I present the results of a search for main belt catastrophic disruptions over a 453-day Interval in the Pan-STARRS1 survey. I describe the design and Implementation of the Pan-STARRS Moving Object Processing System (MOPS), a software environment capable of both a) detecting moving objects in the Pan-STARRS1 transient detection stream and b) characterizing a general survey telescope's efficiency at detecting moving objects, providing a statistical framework from which one can characterize entire populations. I devised a simple model to describe how a catastrophic disruption would appear to the Pan-STARRS1 detection system, constructed simulations containing 1 billion synthetic catastrophic disruptions and used MOPS to measure the efficacy of Pan-STARRS1 to detect catastrophic disruption events. The catastrophic disruption search identifies a candidate catastrophic disruption, named P1 01 Oae, whose apparent brightness V = 18.5 is used to set an upper limit to the rate at which catastrophic disruptions can occur in the main asteroid belt. I adopt the power-law formulation from Bottke et al. (2005) describing differential disruption rates as a function of diameter to compute the largest diameter (more precisely the absolute magnitude HCL) at which one disruption can be occurring per year. The computed HCL suggests that collisional catastrophic disruptions, which are predicted to exhibit brightness Increases of 20 magnitudes, are occurring once per year for objects with H - 2B.7 (about 7 m diameter). At face value this would mean that for 100 m asteroids, collisional catastrophic disruptions are occurring at - 1/500 the rate predicted by Bottke et al. (2005). Recent work by Jacobson et al. (2014) shows that disruption by rotational spin-up from the Yarkovsky-O'Keefe- Radzievskii-Paddock effect (YORP; Rubincam 2000) may occur - 400 times more frequently than colllslonal disruptions, effectively making up the deficit In catastrophically disrupted 100 m asteroids.

No description available.

No description available.

Derelict satellites, rocket bodies, and pieces thereof have been left on orbit. These space debris have been increasing in numbers and simulations of their future evolution have shown that this increase might continue due to collisions between objects. It has been suggested that active debris removal (ADR), i.e. removing objects from orbit by technological means rather than by their natural decay due to drag, might be necessary in order to prevent an excessive increase of the number of debris. Selection of objects to be targeted by ADR is considered important because removal of non-relevant objects will unnecessarily increase the cost of ADR. Collision probability of every object should form part of the metric to select appropriate ADR targets. This work examines how the collision probabilities of all the objects in orbit depend on particular conjunctions, which cannot be forecast far in advance due to increasing orbit propagation uncertainty and variations in solar activity. It is found that conjunctions with high collision probabilities contribute more to the collision probabilities accumulated by objects over a period of time than other close approaches. Objects that are not large in mass and size are found to take part in conjunctions with high collision probabilities. Such objects are not likely to be removed from orbit when using existing ADR target selection schemes, and collisions involving them might not be prevented. Thus, the growth of the number of debris might continue in spite of ADR because collision fragments will continue to be generated. A complementary solution to constraining the number of debris in orbit, i.e. prevention of collisions between derelicts (just in-time collision avoidance, JCA), is thus investigated. It is found that fewer than ten JCA actions per year could constrain the number of objects in orbit. However, certain objects will repetitively take part in conjunctions with high collision probabilities. Permanently removing such objects from orbit via ADR may be more cost-effective than mitigating their collision risk via JCA. The finding that conjunctions with relatively high collision probabilities are the reason why ADR may be insufficient to constrain the number of debris, and analysis of JCA using an evolutionary debris model are the main novel contributions of this work.

In this thesis we consider the data analysis problem of detecting gravitational waves emitted by inspiraling binary systems. Detection of gravitational waves will open a new window on the Universe enabling direct detection of systems such as binary black holes for the first time. In the first Chapter we show how gravitational waves are derived from Einstein's General theory of Relativity and discuss the emission of gravitational waves from inspiraling binaries and how this radiation may be detected using laser interferometers. Around two thirds of stars inhabit binary systems. As they orbit each other they will emit both energy and angular momentum in the form of gravitational waves which will inevitably lead to their inspiral and eventual merger. To date, searches for gravitational waves emitted during the inspiral of binary systems have concentrated on systems with non-spinning components. In Chapter 2 we detail the first dedicated search for binaries consisting of spinning stellar mass compact objects. We analysed 788 hours of data collected during the third science run (S3) of the LIGO detectors, no detection of gravitational waves was made and we set an upper limit on the rate of coalescences of stellar mass binaries. The inspiral of stellar mass compact objects into super massive black holes will radiate gravitational waves at frequencies detectable by the planned space-based LISA mission. In Chapter 3 we describe the development and testing of a computationally cheap method to detect the loudest few extreme mass ratio inspiral events that LISA will be sensitive to.

Observations of astrophysical systems in different wavelengths can reveal insights in to systems which are not available from a single wavelength. The same can be expected from multi-channel observations of systems which also produce gravitational waves (GWs). The most likely source of strong, detectable GWs, which will also produce an electromagnetic (EM) signature, is the merger of compact objects containing neutron stars (NS) and black holes (BH), namely NS-NS and NS-BH systems. The focus of this thesis is to summarise current and past efforts to detect an EM counterpart of a GW event, with emphasis on compact merger sources. To begin, the formulation of GWs in general relativity is brie y discussed, as well as the main classes of GW sources. The global networks of GW interferometers in the recent past and near future are described, together with brief explanations of operational principles and the main challenges GW detectors face to make a confident detection. Current literature is reviewed to give a brief summary of the most promising sources which produce both GW and EM signals. Emphasis is given to gamma-ray bursts (GRBs), their afterglows, and kilonovae. In addition a brief description of GW searches triggered by an external source (such as a GRB) is given. A new form of search is then discussed in which GW events are used to point conventional EM telescopes, with emphasis on rapidly slewing, wide field of view optical telescopes. The main challenge in this form of search is that timing information from a network of GW interferometers yields large error regions for the source sky direction making it diffcult to locate an EM transient. Therefore a new statistic is presented in which galaxies (taken from a galaxy catalogue) within this search region are ranked. The probability of identifying the host galaxy of a GW signal from NS-NS and NS-BH systems is investigated and results presented for past and future GW detector configurations. The ROTSE-III telescope system took part in this first search for EM counterparts of GW triggers. With four identical robotic telescopes located across the world it responded to five GW events. Presented is an automation of the ROTSE image processing pipeline which allows large-scale processing and automated validation and classification of candidates. A background study was conducted to better understand the optical transient background and to determine the statistical significance of candidates. Pipeline performance is tested by inserting simulated transients following kilonova and GRB lightcurves in to images; an efficiency study is described. Finally the results of the images taken in response to the five GW events are presented and discussed.

The main goal of this thesis is to test the viability of some modified theories of gravity suitable to describe gravitational phenomena at cosmological and astronomical scales. In the first part of the Thesis we study the viability of the Brans-Dicke theory (BDT) and the effective scalar-tensor theory according (gBDT) to cosmological observations. We assume that either BDT as gBDT are limiting cases on very large scales of more general scalar-tensor theories involving derivative self-interactions which have running Newton’s constant. In order to implement this assumption in a simple way we consider two types of models. The restricted models that correspond to the standard BDT with Newton constant today equal to measured Newton constant in solar-system experiments. The unrestricted models, correspond to the case where the Newton’s constant today is a free parameter, and the cosmological GN is allowed to be different than in the solar system as in more general theories. We first explore the relevant theoretical aspects of these models. Afterwards, by using different analysis techniques we fitted cosmological observations. Finally we forecast limits of BDT by considering estimated covariance matrices for measurements of the matter power spectrum in redshift space from Euclid. The effective scalar-tensor theory gBDT arises from a phenomenological setup of parametrization of the LSS growth equations, we found estimates of modifications of the growth by using the correspondance between the estimates for the gBDT parameters. In the second part of the Thesis we present an extension of the Parameterized Post-Newtonian (PPN) formalism that is able to handle Vainsteinian corrections. We argue that theories with a Vainshtein mechanism must be expanded using two small parameters. In this Parameterized Post-Newtonian-Vainshteinian (PPNV) expansion, the primary expansion parameter which controls the PPN order is as usual the velocity v. The secondary expansion parameter, α, controls the strength of the Vainshteinian correction and is a theory-specific combination of the Schwarzschild radius and the Vainshtein radius of the source that is independent of its mass. We present the general framework and apply it to the Cubic galileon theory both inside and outside the Vainshtein radius. The PPNV framework can be used to determine the compatibility of such theories with solar system and other strong-field data.

Entanglement in higher dimensions is an attractive concept that is a chal- lenge to realise experimentally. To this end, the entanglement of the orbital angular momentum (OAM) of photons holds promise. The OAM state-space is discrete and theoretically unbounded. In the work that follows, we investi- gate various aspects of OAM entanglement. We show how the correlations in OAM and its conjugate variable, angular position, are determined by phase- matching and the shape of the pump beam in spontaneous parametric down- conversion. We implement tests of quantum mechanics which have been previously done for other variables. We show the Einstein-Podolsky-Rosen paradox for OAM and angle, supporting the incompatibility of quantum me- chanics with locality and realism. We demonstrate violations of Bell-type inequalities, thereby discounting local hidden variables for describing the correlations we observe. We show the Hardy paradox using OAM, again highlighting the nonlocal nature of quantum mechanics. We demonstrate violations of Leggett-type inequalities, thereby discounting nonlocal hidden variables for describing correlations. Lastly, we have looked into the entan- glement of topological vortex structures formed from a special superposition of OAM modes and show violations of Bell-type inequalities confined to a finite, isolated volume.

Gravitational collapse is analysed in terms of a simple model. Both Newtonian and Relativistic treatments are given, and the curious phenomenon of overtaking is discussed from a Newtonian viewpoint. It is shown that the Relativistic description of the motion is closely analogous to the classical treatment. The predicted final stage of the motion is collapse to a point singularity. The asymptotic behaviour near this singularity is examined, and it is shown that the presence of small inhomogeneities in a collapsing dust-sphere will radically affect the motion. The question of Boundary Conditions in General Relativity is considered, insofar as this affects the Relativistic description of the motion. It is shown that the Lichnerowicz conditions may be too restrictive, and conditions in respect of the first and second fundamental forms are proposed. It is shown that the spectral shift of a collapsing body becomes unstable as the gravitational radius is approached. The final stage in the collapse process is examined. In order to suggest possible models involving motion beyond the point singularity, it is necessary to consider General Relativity from a modern mathematical viewpoint; this treatment leads to a consideration of models involving multiply connected manifolds. The concept of time orientation is developed. It is shown that if, in a particular model, a collapsing body passes through the point singularity and then expands into the same spatial region, the model necessarily involves causality violations.

In this thesis, the problem of computing the back-reaction, or self-force, caused by a point particle interacting with its own field is studied. In particular, motivated by the prospect of detecting gravitational waves from extreme mass ratio inspiral systems, we consider the motion of the particle in black hole spacetimes. As a toy model for the most astrophysically relevant scenario of orbits about a rotating black hole we first study the scalar-field self-force (SSF)experienced by a scalar charge moving on a fixed geodesic in Kerr spacetime for a variety of orbits. Our approach is to work in the frequency domain, fully decomposing the scalar field into spheroidal harmonic and frequency modes and numerically solving for the retarded field mode-by-mode. Regularization of the retarded field is performed using the standard mode-sum technique which requires spherical harmonic modes as input, which we obtain by projecting the spheroidal harmonic modes on to a basis of spherical harmonics. We find for circular, equatorial orbits that the black hole spin can have a pronounced effect on the conservative piece of the SSF, causing it to (with respect to the Schwarzschild scalar-field self-force) change sign for certain spins and orbital radii. For eccentric orbits in the equatorial plane, we make use of the recently introduced method of extended homogeneous solutions to overcome the Gibbs phenomenon associated with a naive approach. As an application of our work we compute the shift to the innermost stable circular orbit due to the conservative piece of the scalar-field self-force for a variety of black hole spins. We also present some preliminary results for the SSF along circular, inclined geodesics. As well as studying the toy model SSF, we also consider the gravitational self-force (GSF) problem in the context of orbits around a Schwarzschild black hole. Our approach is again to work in the frequency domain, and we perform a complete decomposition of the metric perturbation in tensor spherical harmonics and frequency modes. The ten metric perturbation fields decouple with respect to the multipole indices but remain coupled within each spherical harmonic mode. We solve the resulting coupled sets numerically with a code set up to run on a computer cluster. Regularization is again performed using the mode-sum technique. Our resulting code is extremely efficient for low eccentricity orbits, and using it we compute the GSF for a great many points in the orbital parameter space. With these results we fit an analytic model to our numerical data and then use a relativistic osculating elements scheme to evolve the orbital inspiral. This allows us, for the first time, to assess the contribution to a complete inspiral from the conservative piece of the gravitational self-force. Finally, as an aside, we investigate the recently discovered phenomenon of isofrequency orbits, whereby it is possible to have pairs of physically distinct bound geodesics about a Kerr black hole that share the same three orbital frequencies.