Astrophysicists make observations that agree with alternative theoretical predictions of gravity

Astrophysicists make observations that agree with alternative theoretical predictions of gravity

In the Hyades star cluster (top), the number of stars (black) in the tail of the front tides is much greater than those in the rear. In a computer simulation with MOND (below), a similar picture appears. Credit: University of Bonn

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 are now published in Monthly Notices of the Royal Astronomical Society.

In their work, the researchers investigated open star clusters. These are formed when thousands of stars are born within a short period of time in a huge 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. Weak gravitational forces hold the mass together.

“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. The other, in turn, takes the lead like a spearhead.

“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 ends must contain approximately 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 clusters we studied, the front tail always contains a much larger number of stars close to the cluster than the back tail ” .

A new method for calculating stars has been developed

Until now, it has been almost impossible to determine which ones belong to their tails among the millions of stars close to the mass. “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 holds a PhD in the Kroupa 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 discrepancy with the current theory. The highly accurate survey data from the European Space Agency’s Gaia space mission were indispensable for this purpose.”

The Monitoring data, by contrast, fits better with the theory that uses the acronym MOND (“MOdified Newtonian Dynamics”) among experts. “Simply put, according to MOND, stars can leave a cluster through two different doors,” Kroupa explains. “One leads to the back tide TailThe other is in the foreground. However, the first is much narrower than the second – so it is unlikely that the star will leave gathering From which. 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 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 computational methods to do so. We currently lack sports tool for 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. “he is called, star groups In nearby galaxies it seems to be disappearing faster than it 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,” Kroupa explains. The team is 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.

Galactic formation simulated without dark matter

more information:
Pavel Kroupa et al, Asymmetric tidal tails of open star clusters: Stars crossing their cluster defy Newtonian gravity, Monthly Notices of the Royal Astronomical Society (2022).

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Bonn University

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