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2 pages, 137 KiB

Open AccessEditor’s ChoiceEditorial

Debate on the Physics of Galactic Rotation and the Existence of Dark Matter

by Anne M. Hofmeister and Robert E. Criss

Galaxies 2020, 8(3), 54; https://doi.org/10.3390/galaxies8030054 - 15 Jul 2020

Cited by 4 | Viewed by 3549

Abstract

This Special Issue was motivated by the disparate explanations of galactic dynamics promulgated by different philosophical camps [...] Full article

(This article belongs to the Special Issue Debate on the Physics of Galactic Rotation and the Existence of Dark Matter)

Research

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6 pages, 1366 KiB

Open AccessArticle

Surface Brightness Plateau in S4G Galaxies

by Alan Sipols and Alex Pavlovich

Galaxies 2020, 8(2), 48; https://doi.org/10.3390/galaxies8020048 - 6 Jun 2020

Cited by 3 | Viewed by 4012

Abstract

Using 3.6-μm data from 2112 galaxies, we show that, contrary to widely held expectations of a continuous steep decline, radial surface brightness profiles of galaxies tend to flatten and form extended plateaus beyond 27–28 mag_AB/arcsec². This phenomenon could be [...] Read more.

Using 3.6-μm data from 2112 galaxies, we show that, contrary to widely held expectations of a continuous steep decline, radial surface brightness profiles of galaxies tend to flatten and form extended plateaus beyond 27–28 mag_AB/arcsec². This phenomenon could be explained by the presence of extended stellar populations dominated by low-mass stars in galactic outskirts. The flattening of radial brightness profiles questions the artificial exponential extrapolations of brightness data and the automatic assumption that light always declines considerably faster than mass density, presenting an empirical challenge for the dark matter hypothesis. Full article

(This article belongs to the Special Issue Debate on the Physics of Galactic Rotation and the Existence of Dark Matter)

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8 pages, 704 KiB

Open AccessArticle

Gravitational Focusing of Low-Velocity Dark Matter on the Earth’s Surface

by Yoshiaki Sofue

Galaxies 2020, 8(2), 42; https://doi.org/10.3390/galaxies8020042 - 16 May 2020

Cited by 20 | Viewed by 3383

Abstract

We show that the Earth acts as a high-efficiency gravitational collector of low-velocity flow of dark matter (DM). The focal point appears on the Earth’s surface, when the DM flow speed is about 17 km/s with respect to the geo-center. We discuss diurnal [...] Read more.

We show that the Earth acts as a high-efficiency gravitational collector of low-velocity flow of dark matter (DM). The focal point appears on the Earth’s surface, when the DM flow speed is about 17 km/s with respect to the geo-center. We discuss diurnal modulation of the local DM density influenced by the Earth’s gravity. We also touch upon similar effects on galactic and solar system objects. Full article

(This article belongs to the Special Issue Debate on the Physics of Galactic Rotation and the Existence of Dark Matter)

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32 pages, 1688 KiB

Open AccessArticle

Dark Matter Dogma: A Study of 214 Galaxies

by Alan Sipols and Alex Pavlovich

Galaxies 2020, 8(2), 36; https://doi.org/10.3390/galaxies8020036 - 28 Apr 2020

Cited by 14 | Viewed by 8530

Abstract

The aim of this paper is to test the need for non-baryonic dark matter in the context of galactic rotation and the apparent difference between distributions of galactic mass and luminosity. We present a set of rotation curves and 3.6 μm surface brightness [...] Read more.

The aim of this paper is to test the need for non-baryonic dark matter in the context of galactic rotation and the apparent difference between distributions of galactic mass and luminosity. We present a set of rotation curves and 3.6 μm surface brightness profiles for a diverse sample of 214 galaxies. Using rotation curves as the sole input into our Newtonian disk model, we compute non-parametric radial profiles of surface mass density. All profiles exhibit lower density than parametric models with dark halos and provide a superior fit with observed rotation curves. Assuming all dynamical mass is in main-sequence stars, we estimate radial distributions of characteristic star mass implied by the corresponding pairs of density and brightness profiles. We find that for 132 galaxies or 62% of the sample, the relation between density and brightness can be fully explained by a radially declining stellar mass gradient. Such idealized stellar population fitting can also largely address density and brightness distributions of the remaining 82 galaxies, but their periphery shows, on average, 14 M_⊙/pc² difference between total density and light-constrained stellar density. We discuss how this density gap can be interpreted, by considering a low-luminosity baryonic matter, observational uncertainties, and visibility cutoffs for red dwarf populations. Lastly, we report tight correlation between radial density and brightness trends, and the discovered flattening of surface brightness profiles—both being evidence against dark matter. Our findings make non-baryonic dark matter unnecessary in the context of galactic rotation. Full article

(This article belongs to the Special Issue Debate on the Physics of Galactic Rotation and the Existence of Dark Matter)

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33 pages, 15972 KiB

Open AccessArticle

Density Profiles of 51 Galaxies from Parameter-Free Inverse Models of Their Measured Rotation Curves

by Robert E. Criss and Anne M. Hofmeister

Galaxies 2020, 8(1), 19; https://doi.org/10.3390/galaxies8010019 - 26 Feb 2020

Cited by 12 | Viewed by 5609

Abstract

Spiral galaxies and their rotation curves have key characteristics of differentially spinning objects. Oblate spheroid shapes are a consequence of spin and reasonably describe galaxies, indicating that their matter is distributed in gravitationally interacting homeoidal shells. Here, previously published equations describing differentially spinning [...] Read more.

Spiral galaxies and their rotation curves have key characteristics of differentially spinning objects. Oblate spheroid shapes are a consequence of spin and reasonably describe galaxies, indicating that their matter is distributed in gravitationally interacting homeoidal shells. Here, previously published equations describing differentially spinning oblate spheroids with radially varying density are applied to 51 galaxies, mostly spirals. A constant volumetric density (ρ, kg m⁻³) is assumed for each thin homeoid in these formulae, after Newton, which is consistent with RCs being reported simply as a function of equatorial radius r. We construct parameter-free inverse models that uniquely specify mass inside any given r, and thus directly constrain ρ vs. r solely from velocity v (r) and galactic aspect ratios (assumed as 1:10 for spirals when data are unavailable). Except for their innermost zones, ρ is proven to be closely proportional to rⁿ, where the statistical average of n for all 36 spirals studied is −1.80 ± 0.40. Our values for interior densities compare closely with independently measured baryon density in appropriate astronomical environments: for example, calculated ρ at galactic edges agrees with independently estimated ρ of intergalactic media (IGM). Our finding that central densities increase with galaxy size is consistent with behavior exhibited by diverse self-gravitating entities. Our calculated mass distributions are consistent with visible luminosity and require no non-baryonic component. Full article

(This article belongs to the Special Issue Debate on the Physics of Galactic Rotation and the Existence of Dark Matter)

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16 pages, 556 KiB

Open AccessArticle

Entropy and Mass Distribution in Disc Galaxies

by John Herbert Marr

Galaxies 2020, 8(1), 12; https://doi.org/10.3390/galaxies8010012 - 8 Feb 2020

Cited by 6 | Viewed by 3735

Abstract

The relaxed motion of stars and gas in galactic discs is well approximated by a rotational velocity that is a function of radial position only, implying that individual components have lost any information about their prior states. Thermodynamically, such an equilibrium state is [...] Read more.

The relaxed motion of stars and gas in galactic discs is well approximated by a rotational velocity that is a function of radial position only, implying that individual components have lost any information about their prior states. Thermodynamically, such an equilibrium state is a microcanonical ensemble with maximum entropy, characterised by a lognormal probability distribution. Assuming this for the surface density distribution yields rotation curves that closely match observational data across a wide range of disc masses and galaxy types and provides a useful tool for modelling the theoretical density distribution in the disc. A universal disc spin parameter emerges from the model, giving a tight virial mass estimator with strong correlation between angular momentum and disc mass, suggesting a mechanism by which the proto-disc developed by dumping excess mass to the core or excess angular momentum to a satellite galaxy. The baryonic-to-dynamic mass ratio for the model approaches unity for high mass galaxies, but is generally <1 for low mass discs, and this discrepancy appears to follow a similar relationship to that shown in recent work on the Radial Acceleration Relation (RAR). Although this may support Modified Newtonian Dynamics (MOND) in preference to a Dark Matter (DM) halo, it does not exclude undetected baryonic mass or a gravitational DM component in the disc. Full article

(This article belongs to the Special Issue Debate on the Physics of Galactic Rotation and the Existence of Dark Matter)

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Review

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38 pages, 7136 KiB

Open AccessReview

Debated Models for Galactic Rotation Curves: A Review and Mathematical Assessment

by Anne M. Hofmeister and Robert E. Criss

Galaxies 2020, 8(2), 47; https://doi.org/10.3390/galaxies8020047 - 1 Jun 2020

Cited by 6 | Viewed by 6730

Abstract

Proposed explanations of galactic rotation curves (RC = tangential velocity vs. equatorial radius, determined from Doppler measurements) involve dramatically different assumptions. A dominant, original camp invoked huge amounts of unknown, non-baryonic dark matter (NBDM) in surrounding haloes to reconcile RC simulated using their [...] Read more.

Proposed explanations of galactic rotation curves (RC = tangential velocity vs. equatorial radius, determined from Doppler measurements) involve dramatically different assumptions. A dominant, original camp invoked huge amounts of unknown, non-baryonic dark matter (NBDM) in surrounding haloes to reconcile RC simulated using their Newtonian orbital models (NOMs) for billions of stars in spiral galaxies with the familiar Keplerian orbital patterns of the few, tiny planets in our Solar System. A competing minority proposed that hypothetical, non-relativistic, non-Newtonian forces govern the internal motions of galaxies. More than 40 years of controversy has followed. Other smaller groups, unsatisfied by explanations rooted in unknown matter or undocumented forces, have variously employed force summations, spin models, or relativistic adaptations to explain galactic rotation curves. Some small groups have pursued inverse models and found no need for NBDM. The successes, failures, and underlying assumptions of the above models are reviewed in this paper, focusing on their mathematical underpinnings. We also show that extractions of RC from Doppler measurements need revising to account for the effect of galaxy shape on flux-velocity profiles and for the possible presence of a secondary spin axis. The latter is indicated by complex Doppler shift patterns. Our findings, combined with independent evidence such as hadron collider experiments failing to produce non-baryonic matter, suggest that a paradigm shift is unfolding. Full article

(This article belongs to the Special Issue Debate on the Physics of Galactic Rotation and the Existence of Dark Matter)

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20 pages, 742 KiB

Open AccessReview

Rotation Curve of the Milky Way and the Dark Matter Density

by Yoshiaki Sofue

Galaxies 2020, 8(2), 37; https://doi.org/10.3390/galaxies8020037 - 29 Apr 2020

Cited by 83 | Viewed by 10725

Abstract

We review the current status of the study of rotation curve (RC) of the Milky Way, and present a unified RC from the Galactic Center to the galacto-centric distance of about 100 kpc. The RC is used to directly calculate the distribution of [...] Read more.

We review the current status of the study of rotation curve (RC) of the Milky Way, and present a unified RC from the Galactic Center to the galacto-centric distance of about 100 kpc. The RC is used to directly calculate the distribution of the surface mass density (SMD). We then propose a method to derive the distribution of dark matter (DM) density in the in the Milky Way using the SMD distribution. The best-fit dark halo profile yielded a local DM density of

ρ_{⊙} = 0.36 \pm 0.02

GeV cm

^{- 3}

. We also review the estimations of the local DM density in the last decade, and show that the value is converging to a value at

ρ_{⊙} = 0.39 \pm 0.09

GeV cm

^{- 3}

. Full article

(This article belongs to the Special Issue Debate on the Physics of Galactic Rotation and the Existence of Dark Matter)

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33 pages, 2742 KiB

Open AccessReview

Predictions and Outcomes for the Dynamics of Rotating Galaxies

by Stacy McGaugh

Galaxies 2020, 8(2), 35; https://doi.org/10.3390/galaxies8020035 - 24 Apr 2020

Cited by 59 | Viewed by 5754

Abstract

A review is given of a priori predictions made for the dynamics of rotating galaxies. One theory—MOND—has had many predictions corroborated by subsequent observations. While it is sometimes possible to offer post hoc explanations for these observations in terms of dark matter, it [...] Read more.

A review is given of a priori predictions made for the dynamics of rotating galaxies. One theory—MOND—has had many predictions corroborated by subsequent observations. While it is sometimes possible to offer post hoc explanations for these observations in terms of dark matter, it is seldom possible to use dark matter to predict the same phenomena. Full article

(This article belongs to the Special Issue Debate on the Physics of Galactic Rotation and the Existence of Dark Matter)

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15 pages, 1195 KiB

Open AccessReview

Rotating Disk Galaxies without Dark Matter Based on Scientific Reasoning

by James Q. Feng

Galaxies 2020, 8(1), 9; https://doi.org/10.3390/galaxies8010009 - 1 Feb 2020

Cited by 6 | Viewed by 4994

Abstract

The most cited evidence for (non-baryonic) dark matter has been an apparent lack of visible mass to gravitationally support the observed orbital velocity of matter in rotating disk galaxies, yet measurement of the mass of celestial objects cannot be straightforward, requiring theories derived [...] Read more.

The most cited evidence for (non-baryonic) dark matter has been an apparent lack of visible mass to gravitationally support the observed orbital velocity of matter in rotating disk galaxies, yet measurement of the mass of celestial objects cannot be straightforward, requiring theories derived from the known physical laws along with some empirically established semi-quantitative relationship. The most reliable means for determining the mass distribution in rotating disk galaxies is to solve a force balance equation according to Newton’s laws from measured rotation curves, similar to calculating the Sun’s mass from the Earth’s orbital velocity. Another common method to estimate galactic mass distribution is to convert measured brightness from surface photometry based on empirically established mass-to-light ratio. For convenience, most astronomers commonly assumed a constant mass-to-light ratio for estimation of the so-called “luminous” or “visible” mass, which would not likely be accurate. The mass determined from a rotation curve typically exhibits an exponential-like decline with galactrocentric distance, qualitatively consistent with observed surface brightness but often with a larger disk radial scale length. This fact scientifically suggests variable mass-to-light ratio of baryonic matter in galaxies without the need for dark matter. Full article

(This article belongs to the Special Issue Debate on the Physics of Galactic Rotation and the Existence of Dark Matter)

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