How does dark energy work against gravity

The rotation of gas-rich galaxies correlates with the visible mass - in accordance with an alternative theory of gravity

Spiral galaxy

College Park (USA) - The rotation of gas-rich galaxies can be described by a simple connection with the mass of the star system. This is shown by measurements on 47 galaxies, which an American astronomer will soon be presenting in the journal "Physical Review Letters". Such a connection is not to be expected in the standard model of cosmology, in which galaxies predominantly consist of dark matter. However, the observed correlation is a natural prediction of a controversial alternative theory for gravity, modified Newtonian dynamics, or MOON for short.

"Dark matter may not exist," concludes Stacy McGaugh of the University of Maryland. If so, according to the researcher, it is a challenge to explain the observed correlation - because it is not a natural consequence of the Standard Model. According to this idea, held by the majority of astronomers, around 80 percent of the mass in the universe is invisible. This dark matter consists of previously unknown elementary particles that interact with normal, visible matter only through gravity.

As early as 1983, the Israeli physicist Mordehai Milgrom proposed an alternative to dark matter with his MOON theory. The core of MOON is the assumption that gravitation is stronger at very weak accelerations than predicted by Newton's law of gravitation - and thus simulates more mass, especially in the outer regions of galaxies. Previous attempts to check the MOON through observations were based on the visible mass of galaxies in the form of stars. But it is difficult to estimate the mass of stars based on their radiation. As a result, these measurements were imprecise and vulnerable.

McGaugh has now avoided this problem by choosing galaxies whose mass is dominated by hydrogen gas rather than stars. The mass of this gas can be measured directly and therefore provides much more accurate results. For the 47 star systems examined, the researcher finds a strong correlation between the galaxy mass and the rotation in the outer areas. The crucial thing about McGaugh's work is not that it provides evidence for MOON, stresses astrophysicist Jerry Sellwood of Rutgers University in New Jersey in the online portal of the journal "Science", but that it points to a phenomenon that is not related to dark matter can explain.