sectors.
3
The Padé-w + $w_{DM}$ model, which describes non-phantom quintessence dark energy with a free dark matter equation of state, provides the best fit to the data among the tested parameterizations.

Conceptual Flow

HIGH LEVEL

Methodology: Testing Dark Sector Assumptions

The researchers checked if dark matter and dark energy act exactly as we thought, or if they have slightly different behaviors.

Universe Data

Standard Ideas

Compare & Adjust

New Dark Matter Rules

New Dark Energy Rules

Results: Interconnected Dark Properties

They found that dark matter might have a tiny pressure, and this changes how we understand dark energy, showing they are connected.

Dark Matter Pressure = Zero

Dark Energy = Constant

Not Quite Right

Dark Matter Has Pressure

Dark Energy Can Change