Dark matter baryonic

Three most popular DM candidates could contribute to the explanation of the above wealth of observations. Historically, faint stars/planetary objects constituted of baryonic matter were invoked first, with masses smaller than 0.1 solar mass (this is the mass limit minimally needed for nuclear burning and the subsequent electromagnetic radiation). The search for massive compact halo objects (MACHOs) was initiated in the early 1990s based on the so-called microlensing effect — a temporary variation of the brightness of a star when a MACHO crosses the line of sight between the star and the observer. This effect is sensitive to all kind of dark matter, baryonic or nonbaryonic. The very conservative combined conclusion from these observations and some theoretical considerations is that at most 20% of the galactic halo can be made up of stellar remnants (Alcock et al. 2000). 

The other kind of dark matter must be non-baryonic (NDM) and is thought to consist of some kind of particles envisaged in extensions of the Standard Model ... 

The existence of dark matter (either baryonic or non-baryonic) is inferred from its gravitational effects on galactic rotation curves, the velocity dispersions and hydrostatic equilibrium of hot (X-ray) gas in clusters and groups of galaxies, gravitational lensing and departures from the smooth Hubble flow described by Eq. (4.1). This dark matter resides at least partly in the halos of galaxies such as our... 

D. Lynden-Bell and G. Gilmore (eds.), Baryonic Dark Matter, Kluwer, Dordrecht, 1990, and in Sarkar (1996). 

In the standard case there are four variables to be calculated the total system mass M (not counting non-baryonic dark matter), the mass of gas g, the mass existing in the form of stars (including compact remnants) s and the abundance Z of the element(s) of interest, assuming certain initial conditions and laws governing the SFR and flows of material into and out of the system. 

Fig. 11.15. Conditions for gas loss from a galaxy, as a function of gas mass Mg and the ratio < > of dark matter to baryons (stars + gas), assuming an energy input of 1038 erg s-1 and maximum dissipation from cloud-cloud collisions. PSS denotes the relation between < > and Mg deduced from observation by Persic, Salucci and Stel (1996). After Ferrara and Tolstoy (2000).

Spectral analysis shows quite clearly that the various types of atoms are exactly the same on Earth as in the sky, in my own hand or in the hand of Orion. Stars are material objects, in the baryonic sense of the term. All astrophysical objects, apart from a noteworthy fraction of the dark-matter haloes, all stars and gaseous clouds are undoubtedly composed of atoms. However, the relative proportions of these atoms vary from one place to another. The term abundance is traditionally used to describe the quantity of a particular element relative to the quantity of hydrogen. Apart from this purely astronomical definition, the global criterion of metallicity has been defined with a view to chemical differentiation of various media. Astronomers abuse the term metaT by applying it to all elements heavier than helium. They reserve the letter Z for the mass fraction of elements above helium in a given sample, i.e. the percentage of metals by mass contained in 1 g of the matter under consideration. (Note that the same symbol is used for the atomic number, i.e. the number of protons in the nucleus. The context should distinguish which is intended.)... 

The fact that the Sun is in the plasma state means that it has the flexibility of a gas. This flexibility in turn ensures its longevity. Indeed, the size of the particles making it up, i.e. separate nuclei and electrons, is much less than the mean distance separating them, and this allows us to identify it with a gas. (Non-baryonic dark matter, with no electrical properties, cannot be ionised. There is no such thing as a dark matter plasma.)... 

Clusters form from large volumes. For a Universe with a mean mass density of 3 x 10 3° gm cm-3 (30% of closure density pc = 3 //HirG, with Ho=70 km s-1), a rich cluster with a mass of 1015M forms from a sphere with a radius of 20 Mpc. Since the dominant process in the formation of the cluster whose mass consists of cold dark matter and baryons is gravitation and the formation of collapsed objects by gravity alone should not affect the ratio of the mass components, it is believed that the mass components of today s clusters are representative of the Universe (e.g., White et al. 1993). 

The first evidence for the existence of dark matter has been provided by dynamical measures performed on the Coma cluster, in 1930 by F. Zwicky. Since that time, our understanding of clusters has greatly increased. There is nearly 100 times more mass in clusters than in the stars that can be seen within them. However, there is much more baryons seen in X-ray clusters in form of hot gas than in stars. The discovery of this hot gas through its X-ray emission has revolutionized the study of clusters. Indeed X-ray observations allows to measure gas density and gas temperatures with a high accuracy and they are likely to provide the most accurate mass measurements. Clusters therefore provide a fascinating laboratory for cosmological studies their stellar, bary-... 

This method is based on the measurement of the baryonic fraction in clusters, consisting mainly of the hot gas seen in X-rays. The X-ray image of a cluster allows one to measure the mass of this X-ray gas. The knowledge of the X-ray temperature allows one to estimate the total mass Mit. It possible therefore to estimate the baryon fraction in clusters (the contribution of stars, around 1% for h = 0.5 is often neglected to first order) assuming that the remaining dark matter is non-baryonic, which can be related to Do ... 

In the late seventies, the history of the early Universe was described with the help of the hot Big-Bang scenario the universe originated from an initial singularity and had then expanded, being filled by radiation and subsequently by non relativistic matter (baryon and Dark Matter). 

The first theoretical predictions of AT/T = 10-2 (Sachs and Wolfe, 1967) and A T/T = 10-3 5 (Silk, 1968) were superseded by predictions based on cold dark matter (Peebles, 1982, Bond and Efstathiou, 1987). These CDM predictions were consistent with the small anisotropy seen by COBE and furthermore predicted a large peak at a particular angular scale due to acoustic oscillations in the baryon/photon fluid prior to recombination. The position... 

The ratios of the anisotropy powers below the peak at l 50, at the big peak at ss 220, in the trough at / 412, and at the second peak at / 546 were precisely determined using the WMAP data which has a single consistent calibration for all Us. Previously, these I ranges had been measured by different experiments having different calibrations so the ratios were poorly determined. Knowing these ratios determined the photon baryon CDM density ratios, and since the photon density was precisely determined by FIRAS on COBE, accurate values for the baryon density and the dark matter density were obtained. These values are Ct h2 = 0.0224 4%, and Vtmh2 = 0.135 7%. The ratio of CDM to baryon densities from the WMAP data is 5.0 1. 

In order to understand the evolution of perturbation on larger scales (compared to the scale of the Horizon), we need to consider the most general perturbation to the various constituents of the universe (dark matter particles, photons, baryons,. ..), which would let their densities and velocities each vary individually. Since the number of degrees of freedom contributing to the entropy come almost entirely from radiation, the specific entropy, or entropy per particle, is defined by... 

But any complete description of the evolution of perturbations in the universe will link all of these terms initial velocity and density perturbations to the various components (baryons, dark matter, photons) evolve prior to last scattering as discussed above, and so photon overdensities occur in potential wells, and velocity perturbations occur in response to gravitational and pressure forces. Indeed, to solve this problem in its most general form, we must resort to the Boltzmann equation. The Boltzmann equation gives the evolution of the distribution function, fi(xp,Pp) for a particle of species i with position Xp, and momentum p/(. In its most general form, the Boltzmann equation is formally... 

On smaller scales, we must track the details of the interactions amongst the various components photons, baryons and dark matter. Hu Sugiy-... 

So far, we have discussed the evolution of perturbations in the dark matter, photons and baryons at any given point, for some particular set of initial conditions. However, our theories are not so specific. Rather, they give us only statistical information about the initial perturbations. 

Already in 1970s suggestions have been made that some sort of non-baryonic elementary particles may serve as candidates for dark matter particles. Gunn et al. (1978) considered heavy stable neutral leptons as possible candidates for dark matter particles, however in a later study Tremaine Gunn (1979)... 

Dark matter in the Galactic disk, if present, must be baryonic (faint stars or jupiters). The amount of local dark matter is low, it depends on the boundary between luminous stars and faint invisible stars. 

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