Dynamics and Mass Distribution of Galactic Systems

The dynamics and mass distribution of galactic systems encompass the study of how stars, gas and dark matter interact to shape the motions and structures of galaxies and their larger assemblies. Central to this field is the measurement of rotation curves, which trace the orbital speeds of tracers as a function of radius, revealing the underlying gravitational potential. Observations routinely show that rotation curves remain flat or decline only gently far beyond the visible disc, implying the presence of massive, extended dark matter haloes. On group and cluster scales, the balance between cosmic expansion and gravitational attraction defines boundaries, such as the turnaround radius, beyond which galaxies recede rather than remain bound. Advances in astrometry, spectroscopy and statistical modelling have refined mass estimates from tens of kiloparsecs to megaparsec scales, with implications for galaxy formation, the nature of dark matter and tests of cosmological parameters.

Research from Nature Portfolio

Recent studies have explored an alternative dark matter candidate based on an electron Born self-energy (eBse) model, in which electrons possess both a rest mass and a much larger Born mass arising from their surrounding electric field. In this framework, Born masses interact gravitationally with both the central galactic mass and one another, with a repulsive component stabilising a dark halo of typical radius ~100 kpc. By solving a linearised Poisson–Boltzmann equation, researchers derived a rotational velocity profile that, when combined with contributions from the stellar bulge and disc, reproduces the grand rotation curves of the Milky Way and M31. This composite model offers a concrete example of how novel particle physics concepts can be tested against precise galactic kinematics.

Dynamics and Mass Distribution of Galactic Systems publication trend

The graph below shows the total number of articles in dynamics and mass distribution of galactic systems across all publications each year (not limited to Nature Index journals).

Technical terms

Rotation curve: Graph of orbital velocity versus radius in a galaxy, used to infer the enclosed mass.
Dark matter halo: Extended, roughly spherical distribution of unseen mass surrounding galaxies, inferred from gravitational effects.
Navarro–Frenk–White (NFW) profile: A theoretical density model for dark matter haloes characterised by a central cusp and declining outer slope.
Einasto profile: A model for halo density featuring a continuously varying slope, often fitting outer regions better than NFW.
Keplerian decline: A decrease in orbital velocity proportional to R^–0.5, indicating mass concentrated within the inner regions.
Zero radial acceleration surface: The boundary in an expanding universe at which local gravitational attraction balances cosmic expansion.

References

1. Comparison of a new type of Dark Matter with the Milky Way and M31 grand rotation curves. Scientific Reports (2024).
2. Detection of the Keplerian decline in the Milky Way rotation curve. Astronomy & Astrophysics (2023).
3. The dark matter profile of the Milky Way inferred from its circular velocity curve. Monthly Notices of the Royal Astronomical Society (2024).
4. Galaxy groups in the presence of cosmological constant: Increasing the masses of groups. Physics Letters B (2024).