scholarly journals Dark Matter Near the Sun: Simulated Star Counts and the Oort Limit

1984 ◽  
Vol 81 ◽  
pp. 326-329
Author(s):  
David Gilden ◽  
John N. Bahcall
Keyword(s):  
Dark Matter ◽  
Galactic Disk ◽  
The Sun ◽  
Sampling Errors ◽  
Specific Mass ◽  
Mass Model ◽  
Density Distributions ◽  
Self Consistent ◽  
The Galaxy ◽  
Solar Position

AbstractAn ensemble of orbits passing through the solar position have been generated for a specific mass model of the galaxy. These orbits are randomly sampled to form simulated density distributions of tracer stars perpendicular to the galactic disk. The simulated distributions are analyzed in order to determine the sampling errors in a self-consistent derivation of the total amount of matter near the sun (the Oort limit).

scholarly journals Dark Matter in the Galactic Disk

1987 ◽  
Vol 117 ◽  
pp. 17-31 ◽  
Author(s):  
John N. Bahcall
Keyword(s):  
Dark Matter ◽  
Proper Motion ◽  
Column Density ◽  
Galactic Disk ◽  
Volume Density ◽  
Scale Height ◽  
The Sun ◽  
Vlasov Equations ◽  
Disk Mass ◽  
The Galaxy

The Poisson and Vlasov equations are solved self-consistently for realistic Galaxy models which include multiple disk components, a Population II spheroid, and an unseen massive halo. The total amount of matter in the vicinity of the Sun is determined by comparing the observed distributions of tracer stars, samples of F dwarfs and of K giants, with the predictions of the Galaxy models. Results are obtained for a number of different assumed distributions of the unseen disk mass. The major uncertainties, observational and theoretical, are estimated. For all the observed samples, typical models imply that about half of the mass in the solar vicinity must be in the form of unobserved matter. The volume density of unobserved material near the Sun is about 0.1M⊙pc−3; the corresponding column density is about 30M⊙pc−2. This so far unseen material must be in a disk with an exponential scale height of less than 0.7 kpc. If the unseen material is in the form of stars with masses less than 0.1M⊙, then the nearest such object is about 1 pc away and has a proper motion of more than 1 arcsecond per year.

Dark matter near the Sun

1986 ◽  
Vol 320 (1556) ◽  
pp. 543-551 ◽  
Keyword(s):  
Dark Matter ◽  
Volume Density ◽  
Scale Height ◽  
The Sun ◽  
Clusters Of Galaxies ◽  
Low Mass Stars ◽  
Disc Material ◽  
The Galaxy ◽  
Low Mass ◽  
Solar Position

The amount of dark matter in the disc of the Galaxy at the solar position is determined by comparing the observed distributions of tracer stars with the predictions obtained from different assumptions of how the unseen matter is distributed. The major uncertainties, observational and theoretical, are estimated. For all the observed samples, typical models imply that about half of the mass in the solar vicinity must be in the form of unobserved matter. The volume density of unobserved material near the Sun is about 0.1 M pc -3 ; the corresponding column density is about 30 M pc -2 (1 pc ~ 30857 x 10 12 m). This, so far unseen, material must be in a disc with an exponential scale height of less than 0.7 kpc. All the existing observations are consistent with the unseen disc material being in the form of stars not massive enough to burn hydrogen. It is suggested that the unseen material that is required to hold up the rotation curves of galaxies and to satisfy the virial theorem for clusters of galaxies might also be in the form of low-mass stars.

scholarly journals The Evolution of 3He, 4He and D in the Galaxy

2000 ◽  
Vol 198 ◽  
pp. 540-546 ◽  
Author(s):  
Cristina Chiappini ◽  
Francesca Matteucci
Keyword(s):  
Chemical Evolution ◽  
Present Model ◽  
Galactic Disk ◽  
The Sun ◽  
Mixing Process ◽  
Low Mass Stars ◽  
A Value ◽  
The Galaxy ◽  
Low Mass ◽  
Standing Problem

In this work we present the predictions of a modified version of the ‘two-infall model’ (Chiappini et al. 1997 - CMG) for the evolution of 3He, 4He and D in the solar vicinity, as well as their distributions along the Galactic disk. In particular, we show that when allowing for extra-mixing process in low mass stars (M < 2.5 M⊙), as predicted by Charbonnel and do Nascimento (1998), a long standing problem in chemical evolution is solved, namely: the overproduction of 3He by the chemical evolution models as compared to the observed values in the sun and in the interstellar medium. Moreover, we show that chemical evolution models can constrain the primordial value of the deuterium abundance and that a value of (D/H)p < 3 × 10—5 is suggested by the present model. Finally, adopting the primordial 4He abundance suggested by Viegas et al. (1999), we obtain a value for ΔY/ΔZ ≃ 2 and a better agreement with the solar 4He abundance.

scholarly journals Interaction between the Galactic Disk and Halo Components

1977 ◽  
Vol 45 ◽  
pp. 241-246 ◽  
Author(s):  
Jeremiah P. Ostriker
Keyword(s):  
Rotational Motion ◽  
Galactic Disk ◽  
Stellar Mass ◽  
Point Of View ◽  
The Sun ◽  
Disk System ◽  
The Galaxy ◽  
Metal Abundance ◽  
Random Motions ◽  
Disk Component

At least three component parts of the galaxy must be recognized. TheDisk Componentof the galaxy might be defined as follows. Spatially it is largely confined between the planes ± 1 kpc from the plane of symmetry. With regard to velocities, it is acoldsubsystem in that the random motions within it (~ 20 km/s) are small compared to the systematic flow of rotational motion (~ 200 km/s). Finally, its composition is largely stellar with stars of all ages and masses being present. Few galaxies are known where the ratio of (gas/stellar) mass is &gt; 10% (cf. Roberts 1975a), and the metal abundance is typically high with at most one percent of the stars having metallicity less than 1/4 that of the Sun (cf. Schmidt 1963). From this point of view the spiral parts are a relatively unimportant (in terms of mass and composition) sub-part of the disk system.

scholarly journals КОМПОНЕНТ ТЕМНОЇ МАТЕРІЇ І СОНЦЕ

2021 ◽  
pp. 138-153
Author(s):  
А. Н. Нарожный ◽  
Д. М. Шлифер
Keyword(s):  
Dark Matter ◽  
Microwave Radiation ◽  
Gravitational Interaction ◽  
Emission Spectra ◽  
Observation Point ◽  
The Sun ◽  
Temperature Deviation ◽  
Conservation Of Energy ◽  
Stellar Radiation ◽  
The Galaxy

Some consequences from the hypothesis of the origin of particles of one of the components of dark matter are presented. The reason for the hypothesis was the observational data of stellar radiation, considered through the prism of the relationship of all phenomena in Nature and the law of conservation of energy. It is argued that a part of the stellar electromagnetic radiation, which does not participate in the interaction with baryonic matter, will not wander forever in space. This radiation will interact with a subtle level of matter, continuously giving it its energy, shifting to the microwave region. In this frequency region, two quanta of close energies can form a neutral boson of spin 0, or spin 2, on opposite “courses”. Based on the observed spectrum of cosmic microwave radiation, it is assumed that these Bose particles have a continuous mass spectrum. These light nonrelativistic bosons are precisely the component of the thin medium that interacts with stellar radiation, taking energy from it. Bose particles participate in gravitational interactions. This means that in addition to the distribution of dark matter around galaxies, an increased concentration of particles in the form of large clouds can be observed in it. If an internal shock wave appears in such a cloud, located far from galactic streams of baryon particles, it will destroy the particles of the cloud, creating “strange radio circles” visible exclusively in the radio range. The gravitational interaction causes dark particles to drift towards large clusters of visible matter. The process of their drift to massive objects will be accompanied by resistance from the outgoing stellar radiation. Therefore, near the surface of a burning star, these particles themselves will resist the outgoing radiation, shifting it towards longer wavelengths. The plasma ejected by the star, with sufficient energy of its particles, is capable of destroying the particles of the dark component, creating pairs of photons and providing itself with "seed" quanta for bremsstrahlung. Free quanta remaining from the decay of dark particles will give microwave radiation. Therefore, burning stars should exhibit a redshift in the emission spectra and microwave radiation. Taking a certain model in the distribution of the dark component of matter near the Sun, it is possible to predict the nature of the redshift in the spectra of its radiation as the observation point moves along the solar disk from its center to the limb. A similar conclusion is made regarding the intensity of microwave radiation near the surface of the star. The galactic movement of the Sun should lead to some temperature effects associated with a denser counter flow of dark particles to the corresponding area of the solar surface. Knowing the direction of motion of the Sun in the Galaxy, based on the results of the temperature deviation on the surface of the star, one can determine the local speed and direction of movement of the cloud of the dark component of matter.

scholarly journals Self-consistent redshift estimation using correlation functions without a spectroscopic reference sample

2019 ◽  
Vol 485 (3) ◽  
pp. 3642-3660 ◽  
Author(s):  
Ben Hoyle ◽  
Markus Michael Rau
Keyword(s):  
Dark Matter ◽  
Correlation Functions ◽  
Reference Sample ◽  
Data Driven ◽  
Model Parameters ◽  
Redshift Distribution ◽  
Self Consistent ◽  
The Galaxy ◽  
Consistent Manner ◽  
Order Of Magnitude

ABSTRACT We present a new method to estimate redshift distributions and galaxy-dark matter bias parameters using correlation functions in a fully data driven and self-consistent manner. Unlike other machine learning, template, or correlation redshift methods, this approach does not require a reference sample with known redshifts. By measuring the projected cross- and auto-correlations of different galaxy sub-samples, e.g. as chosen by simple cells in colour–magnitude space, we are able to estimate the galaxy-dark matter bias model parameters, and the shape of the redshift distributions of each sub-sample. This method fully marginalizes over a flexible parametrization of the redshift distribution and galaxy-dark matter bias parameters of sub-samples of galaxies, and thus provides a general Bayesian framework to incorporate redshift uncertainty into the cosmological analysis in a data-driven, consistent, and reproducible manner. This result is improved by an order of magnitude by including cross-correlations with the cosmic microwave background and with galaxy–galaxy lensing. We showcase how this method could be applied to real galaxies. By using idealized data vectors, in which all galaxy-dark matter model parameters and redshift distributions are known, this method is demonstrated to recover unbiased estimates on important quantities, such as the offset Δz between the mean of the true and estimated redshift distribution and the 68 per cent, 95 per cent, and 99.5 per cent widths of the redshift distribution to an accuracy required by current and future surveys.

Approaches of stars to the Sun

1999 ◽  
Vol 173 ◽  
pp. 345-352 ◽  
Author(s):  
P.A. Dybczyński ◽  
P. Kankiewicz
Keyword(s):  
Minimum Distance ◽  
Galactic Disk ◽  
Equations Of Motion ◽  
Oort Cloud ◽  
The Sun ◽  
The Past ◽  
Straight Line ◽  
The Galaxy ◽  
Hipparcos Catalogue ◽  
Nearby Stars

AbstractClose approaches of stars to the Solar System perturb comets from the Oort cloud so that they pass into the planetary system − the gravitational impulse changes the distribution of observable comets. This paper presents the results of calculations of the motion of stars in the solar neighbourhood in the past and future. The main results for each star are: the time of the encounter and the minimum distance between the Sun and the star. They are calculated using three different methods: a straight line motion model, a model with a Sun − star Keplerian interaction, and the numerical integration of the equations of motion with galactic perturbations included. In the last case, two models of the Galactic potential are used: a simplified potential of the Galactic disk and the more complex potential of the Galaxy by Dauphole and Colin. Coordinates and velocities of nearby stars are taken from several different catalogues: the Gliese catalogue, the Hipparcos catalogue, and the Barbier-Brossat catalogue of Radial Velocities.

scholarly journals Global Instabilities of Disks

1975 ◽  
Vol 69 ◽  
pp. 297-320 ◽  
Author(s):  
J. M. Bardeen
Keyword(s):  
Kinetic Energy ◽  
Local Stability ◽  
Galactic Disk ◽  
The Sun ◽  
Global Instability ◽  
Precise Form ◽  
The Galaxy ◽  
Central Bulge ◽  
Theoretical Evidence ◽  
The Stability

Current understanding of the stability of gas and stellar disks suggests very strongly that local stability to axisymmetric modes is not sufficient for global stability. A global instability to a bar mode will develop unless the rotational kinetic energy is sufficiently small compared with the random kinetic energy for the system as a whole. A disk as cool as the galactic disk near the Sun can survive only if most of the mass of the Galaxy is in a ‘hot’ component, such as a central bulge and/or an extended halo. We review the theoretical evidence for this conclusion coming from analytic results for simple gas and stellar disks, from numerical simulations of stellar disks, and from numerical calculations of the stability of gas disks. Some new results on the precise form of dynamic bar instabilities of gas disks with and without halos are reported.

scholarly journals The Hot Galactic Corona and the Soft X-ray Background

1997 ◽  
Vol 166 ◽  
pp. 503-512
Author(s):  
Q. Daniel Wang
Keyword(s):  
Galactic Disk ◽  
Relative Dispersion ◽  
Polytropic Index ◽  
The Sun ◽  
X Ray ◽  
Large Intensity ◽  
The Galaxy ◽  
Electron Density And Temperature ◽  
X Ray Background ◽  
X Ray Absorption

AbstractI characterize the global distribution of the ¾ keV band background with a simple model of the hot Galactic corona, plus an isotropic extragalactic background. The corona is assumed to be approximately polytropic (index = 5/3) and hydrostatic in the gravitational potential of the Galaxy. The model accounts for X-ray absorption, and is constrained iteratively with the ROSAT all-sky X-ray survey data. Regions where the data deviate significantly from the model represent predominantly the Galactic disk and individual nearby hot superbubbles. The global distribution of the background, outside these regions, is well characterized by the model; the 1σ relative dispersion of the data from the model is ~ 15%. The electron density and temperature of the corona near the Sun are ~ 1.1 × 10−3 cm−3 and ~ 1.7 × 106 K. The same model also explains well the 1.5 keV band background. The model prediction in the ¼ keV band, though largely uncertain, qualitatively shows large intensity and spectral variations of the corona contribution across the sky.

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