Massless topological defects and cosmic structure binding

Recent research has unveiled intriguing insights into the universe's intricate fabric through the binding of cosmological structures by massless topological defects. This groundbreaking study, published in the Monthly Notices of the Royal Astronomical Society, explores how massless topological defects contribute to the formation and stability of large-scale structures in the cosmos.

The Binding of Cosmological Structures by Massless Topological Defects

The study delves into the role of these defects, which are theoretical constructs arising in various high-energy physics models. Unlike massive particles that contribute to structure formation through gravitational forces, massless topological defects, such as cosmic strings and domain walls, influence the cosmos through their unique topological properties.

A significant portion of the study focuses on the gravitational Poisson equation, particularly its Green function solution, which explains the attractive inverse-square force outside a spherically symmetric shell of mass and the absence of net force inside it. However, the research introduces another singular shell solution that, while sourcing no mass, drives an attractive 1/r1/r1/r force on the shell itself. This finding is pivotal as it suggests that galaxies and clusters, comprising many such concentric singular shells, can exhibit flat rotation curves and large Keplerian velocities. These phenomena are typically associated with dark matter, yet the study proposes they could occur without requiring dark matter or with significantly less of it than previously thought necessary.

Moreover, the research addresses the thermal motion of gases within these shells, leading to high-temperature conditions that align with observational data. The proposed model also accounts for the observation of giant arcs and rings, such as those documented by Lopez et al. (2022), supporting the alternative explanation to dark matter. The study emphasizes that these thin shells do not need to cover an entire spherical surface to be effective, suggesting their applicability even in partial configurations.

In addition to rotational curves and virialization, the study tackles gravitational lensing, another critical piece of evidence for dark matter in large-scale structures. The concentric singular shells proposed can deflect light paths to distant points by a small, constant angle, independent of the impact parameter in the weak lensing limit, provided the spacing between consecutive shells widens with radius following a Δ∝r1/3\Delta \propto r^{1/3}Δ∝r1/3 relation. This deflection mechanism further diminishes the necessity for dark matter in explaining these observations.

However, the study does not address the problem of structure formation or argue against the role of dark matter in explaining the first two acoustic peaks of the cosmic microwave background and the presence of trace deuterium from Big Bang nucleosynthesis. Instead, it focuses on the evidence provided by galaxies and clusters of galaxies, offering a compelling alternative to the dark matter model.

Dr. Richard Lieu, a UAH researcher shows gravity can exist without mass, potentially mitigating the need for dark matter

Dark matter, a hypothetical form of matter, is inferred from gravitational effects that cannot be explained by general relativity unless more matter is present in the universe than can be seen. It remains nearly as mysterious as it was when first suggested by Dutch astronomer Jan Oort in 1932 to explain the “missing mass” necessary for galaxies to clump together. Now, Dr. Richard Lieu at The University of Alabama in Huntsville (UAH) has published a paper in the Monthly Notices of the Royal Astronomical Society showing how gravity can exist without mass, offering an alternative theory that could reduce the need for dark matter.

Dr. Lieu argues that the “excess” gravity required to bind a galaxy or cluster could be due to concentric sets of shell-like topological defects commonly found throughout the cosmos, likely created during the early universe's phase transition. A cosmological phase transition is a process where the overall state of matter changes together across the entire universe.

As gravitational force involves the warping of space-time itself, it allows all objects to interact, whether they have mass or not. For example, massless photons have been confirmed to experience gravitational effects from astronomical objects.
Future research will likely focus on how galaxies or clusters form through the alignment of these shells and how the evolution of these structures takes place.

UAH study reveals gravity can exist without mass, challenging dark matter theory

"My own inspiration came from my pursuit for another solution to the gravitational field equations of general relativity - the simplified version of which, applicable to the conditions of galaxies and clusters of galaxies, is known as the Poisson equation - which gives a finite gravitation force in the absence of any detectable mass. This initiative is in turn driven by my frustration with the status quo, namely the notion of dark matter's existence despite the lack of any direct evidence for a whole century," said Lieu. a distinguished professor of physics and astronomy at UAH, a part of the University of Alabama System.

"It is unclear presently what precise form of phase transition in the universe could give rise to topological defects of this sort. Topological effects are very compact regions of space with a very high density of matter, usually in the form of linear structures known as cosmic strings, although 2-D structures such as spherical shells are also possible. The shells in my paper consist of a thin inner layer of positive mass and a thin outer layer of negative mass; the total mass of both layers - which is all one could measure, mass-wise - is exactly zero, but when a star lies on this shell it experiences a large gravitational force pulling it towards the center of the shell," said Lieu.

New research by Dr. Richard Lieu suggests alternative to dark matter

"Gravitational bending of light by a set of concentric singular shells comprising a galaxy or cluster is due to a ray of light being deflected slightly inwards - that is, towards the center of the large-scale structure, or the set of shells - as it passes through one shell. The sum total effect of passage through many shells is a finite and measurable total deflection which mimics the presence of a large amount of dark matter in much the same way as the velocity of stellar orbits," said Lieu.

"Both the deflection of light and stellar orbital velocities is the only means by which one gauges the strength of the gravitational field in a large-scale structure, be it a galaxy or a cluster of galaxies. The contention of my paper is that at least the shells it posits are massless. There is then no need to perpetuate this seemingly endless search for dark matter," said Lieu.

"This paper does not attempt to tackle the problem of structure formation. A contentious point is whether the shells were initially planes or even straight strings, but angular momentum winds them up. There is also the question of how to confirm or refute the proposed shells by dedicated observations. Of course, the availability of a second solution, even if it is highly suggestive, is not by itself sufficient to discredit the dark matter hypothesis - it could be an interesting mathematical exercise at best. But it is the first proof that gravity can exist without mass," concluded Lieu.

In conclusion, the binding of cosmological structures by massless topological defects represents a significant advancement in our understanding of the universe. This research not only sheds light on the mechanisms of cosmic structure formation but also paves the way for future studies exploring the deep, underlying principles of cosmology and high-energy physics. For those interested in delving deeper, the full article offers a comprehensive exploration of these fascinating concepts.