scholarly journals A comparison of two spherical mass-distribution models

2001 ◽  
pp. 17-19
Author(s):  
S. Ninkovic
Keyword(s):  
Density Dependence ◽  
Mass Distribution ◽  
Spherically Symmetric ◽  
Distribution Models ◽  
Mass Distributions ◽  
Spherical Mass ◽  
Special Case ◽  
Scale Length

Two spherically symmetric mass-distribution models - a special case of the generalized Schuster density law and the generalized isochrone model (both yield the same approximate density dependence on the distance in the outer parts) - are compared. It is shown that in the interval of the relative second scale length for the latter case of 0.5-0.6 the two mass distributions are almost identical. Considering to advantages, i.e. disadvantages, of the formulae describing these mass distributions this result can be of interest.

scholarly journals On the generalized Schuster density law

1998 ◽  
pp. 15-21 ◽  
Author(s):  
S. Ninkovic
Keyword(s):  
Positive Integer ◽  
Mass Distribution ◽  
Axial Symmetry ◽  
Total Mass ◽  
Spiral Galaxies ◽  
Stellar Systems ◽  
Finite Radius ◽  
Mass Distributions ◽  
Almost All ◽  
Special Case

A special case of the generalized Schuster density law for stellar systems with spherical symmetry is discussed; here the exponent in the denominator is equal to i/2 where i is a positive integer. Special attention is paid to the situation 2 ? i ? 5 since then the mass distributions in almost all approximately spherical stellar systems and subsystems known to exist - e. g. dark coronae of galaxies, bulges and halos of spiral galaxies, as well as the systems with the classical Schuster density law - are included. With certain improvements one can also obtain more ample variants including the density continuously attaining zero at a finite radius, somewhat different descriptions of the mass distribution, as well as generalizations towards axial symmetry. It is shown among others, that a spheroid with this mass distribution (i=4) yields the same total mass as the exponential disc and that the mass distribution proposed by King belongs asymptotically to the generalized Schuster density law (i=3).

scholarly journals Dark Matter or Additional Gravitational Forces Generated by Non-Spherical Mass Distributions?

2017 ◽  
Vol 01 (02) ◽  
pp. 1750004
Author(s):  
Enbang Li
Keyword(s):  
Dark Matter ◽  
Galaxy Clusters ◽  
Gravitational Lensing ◽  
Modern Science ◽  
Theory Of Relativity ◽  
Distribution Models ◽  
Mass Distributions ◽  
Negative Results ◽  
Spherical Mass ◽  
The Masses

The measured orbital velocity distributions of stars in galaxies and the observed gravitational lensing effects in galaxy clusters suggest that there should be more mass than that can be explained by the visible mass of stars, gas and dust in the galaxies. This unseen mass or matter, generally referred to as dark matter, has puzzled physicists for a few decades and has now become one of the greatest unsolved mysteries in modern science. So far, all of the efforts aiming to generate and detect the exotic dark matter substance have yielded negative results. Here, starting from Newton’s law of gravity, we show that the spherical mass distribution models originally employed for estimating the masses of galaxies could cause the discrepancy between the actual masses and those calculated from the rotational velocities. It is demonstrated that additional gravitational effects are generated from non-spherical mass distributions in the cosmic structures. The currently observed rotation curves and gravitational lensing effects in galaxies and galaxy clusters could be explained under the frameworks of Newtonian gravity and Einstein’s general theory of relativity when proper mass distributions are considered.

QELSS diffusion data for moderately broad molar mass distribution polymer samples compared with data from classical gradient techniques

1989 ◽  
Vol 54 (7) ◽  
pp. 1821-1829
Author(s):  
Bedřich Porsch ◽  
Simon King ◽  
Lars-Olof Sundelöf
Keyword(s):  
Diffusion Coefficient ◽  
Mass Distribution ◽  
Molar Mass ◽  
Molar Mass Distribution ◽  
Diffusion Data ◽  
Mass Distributions ◽  
Classical Diffusion ◽  
Polydisperse Polymer

The differences between the QELSS and classical diffusion coefficient of a polydisperse polymer resulting from distinct definitions of experimentally accessible average values are calculated for two assumed specific forms of molar mass distributions. Predicted deviations are compared with the experiment using NBS 706 standard polystyrene. QELSS Dz of this sample relates within 2-4% to the classical diffusion coefficient, if the Schulz-Zimm molar mass distribution is assumed to be valid. In general, differences between the height-area and QELSS diffusion coefficient of about 20% may be found for Mw/Mn ~ 2, and this value may increase above 35%, if strongly tailing molar mass distribution pertains to the sample.

AN APPLICATION OF THE TOPOLOGICAL DEGREE TO GRAVITATIONAL LENSES

1998 ◽  
Vol 13 (02) ◽  
pp. 83-86 ◽  
Author(s):  
MARCO LOMBARDI
Keyword(s):  
Point Source ◽  
Mass Distribution ◽  
Topological Degree ◽  
General Theorem ◽  
Gravitational Lens ◽  
Gravitational Lenses ◽  
General Proof ◽  
Special Case

In this letter we provide a new proof of a general theorem on gravitational lenses, first proven by Burke (1981) for the special case of thin lenses. The theorem states that a transparent gravitational lens with non-singular mass distribution produces an odd number of images of a point source. Our general proof shows that the topological degree finds natural and interesting applications in the theory of gravitational lenses.

scholarly journals Dynamical Instabilities in Spherical Stellar Systems

1985 ◽  
Vol 113 ◽  
pp. 297-299
Author(s):  
Joshua Barnes
Keyword(s):  
Mass Distribution ◽  
Spherical Symmetry ◽  
Mean Field ◽  
The Other ◽  
Stellar Systems ◽  
Spherically Symmetric ◽  
Quadrupole Mode ◽  
Radial Forces ◽  
The Mean ◽  
Dynamical Instabilities

Equlibrium spherical stellar systems exhibiting instabilities on a dynamical timescale were first studied by Henon (1973), using a spherically symmetric N-body code. We have re-examined Henon's models using an improved code which includes non-radial forces to quadrupole order. In addition to the radial instability reported by Henon, two new non-radial instabilities are also observed. In one, found in models with highly circular orbits, the mass distribution exhibits quadrupole-mode oscillations. In the other, seen in models with highly radial orbits, the system spontaneously breaks spherical symmetry and settles into a tri-axial ellipsoid. These instabilities, which are driven by fluctuations of the mean field, offer some analogies to the well-known dynamical instabilities of a cold disk of stars. While our models are rather artificial, they indicate that dynamical instabilities may be more common in spherical systems than had been thought.

scholarly journals The Distance and Orientation of the Galactic Bulge from Mira Variables: A Preliminary Report

1999 ◽  
Vol 192 ◽  
pp. 89-94 ◽  
Author(s):  
R. M. Catchpole ◽  
P. A. Whitelock ◽  
M. W. Feast ◽  
S.M.G. Hughes ◽  
C. Alard ◽  
...  
Keyword(s):  
Preliminary Report ◽  
Near Infrared ◽  
Major Axis ◽  
Galactic Centre ◽  
Spherically Symmetric ◽  
Axis Ratio ◽  
Circular Symmetry ◽  
Mira Variables ◽  
Axis Of Rotation ◽  
Scale Length

Near-infrared, JHKL, observations of 595 Mira variables in two fields on either side of the centre of our Galaxy, confirm that the Bulge is not spherically symmetric about its axis of rotation, but is elongated so that the part to the east of the centre is closer to us. The shape of the Bulge about its axis of rotation is not uniquely defined by these data, but the shape that deviates least from circular symmetry has an axis ratio xo/yo = 1.7, with a major axis at an angle, θ = 58° ± 7, to the plane of the sky, for a galactic centre distance, R0 = 9.4 ± 0.5 kpc. This is based on an assumed scale length in galactic coordinates of bo = 375 pc and lo/bo = 2.0.

scholarly journals N-Body Results on Dark Matter

1987 ◽  
Vol 117 ◽  
pp. 263-278
Author(s):  
Simon D. M. White
Keyword(s):  
Dark Matter ◽  
Mass Distribution ◽  
Cold Dark Matter ◽  
Density Fluctuations ◽  
Major Difficulty ◽  
Mass Distributions ◽  
Galaxy Distribution ◽  
Galaxy Halos ◽  
Flat Rotation Curves ◽  
The Universe

The structure of the dominant “dark” component of the Universe may evolve primarily under the influence of gravity. A number of models for the evolution of the Universe make specific predictions for the statistical properties of density fluctuations at early times. N-body simulations can follow the nonlinear development of such fluctuations to the present day. A major difficulty arises because we cannot observe the present mass distribution directly. Recent N-body work has concentrated on models dominated by weakly interacting free elementary particles. Neutrino-dominated but otherwise conventional cosmologies pass rapidly from a smooth distribution to one dominated by lumps with masses greater than those of any known object. Cosmologies dominated by “cold dark matter” produce mass distributions which fit the observed galaxy distribution (i) if Ω = 0.1–0.2 and galaxies follow the mass distribution, or (ii) if Ω = 1, HO< 50 km/s/Mpc and galaxies form preferentially in high density regions. In the latter case, clumps form with flat rotation curves with about the amplitude and abundance expected for galaxy halos.

scholarly journals Differences in Mass Distribution for Field and Cluster Spiral Galaxies

1987 ◽  
Vol 117 ◽  
pp. 66-66 ◽  
Author(s):  
David Burstein ◽  
Vera C. Rubin
Keyword(s):  
Mass Distribution ◽  
Classification Scheme ◽  
Spiral Galaxies ◽  
Three Dimensional ◽  
Rotation Curves ◽  
Mass Distributions ◽  
Distribution Form ◽  
Simple Classification ◽  
Observational Fact

Our group has now obtained rotation curves for 80 spiral galaxies, Hubble types Sa through Sd. As described in Rubin et al. (Ap. J. 289, 81; 1985), the forms of these rotation curves are similar for all Hubble types. Given this observational fact, we have chosen to analyze the mass distributions for these galaxies under the assumption that the mass distributions for all spirals can be described by the same three-dimensional form, here taken to be spherical for simplicity. The mass distribution forms for 71 of these galaxies can be placed into a simple classification scheme based on the curvature of mass distribution form in a log(radius) - log (integral mass) diagram. The three most common mass forms among this continuum are termed Types I, II and III, the forms of which are displayed below (see also the discussion by Rubin elsewhere in this Symposium).

Spherically symmetric static matter configurations with vanishing radial pressure

2014 ◽  
Vol 24 (01) ◽  
pp. 1550002 ◽  
Author(s):  
S. Thirukkanesh ◽  
M. Govender ◽  
D. B. Lortan
Keyword(s):  
Gravitational Field ◽  
Radial Pressure ◽  
Constant Density ◽  
Spherically Symmetric ◽  
Einstein Field Equations ◽  
Field Equations ◽  
New Family ◽  
Generating Method ◽  
Static Solutions ◽  
Special Case

We present a new family of spherically symmetric, static solutions of the Einstein field equations in isotropic, comoving coordinates. The radial pressure at each interior point of these models vanishes yet equilibrium is still possible. The constant density Florides solution which describes the gravitational field inside an Einstein cluster is obtained as a special case of our solution-generating method. We show that our solutions can be utilized to model strange star candidates such as Her. X-1, SAX J1808.4-3658(SS2), SAX J1808.4-3658(SS1) and PSR J1614-2230.

scholarly journals Bivariate luminosity-HI mass distribution function of galaxies based on the NIBLES survey

2018 ◽  
Vol 619 ◽  
pp. A89 ◽  
Author(s):  
Z. Butcher ◽  
S. Schneider ◽  
W. van Driel ◽  
M. D. Lehnert
Keyword(s):  
Mass Distribution ◽  
Luminosity Function ◽  
Hubble Constant ◽  
Mass Function ◽  
Volume Density ◽  
Local Universe ◽  
Mass Distributions ◽  
Low Mass ◽  
The Mean ◽  
Mass Distribution Function

We present a new optical luminosity-HI mass bivariate luminosity function (BLF) based on HI line observations from the Nançay Interstellar Baryons Legacy Extragalactic Survey (NIBLES). NIBLES sources lie within the local universe (900 ≤ c z ≤ 12 000 km s−1) and were chosen from SDSS DR5 such that the optical luminosity function was sampled as uniformly as possible. The HI mass function (HIMF) derived from our raw-data BLF, which is based on HI detections only, is consistent with the HIMFs derived from other optically selected surveys in that the low-mass slope is flatter than those derived from blind HI surveys. However, spanning the entire luminosity range of NIBLES, we identify a highly consistent distribution of the HI gas mass to luminosity ratio (gas-to-light ratio) with a predictable progression in the mean MHI/L r ratio as a function of L r. This consistency allows us to construct plausible gas-to-light ratio distributions for very low-luminosity bins which lie outside the NIBLES sample. We also identify a ∼10% decrease in detection fraction for galaxies fainter than log(L r) = 9.25, consistent with the expected decrease due to distance and sensitivity effects. Accounting for these trends, we reconstruct plausible gas-to-light distributions spanning luminosity bins down to log(L r) = 5.25, thus producing a corrected BLF. This corrected BLF is in good qualitative agreement with optical luminosity-HI mass distributions from the ALFALFA survey and is able to accurately reproduce blind survey HIMFs, lending credibility that this two dimensional optical luminosity-HI mass distribution is an accurate representation of the volume density distribution of galaxies in the local universe. We also note that our agreement with HIMFs from other surveys is dependent on accounting for all systematic differences such as selection method, Hubble constant and HI flux scale.

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