The nature of the Dark Matter is one of the biggest open questions in modern cosmology and particle physics. The work in this thesis concerns a search for the observational effects of one... Show moreThe nature of the Dark Matter is one of the biggest open questions in modern cosmology and particle physics. The work in this thesis concerns a search for the observational effects of one particular class of hypothetical Dark Matter particles, namely those that are allowed to decay. In decaying, X-ray photons are emitted and should be observable. One part of the thesis details the discovery of a potential Dark Matter decay signal in X-ray spectra of galaxies and galaxy clusters, and the subsequent efforts to identify its origin. To this end archival data and new observations are compared to the respective Dark Matter masses of the observed objects. Interpretations of the signal as an instrumental effect, or due to regular astrophysical processes are unsatisfactory. Although the Dark Matter interpretation remains plausible, definitive conclusions about the origin of the signal can not be drawn yet and will require measurements by next generation observatories. The last chapter of the thesis contains the proof-of-concept of a novel technique to search for such weak signals that combines increased statistical power with the ability to determine the physical origin of a signal, while avoiding some of the disadvantages of traditional methods. Show less
In this thesis we present multiple techniques to suppress starlight in order to better directly image planets around other stars. We propose a laboratory setup to test a new focal-plane... Show more In this thesis we present multiple techniques to suppress starlight in order to better directly image planets around other stars. We propose a laboratory setup to test a new focal-plane wavefront sensing technique. We also show an optical device that suppresses starlight using liquid crystals (the vector Apodizing Phase Plate or vAPP). A broadband prototype (500-900 nm) is tested in the optical lab and its properties are determined. We suggest an simple but effective adaptation called the grating-vAPP which is insensitive to one of the common manufacturing errors (retardance offset). Two versions are tested on-sky. One narrow-band prototype at the Large Binocular Telescope that shows that the concept of the grating vAPP works. A second at Magellan/Clay that shows that we can produce a single optic with a broadband behaviour from 2 to 5 microns bandwidth that suppresses both sides of the star simultaneously. The on-sky 5 sigma contrast is 8.3 magnitudes at 2 lambda/D and 12.2 magnitudes at 3.5 lambda/D which makes this coronagraph extremely suited for imaging and characterizing planets close to nearby bright stars. Show less
This thesis is centered around the embedded phase of star formation and the chemical links between the various stages of evolution. The primary goal of this work is to pinpoint the origins... Show more This thesis is centered around the embedded phase of star formation and the chemical links between the various stages of evolution. The primary goal of this work is to pinpoint the origins of cometary complex organic molecules in the preceding protoplanetary disk and prestellar stages, both in the gas and solid phases. The grand motivation is to identify our interstellar roots. This work is unique in comparison to earlier publications due to the dynamic nature of the models used in combination with the large comprehensive chemical network. Three chapters in this book pertain to physicochemical models and an additional one is of observational nature. Altogether, this thesis is an attempt to piece together the chemical connection between the prestellar core, the protoplanetary disk and the protoplanetary and cometary materials. The main take-home message is that the seeding of infant Solar System building blocks with complex organic molecules is unavoidable as a result of chemistry during protoplanetary disk assembly. Show less
According to Einstein's theory of general relativity the light of an object is deflected by a mass in its foreground. The deflections can be very weak or so strong that they are visible by eye... Show moreAccording to Einstein's theory of general relativity the light of an object is deflected by a mass in its foreground. The deflections can be very weak or so strong that they are visible by eye yielding strangely distorted arcs or even multiple images of the same source. Measurements of strong or weak lensing let us infer the total mass of the light-deflecting object which is an important cosmological observable. In this thesis we employ gravitational lensing to measure key cosmological observables, such as dark matter and dark energy. Instead of observing the effects of gravitational lensing around single galaxies or galaxy clusters, the Universe itself can be used as a lens: light travelling to us through the cosmic large-scale structure is also weakly lensed by it. Measuring this effect at different cosmic times allows us to infer the evolution of structure in the cosmic web. Hence, we can study how that is affected by dark energy or massive neutrinos. A key result of this thesis is that we find a lower amplitude for the clustering of matter at fixed matter density than that inferred from the most recent measurements of the cosmic microwave background radiation by the Planck satellite. Show less
This thesis uses novel observations from the Low Frequency Array to address open questions on the topic of galaxy evolution. The highest resolution images at ultra low radio frequencies are used to... Show moreThis thesis uses novel observations from the Low Frequency Array to address open questions on the topic of galaxy evolution. The highest resolution images at ultra low radio frequencies are used to investigate the physical processes present in the radio emission from distant galaxies. Detections of spectral features from carbon atoms in a nearby galaxy are also presented and used to constrain the temperature and density of cold gas that is a key component of all galaxies. Show less
Galaxy clusters are the largest reservoirs of matter in the Universe, and as such are unique laboratories to understand the connection between dark and luminous, 'normal' matter. We use... Show more Galaxy clusters are the largest reservoirs of matter in the Universe, and as such are unique laboratories to understand the connection between dark and luminous, 'normal' matter. We use several techniques and galaxy cluster samples to study this connection from various angles. In particular, we try to understand how does the motion of galaxies within clusters relate to their luminous mass content; how do the shapes of galaxies respond to the strong gravitational potential of their host cluster (analogous to tidal waves produced by the Earth-Moon gravitational interaction), and how much of their total mass are galaxies able to retain once they fall under the influence of their host cluster, in connection with the same interactions. Our results provide important information for models of galaxy formation and evolution, particularly their dark matter content, and for studies trying to link observations of galaxy clusters to the overall properties of the Universe such as its total matter content. Show less
In recent years it has become clear that the space in between the stars, contains a remarkable amount of highly diverse molecules, ranging from simple diatomics to large complex species.... Show moreIn recent years it has become clear that the space in between the stars, contains a remarkable amount of highly diverse molecules, ranging from simple diatomics to large complex species. Astronomical observations and dedicated laboratory experiments show that icy dust grains play a prominent role in the chemical enrichment of matter in space. Exotic solid state reactions taking place for temperatures as low as -260 degree merge small abundant species to larger and larger compounds until species are formed that are considered to be of relevance for life; sugars, fats and precursors of amino acids. Ultimately this material is embedded in matter from which stars and planets form. So, could it be possible, that the ingredients for life form everywhere, in space, following very similar chemical pathways? In this thesis a dedicated laboratory study is described that studies exactly these processes. With a new experimental setup the physical and chemical processes are characterized that are needed to interpret and guide astronomical observations and that yield parameters needed as input in astrochemical models. It is concluded that the chemical complexity in the solid state reaches out much further than assumed so far. Show less
The thesis addresses the long-term dynamical evolution of hierarchical multiple systems. First, we consider the evolution of orbits of stars orbiting a supermassive black hole (SBH). We... Show more The thesis addresses the long-term dynamical evolution of hierarchical multiple systems. First, we consider the evolution of orbits of stars orbiting a supermassive black hole (SBH). We study the long-term evolution and compute tidal disruption rates of stars by the SBH. Such disruption events reveal the physics and properties of stars and SBHs. Furthermore, we study the dynamics of planetesimals in the galactic center (GC). When planetesimals are tidally disrupted by the SBH, this can produce a potentially observable flare. We compute the rates of such disruptions, and find rates consistent with observations, suggesting that planetesimals are formed in the GC around stars, similarly to stars in the solar neighbourhood. Subsequently, we consider the long-term evolution of hierarchical quadruple systems. We appy our techniques to provide an explanation for the lack of transiting circumbinary planets around short-period binaries. Lastly, we generalise our methods, and apply them to study the implications of the long-term dynamical evolution of multiplanet systems on hot Jupiters (HJs). We find that the long-term dynamical evolution in multiplanet systems can explain at most a few per cent of the observed HJs, unless the efficiency of tidal dissipation is much higher than is currently believed. Show less
This thesis is focused on studying the motion of the Sun and the Solar siblings through the Galaxy. The Solar siblings are stars that were born with the Sun in the same molecular cloud 4.6... Show more This thesis is focused on studying the motion of the Sun and the Solar siblings through the Galaxy. The Solar siblings are stars that were born with the Sun in the same molecular cloud 4.6 Gyr ago. In the first part of the thesis, we present an efficient method to calculate the evolution of small systems embedded in larger systems. Generalizations of this method are used to calculate the motion of the Sun and the Solar siblings in an analytical potential containing a central bar and spiral arms. By integrating the orbit of the Sun backwards in time, we determine its birth radius and the amount of radial migration experienced by our star. The birth radius of the Sun is used to investigate the evolution and disruption of the Sun's birth cluster. Depending on the Galaxy model parameters, the present-day phase-space distribution of the Solar siblings might be quite different. We used these data to predict the regions in the Galaxy where it will be more likely to search for Solar siblings in the future. Finally, we compute the stellar encounters experienced by the Sun along its orbit and their role on the stability of the outer Solar System. Show less
One of the major unresolved questions in astronomy is: how do galaxies form and evolve? In the local universe we can distinguish between actively star-forming and quiescent galaxies. Quiescent... Show moreOne of the major unresolved questions in astronomy is: how do galaxies form and evolve? In the local universe we can distinguish between actively star-forming and quiescent galaxies. Quiescent galaxies are typically the most massive, with elliptical morphologies and red optical colors. The mechanisms that cause star-formation in galaxies to be turned off, so that star-forming galaxies become quiescent, are not yet well understood. Using the FourStar Galaxy Evolution Survey (ZFOURGE), comprising near-infrared data of over seventy thousand galaxies, we aim to find and study the first quiescent galaxies. First we describe the data products of ZFOURGE. Then we present the discovery of 15 very massive quiescent galaxies over 12 billion years ago, when the universe was only 1.6 billion years old. The implication is that they must have formed extremely rapidly, with explosively high star-formation rates. They are very compact, and much smaller than nearby quiescent galaxies as well as equally distant star-forming galaxies. Considering number counts and average properties of star-forming galaxies at even earlier times, we speculate that their formation history may have included a dust-obscured star-burst, possibly also forming a dense stellar core. Finally, we present a study of star-forming galaxy kinematics 11 billion years ago. Show less
This thesis uses catastrophic stellar events (supernovae and stellar collisions) to investigate different aspects of their environment. The first part of the thesis examines what happens to... Show moreThis thesis uses catastrophic stellar events (supernovae and stellar collisions) to investigate different aspects of their environment. The first part of the thesis examines what happens to supernova remnants near supermassive black holes like the one in the Milky Way Galaxy. To do so, a technique is first developed for predicting the evolution of supernova remnants in non-uniform densities. This is used to demonstrate how supermassive black hole environments determine the evolution and lifetime of supernova remnants. Conversely, observations of supernova remnants can then be used to infer properties of the surroundings of supermassive black holes. Therefore, predictions are then given for the X-ray emission that could be observed from core-collapse supernova remnants in these regions. This emission can compete with other sources, such the accretion flow of the supermassive black hole itself. Next, the problem of a core-collapse supernova in a close binary system is considered, where the effect on the companion is studied to predict the properties of runaway stars from binaries disrupted after a supernova. Finally, simulations of blue stragglers, formed from stellar collisions, are used to learn about the globular clusters containing them. Estimating the collision times reveals details about the evolutionary history of the cluster. Show less
