Undergrad Can magnetic fields explain anomalous galaxy rotation curves?

[elcaro]

TL;DR

The anomolous behaviour of galaxies rotation curves is predominantly attributed to the existence of dark matter or to modified gravity. But an alternative explenation for the anomalous rotation curves could be formed by magnetic fields

Magnetic fields as an alternative explanation for the rotation curves of spiral galaxies ​

​

ABSTRACT
THE flat rotation curves of spiral galaxies are usually regarded as the most convincing evidence for dark matter. The assumption that gravity alone is responsible for the motion of gas beyond the visible disks of galaxies leads directly to the conclusion that there must be perhaps 10 times as much dark matter as visible matter. Other forces besides gravity are usually neglected, as order-of-magnitude arguments seem to suggest they cannot be important. The existence of dark matter is, however, so important an issue that we believe it is wise to consider other possibilities. Here we argue that an azimuthal magnetic field can carry slightly ionized gas with the general galactic rotation, rendering dark matter unnecessary (a related idea was first proposed by Nelson1). For the illustrative case of M31, a magnetic field of 6 μG is required, and the synchrotron emission of relativistic electrons in this field is compatible with the observations.

​

https://www.researchgate.net/publication/336378361_Effect_of_magnetic_field_on_the_rotation_curves_of_spiral_galaxies​

​

 

[kimbyd]

This sounds like a complete non-starter. The much more convincing evidence for dark matter stems not from galactic rotation curves, but from galaxy clusters and the CMB in particular. Both of which would have far, far less of an organized magnetic field than do spiral galaxies.

 

[ohwilleke]

Almost certainly not. We are very good at measuring electromagnetic fields and their indirect effects and haven't seen them. And, most of the things affected by phenomena attributed to dark matter are electromagnetically neutral.

The idea may have made sense in 1992 (a publication in the premier journal Nature isn't made available to people who are crackpots at the time they're doing their work), but 19 years later, we have far more observations and if it was viable it would have been pursued more actively in that time frame.

For example, a 2020 paper re-evaluated the hypothesis in light of dwarf galaxies and concluded that magnetic fields could not account for all of the effects attributed to dark matter, although it could conceivably account for some portion of the effect. https://ui.adsabs.harvard.edu/abs/2020AIPC.2234d0028W/abstract

Another paper ruling out this hypothesis in 2013 is https://ui.adsabs.harvard.edu/abs/2013MNRAS.433.2172S/abstract

At most papers have found that magnetic fields are a non-negligible factor that shouldn't be completely disregarded when trying to estimate the true dark matter attributed portion of the phenomena.