Relativity Revisited: How Modified Gravity Challenges Einstein and Dark Matter

Using gravitational lensing, scientists discovered that dark matter can extend over a million light-years from galactic centers, proposing important adjustments to our gravitational theories or the concept of dark matter itself. Credit: SciTechDaily.com

Groundbreaking new research reveals that the rotation curves of galaxies stay flat at infinity, confirming the predictions of the modified theory of gravity as an alternative to dark matter.

This discovery challenges existing models of cosmology and suggests that either dark matter halos are too extended or our understanding of gravitational theory needs a fundamental reassessment.

Progress in Cosmology

In a breakthrough that challenges the conventional understanding of cosmology, scientists at Case Western Reserve University have discovered new evidence that could reshape our perception of the cosmos.

Tobias Mistele, a postdoctoral researcher in the Department of Astronomy at Case Western Reserve College of Arts and Sciences, pioneered a revolutionary technique using “gravitational lensing” to delve into the enigmatic realm of dark matter. He found that the rotation curves of galaxies remain flat for millions of light years with no end in sight.

Scientists previously believed that the rotation curves of galaxies should decrease the farther you look into space.

Weak lensing rotation curve modeling. Credit: Case Western Reserve University

Challenging traditional cosmic models

Traditionally, the behavior of stars within galaxies has puzzled astronomers. According to Newtonian gravity, the stars at the outer edges MUST be slower due to the reduced gravitational pull. This was not observed, leading to the conclusion of dark matter. But dark matter halos must also come to an end, so rotation curves must not remain flat indefinitely.

Mistele’s analysis defies this expectation, providing a surprising discovery: the influence of what we call dark matter extends far beyond previous estimates, extending at least a million light-years from the galactic center.

Tobias Mistele. Credit: Case Western Reserve University

Such a long-range effect could indicate that dark matter – as we understand it – may not exist at all.

“This discovery challenges existing models,” he said, “suggesting that either very extended dark matter halos exist or that we need to fundamentally reevaluate our understanding of gravitational theory.”

Revolutionary Implications for Astrophysics

Stacy McGaugh, professor and director of the Department of Astronomy in the College of Arts and Sciences, said the Mistele findings, scheduled for publication in Astrophysical Journal Letterspush traditional boundaries.

“The implications of this discovery are profound,” McGaugh said. “Not only could it redefine our understanding of dark matter, but it also calls us to explore alternative theories of gravity, challenging the very fabric of modern astrophysics.”

Turning Einstein’s theory on its head

The main technique Mistele used in his research, gravitational lensing, is a phenomenon predicted by Einstein’s theory of general relativity. Basically, it happens when a massive object, like a cluster of galaxies or even a single massive star, bends the path of light coming from a distant source. This bending of light occurs because the object’s mass distorts the structure of space-time around it. This bending of light by galaxies continues on much larger scales than expected.

Stacy McGaugh. Credit: Case Western Reserve University

As part of the research, Mistele plotted what’s called the Tully-Fisher relation in a table to highlight the empirical relationship between a galaxy’s apparent mass and its rotation rate.

“We knew this relationship existed,” Mistele said. “But it wasn’t clear that the relationship would last the further you went out. How long does this behavior continue? That’s the question, because it can’t go on forever.”

Mistele said his discovery underscores the need for further exploration and collaboration within the scientific community — and possible analysis of other data.

Reassessing dark matter theories

McGaugh noted the Herculean — but so far, unsuccessful — efforts in the international particle physics community to detect and identify dark matter particles.

“Either dark matter haloes are much larger than we expected, or the whole paradigm is wrong,” McGaugh said. “The theory that predicted this behavior in advance is the modified MOND theory of gravity hypothesized by Moti Milgrom as an alternative to dark matter in 1983. So the obvious and inevitably controversial interpretation of this result is that dark matter is a chimera; perhaps the evidence for it is pointing to a new theory of gravity beyond what Einstein taught us.”

Reference: “Infinitely flat circular velocities and baryonic Tully-Fisher connection from weak lensing” by Tobias Mistele, Stacy McGaugh, Federico Lelli, James Schombert, and Pengfei Li, Accepted, Astrophysical Journal Letters.
arXiv:2406.09685