One proposed modification of General Relativity that has been proposed to explain dark matter phenomena is Conformal Gravity, which basically preserves angles in transformations adding an additional symmetry to GR.
A new paper suggests that Conformal Gravity fails in elliptical galaxies.
As an alternative gravitational theory to General Relativity (GR), the Conformal Gravity (CG) has recently been successfully verified by observations of Type Ia supernovae (SN Ia) and the rotation curves of spiral galaxies.
The observations of galaxies only pertain to the non-relativistic form of gravity. In this context, within the framework of the Newtonian theory of gravity (the non-relativistic form of GR), dark matter is postulated to account for the observations. On the other hand, the non-relativistic form of CG predicts an additional potential: besides the Newtonian potential, there is a so-called linear potential term, characterized by the parameter γ∗, as an alternative to dark matter in Newtonian gravity.
To test CG in its non-relativistic form, much work has been done by fitting the predictions to the observations of circular velocity (rotation curves) for spiral galaxies.
In this paper, we test CG with the observations from elliptical galaxies. Instead of the circular velocities for spiral galaxies, we use the velocity dispersion for elliptical galaxies. By replacing the Newtonian potential with that predicted by non-relativistic form of CG in Hamiltonian, we directly extend the Jeans equation derived in Newtonian theory to that for CG. By comparing the results derived from the ellipticals with that from spirals, we find that the extra potential predicted by CG is not sufficient to account for the observations of ellipticals. Furthermore, we discover a strong correlation between γ∗ and the stellar mass M∗ in dwarf spheroidal galaxies. This finding implies that the variation in γ∗ violates a fundamental prediction of Conformal Gravity (CG), which posits that γ∗ should be a universal constant.
Li-Xue Yue, Da-Ming Chen, "Test of conformal gravity as an alternative to dark matter from the observations of elliptical galaxies" arXiv:2506.03955 (June 4, 2025).
6 comments:
we talk about this before
arXiv:2506.03334 (gr-qc)
[Submitted on 3 Jun 2025]
Could Planck Star Remnants be Dark Matter?
Oem Trivedi, Abraham Loeb
We explore the end state of gravitational collapse under quantum gravity effects and propose that Planck Star Remnants (PSR), formed via nonsingular bounces, could serve as viable dark matter candidates. Within the framework of Loop Quantum Cosmology, we model the collapse of a homogeneous matter distribution and show that the classical singularity is replaced by a quantum bounce at the Planck density. By analytically matching the Friedmann Lemaitre Robertson Walker (FLRW) interior to an exterior Schwarzschild spacetime using the Israel junction conditions, we demonstrate that the bounce remains causally hidden from external observers, avoiding any observable re-expansion. This naturally leads to the formation of stable, non-radiating PSR, whose radius coincides with the Schwarzschild radius when the black hole mass approaches the Planck mass as a result of Hawking evaporation. We suggest that such remnants may originate from evaporating primordial black holes in the early universe, and estimate the relic abundance needed for PSR to account for the observed dark matter density. We also discuss some crucial differences between PSR and previous proposals of Planck mass relics. The scenario is shown to be consistent with existing astrophysical and cosmological constraints, offering a unified framework connecting quantum gravitational collapse, and the nature of dark matter.
Comments: 12 pages with 2 figures, comments are very welcome!
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)
Cite as: arXiv:2506.03334 [gr-qc]
(or arXiv:2506.03334v1 [gr-qc] for this version)
https://doi.org/10.48550/arXiv.2506.03334
when the black hole mass approaches the Planck mass as a result of Hawking evaporation.
We suggest that such remnants may originate from evaporating primordial black holes in the early universe, and estimate the relic abundance needed for PSR to account for the observed dark matter density. We also discuss some crucial differences between PSR and previous proposals of Planck mass relics.
Not a very promising line of theoretical exploration. Plank star remnants, primordial black holes, and basically all forms of heavy dark matter candidates (i.e. >> 1 GeV in mass), are disfavored by the astronomy data and don't deserve serious attention.
javisot also references it. are there any papers that specifically addresses planck mass relics as disfavored? or perhaps it only makes 1 component out of many others, such as sterile neutrinos.
planck mass relics won't require new particles to the standard model.
The problem is that, generically, heavy dark matter particle candidates aren't wave-like and would produce cuspy NFW dark matter halos which aren't what we see IRL.
MOND for galaxy rotation and planck mass relics for galaxies clusters + CMB
"planck mass relics for galaxies clusters + CMB" doesn't work. You can't segregate it like that.
Post a Comment