The last decade has seen huge advances in studies of astrophysical cosmology, primarily as a result of developments in telescopic facilities. One of the primary observational signatures of actively star forming galaxies in the distant universe is the Lyman-alpha emission line (Lyα). The line is used either to search for objects or as a spectral feature for definite redshift confirmation. In recent years, high-z Lyα surveys have been used to constrain cosmic star formation history, investigate large scale structure, and examine the neutral hydrogen fraction of the universe. This doctoral thesis is directly concerned with studies of the Lyα emission from star-forming galaxies and the validity of Lyα as a cosmological tool. The approach is to study a sample of local actively star forming galaxies using data obtained with the Hubble Space Telescope (HST). Imaging observations have been performed in the Lyα line, Hα, and various continuum bandpasses in the ultraviolet and optical wavelength domains. Sophisticated tools have been developed for the analysis of the images, resulting also in theoretical exploration of Lyα-related observables from galaxies at high-z. Model simulations are presented, along with a methodology by which to interpret high-z survey data. HST imaging results call into question the interpretations of many high-z Lyα surveys. More specifically, the first direct observational evidence is presented for the emission of Lyα photons after resonant scattering in neutral hydrogen and low surface-brightness Lyα halos are found as a result. Imaging reveals Lyα morphologies that systematically differ from morphologies probed by stellar light or non-resonant tracers of the nebular gas. Based upon Hα observations and recombination theory, the fraction of Lyα photons that escape is found never to exceed 20% in any of the observed targets, despite the violent star-formation known to be taking place. Even after internal dust corrections, a deficit from the predicted Lyα/Hα line ratio is always found. The interpretation is that scattering events systematically enhance the probability of absorption of Lyα by dust grains. If these galaxies are representative of those that fall into the data-sets of high-z Lyα surveys, some cosmological estimates may be in error by an order of magnitude.

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There are over 300 exoplanets detected through radial velocity surveys and photometric studies showing a tremendous variety of masses, compositions and orbital parameters. Understanding the way these planets formed and evolved within the circumstellar disks they were initially embedded in is a crucial issue. In the first part of this thesis we study the physical interaction between a gaseous protoplanetary disk and an embedded planet using numerical simulations. In order to trust the results from simulations it is important to compare different methods. However, the standard test problems for hydrodynamic codes differ considerably from the case of a protoplanetary disk interacting with an embedded planet. We have carried out a code comparison in which the problem of a massive planet in a protoplanetary disk was studied with various numerical schemes. We compare the surface density, potential vorticity and azimuthally averaged density profiles at several times. There is overall good agreement between our codes for Neptune and Jupiter-sized planets. We performed simulations for each planet in an inviscid disk and including physical viscosity. The surface density profiles agree within about 5% for the grid-based schemes while the particle codes have less resolution in the low density regions and weaker spiral wakes. In Paper II, we study hydrodynamical instabilities in disks with planets. Vortices are generated close to the gap in our numerical models in agreement with the linear modal analysis. The vortices exert strong perturbations on the planet as they move along the gap and can change its migration rate. In addition, disk viscosity can be modified by the presence of vortices. The last part of this thesis studies the mass transfer in symbiotic binaries and close T Tauri binary systems. Our simulations of gravitationally focused wind accretion in binary systems show the formation of stream flows and enhanced accretion rates onto the compact component.

Av de 61 studenter som börjat på kandidatprogrammet i fysik med inriktning astronomi 2007 till och med 2012 vid Uppsala universitet, är det endast fem som har tagit ut en examen. Nästan hälften har hoppat av och lämnat universitetet. Flera av dem utan att ens försöka på en annan utbildning.En anledning till att studenter hoppar av högre utbildningar är de stora klyftor som kan uppstå mellan vad studenterna förväntat sig av utbildningen och deras erfarenheter av den. Om inte bra strategier, för att hantera klyftorna, hittas är det svårt att motivera att stanna på utbildningen. Denna rapport presenterar förväntningar blivande studenter har när de börjar på kandidatprogrammet med inriktning mot astronomi och vilka förväntningar som ställs från universitetets sida. Undersökningen har genomförts framförallt med hjälp av intervjuer med två astronomistudenter och grundutbildningskoordinatorn för astronomi, men enkätdata och statistik över studieresultat har också använts för att ge en heltäckande bild. Bilden som ges kan tolkas som att kandidatutbildningen inte ger tillräcklig kunskap inom astronomi för att de på avdelningen för astronomi och rymdfysik ska känna sig trygga med att studenterna ska klara av att göra ett kandidatarbete inom astronomi. Resultaten visar på att studenterna har stora förväntningar och längtan att lära sig mer om astronomi, men att förväntningarna från kandidatprogrammet är att de hellre ska läsa rena fysikkurser om de vill bli astronomer. / Of the 61 students who started the Bachelor's program in physics and astronomy, 2007 to 2012 at Uppsala University, only five have received a degree. Almost half have dropped out and left the university, several of them without even trying a different education. One of the reasons as to why students choose to drop out of higher educations as gaps between students expectations and what they experience when studying. If strategies can’t be found to overcome these gaps, students can have a hard time motivating continuing on the program. This report presents expectations prospective students may have when they start the bachelor program with specialization in astronomy and the expectations placed by the University. The project was carried out primarily through research interviews with two astronomy students and the undergraduate coordinator of the Astronomy program, but results from surveys as well as statistics of student achievement has also been used to give a comprehensive picture. The overall picture can be interpreted as the bachelor program not having provided sufficient knowledge in astronomy for the Division of Astronomy and Space Physics to feel confident that students will be able to write a Bachelor's thesis within astronomy. The results show that students have high expectations and desire to learn more about astronomy, but the expectations from the Bachelor program are that students need to learn more pure physics before taking astronomy courses.

The study of dynamical stability in planetary systems has become possible during the last few decades due to the development of numerical methods for long-term integrations of N-body systems. Since the 90’s the number of exoplanet detections has been increased significantly, making the simulations of other real planetary systems besides the Solar System feasible. One of the exciting new-found worlds is the system Kepler-11. Six planets which are located very close to each other orbit a solar-type star. In this project we first investigate the behavior of Kepler-11 when we change some of the initial conditions of the outermost planet of the system and then we approximate the Red Giant phase of solar-type stars in order to see how the planetary orbits are altered. For the first part we run three series of simulations (groups A,B,C). Each group has a different value for the mean density of planet Kepler-11g (1.0,1.5,2.0 g/cm 3 ). We run simulations for 36 different combinations of mass and eccentricity of planet Kepler-11g for each group. In nine configurations all six planets of the system continue to orbit the star until the end of the simulations. These nine stable configurations of Kepler-11 are used in the second part where we implement a constant mass-loss rate for the star which results in 30% mass loss after 30 million years, trying to approximate that way the mass loss of solar-type stars in Red Giant Branch. We also run nine simulations of a hypothetical system consisting only of the Sun, Earth and Jupiter where we implement the constant mass-loss rate to the Sun. In the Kepler-11 system, the orbits of planets Kepler-11g and Kepler-11e change by ∼45% and ∼54% respectively, after 30 million years, due to the mass loss of the star, while in the hypothetical planetary system the orbits of the two planets change by ∼43%. The study of orbits and how they move outward during the Post-Main Sequence evolution of stars is essential for our understanding of the existence of a Habitable Zone, not just around stars in Main-Sequence phase, but also around stars in late stages of their evolution.

In this paper, we write a summary about general relativity and, in particular,gravitational waves. We start by discussing the mathematics that generalrelativity uses, as well as the geometry in general relativity's spacetime. Afterwards,we explain linearized general relativity and derive the linearizedversions of Einstein's equations. From here, we construct wave solutionsand explain the polarization of gravitational waves. The quadrupole formulais derived, and generation and detection of gravitational waves is brie ydiscussed. Finally, LIGO and its latest discovery of gravitational waves isreviewed.

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Studying weak gravitational lensing of type Ia supernovae is a valuable tool to have in cosmology. Gravitational lensing may amplify the brightness of the source, affecting the brightness distribution of observed supernovae in a non-Gaussian way. Testing this magnified distribution for normality may thus reveal the observation of weak lensing. Simulation of lensing and studying the feasibility of current telescopes (ZTF) detecting it gives a first look into when this mechanism may be fully utilized.

In this research, the validity of using an effective potential to approximate general relativistic effects in an otherwise Newtonian setting was investigated, by making simulations of core collapse supernovae on one hand in full general relativity, and on the other hand in said Newtonian setting. This was done for a mass range covering progenitors of 12 − 60 solar masses; a much wider mass range than has been used in earlier research, that also includes progenitors that form black holes. Two numerical codes were used; the general relativistic hydrodynamic code GR1D, and the Newtonian hydrodynamic code FLASH. For simplicity, spherical symmetry was assumed, and a M1 neutrino transport was employed rather than solving the full Boltzmann transport equation for neutrinos. Three different versions of the effective potential; GREP1, GREP2, and GREP3, were tested, and their results compared to a general relativistic case; GR, in an attempt to investigate possible improvements of earlier research. For all parameters investigated in this research, case GREP1 (and GREP2) yielded results that agreed very well with case GR at the time around bounce, though somewhat worse later on in the evolution. This observation is consistent with that made by Marek et al. (2006), but for a much larger set of progenitors, and therefore, the reliability of using this version of the effective potential to approximate general relativistic effects in an otherwise Newtonian setting, is not only confirmed, but extended as well. Another exceptional result not seen before was the black 1 hole formation times, which all three effective potentials could reproduce within ∼ 5% compared to case GR. In addition to this, case GREP3 yielded excellent results for the central density, but rather poor results for the remaining properties, and is thus not recommended to use to approximate general relativistic effects, although further investigation of this potential might give valuable clues for further improvements