Sharif Digital Repository

One of the most important topics of interest to cosmologists and astrophysicists is the origin of supermassive black holes that form the center of most galaxies.In this research, we will introduce a mechanism for the growth of primordial black holes at the early universe, and we will argue that by this mechanism, with the assumptions that will be given in the relevant section, black holes of the order of 〖10〗^6 M_⊙ can be formed.Then assuming that there are supermassive black holes at the center of most galaxies, by calculating the number density of galaxies in comoving coordinate We will set the number density of galaxies in comoving coordinate and the number density of grown primordial... 

When in a binary system one of the stars passes behind another star eclipsing binary will occur and light’s intensity will decrease. Now with assumption that one of its component be Black Hole When another star passes behind of it the star’s light is amplified by Microlensing.With detection of this amplification we can find black hole’s mass. Of course in this phenomenon the degeneracy will be broken completely and we can obtain all of the quantity. From another specification of this event we can call the shortness and repetitive of Einestein’time .The Einestein’s time is approximately a few hours and depending on system’s period this event will be repeated in specific time.Finally Black... 

We simulated the structure formation in the context of Modified Newtonian Dynamics with the spherical collapse model. We supposed a spherical region with mass of galactic order, positive density contrast and uniform distribution of matter as the initial condition and investigated the evolution of its internal regions, containing different amounts of matter. We began the simulation when the region was in Newtonian regime. The overdense region, which expands with cosmic fluid in Newtonian regime, gradually enters MONDian regime and gets separated from the background due to its stronger central acceleration; then it collapses and virializes after some swings. The density distribution of the... 

It has been about a decade that cosmological datas have shown the universe is accelerating. To describe this acceleration, cosmologosts use cosmological constant as the easiest way to describe,or the modified gravity models or smooth dark energy models as other ways. In this thesis we solved a specific structure formation problem, density contrast, for linear structures, in two different methods. the first method was LCDM model and the second method was a specific f (R) gravity model. We shpwed that these two solutions are about the same.
 

In this thesis, we investigate two subjects in gravitational microlensing. In first part we study wave optics effect in light curve of a binary system. Gravitational lensing occurs when light deflects in a gravitational field. This deflection produces multi-images from real one. In microlensing regime, images can not be detected separately and gravitational lensing appears as magnifying source’s flux . Microlensing has been studied mostly in geometric optics regime. At larger wavelengths, mostly at radio wavelengths, we expect to see the effects of wave optics in microlensing. Stars at radio wave are faint and to detect them we need a powerful radio telescope. In the near future, SKA (Square... 

With discovery of each exoplanet in habitable zone around a star, we expect to find life happening in the planet or it can be a place to move in. Life needs time to evolve. If our search is for complicated or intelligent type of life, there must be enough time for it i.e. billions of years. If the planet is ripped off of its life-supporting properties in midst of its evolution by a hazard, complicated species will not be born.In this thesis I examine the near stellar flyby hazard, which can send the planet out of the circumstellar habitable zone. In this research, by gravitational simulations, various near stellar encounters are studied and by using the environmental parameters around... 

Gravitational microlensing with the binary lenses are one the tools for detection of exoplanets. Due to the degeneracy nature of the solutions for the observed light curves additional features such as parallax and finite-size effects help to break the degeneracy. Here in this work we introduce the application of frequency shift effect in the microlensing observations where for the single lens, it has been studied in [5] .In this work our purpose is to study the frequency shifts in binary lenses. Therefore, after reviewing the frequency shift in single gravitational lens systems, we will study this phenomenon in binary systems.In binary lenses, which are mainly used to detect extrasolar... 

Discovery of the effect of a massive object on the light path, reaching its exact formalism through general relativity and utilizing this phenomenon as a natural lens, opened a new window in astronomical research. Gravitational lensing occurs in three different ways; strong lensing, weak lensing, and microlensing which we focus on the third one. Gravitational microlensing is useful in studying dark matter candidates, discovering exoplanets, finding the surface properties of stars, and calculating the mass distribution of galactic objects. From a typical microlensing event, Einstein crossing time is obtained which is the time scale of source star passing by the lens. This is the only... 

During the past decades, structural parameters are used as a tool for studying the formation and evolution of galaxies. Sersic parameter is one of these parameterswhich also known as shape parameter. Sometimes, measuring such parameters depend on the observed wavelength. So far, this dependence has been rarely attended. In this thesis we are trying to know how and why these parameters depend on the wavelength  

Aims: Stars twinkle because their light propagates through the atmosphere. The same phenomenon is expected at a longer time scale when the light of remote stars crosses an interstellar molecular cloud, but it has never been observed at optical wavelength. In a favorable case, the light of a background star can be subject to stochastic fluctuations on the order of a few percent at a characteristic time scale of a few minutes. Our ultimate aim is to discover or exclude these scintillation effects to estimate the contribution of molecular hydrogen to the Galactic baryonic hidden mass. This feasibility study is a pathfinder toward an observational strategy to search for scintillation, probing... 

One of the biggest challenges facing cosmologists is finding the nature of dark matter. The cosmological observations, like the Rotation Curve, Gravitational Weak Lensing and Cosmic Microwave Background radiation indicate that baryonic matter alone cannot explain the density of matter in the universe. In the context of standard cosmological models, it means that the universe is made of an unknown component(Dark Matter), which aprroximately has 27% of total energy-momentum of the universe. The Modify Gravity and General Relativity are alternative theories that introduced to describe this observation. In This thesis, we introduce the issue of the measurements of accelerated observers in... 

In this thesis, the star formation history and evolution of IC 1613 dwarf galaxy and NGC 5128 giant elliptical galaxy has been studied. About IC 1613, our result shows that the star formation history of the galaxy is roughly constant in 5 Gyr ago and this support that the galaxy had been isolated at least in 5 Gyr ago. About NGC 5128, we can see that the star formation rate has suddenly increased in 700 Myr and 3.5 Gyr ago. This results in very good agreement with literature support that the galaxy has experienced some mergers with smaller gas rich galaxies  

In the standard cold dark matter (CDM) family of cosmological models,the cosmological structures form hierarchically with the assumption of cold dark matter existence. The structure formation in the current CDM paradigm is capable of estimating the distribution function of the structures. It gives us a correct view from our observations of galaxies and structures. One of the successful methods to explain the statistics of cosmlogoical structures and their formation time is Excursion Set Theory. The excursion set theory considers the density field for each point in the universe smoothed with a spatial window function using the physics of random processes. The statistics of the structures can... 

Platelet Rich Plasma (PRP) is a blood-derived product containing concentrate of platelets, which are a rich source of autologous growth factors. PRP injection has been used clinically as a therapeutic method for cartilage repair. However, clinical efficiency of this method is unpredictable, maybe as a result of burst release of growth factors then fail cell-stimulating potential as most biomolecules are cleaned before they can exert a therapeutic effect. The aim of this project was to prepare a suitable scaffold for PRP delivery to regenerate cartilage injuries. In order to resemble polysaccharide-protein nature of the cartilaginous extracellular matrix, in this study, we developed an... 

Gravitational microlensing is one of the experimental tests to confirm the theory of general relativity. In this phenomenon, the light of the source star is deflected by the gravitational field of the foreground star which plays the role of the lens. As a result of this deviation, images of source star are formed on the sky plane. The observer records the light of the source star as a variable with time. The gravitational microlensing illustrates the possibility to discover extrasolar planets, study the atmosphere of stars, and probe the nature of Dark matter. In this thesis, at first, we introduce the basic concepts of gravitational microlensing and its history. Then by simulation of... 

In this thesis, we have investigated the light scalar field models for describing the dark sector(Dark Matter and Dark Energy) of the universe in cosmology. As a result of tiny mass, the de Broglie wavelength becomes large, and consequently, the quantum mechanical behavior is essential in large scales. Our main attempt is to investigate a model of scalar fields consisting of particles with a mass range of ($10^{-21}-10^{-23}$)eV, often called Fuzzy Dark Matter (FDM). In the FDM hypothesis, the dark matter halo consists of a solitonic core that formed Bose-Einstein-Condensation BEC at the halo's inner region and non-condensed dark matter particles at the outer region. We took into account...