New cosmic observations can't be explained by classical theory of gravity

The observations could not be explained by Newton's law of universal gravitation. An alternative theory of gravity might provide the answer.
Chris Young
Study author Prof. Dr. Pavel Kroupa.
Study author Prof. Dr. Pavel Kroupa

Volker Lannert / University of Bonn 

Astrophysicists observed mysterious behavior in star clusters that could lead to a rewrite of fundamental principles of the theory of gravity and even disprove the existence of dark matter, a press release explains.

The new findings challenge existing preconceptions based on widely-accepted principles from Newton's law of universal gravitation, which explain the large-scale structure and movements of the universe.

It also lends weight to a controversial fringe theory that was able to accurately predict the behavior observed by the group of scientists.

Star cluster observations yield surprising results

An international team of astrophysicists made the discovery when they were investigating open star clusters. These are a type of star cluster in which thousands of young stars are born in a large cloud of dust and gas. These clusters eventually dissolve, and the newborn stars form into two "tails," one of which is positioned in front of the cluster and the other behind.

“According to Newton's laws of gravity, it's a matter of chance in which of the tails a lost star ends up," said Dr. Jan Pflamm-Altenburg, co-author of the study. “So both tails should contain about the same number of stars. However, in our work we were able to prove for the first time that this is not true: In the clusters we studied, the front tail always contains significantly more stars nearby to the cluster than the rear tail."

In order to carry out their investigation, the researchers had to devise a method for determining which stars belong to which of the cluster's tails. They used their new technique, named the Jerabkova-compact-convergent-point (CCP) method, on data of four open star clusters gathered by surveys, including the Gaia mission.

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The scientists were surprised to find that, in all four clusters, the tail in front of the clusters had many more stars than the one that was trailing behind. Their observations directly contradicted Isaac Newton's laws.

The team then decided to simulate the cluster using a different hypothesis called Modified Newtonian Dynamics (MOND). According to this model, gravity's effects are stronger at low accelerations than Newton's laws suggest. After carrying out their simulations, the scientists found that the MOND model predictions very closely resembled their real-life observations.

"Put simply, according to MOND, stars can leave a cluster through two different doors," said Professor Pavel Kroupa, first author of the study. “One leads to the rear tidal tail, the other to the front. However, the first is much narrower than the second – so it’s less likely that a star will leave the cluster through it. Newton's theory of gravity, on the other hand, predicts that both doors should be the same width.”

All of this is also in line with the fact that star clusters in nearby galaxies have been observed to be dissolving faster than Newton's laws predict. That faster rate is also better explained by the MOND model.

New observations cast dark matter theory into doubt

The new discovery could cause a paradigm shift in the world of astrophysics by completely changing a widely-held theory about one of the largest forces in the universe. If the MOND model is true, then dark matter does not exist.

Dark matter was first theorized in the 1930s to explain movements of stars and galaxies that couldn't be explained by Newton's laws of gravity. Many stars and galaxies were moving too fast based on their mass, so scientists believed that huge amounts of invisible mass, described as dark matter, must provide the answer.

Still, the dark matter theory is still widely accepted, and a lot of indirect evidence does still point to its existence. MOND, meanwhile, isn't widely accepted by the scientific community, and it is disputed by many experts. That could potentially change, though. The team behind the new findings said they will continue to investigate by applying the MOND model to other observations. If they continue to draw up compelling evidence, their discoveries could have massive, far-ranging implications for the entire field of physics.

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