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Space Science

Behavior of Star Clusters Challenges Newton's Laws of Gravity (jpost.com) 90

Posted by EditorDavid from the breaking-the-laws dept.
The Jerusalem Post reports that "Certain star clusters do not seem to be following current understandings of Isaac Newton's laws of gravity, according to new research published on Wednesday." (Specifically open star clusters, formed when thousands of stars are born in a gas cloud within a short time period.)

The researchers examined data on each stars' velocity, direction of motion and age using data from the European Space Agency's Gaia mission that allowed them to count the stars accurately for the very first time. The results? As the clusters dissolve, the stars accumulate on two "tidal tails:" one pulled behind the cluster and the other pushed forward. "According to Newton's laws of gravity, it's a matter of chance in which of the tails a lost star ends up," explains Dr. Jan Pflamm-Altenburg of the Helmholtz Institute of Radiation and Nuclear Physics at the University of Bonn. "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...."

When the researchers looked at the data, they found that it did not fit Newton's law of gravity and instead fit better with an alternate theory called Modified Newtonian Dynamics (MOND).

"Put simply, according to MOND, stars can leave a cluster through two different doors," explained Prof. Dr. Pavel Kroupa of the Helmholtz Institute of Radiation and Nuclear Physics. "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...."

The simulations also coincided with the Gaia data in terms of how long the star clusters typically survive, which is much shorter than would be expected according to Newton's laws....

The MOND theory is controversial as modifications to Newton's laws of gravity would have far-reaching consequences for other areas of physics as well, although they would solve many problems facing cosmology.
Thanks to long-time Slashdot reader schwit1 for submitting the story!
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Behavior of Star Clusters Challenges Newton's Laws of Gravity More

Behavior of Star Clusters Challenges Newton's Laws of Gravity

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  • Tenuous. (Score:1, Insightful)

    by greytree ( 7124971 )
    I am not an astrophysicist, but...

    • Isn't this where the whole "dark matter" thing comes from - that galaxys don't seem to follow the laws of gravity.

      If so, why is this "new"?

      • For some reason, some astronomers can't let MOND go.

        • Re:Tenuous. (Score:5, Interesting)

          by Immerman ( 2627577 ) on Monday October 31, 2022 @10:49AM (#63012437)

          Perhaps because it does a better job of describing what we see than dark matter?

          Dark matter is an ugly bandaid with zero supporting evidence *except* that at galactic scales gravity doesn't behave in the way either Newton or Einstein predicted. Despite decades of searching we've yet to find any direct evidence of the vast mass of dark matter that should be continuously streaming through our planet, if it exists.

          Meanwhile MOND does a *much* better job of describing the overwhelming majority what we actually see out in the universe, WITHOUT relying on photon-dodging fairies, dismissing it out of hand is intellectually dishonest.

          Perhaps the biggest damning evidence *against* dark matter, is that MOND *can* accurately predict galactic rotation curves based on the luminous matter alone. If dark matter is real, then the ratios between dark and luminous matter should vary - there's no good explanation for why *every* galaxy should have *exactly* enough dark matter to cause exactly the same rotation curves that MOND predicts from the luminous matter alone.

          Now, there are still exceptions, weird things like the bullet cluster that MOND can't easily explain. But the universe is big, and full of really weird hard-to-explain shit. A handful of examples where "invisible fairies" are the best explanation we've come up with is not an especially compelling argument to discard a theory that gives much more accurate predictions in every other case.

          Because that's the thing with dark matter - it's a non-predictive hypothesis. For *any* observed behavior of gravity, no matter how bizarre, there's a distribution of dark matter that can explain it. And there's no theories to predict what the actual distribution of dark matter should be expected, except in the most vague and general terms. It's the driving force, not something that can be predicted from what we see. Only a stone's throw away from "God did it" as a scientific explanation.

          • Is there a MOND theory than can explain the bullet cluster?
            https://en.wikipedia.org/wiki/... [wikipedia.org]
            If so please cite it.

            • Not that I've heard... but it's a MUCH less mature theory, with thousands of times fewer man-hours having been spent figuring out possible explanations for the outliers. And the only way that changes is if huge numbers of people start exploring the theory and its implications. We should always be cautious of mistaking a more mature theory for a more accurate accurate theory. Especially when the mature theory includes a "Get out of uncomfortable situations free" card.

              Take the bullet cluster - under GR we

          • It's well know that MOND can be parameterized to explaing galaxy rotation curves better than dark matter. Well, most of them. From the MOND prospective, those galaxies that others would call deficient in dark matter must... be immune from MOND? use a different parameterization? It's almost as if some kind of je ne sais quoi was present or absent in galaxies, affecting their gravitational behavior.

            Plus, dark matter explains a lot of things that MOND can't begin to explain.

            I'll join Arizona's AG in quoti

          • Except we CAN MAP dark matter in the universe, so we know it is there. MOND does a poor job of explaining that map. There are also a few good explanations for what Dark Matter is, my personal fav is Axions.

            • No, we can map gravitational lensing.

              That only translates to a dark matter map if you assume gravity behaves in the way GR predicts. And ALL of GRs predictions fail at galactic and larger scales, unless you assume dark matter exists.

    • Re: (Score:2)

      by fermion ( 181285 )
      Newtons laws fail regularly. They cannot even predict the orbit of the planets around the sun. It is important and interesting to define exactly where they fail.

  • Einstein (Score:5, Interesting)

    by jemmyw ( 624065 ) on Monday October 31, 2022 @03:05AM (#63011729)
    I didn't think we used Newton's laws for this kind of astrophysics.
    • Why wouldn't we use Newton's laws when they work so well? Gravity diminishes at the square of the distance. Simple and elegant.

      • Even the victorians noticed that the planets weren't behaving precisely according to newtons theory and eventually this led einstein to his theory of relativity. On the scale of a galaxy over millions of years the difference in motion will be huge between pure newtonian vs newtonian + relativity.

        • Even the victorians noticed that the planets weren't behaving precisely according to newtons theory and eventually this led einstein to his theory of relativity.

          I'm pretty sure it was the Michelson–Morley experiment that led to that...

          https://en.wikipedia.org/wiki/... [wikipedia.org]

          • Re:You're 150 years out of date. (Score:4, Interesting)

            by Immerman ( 2627577 ) on Monday October 31, 2022 @11:11AM (#63012493)

            Not even remotely.

            Michelson–Morley was searching for evidence of the luminiferous ether - the medium through which light was believed to propagate. Light was known to be a wave, and a wave can only exist in a medium, right? And if Earth (and the sun) is passing through the ether, then light should travel faster "with the flow" than "against the flow".

            None of that has anything to do with gravity or the motion of planets. In fact one of the known constraints on the ether's properties was that it must not impede the movement of physical objects in any way. Otherwise the planets would rapidly spiral into the sun.

            I believe the first flaw found in Newtonian gravity was the observed precession of the orbit of Mercury, which didn't match what was predicted from the influence of the known planets. For Netwon's gravity to accurately describe Mercury's orbit, there would have to be another planet, "Vulcan", orbiting even closer to the sun. And despite exhaustive searching, none was ever found.

            Meanwhile, one of the earliest testable victories of Einstein's gravity was that it *did* accurately predict Mercury's orbit.

        • Re: (Score:2)

          by HiThere ( 15173 )

          You've got your chronology backwards. And the explanation offered by relativity was wrong for that one. It was caused by the sun being oblate rather than spherical. (Relativity did offer a correction, but eventual calculations didn't match the orbit of Mercury until you ALSO factor in the oblateness of the sun as the major factor causing the change.)

          • Re: (Score:2)

            by Viol8 ( 599362 )

            Right, because no astronomers noticed the sun was slightly wider than it was high though they were quite capable of measuring all other parameters.

            Seriously?

    • Why not? When size is large and speed is low classical mechanics is exactly what we need. Leave Einstein to light bending around black holes. Newton is still ideal when discussing the movement of astronomical bodies.

      • Re: (Score:1, Troll)

        by jabuzz ( 182671 )
        Astronomical bodies tend to move very fast, to the point where observations can determine that Newton's Laws of gravity are lacking. The perihelion precession of Mercury's orbit is one of the classical proofs of General Relativity.

        Further, the <b>moment</b> that Newton's Laws of gravity don't describe an observation the default position should be to switch to General Relativity and redo the calculations <b>BEFORE</b> deciding that we need some wacky modified theory of gravity. It's i

      • If light bends around gravity sources, what effects does gravity have on light emanating from a gravity source?

        Would having a gravitational source emanating gravitational waves along the same axis that photons are emitted cause redshift of those photons?

      • I'm glad that you weren't hired to work for the Global Positioning Satellite team.

        • I'm glad that you weren't hired to work for the Global Positioning Satellite team.

          So am I. It would be insanely stupid to hire someone talking about massive astronomical objects to solve problems related to high speed radio transmission requiring insanely precise timing highly sensitive to relativistic effects. Mind you if they did hire me I would turn the job down. Wouldn't want to work for an idiot who can't select the right team.

          • On your job application you said:

            Leave Einstein to light bending around black holes.

            Last I checked, planet Earth is not a black hole. But it is a massive, low speed astronomical object.

    • Re: (Score:2)

      by HiThere ( 15173 )

      Newton's laws should work fine. But you also need to factor in electro-magnetic effects. Stars are probably hot cathodes, so one would expect them to be charged. This would make them attractive to the emitted electrons, if the emitted velocity was anything approximately correct. And moving electrons create magnetic fields that would also react on the charge of the stars.

      I have no idea how strong these effects would be, but they should be present, and an open cluster is likely to be the place where they

  • Actual paper (Score:5, Informative)

    by Tx ( 96709 ) on Monday October 31, 2022 @03:56AM (#63011767) Journal

    Did I miss it, or did they fail to link to the paper they're talking about? I think this is the actual paper [oup.com], accessible via unpaywall, if anyone wants to go beyond the journalistic interpretation.

  • I remember having discussions with the likes of flat earthers and their counterparts. Religious extremists and let's call them obnoxious atheists.

    Sooner or later you could bet pennies to dollars that someone would question science, no matter how accurately or not, and the "good, rational guys" would immediately jump in and defend science by clauming some things were so well understood as to be taken as an undisputable fact.

    Gravity would usually be the example of choice.

    It usually ended with these people acc

    • Okay, have to ask - "determ"?

      • Re: (Score:2)

        by Kokuyo ( 549451 )

        Determine. Touch screens and I don't get along...

        Then again, the older I get, the less keyboards and I get along as well... so yeah, let's call it onset of dyslexia and let's not talk about any of the other much more scary possibilities ;).

    • The process of science itself demonstrates that scientist are well aware that we don't know everything. When people make wild claims and the pro-science crowd jumps in to defend the truth as they see it, it often revolves around the debate that because science doesn't know everything it therefor knows nothing. Completely reasonable for people to kick back any fallacy like that. But it does grow tiresome watching both sides repeat the same stupid arguments over and over.

  • For any astrophysicists out there ... (Score:5, Informative)

    by As_I_Please ( 471684 ) on Monday October 31, 2022 @04:08AM (#63011791)

    The arxiv preprint: https://arxiv.org/abs/2210.134... [arxiv.org]

  • But this doesn't seem like a very strong argument for MOND.

    It seems much more likely that we just don't know details of the initial conditions/ formation process than it needs revision to Newtonian Dynamics.

    • Re:Not a fan of Dark Matter (Score:5, Interesting)

      by jd ( 1658 ) <imipakNO@SPAMyahoo.com> on Monday October 31, 2022 @06:15AM (#63011919) Homepage Journal

      It's a very weak argument for MOND, -unless- using an estimated distribution of Dark Matter cannot produce a workable initial condition.

      This sort of physics is time reversible, so with the current positions and velocities, it should be possible to model any system backwards in time. The problem with thousands of stars is that you can't solve for a system with that many bodies, you have to simulate.

      We can estimate how old the stars are. If any given simulation would result in stars colliding within their lifetimes or doing other impossible things, the model being simulated cannot accurately reflect the physics that took place.

      Maybe there aren't powerful enough computers to do this for vanilla GR, GR+DM, and then GR+MOND. Or maybe researchers don't have the budget. But this would seem an obvious sanity check if it's doable.

      • Re: (Score:2)

        by HiThere ( 15173 )

        This seems like a situation were one could expect weak electromagnetic effects. Model the stars a "really massive cathodes", so expect them to have a positive charge. (How big? Can we determine that?) Then they'll try to avoid each other, so Newton's laws won't be quite correct, just very close.

        This may not require any new physics, just more complete models.

  • To the Physisists of /. : How does this compare to relativity? Does it still lie within what is expected from it? Or is relarivity simply not applicable at this scale? Im missing any form of statement regarding that in the article.

    • Re: (Score:2)

      by HiThere ( 15173 )

      Not exactly a physicist, but I wouldn't expect any relativistic effects due to motion at that scale of relative velocities. (You could still get neutron stars, etc. of course.)

  • MOND is needed... (Score:4, Insightful)

    by bradley13 ( 1118935 ) on Monday October 31, 2022 @05:17AM (#63011873) Homepage

    MOND, or something like it, is very much needed. The whole "dark matter" idea just reeks of "we don't understand this, so we're going to fudge it". It is also completely non-falsifiable. Dark matter particles are like unicorns: just because you haven't found one yet, doesn't mean they don't exist. /s

    The hard part is defining local experiments that we can carry out, to prove one or the other.

    • Re: MOND is needed... (Score:5, Interesting)

      by jd ( 1658 ) <imipakNO@SPAMyahoo.com> on Monday October 31, 2022 @05:53AM (#63011899) Homepage Journal

      The test would not have to be local.

      1. There are galaxies with little or no Dark Matter indicators. If these are rotating in a manner incompatible with Newton + Relativity, then whatever the indicators are indicating elsewhere, it has nothing to do with galaxy rotation, and we need MOND to explain things.

      2. We've mapped where we believe Dark Matter to be and it's rather strung out. If we evenly distribute Dark Matter in the manner indicated, do the simulations match observation? If not, then we've a problem with using it as an explanation.

      3. Projected distributions of matter in the universe will be differently affected by MOND Vs Dark Matter. If we compare what is expected with discoveries made after those projections, which model best matches new observations?

      We might, however, be able to do local. Clocks using things like quantum gas, etc, can measure the effects on time from gravity over very short distances (a difference in elevation of a few meters is sufficient). Given this level of sensitivity, how far apart would the clocks need to be to show a different prediction from GR after, say, a couple of months of running?

      If the distance is realistic (geostationary orbit is about the outer limit of realistic), then we can experimentally test MOND.

      If that's simply not a big enough distance, even on the suggested timeframe, then we don't have the means to test MOND experimentally at this time.

    • One requires modifying the fundamental laws of physics, with no mechanism proposed .... the other just needs a form of matter we can't currently detect ...

      MOND also still requires some extra unseen matter in some cases ...

      It seems an overcomplicated solution looking for a problem

      • Dark matter doesn't fit with know physics either. You could argue that dark matter is the simpler explanation, though simpler is sometimes in the eye of the observer.

        • Re: (Score:2)

          by DRJlaw ( 946416 )

          Dark matter doesn't fit with know physics either. You could argue that dark matter is the simpler explanation, though simpler is sometimes in the eye of the observer.

          The Higgs field didn't "fit" with known physics either for about 50 years, until they finally figured out how to detect it [wikipedia.org] in 2013-14.

    • MOND, or something like it, is very much needed. The whole "dark matter" idea just reeks of "we don't understand this, so we're going to fudge it"

      In that sense MOND is exactly the same: we have observations our current understanding of physics cannot explain so something we do not understand is happening. DM solves this by adding a new type of matter that only weakly interacts with ordinary, baryonic matter. MOND tries, and largely fails to explain the observations by altering Newton's laws of motion.

      That's the problem with MOND: there are lots of things it cannot explain most notable is the bullet cluster where two colliding clusters of galaxie

    • MOND, or something like it, is very much needed. The whole "dark matter" idea just reeks of "we don't understand this, so we're going to fudge it". It is also completely non-falsifiable. Dark matter particles are like unicorns: just because you haven't found one yet, doesn't mean they don't exist. /s

      It’s only non-falsifiable to the degree that it’s undefined, but it’s only useful to us inasmuch as it is defined. Dark matter is a placeholder: there’s something(s) going on that we can’t yet explain, so we’re going to measure and quantify them in order to define their shape. We may not understand them or how they work, but we can start to understand the shape of the block box in which these ideas live and how they interact with the rest of the universe.

      I mean, really, t

    • With MOND, dark matter is still required for some known observations. So using it does not mean things get simpler but more complex.

      It is also completely non-falsifiable.

      What does that mean? Dark matter has been observed in multiple ways. For now the name is a placeholder for non-baryonic matter that does not have properties of baryonic matter.

    • Don't most people look at dark matter as a mathematical model of observed reality? Whether or not there is a "dark matter particle" is not relevant to the theory and so has its falsifiability has no bearing on the theory.

  • Link error (Score:3)

    by Meneth ( 872868 ) on Monday October 31, 2022 @05:39AM (#63011883)
    The link "alternate theory" led me to https://www.jpost.com/science/... [jpost.com], which does not mention "MOND", "Newton" or "dynamics", but instead deals with neutrino experiments.

  • The angular velocities in Gaia data are based on an observational period of something like 5 years or less at this point and the radial velocity measurements one would use for a full 3D position+velocity estimate on any star are skewed toward brighter stars.

    This is neat, but you can't really claim to modify all of gravity for a whole universe by looking only at a small bubble of it.

    A longer baseline of data, and radial velocity measurements for more distant stars (probably from ground observatories with big

  • Laws of physics/nature are just 'laws' that people thought up to explain certain phenomena, they aren't set in stone. So it won't be a suprise if something doesn't behave like you'd expect based on those 'laws'.

  • I don't understand why MOND is even being invoked. If you have results that don't comport to expected results you should be focusing on your observations not canvassing the world for pet theories that may or may not comport to your observations. They don't even have MOND specific n-body codes and the effects are non-linear so really they are just guessing at this point.

  • There's probably just another mechanism that they can't find changing the stres in the dust cloud. If gravity was wrong I think you'd also find more than just one instance in the universe of it being wrong

  • I skimmed through the article a few times and didn't see any exact numbers, and I'm not an astrophysicist. What is meant by a "short amount of time'? 100 years? 1 million?

  • Depth perception at extremely long distances, is really, really hard. There are so many factors that could influence the apparent distance to a specific star. To be able to determine which stars are in the "front" or "back" tail, we would need to be able to measure the stars' relative distances very precisely. Do we really have that kind of precision available to us?

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