Astrophysicists made a puzzling discovery while analyzing some star clusters. This discovery defies Newton’s laws of gravitation. Instead, the observations are consistent with predictions of an alternative theory of gravity. (The technical concept of alien gravity.)
The discovery cannot be explained by classical assumptions.
An international team of astrophysicists has made a puzzling discovery while analyzing some star clusters. This discovery defies Newton’s laws of gravitation, the researchers write in their publication. Instead, the observations are consistent with predictions of an alternative theory of gravity. However, this is controversial among experts. The results have now been published in the Monthly Notices of the Royal Astronomical Society. The University of Bonn played a major role in the study.
In their work, the researchers investigated so-called open star clusters, unconnected groups of a few dozen to a few hundred stars found in spiral and irregular galaxies. Open clusters form when thousands of stars are born within a short period of time in a massive gas cloud. When it “ignites”, newcomers from the galaxy blow off the remnants of a gas cloud. In the process, the mass expands significantly. This creates a loose formation of several tens to several thousand stars. Mass is held together by the weak gravitational forces that act among themselves.
“In most cases, open star clusters live only a few hundred million years before they melt,” explains Professor Dr. Pavel Krupa from the Helmholtz Institute for Radiation and Nuclear Physics at the University of Bonn. In the process, stars are regularly lost, which accumulate in the so-called “tidal tails”. One of these tails is pulled behind the block as it travels through space. In turn, the other takes the lead like a spearhead.
Prof. Dr. Pavel Krupa from the Helmholtz Institute for Radiation and Nuclear Physics at the University of Bonn. Credit: Volker Lanert/University of Bonn
“According to Newton’s laws of gravitation, it is a matter of chance which of the tails ends up in the missing star,” explains Dr. Jan Pvalam-Altenberg of the Helmholtz Institute for Radiation and Nuclear Physics. “So both parties should have roughly the same number of stars. However, in our work we were able for the first time to prove that this is not true: in the groups we studied, the front tail always contains more stars close to the mass than the back tail.”
A new method for calculating stars has been developed
Among the millions of stars close to the mass, it has been nearly impossible to determine which ones belong to their tails — until now. “To do this, you have to look at the speed and direction of movement and the age of each of these objects,” Dr. Teresa Yarabkova explains. The research co-author, who received a PhD in Kroupa’s group, recently moved from the European Space Agency (ESA) to the European Southern Observatory in Garching. She developed a method that allowed her to accurately count the stars in their tails for the first time. “So far, five open clusters have been investigated near us, including four by us,” she says. “When we analyzed all the data, we encountered the contradiction with the current theory. The highly accurate survey data from the European Space Agency’s Gaia space mission is indispensable for this.”
In the Hyades star cluster (top), the number of stars (black) in the front tidal tail is much greater than those in the rear. In a computer simulation with MOND (below), a similar picture appears. Credit: AG Kroupa / Uni Bonn
In contrast, the observational data fit better with the theory known for the acronym MOND (“Modified Newtonian Dynamics”) among experts. “Simply put, according to MOND, stars can leave a group through two different doors,” Kroupa explains. “One leads to the rear tail tides, the other forward. However, the first is much narrower than the second – so the star is unlikely to leave the mass through it. On the other hand, Newton’s gravitational theory predicts that both doors should be the same width.
Star clusters are shorter-lived than Newton’s laws predict
The team of astrophysicists has calculated the expected stellar distribution according to MOND. “The results are surprisingly consistent with the observations,” highlights Dr. Ingo Thies, who played a key role in the corresponding simulations. However, we had to resort to relatively simple arithmetic methods to do so. We currently lack the mathematical tools to perform more detailed analyzes of Modified Newtonian dynamics.” However, the simulations also coincided with observations on the other hand: they predicted how long normally open star clusters should remain. This time period is much shorter than expected by Newton’s laws. “This explains a long-known mystery,” notes Kroupa. “Specifically, star clusters in nearby galaxies appear to be disappearing faster than they should.”
However, the MOND theory is not undisputed among experts. Since Newton’s laws of gravitation would not be valid under certain conditions, but would have to be modified, this would have far-reaching consequences for other areas of physics as well. “Then again, it solves many of the problems that cosmology faces today,” explains Kroupa, who is also a member of the interdisciplinary research areas “Modeling” and “Matter” at the University of Bonn. Astrophysicists are now exploring new mathematical methods for more accurate simulations. They can then be used to find more evidence about whether or not the MOND theorem is true.
Reference: “Asymmetrical Tidal Tails of Open Star Clusters: Stars Crossing their Brah Cluster Defying Newtonian Gravity” by Pavel Karpa, Teresa Yarabkova, Ingo Theis, Jan Pvalam-Altenberg, Benoit Famy, Henry MJ Boffin, Jörg Dabringhausen, Giacomo Beccari, Timo Beccari, Christian Boyle, Hossein Hajji, Zuven Wu, Jaroslav Hass, Akram Hosni Zunuzzi, Guillaume Thomas, Ladislav Uber and J Arsith Ambassador, October 26, 2022, Monthly Notices of the Royal Astronomical Society.
DOI: 10.1093 / mnras / stac2563
In addition to the University of Bonn, the study included Charles University in Prague, the European Southern Observatory ([{”attribute=””>ESO)inGarchingtheObservatoireastronomiquedeStrasbourgtheEuropeanSpaceResearchandTechnologyCenter(ESAESTEC)inNordwijktheInstituteforAdvancedStudiesinBasicSciences(IASBS)inZanjan(Iran)theUniversityofScienceandTechnologyofChinatheUniversidaddeLaLagunainTenerifeandtheUniversityofCambridge[{”attribute=””>ESO)inGarchingtheObservatoireastronomiquedeStrasbourgtheEuropeanSpaceResearchandTechnologyCentre(ESAESTEC)inNordwijktheInstituteforAdvancedStudiesinBasicSciences(IASBS)inZanjan(Iran)theUniversityofScienceandTechnologyofChinatheUniversidaddeLaLagunainTenerifeandtheUniversityofCambridge
The study was funded by the Scholarship Program of the Czech Republic, the German Academic Exchange Service (DAAD), the French funding organization Agence nationale de la recherche (ANR), and the European Research Council ERC.