Spiral galaxies rotate at such a high speed that the gravity calculated only from their visible stars could not prevent them from dispersing.
To solve this puzzle, physicists have postulated the existence of an invisible substance, dark matter, which neither emits nor absorbs light. This hypothetical entity, constituting most of the cosmic mass, would provide the extra attraction needed to bind galaxies. Yet this component remains elusive, having never been confirmed by direct observation so far.
The Messier 33 galaxy, shown with a dark matter halo (left) and without this component (right), illustrating competing models.
Credit: ESO/S. Brunier
A recent study, led by Naman Kumar from the Indian Institute of Technology and published in
Physical Review Letters B, proposes a different path. This research challenges the need for dark matter by examining the hypothesis that gravity behaves differently at galactic scales. The approach is based on advanced concepts from theoretical physics.
The researcher used quantum field theory to scrutinize gravity at tiny scales, close to the wavelength of infrared light. In this framework, called the infrared scheme, the gravitational force would no longer strictly follow the inverse square law of distance. Instead, it would exert a more persistent influence over long distances, which could explain the rapid rotation of galaxies.
This alteration of gravitational properties could explain the observations without resorting to dark matter halos. Thus, the high velocities of stars located at the outskirts of galaxies, a persistent puzzle, would receive a natural interpretation.
The model proposed by Naman Kumar will nevertheless need to be tested against other data sets, such as those from gravitational lenses where light is bent by large masses. If validated, it could transform our view of cosmic evolution and simplify current models.
This proposal thus encourages the scientific community to examine alternative avenues and reconsider some well-entrenched concepts, which could lead to new advances in astrophysics.
Modified gravity: a line of research
Modified gravity theories propose that the laws of gravitation may not be immutable and could evolve depending on the scale considered. These frameworks allow for adjustments to account for observed phenomena.
Naman Kumar's approach, based on quantum field theory, suggests that the gravitational force could exhibit a different dependence on distance than that derived from currently used equations, with a stronger, longer-range attraction.
If this conception is verified, it could account for the rapid rotation of galaxies and other anomalies without invoking dark matter. This would offer a simpler representation of the Universe, by reducing the number of unknown entities and directly linking observations to the properties of gravity.
For now, these theories must be rigorously tested against all available data, from laboratory experiments to cosmological observations.