Science

Puzzling astronomical observations support alternative theory of gravity

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Professor Pavel Kroupa and his team have found evidence of an alternative theory of gravity
Volker Lannert/University of Bonn
Professor Pavel Kroupa and his team have found evidence of an alternative theory of gravity
Volker Lannert/University of Bonn
Top: a graph of the distribution of stars in the Hyades cluster, as seen in astronomical observations. Bottom: A computer simulation of MOND, which shows a similar distribution
AG Kroupa/Uni Bonn

Astrophysicists have observed some puzzling behavior in star clusters that seem to defy our current understanding of gravity at cosmic scales. Intriguingly, the observations fit with an alternative theory of gravity that could negate the need for dark matter.

Although it’s since been superseded by Einstein’s theory of general relativity, Newton’s law of universal gravitation still holds pretty well as an explanation for the large-scale structure and movements of the universe. But now, new observations have been made that don’t quite fit these currently accepted models.

An international team of astrophysicists had been investigating open star clusters, which contain thousands of young stars being born from a large cloud of dust and gas. These clusters have a relatively short lifespan before they dissolve, as the stars drift into two “tails” – one in front of the cluster and one 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 the past it’s been tricky to determine which of a cluster’s stars belong to which tail, but the researchers on the new study developed a method to do so. They call it the Jerabkova-compact-convergent-point (CCP) method, and this was applied to data on four open star clusters gathered by surveys like the Gaia mission. To their surprise they found that in all four clusters, the leading tail had far more stars than the trailing one, in an apparent contradiction of Newton’s laws.

So, the team then simulated the movements of stars in these clusters according to a different hypothesis, known as Modified Newtonian Dynamics (MOND). Essentially, this model suggests that gravity’s effects are stronger at low accelerations than they are in Newton’s laws. And intriguingly, this model’s predictions lined up very well with the 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.”

Top: a graph of the distribution of stars in the Hyades cluster, as seen in astronomical observations. Bottom: A computer simulation of MOND, which shows a similar distribution
AG Kroupa/Uni Bonn

This isn’t the only way in which the MOND model fits real-world observations better. Star clusters in nearby galaxies have been found to be dissolving faster than Newton’s laws predict – but this would be a natural by-product of MOND.

Another major implication of MOND could shake up astrophysics as we know it – if it was true, then dark matter wouldn’t exist. This mysterious substance was conjured up in the 1930s to explain discrepancies in the observed motion of stars and galaxies, which were seen to be moving much too fast for how much mass they apparently contained. Dark matter fills the gap by adding huge amounts of invisible mass, which scientists have been searching for ever since. Decades of experiments designed to detect dark matter particles have come up empty.

Still, dark matter is the prevailing theory, because it does a very good job of explaining many observed features of the universe and there’s plenty of other evidence that points to its existence. Although there has been other observational evidence supporting MOND, it remains a fringe hypothesis that isn’t widely accepted by the scientific community.

The researchers on the new study are currently exploring other methods to produce more accurate simulations, which could then be applied to other astronomical objects to find more evidence for or against MOND.

The research was published in the journal Monthly Notices of the Royal Astronomical Society.

Source: University of Bonn

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17 comments
NMBill
"The universe is not only stranger than we imagine; it is stranger than we can imagine."
Spud Murphy
I've always thought dark matter was a classic example of "we don't know why things work like this, so let's make up something that explains it". It seems like MOND actually makes more sense than dark matter, maybe this fringe idea is actually the correct one, it wouldn't be the first time that mainstream scientific concepts have had to be thrown out because the fringe idea was actually correct.
Catweazle
"There are more things in heaven and earth Horatio than are dreamt of in your philosophy".
Scott Anderson
Dark matter doesn't exist on its own it's a calculation error. The difference between prediction and observation. Missing the majority of mass and energy in the universe should have been our first clue the foundational mathematics were flawed, instead of considering we may be wrong on some key point we doubled down folding the missing mass and energy into the problem, qe should have started over in the 60s. The perfect vacuum does not exist the has never been a zero in mass, therefore we have never separated light or energy from matter to isolate them as their own entities there has never been a reason to invent the electron or photon.... these are mistakes Eistien and jj Thomson were both wrong and so is everyone who has followed them, we can correct this.
Voice of Reason
Agreed Spud. 'Dark Matter' seems to be a similar explanation today as 'Aether' was long ago. I think MOND hasn't caught on because to date our observational instruments had not been sensitive enough. New technology brings better data and new evidence, which leads to breakthroughs in understanding.
AbbottFord
What's drawing them into the leading tail? Is there another kind of vacuum?
Cymon Curcumin
If MOND does away with the need to have dark matter it will need to explain things like the dumbbell cluster; where two galaxies have collided and while everything visible has been shown down by interactions with the EM field, a large enough mass to cause gravitational lensing without being visible was not slown down. I really wish that people who claim dark mater is fake would provide their explanation for this. It would really bolster their credibility.
Expanded Viewpoint
Before I give any support to the "dark matter" idea, I need to see its periodic table of the elements. Surely it must have one, even if it's only just one or a few elements that comprise it! And after that, I need to actually see some of them. If this dark matter really does exist and is prevalent enough to cause the huge effects that are being attributed to it, then surely, by logic, we should be able to find some of it! It sounds more like the invisible flying spaghetti monster than anything else. If we cannot perceive this "dark matter" with the instrumentation of our "white matter" universe, then how could it possibly be causing any kind of effects with our "white matter"? One would beget the other, right?
Randy Weiss
I understand the Bernoulli effect where movement of air affects air pressure. Complex as it is it's quite well understood, and utilized in every airplane wing. This sounds similar, but obviously can't be a similar mechanism. Considering what little is known about gravity waves (although their speed seems to be near or at the speed of light), it may be more of a Doppler effect. Are the gravity waves 'piling up' in front of the cluster's motion? We're not in Newton's universe, nor Einstein's any longer. Uncomfortable as this murky information may be I'm thrilled that recent (and yet to be done) OBSERVATIONS are pushing back our veil of ignorance.
akarp
I remember a dynamics professor saying Newtonian Physics (mathematical equations for observational data) only really works for ~2% the speed of light (where we mostly experience the world). Thus why quantum mechanics is better at describing the universe (Though we really don't have much defined here).

Seems the "Modified Newtonian Dynamics (MOND)" is another way to correct or modify these equations rather than actually explaining what is the driving "force" (pun intended). ALL engineering equations seem to have these 'correction factors' or 'lookup table' so the mathematical model actually fit the observations. There most likely is an explanation that we are still unware of...