This talk on Black Holes marked the return of our Vice President, Prof Bob Lambourne. Many of us remember Bob’s previous talks in this area, and to open his talk he provided a welcome revision of material covered earlier: Newtonian –v– Einsteinian theories of gravity, LIGO and the detection of a black hole collision, and the more recent radio telescope interferometry imaging of M87’s black hole.
He went on to remind us that it was Einstein’s Nobel Prize winning work in 1915 on General Relativity and Gravity that gave us the concept of dynamic, curved spacetime; as American physicist John Wheeler commented “Matter tells space how to curve – Space tells matter how to move”. And Black Holes emerge from this understanding. Though caused by stellar collapse and the aggregation of large amounts of matter, black holes are not actually made from that matter. Rather, they are composed of highly distorted space-time, the distortion (or curvature) being a consequence of the matter that has gathered together. Any star reaching beyond a certain point in its mass (the Schwarzschild Radius) would exert a gravitational force so intense that it would collapse to form a singularity (a region where the spacetime curvature becomes infinite) surrounded by an event horizon from which no light, matter or signal can escape.
Mathematical solutions have now been found for the four main types of black hole (non-rotating, charged, rotating, rotating and charged). Kerr for example in 1963, in his solution to a rotating black hole, showed it had two event horizons and an ergosphere. M87’s black hole has now been fairly well characterised – its mass is known, it has an accretion disc around it and it possesses a highly collimated jet. Of course, one might conclude that Black Holes are highly dangerous and destructive – and certainly you don’t want to fall into one because it would stretch you to bits! – but it may turn out that they are major stabilising entities of a galaxy.
As Bob stated at the beginning of his talk, our understanding in this area is moving extremely rapidly. We look forward to another visit when one can be sure that he will reveal yet further advancements in our knowledge and understanding.
Sandy Giles