scholarly journals Modelling the Rising Tails of Galaxy Rotation Curves

2018 ◽  
Author(s):  
Fan Zhang
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Weak Field ◽  
Rotation Curves ◽  
Gravitational Fields ◽  
Modified Newtonian Dynamics ◽  
Rotation Periods ◽  
Weak Field Limit ◽  
Modified Gravity Theories ◽  
Galaxy Rotation Curves

It is well known but under-appreciated in astrophysical applications, that it is possible for gravity to take on a life of its own in the form of Weyl-curvature-only metrics (note we are referring to the Weyl-only solutions of ordinary General Relativity, we are not considering Weyl conformal gravity or any other modified gravity theories), as numerous examples demonstrate the existence of gravitational fields not being sourced by any matter. In the weak field limit, such autonomous gravitational contents of our universe manifest as solutions to the homogeneous Poisson's equation. In this note, we tentatively explore the possibility that they may perhaps account for some phenomenologies commonly attributed to dark matter. Specifically, we show that a very simple solution of this kind exists that can be utilized to describe the rising tails seen in many galaxy rotation curves, which had been difficult to reconcile within the cold dark matter or modified Newtonian dynamics frameworks. This solution may also help explain the universal $\sim 1$Gyr rotation periods of galaxies in the local universe.

scholarly journals Modelling the Rising Tails of Galaxy Rotation Curves

2019 ◽  
Author(s):  
Fan Zhang
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Weak Field ◽  
Rotation Curves ◽  
Gravitational Fields ◽  
Modified Newtonian Dynamics ◽  
Rotation Periods ◽  
Weak Field Limit ◽  
Modified Gravity Theories ◽  
Galaxy Rotation Curves

It is well known but under-appreciated in astrophysical applications, that it is possible for gravity to take on a life of its own in the form of Weyl-curvature-only metrics (note we are referring to the Weyl-only solutions of ordinary General Relativity, we are not considering Weyl conformal gravity or any other modified gravity theories), as numerous examples demonstrate the existence of gravitational fields not being sourced by any matter. In the weak field limit, such autonomous gravitational contents of our universe manifest as solutions to the homogeneous Poisson's equation. In this note, we tentatively explore the possibility that they may perhaps account for some phenomenologies commonly attributed to dark matter. Specifically, we show that a very simple solution of this kind exists that can be utilized to describe the rising tails seen in many galaxy rotation curves, which had been difficult to reconcile within the cold dark matter or modified Newtonian dynamics frameworks. This solution may also help explain the universal $\sim 1$Gyr rotation periods of galaxies in the local universe.

scholarly journals Modeling the Rising Tails of Galaxy Rotation Curves

Galaxies ◽  
2019 ◽  
Vol 7 (1) ◽  
pp. 27 ◽  
Author(s):  
Fan Zhang
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Weak Field ◽  
Rotation Curves ◽  
Gravitational Fields ◽  
Modified Newtonian Dynamics ◽  
Rotation Periods ◽  
Weak Field Limit ◽  
Modified Gravity Theories ◽  
Galaxy Rotation Curves

It is well known, but under-appreciated in astrophysical applications, that it is possible for gravity to take on a life of its own in the form of Weyl-curvature-only metrics (note that we are referring to the Weyl-only solutions of ordinary General Relativity; we are not considering Weyl conformal gravity or any other modified gravity theories), as numerous examples demonstrate the existence of gravitational fields not being sourced by any matter. In the weak field limit, such autonomous gravitational contents of our universe manifest as solutions to the homogeneous Poisson’s equation. In this note, we tentatively explore the possibility that they may perhaps account for some phenomenologies commonly attributed to dark matter. Specifically, we show that a very simple solution of this kind exists that can be utilized to describe the rising tails seen in many galaxy rotation curves, which had been difficult to reconcile within the cold dark matter or modified Newtonian dynamics frameworks. This solution may also help explain the universal ∼1 Gyr rotation periods of galaxies in the local universe.

scholarly journals Galaxy rotation curves in the light of the Spinor Theory of Gravity

2021 ◽  
Vol 36 (34) ◽  
Author(s):  
M. Novello ◽  
A. E. S. Hartmann ◽  
E. Bittencourt
Keyword(s):  
Weak Field ◽  
Dark Matter Halo ◽  
Newtonian Potential ◽  
Rotation Curves ◽  
Spinor Theory ◽  
Weak Field Limit ◽  
The Galaxy ◽  
Theory Of Gravity ◽  
Interesting Analogy ◽  
Galaxy Rotation Curves

We analyze the recently obtained static and spherically symmetric solutions of the Spinor Theory of Gravity (STG) which, in the weak field limit, presents an effective Newtonian potential that contains an extra logarithmic behavior. We apply this solution to the description of the galaxy rotation curves finding an interesting analogy with the dark matter halo profile proposed by Navarro, Frenk and White.

scholarly journals THE REAL PROBLEM WITH MOND

2011 ◽  
Vol 20 (14) ◽  
pp. 2749-2753 ◽  
Author(s):  
SCOTT DODELSON
Keyword(s):  
Dark Matter ◽  
Local Group ◽  
Weak Field ◽  
Gravity Models ◽  
Real Problem ◽  
Fundamental Particle ◽  
Modified Newtonian Dynamics ◽  
Weak Field Limit ◽  
Newtonian Dynamics ◽  
Baryonic Mass

Gravitational potentials in the cosmos are deeper than expected from observed visible objects, a phenomenon usually attributed to dark matter, presumably in the form of a new fundamental particle. Until such a particle is observed, the jury remains out on dark matter, and modified gravity models must be considered. The class of models reducing to modified Newtonian dynamics (MOND) in the weak field limit does an excellent job fitting the rotation curves of galaxies, predicting the relation between baryonic mass and velocity in gas-dominated galaxies, and explaining the properties of the local group. Several of the initial challenges facing MOND have been overcome, while others remain. Here we point out the most severe challenge facing MOND.

scholarly journals The Phantom Dark Matter Halos of the Local Volume in the Context of Modified Newtonian Dynamics

2021 ◽  
Vol 923 (1) ◽  
pp. 68
Author(s):  
P.-A. Oria ◽  
B. Famaey ◽  
G. F. Thomas ◽  
R. Ibata ◽  
J. Freundlich ◽  
...  
Keyword(s):  
Dark Matter ◽  
External Field ◽  
Cold Dark Matter ◽  
Average Density ◽  
Mass Relation ◽  
Rotation Curves ◽  
Local Volume ◽  
Linear Version ◽  
Observational Estimate ◽  
Galaxy Rotation Curves

Abstract We explore the predictions of Milgromian gravity (MOND) in the local universe by considering the distribution of the “phantom” dark matter (PDM) that would source the MOND gravitational field in Newtonian gravity, allowing an easy comparison with the dark matter framework. For this, we specifically deal with the quasi-linear version of MOND (QUMOND). We compute the “stellar-to-(phantom)halo mass relation” (SHMR), a monotonically increasing power law resembling the SHMR observationally deduced from spiral galaxy rotation curves in the Newtonian context. We show that the gas-to-(phantom)halo mass relation is flat. We generate a map of the Local Volume in QUMOND, highlighting the important influence of distant galaxy clusters, in particular Virgo. This allows us to explore the scatter of the SHMR and the average density of PDM around galaxies in the Local Volume, ΩPDM ≈ 0.1, below the average cold dark matter density in a ΛCDM universe. We provide a model of the Milky Way in its external field in the MOND context, which we compare to an observational estimate of the escape velocity curve. Finally, we highlight the peculiar features related to the external field effect in the form of negative PDM density zones in the outskirts of each galaxy, and test a new analytic formula for computing galaxy rotation curves in the presence of an external field in QUMOND. While we show that the negative PDM density zones would be difficult to detect dynamically, we quantify the weak-lensing signal they could produce for lenses at z ∼ 0.3.

scholarly journals Baryonic clues to the puzzling diversity of dwarf galaxy rotation curves

2020 ◽  
Vol 495 (1) ◽  
pp. 58-77 ◽  
Author(s):  
Isabel M E Santos-Santos ◽  
Julio F Navarro ◽  
Andrew Robertson ◽  
Alejandro Benítez-Llambay ◽  
Kyle A Oman ◽  
...  
Keyword(s):  
Dark Matter ◽  
Surface Density ◽  
Rotation Curve ◽  
Cold Dark Matter ◽  
Dwarf Galaxy ◽  
High Surface ◽  
Curve Shape ◽  
Disc Galaxy ◽  
Rotation Curves ◽  
Galaxy Rotation Curves

ABSTRACT We use a compilation of disc galaxy rotation curves to assess the role of the luminous component (‘baryons’) in the rotation curve diversity problem. As in earlier work, we find that rotation curve shape correlates with baryonic surface density: high surface density galaxies have rapidly rising rotation curves consistent with cuspy cold dark matter haloes; slowly rising rotation curves (characteristic of galaxies with inner mass deficits or ‘cores’) occur only in low surface density galaxies. The correlation, however, seems too weak to be the main driver of the diversity. In addition, dwarf galaxies exhibit a clear trend, from ‘cuspy’ systems where baryons are unimportant in the inner mass budget to ‘cored’ galaxies where baryons actually dominate. This trend constrains the various scenarios proposed to explain the diversity, such as (i) baryonic inflows and outflows during galaxy formation; (ii) dark matter self-interactions; (iii) variations in the baryonic mass structure coupled to rotation velocities through the ‘mass discrepancy–acceleration relation’ (MDAR); or (iv) non-circular motions in gaseous discs. Together with analytical modelling and cosmological hydrodynamical simulations, our analysis shows that each of these scenarios has promising features, but none seems to fully account for the observed diversity. The MDAR, in particular, is inconsistent with the observed trend between rotation curve shape and baryonic importance; either the trend is caused by systematic errors in the data or the MDAR does not apply. The origin of the dwarf galaxy rotation curve diversity and its relation to the structure of cold dark matter haloes remains an open issue.

scholarly journals A FLUID OF STRINGS AS A VIABLE CANDIDATE FOR THE DARK SIDE OF THE UNIVERSE

2006 ◽  
Vol 15 (01) ◽  
pp. 69-94 ◽  
Author(s):  
S. CAPOZZIELLO ◽  
V. F. CARDONE ◽  
G. LAMBIASE ◽  
A. TROISI
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Cosmological Constant ◽  
Cold Dark Matter ◽  
Weak Field ◽  
Dark Side ◽  
Density Parameter ◽  
Weak Field Limit ◽  
Type Ia ◽  
The Universe

We investigate the possibility that part of the dark matter is not made out of the usual cold dark matter (CDM) dust-like particles, but is in the form of a fluid of strings with barotropic factor ws= -1/3 of cosmic origin. To this aim, we split the dark matter density parameter into two terms and investigate the dynamics of a spatially flat universe filled with baryons, CDM, a fluid of strings and dark energy, modeling the latter as a cosmological constant or a negative pressure fluid with a constant equation of state w < 0. To test the viability of the models and to constrain their parameters, we use the Type Ia supernovae Hubble diagram and data on the gas mass fraction in galaxy clusters. We also discuss the weak field limit of a model comprising a significant fraction of dark matter in the form of a fluid of strings and show that this mechanism makes it possible to reduce the need for the elusive and up to now undetected CDM. We finally find that a model comprising both a cosmological constant and a fluid of strings fits the data very well and eliminates the need for phantom dark energy, thus representing a viable candidate for alleviating some of the problems plaguing the dark side of the universe.

scholarly journals Dark Matter as Gravitational Solitons in the Weak Field Limit

Universe ◽  
2020 ◽  
Vol 6 (12) ◽  
pp. 234
Author(s):  
Torsten Asselmeyer-Maluga ◽  
Jerzy Król
Keyword(s):  
Dark Matter ◽  
Equation Of State ◽  
Gravitational Lensing ◽  
Weak Field ◽  
Field Limit ◽  
Gravitational Fields ◽  
Weak Field Limit ◽  
Lensing Effect ◽  
The Stability

In this paper, we will describe the idea that dark matter partly consists of gravitational solitons (gravisolitons). The corresponding solution is valid for weak gravitational fields (weak field limit) with respect to a background metric. The stability of this soliton is connected with the existence of a special foliation and amazingly with the smoothness properties of spacetime. Gravisolitons have many properties of dark matter, such as no interaction with light but act on matter via gravitation. In this paper, we showed that the gravitational lensing effect of gravisolitons agreed with the lensing effect of usual matter. Furthermore, we obtained the same equation of state w=0 as matter.

scholarly journals MODIFIED GRAVITY AS A COMMON CAUSE FOR COSMIC ACCELERATION AND FLAT GALAXY ROTATION CURVES

2012 ◽  
Vol 21 (11) ◽  
pp. 1242002 ◽  
Author(s):  
PRITI MISHRA ◽  
TEJINDER P. SINGH
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Cosmic Acceleration ◽  
Accelerating Universe ◽  
Rotation Curves ◽  
Common Cause ◽  
Order Of Magnitude ◽  
Flat Rotation Curves ◽  
Acceleration Of The Universe ◽  
Galaxy Rotation Curves

Flat galaxy rotation curves and the accelerating Universe both imply the existence of a critical acceleration, which is of the same order of magnitude in both the cases, in spite of the galactic and cosmic length scales being vastly different. Yet, it is customary to explain galactic acceleration by invoking gravitationally bound dark matter, and cosmic acceleration by invoking a "repulsive" dark energy. Instead, might it not be the case that the flatness of rotation curves and the acceleration of the Universe have a common cause? In this essay we propose a modified theory of gravity. By applying the theory on galactic scales we demonstrate flat rotation curves without dark matter, and by applying it on cosmological scales we demonstrate cosmic acceleration without dark energy.

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