Coronal mass ejections (CMEs) are some of the extraterrestrialevents most impactful to earth. Eorts to model and predict theireects have seen new possibilities in the two most recent decades dueto multiple new spacecrafts providing a wider range of data than everbefore. Models of these events suer from a number of inaccuracies,one of them being the density ratio between the CME and the ambientsolar wind. Since the arrival time for potentially harmful disturbancespredicted by models has been proved to be highly sensitive to thisparameter we therefore take care to set it as accurately as possible.Traditionally this value is either set to a default, justied by denitionand theory, or set to the density ratio between the bulk if the ejectedgas and the surrounding medium. A proposition has been made tomeasure density enhancement dierently, using a reference point at theshock wave preceding the CME for each event. This method strives toimprove arrival time predictions and was in this paper tested for onecoronal mass ejection event. Two runs if the model WSA-ENLIL+Conewas made; one with the default value of density enhancement, onewith a value determined through the revised method using coronographdata. Running the model with the revised value improved the predictedarrival time by moving it forwards in time by 4h, which was still tooearly. Other input data into the model run was then discussed as apossible cause of the remaining inaccuracy. / Koronamassutkastningar är ett av solfenomenen som påverkar jorden mest.Nya rymdfarkoster med instrument som satts i arbete de senaste två decenniernahar gett data som gjort det möjligt att modellera och förutse dessaevent till en högre precision än någonsin. Alla dessa modeller lider av någonform av felkälla, en av vilka är kvoten mellan densitet för massutkastningenoch den omgivande miljön. Eftersom förutsedda ankomsstider för potentielltskadliga störningar har visat sig vara särskilt känsliga för denna parameterså tar vi särskild hänsyn till att ange den så precist som möjligt. Vanligtvissätts detta värde till ett fast standardvärde, som anges av dess denitionoch bakomliggande teori, eller till kvoten mellan utkastningens bulk ochomgivningen. Ett förslag har dock lagts fram om att omdeniera parametern.Denna metod strävar efter att förbättra förutsedda ankomsttider ochhar i denna text testats för en koronamassutkastning. Två körningar avmodellen WSA-ENLIL+Cone gjordes; en med defaultvärdet för densitetsratiot,en med värdet satt genom mätning av empirisk cononagrafdata enligtden föreslagna metoden. Att köra modellen med den nya parametern förbättrade den förutsedda ankomsttiden genom att ytta den framåt i tidenmed 4 timmar, vilket fortfarande är för tidigt. Andra inputdata i modellendiskuterades då som möjliga orsaker till den återstående diskrepansen.

The current paradigm in planet formation theory is developed around a hierarquical growth of solid bodies, from interstellar dust grains to rocky planetary cores. A particularly difficult phase in the process is the growth from meter-size boulders to planetary embryos of the size of our Moon or Mars. Objects of this size are expected to drift extremely rapid in a protoplanetary disk, so that they would generally fall into the central star well before larger bodies can form. In this thesis, we used numerical simulations to find a physical mechanism that may retain solids in some parts of protoplanetary disks long enough to allow for the formation of planetary embryos. We found that such accumulation can happen at the borders of so-called dead zones. These dead zones would be regions where the coupling to the ambient magnetic field is weaker and the turbulence is less strong, or maybe even absent in some cases. We show by hydrodynamical simulations that material accumulating between the turbulent active and dead regions would be trapped into vortices to effectively form planetary embryos of Moon to Mars mass. We also show that in disks that already formed a giant planet, solid matter accumulates on the edges of the gap the planet carves, as well as at the stable Lagrangian points. The concentration is strong enough for the solids to clump together and form smaller, rocky planets like Earth. Outside our solar system, some gas giant planets have been detected in the habitable zone of their stars. Their wakes may harbour rocky, Earth-size worlds.

Carbon is the basis for life, as we know it, but its origin is still largely unclear. Carbon-rich Asymptotic Giant Branch (AGB) stars (carbon stars) play an important rôle in the cosmic matter cycle and may contribute most of the carbon in the Galaxy. In this thesis it is explored how the dust-driven mass loss of these stars depends on the basic stellar parameters by computing a large grid of wind models. The existence of a critical wind regime and mass-loss thresholds for dust-driven winds are confirmed. Furthermore, a steep dependence of mass loss on carbon excess is found. Exploratory work on the effects of different stellar metallicities and the sizes of dust grains shows that strong dust-driven winds develop also at moderately low metallicities, and that typical sizes of dust grains affect the wind properties near a mass-loss threshold. It is demonstrated that the mass-loss rates obtained with the wind models have dramatic consequences when used in models of carbon-star evolution. A pronounced superwind develops soon after the star becomes carbon rich, and it therefore experiences only a few thermal pulses as a carbon star before the envelope is lost. The number of dredge-up events and the thermal pulses is limited by a self-regulating mechanism: each thermal pulse dredges up carbon, which increases the carbon excess and hence also the mass-loss rate. In turn, this limits the number of thermal pulses. The mass-loss evolution during a thermal pulse (He-shell flash) is considered as an explanation of the observations of so-called detached shells around carbon stars. By combining models of dust-driven winds with a stellar evolution model, and a simple hydrodynamic model of the circumstellar envelope, it is shown that wind properties change character during a He-shell flash such that a thin detached gas shell can form by wind-wind interaction. Finally, it is suggested that carbon stars are responsible for much of the carbon in the interstellar medium, but a scenario where high-mass stars are major carbon producers cannot be excluded. In either case, however, the carbon abundances of the outer Galactic disc are relatively low, and most of the carbon has been released quite recently. Thus, there may neither be enough carbon, nor enough time, for more advanced carbon-based life to emerge in the outer Galaxy. This lends some support to the idea that only the mid-part of the Galactic disc can be a “Galactic habitable zone”, since the inner parts of the Galaxy are plagued by frequent supernova events that are presumably harmful to all forms of life.

Aim. In this project, theoretical models of dust driven winds of asymptotic giant branch (AGB) stars with effective temperatures within a range of 2400 − 3200 [K] and relative carbon-to-oxygen abundance C/O > 1 are studied. The aim is to understand if and how a detailed description of the grain size in winds of carbon rich AGB stars affects the wind formation and wind driving processes. Method. The computations were performed with a well tested FORTRAN code by calculating a grid of 60 models with different stellar parameters using grain size-dependent opacities. The results were then compared with models where the small particle approximation (SPA) had been used. Conclusions. The results indicate a certain dependency on grain size of the wind properties. The results from the computations of the majority of the models show no significant diferences however, especially not for the mass loss rates. Thus earlier computations performed using the SPA need not necessarily to be rejected.

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No description available.

Classical theory cannot provide a satisfying scenario for a unitary thermodynamic evolution of black holes. To preserve information one requires quantum mechanical effects on scales reaching beyond the traditional horizon radius. Therefore, common to many of the theories attempting to resolve the paradox is the existence of exotic horizon structures. The recent advent of gravitational wave astronomy provides a possible means for detecting the existence of such structures through gravitational wave emission in the ringdown phase of binary black hole mergers. Such emission is described by quasinormal modes (QNMs) in which the gravitational waves originates outside the black hole, in the vicinity of the photon spheres. Requiring reflective properties of the horizon structure results in the existence of gravitational echoes that may be detected by facilities such as LIGO etc.. This thesis studies geodesic motion of such echoes in the equatorial plane of a rotating black hole. Depending on the extent of the horizon structure, and the particular mode of emission, one can expect different timescales for the echoes. For a horizon structure extending <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5CLambda%20r%20=" /> <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?10%5E%7B-12%7D" /> <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?M" /> outside the traditional horizon of a  <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?M%20=%2022.6%20M_%7B%5Codot%7D" />, <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?a%20=%200.74%20M" /> black hole one would ideally find echoes appearing as integer multiples of <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5CDelta%20t_%7Becho%7D" /><img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?=%200.0204%20s" /> after the primary signal. The time delay is expected to increase by at least an order of magnitude if one lets <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5CDelta%20r%20%5Csim%2010%5E%7B-80%7D%20M" />. The expected echo timescales for gravitational waves emitted from any point around the black hole, in arbitrary modes, is an interesting further study.

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This project aims to study general relativity to the extent to understand the occurrence and behaviors of closed timelike curves (CTCs) in several exact solutions of Einstein’s field equations. The rotating black hole solution, the Gödel universe and the cosmic string solutions are studied in detail to show how CTCs arise in these spacetimes. The chronology-violationing paradoxes and other unphysical aspects of CTCs are discussed. The spacetimes where CTCs arise possess properties which are argumented to be unphysical, such as lack of asymptotic flatness and being innite models. With quantum computational networks it is possible to resolve the paradoxes which CTCs evoke. With all these attempts of resolving CTCs, our conclusion is that CTCs exist quantum mechanically, but there is a mechanism which inhibits them to be detected classically. / Detta projekt åsyftar att studera allmän relativitet i den grad att kunna förstå uppkomsten och företeelsen av tidsliknande slutna kurvor (CTC) i några exakta lösningar till Einsteins ekvationer. Dessa lösningar inkluderar Gödel universen, kosmiska strängar och det roterande svarta hålet, där CTC studeras i mer detalj. CTC är kronologi-kränkande företeelser och paradoxen som uppstår presenteras, samt de argument som ligger till grund till att CTC inte är fysikaliskt verkliga objekt. De tidrum där CTC uppkommer delar gemensamma egenskaper som anses ofysikaliska, som att vara icke asymptotiskt platta tidrum, samt att vara oändliga modeller. Med kvantinformatiska nätverk kan CTC illustreras och de klassiska kronologi-paradoxen kan rättas ut. Slutsatsen är att CTC existerar kvantmekaniskt, men det fnns en mekanism i verkligheten som förhindrar dessa att bli detekterade klassiskt.

This project highlights various methods used to detect the elongated elemental particle neutrino. It is especially focused on the IceCube observatory, which uses Cherenkov light to detect these particles. Neutrino is an importnant building block in astrophysics and particle physics research as this particle can travel from great distances in time and space without interacting with matter. This means that high-energy neutrinos that are detected can orginate from strong explosions from outer space, even from explosions billion years ago, like Big Bang. This means that these particles carry a huge amount of information about the universe. The project also contains an experiment whose purpose is to demonstrate that with simple materials it is possible to detect particles that are not otherwise visible to the naked eye.