The compact and, with \ M\, very massive object located at the center of the Milky Way is currently the very best candidate for a supermassive black hole in our immediate vicinity. The strongest evidence for this is provided by measurements of stellar orbits, variable X-ray emission, and strongly variable polarized near-infrared emission from the location of the radio source Sagittarius A* in the middle of the central stellar cluster. Simultaneous near-infrared and X-ray observations of SgrA* have revealed insights into (...) the emission mechanisms responsible for the powerful near-infrared and X-ray flares from within a few tens to one hundred Schwarzschild radii of such a putative SMBH. If SgrA* is indeed a SMBH it will, in projection onto the sky, have the largest event horizon and will certainly be the first and most important target for very long baseline interferometry observations currently being prepared by the event horizon telescope. These observations in combination with the infrared interferometry experiment GRAVITY at the very large telescope interferometer and other experiments across the electromagnetic spectrum might yield proof for the presence of a black hole at the center of the Milky Way. The large body of evidence continues to discriminate the identification of SgrA* as a SMBH from alternative possibilities. It is, however, unclear when the ever mounting evidence for SgrA* being associated with a SMBH will suffice as a convincing proof. Additional compelling evidence may come from future gravitational wave observatories. This manuscript reviews the observational facts, theoretical grounds and conceptual aspects for the case of SgrA* being a black hole. We treat theory and observations in the framework of the philosophical discussions about “realism and underdetermination”, as this line of arguments allows us to describe the situation in observational astrophysics with respect to supermassive black holes. Questions concerning the existence of supermassive black holes and in particular SgrA* are discussed using causation as an indispensable element. We show that the results of our investigation are convincingly mapped out by this combination of concepts. (shrink)

This paper gives a philosophical outline of the importance of plausible ontologies in the social sciences and argues how mechanisms and processes should be placed as the foundation in the social world. The argumentation is mainly based on a critical appraisal of the use of mechanisms and processes in the works of Norbert Elias, Charles Tilly, and Jon Elster. I start by elaborating on how inquiries of scientific interest evolve to shed light on cases, facts and the things that constitute (...) such facts, whilst the actual explanation demands the description of mechanisms and processes. Basically, focusing on variation and difference making is not sufficient to sustain claims of ontological plausibility and reasonableness. It is thus pointed out how the practices and proceedings of the social sciences can be ontologically enhanced by embracing the complementary roles of mechanisms plus processes together with difference making, as is performed in a special science such as biology, as well as is informally but promisingly pursued in the works of the discussed social scientists. While discussing their work, it is also argued that we should differentiate between processes and mechanisms in order to formalize this approach, which highlights the role of technologies and institutions as prime building blocks for social explanation. I conclude by presenting a claim that in taking seriously that the purported relations between beings and entities need to make discursive sense and historical sense, the social sciences will increase our cognitive success about the things of the world. (shrink)