Abstract: The main work of this doctoral thesis is a study on black holes of both very high and very low masses, and their possible observational consequences.
Very low mass primordial black holes (PBHs) could be all of the dark matter, but only in a very small range of masses. There is however a window near asteroid masses, one that is very hard to constrain through their observational consequences
A way to constrain that window could be the capture of those PBHs by a main sequence star. These kind of events could happen at high redshifts with very high densities and very low dispersion velocities. We study this process through our own original model. Despite its simplicity, the model improves over the literature by computing numerically the dynamical friction in two different ways with current stellar models and taking into account possible external perturbations on the system. We also make use of a dimensionless parameter we call Xi which allows us to make our results generic. We conclude that for high redshfits the capture of PBHs would be important and erase a notable percentage of low mass stars, leaving black holes below one solar mass as result.
Another interesting case is supermassive black holes (SMBHs), most specifically quasars. A way to study them is through the Lyman alpha nebula surrounding the brightest quasars, but this diffuse radiations is very weak, so their generalised existence for all quasars is in doubt. Through the technique of stacking we can however reach increased luminosity depths at the cost of also magnifying the Point Spread Function (PSF). We make use of current survey J-PLUS, as a first step to the successor survey J-PAS. While J-PLUS cannot reach the magnitudes needed to confirm the Lyman alpha nebulae, we use stars to test the depths and systematics of stacking and we achieve very positive results. With J-PAS it should be possible to confirm the existence and brightness of the Lyman alpha nebulae.