How Modified Gravity Challenges Einstein and Dark Matter

Groundbreaking new research reveals that the rotation curves of galaxies remain flat infinitely far away, confirming the predictions of a modified theory of gravity as an alternative to dark matter.

This finding challenges existing models of cosmology and suggests that either the dark matter halo is greatly expanded or our understanding of gravity theory needs a major rethink.

A breakthrough in cosmology

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

Tobias Mistele, a postdoctoral fellow in the Department of Astronomy at Case Western Reserve’s College of Arts and Sciences, is pioneering a revolutionary technique that uses “gravitational lensing” to delve into the mysterious realm of dark matter. He discovered that the rotation curves of galaxies remain flat for millions of light years with no end in sight.

Scientists had previously thought that the rotation curves of galaxies must decrease the further you look into space.

Challenging traditional space models

The behavior of stars in galaxies has traditionally puzzled astronomers. According to the Newtonian gravity of stars at the outer edges should be slower due to the reduced gravitational force. This was not observed, leading to the conclusion of dark matter. But even the dark matter halo should end, so the rotation curves should not remain flat indefinitely.

Mistele’s analysis defies this expectation, yielding a surprising revelation: the influence of what we call dark matter far exceeds previous estimates, stretching at least a million light-years from the galactic center.

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

“This finding challenges existing models,” he said, “suggesting that there is either a vastly extended dark matter halo, or that we need to fundamentally rethink our understanding of gravitational theory.”

Revolutionary implications for astrophysics

Stacy McGaugh, professor and chair of the Department of Astronomy in the College of Arts and Sciences, said Mistele’s findings, to be published 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 entices us to explore alternative theories of gravity that challenge the very fabric of modern astrophysics.”

Turning Einstein’s theory on its head

The primary technique Mistele used in his research, gravitational lensing, is a phenomenon predicted by Einstein’s theory of general relativity. Basically, it occurs when a massive object, such as a galaxy cluster or even a single massive star, bends the path of light coming from a distant source. This bending of light occurs because the mass of the object wraps the fabric of spacetime around it. This bending of light by galaxies persists on much larger scales than expected.

As part of Mistele’s research, he graphed what is called the Tully-Fisher relation 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 obvious that the relationship would hold the further you went out. How far does this behavior persist? That’s the question because it can’t last forever.”

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

A reassessment of dark matter theories

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

“Either the dark matter halo is 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, which was proposed by Moti Milgrom in 1983 as an alternative to dark matter. So the obvious and inevitably controversial interpretation of this result is that dark matter is a chimera; perhaps the evidence for this points to some new theory of gravity beyond what Einstein taught us.”

Reference: “Uncertainly Flat Circular Velocities and the Baryonic Tully-Fisher Relation from Weak Lensing” by Tobias Mistele, Stacy McGaugh, Federico Lelli, James Schombert, and Pengfei Li, accepted Astrophysical Journal Letters.
arXiv:2406.09685