Black Hole Hunting: Professor Andrea Marinucci
On Tuesday, October 18, 2017, John Cabot University Professor Andrea Marinucci gave the lecture “Black Hole Hunting: A journey through the discovery of these mysterious objects.” Andrea Marinucci holds a Dottorato di Ricerca (2012) in Physics from the University of Roma Tre. He spent half of his Ph.D. as a research fellow at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. As a post-doctoral research fellow, he worked at the Centro de Astrobiología in Madrid, Spain and on the European FP7- Strong Gravity project in Rome. In 2016 he joined John Cabot University as a Lecturer in Mathematics. He is currently a Researcher at the Department of Mathematics and Physics of the University of Roma Tre. His main field of research is Supermassive Black Holes and their surroundings.
The existence of black holes was first postulated in 1783 by English natural philosopher John Mitchell. His research stems from the concept of escape velocity, which is the minimum speed required for an object to escape the gravitational field it is in. Such velocity strictly depends on two intrinsic characteristics of the body to be escaped: the mass and the radius. Mitchell, who was aware of the finiteness of the speed of light, calculated that an hypothetical object with a large enough mass/radius ratio would have a gravity so powerful that not even light could escape from it. He called it a “dark star.”
The modern notion of black holes comes from the research of scientists Karl Schwarzschild, Roy Kerr and Albert Einstein, who first introduced the concept of curved space-time. Space-time fuses the three dimensions of space and the time dimension into a single 4‑dimensional continuum. According to Einstein’s theory of gravity, empty space-time is flat. However, in the presence of a mass, it becomes curved. A black hole, having an extraordinarily large mass, would therefore curve space-time to a significant degree. One of the many confirmations of this theory was given in 1963 by the discovery of the first quasi-stellar object (quasar). The quasar, named 3C273, was extremely luminous. This effect was caused by the accretion disk, an area of extremely heated gas, surrounding an active black hole. As gas spirals into the black hole, it becomes hotter and hotter, the closer it gets to the event horizon (the area where gravity becomes inescapable), which results in extreme brightness. This particular class of galaxies is called Active Galactic Nuclei.
The issue with looking for black holes, is that they are “black”, so that it is impossible to directly observe them. However, their gravitational pull has a deep effect on the surrounding objects, allowing astrophysicists to study them through the perturbations they generate. This is how astrophysicists discovered that supermassive black holes (of the order of million solar masses) are at the center of most galaxies, including the Milky Way. In 2008 the effect of our galaxy’s black hole, Sagittarius A* (SgrA*), on nearby stars was observed, via a series of images taken over a ten-year period.
Professor Marinucci concluded by explaining where the future research will lead. Currently a project named “Event Horizon Telescope” is under way. It is an international collaboration aiming to capture the first image of a black hole by creating a virtual Earth-sized telescope. Scientists are building and linking together new telescopes in order to allow the observation of SgrA* at the center of the Milky Way at the maximum possible resolution from Earth. The Event Horizon Telescope will constitute a new frontier for the study of black hole physics and general relativity.