Physics

Evidence of "modified gravity" in 150 galaxies strengthens dark matter alternative

Evidence of "modified gravity"...
Astronomers have discovered a strange quirk of gravity in 153 galaxies, which appears to support an alternative hypothesis to dark matter
Astronomers have discovered a strange quirk of gravity in 153 galaxies, which appears to support an alternative hypothesis to dark matter
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Astronomers have discovered a strange quirk of gravity in 153 galaxies, which appears to support an alternative hypothesis to dark matter
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Astronomers have discovered a strange quirk of gravity in 153 galaxies, which appears to support an alternative hypothesis to dark matter

Dark matter is currently the most widely accepted hypothesis for explaining some of the weirdness we see in the cosmos – but it’s not the only possibility. Now, a team of astronomers has discovered evidence in over 150 galaxies for a long-standing alternative model of “modified gravity.”

The idea of dark matter was conjured up in the 1930s in response to astronomical observations that flew in the face of Newton’s laws of gravity. Basically, the more mass an object has, the stronger its gravitational pull – but Swiss astrophysicist Fritz Zwicky noticed that galaxy clusters were rotating much faster than their gravity should allow, based on the mass of their visible matter. Zwicky came to the conclusion that these galaxy clusters contained much more mass than we could see, and he dubbed it dark matter.

The hypothesis has stood up to scrutiny in the decades since, with observations continuing to support the idea of dark matter. But one major piece of the puzzle is still missing – finding the stuff itself. Plenty of experiments have tried to detect particles of the elusive dark matter, or even create them, but so far none have been successful.

Perhaps that’s because it’s not really there after all, and instead it might be that our models of gravity and physics need some tweaking. This class of hypotheses is known as modified gravity, and now astronomers claim to have found evidence supporting one particular model, known as Modified Newtonian dynamics (MOND).

First proposed in 1982 by physicist Mordehai Milgrom, MOND suggests that at low accelerations, gravity’s effects are stronger than Newton’s laws describe. A side effect of this is that the motions of objects would depend not just on their own mass, but all other masses in their neighborhood. This phenomenon is known as the external field effect (EFE).

And now, researchers on the new study say they’ve observed the EFE in action in 153 different galaxies. The team was studying the rotation curve of the galaxies, which plots the orbital speed of stars and gas against their distance from the center of the galaxy.

The researchers discovered that galaxies in strong external fields slowed down much more frequently than galaxies in weaker external fields did. That’s a prediction made only by MOND, and the discovery surprised even the astronomers themselves.

“The external field effect on rotation curves is expected to be very tiny,” says Federico Lelli, co-author of the study. “We spent months checking various systematics. In the end, it became clear we had a real, solid detection.”

It’s an intriguing result, and it may lend some weight to the MOND hypothesis for further study. But it’s important to keep in mind that so far the bulk of the evidence still points towards dark matter, and it’ll take much more work to topple that hypothesis entirely.

The research was published in the Astrophysical Journal.

Source: Case Western Reserve University

10 comments
10 comments
FB36
Modified Gravity (MOND) is an idea that creates more problems than it solves!

Here is another possibility that does not require modifying laws of gravity nor new/unknown particles:
Spacetime could be a superfluid/supergas that is just denser at some places in the universe!
(Imagine if incoming Dark Energy was like boiling spacetime & creating large bubbles/voids!)
Chris Coles
Their problem remains; that they have based their concepts upon a universe that was created in a big bang; where the mass released from that big bang is not rotating, instead rapidly expanding from points of mass evolving into galaxies from the creation of the visible universe. whereas, if they accept that the universe is in steady state and that all galaxies are the result of the depletion of energy and mass from an existing active galaxy Galactic Core Object, essentially a massive black hole . . . that will be revolving while depleting . . . and thus creating new galaxies that were always rotating from the moment of their creation. That will be all that needs to be accepted to bring this debate back to a logical conclusion.
alcalde
No evidence points towards "dark matter" since no one can even say what dark matter is. Plus the fact that there's supposed to be massive amounts of it yet not one particle of it has ever been detected is absurd on its face. It belongs in the "extraordinary claims require extraordinary evidence" category.
McDesign
one word, "Phlogistin"
Catweazle
I believe George Berkeley and subsequently Ernst Mach postulated something similar over a century ago.
bwana4swahili
Finally getting close to the correct answer! The KISS principle always applies and modified gravity fits the bill.
Signguy
Accorxing to the genious Tesla, "gravity" is not what we think it is...
bahbah
All the observations of astronomy is based on the assumption that the speed of light is constant everywhere in the universe and has been so since the big bang. We know that it changes in an increased energy medium, such as diamond where the speed reduces by 60 %. The vacuum energy of space is constantly decreasing due to the expansion of the universe, thus the speed of light could well be increasing, in which case we would see a red shift in distant galaxies even if they were not moving away from us. This could easily account for the discrepancies we now have in the Hubble constant.
Nobody
Dark matter is just regular matter from earlier generations of burnt out stars. It's just dark and cold now.
aki009
I'd wager that 50% of what we think we know, we really don't know. Once we figure out what's in that 50% and ignore them, we then might be able to ask and maybe even answer more fundamental questions that are eluding us today.