University of Southampton
Black holes in our Galaxy have masses between 5 and 15 times that of our Sun, and are formed when a massive star explodes in a Supernova. A black hole is so massive and confined in such a small volume in space, that not even light can escape its gravitational attraction. Fortunately, some black holes are in binary systems with a star similar to, or smaller than our Sun. If the black hole and the companion star are close enough, the strong gravity produced by the
black hole will slowly ``suck'' gas from its companion, deforming it into a pear-shape star. The gas pulled off by the black hole does not fall directly into it, but swirls in like bath water around a plug-hole, forming a disk of gas which astronomers call accretion disk. This disk can be described as a set of thin rings of gas, one inside each other, all rotating at a speed that depends on the distance to the black hole: the closer to it, the faster the ring rotates. Contiguous rings rub against each other, becoming hot due to friction. At a few km from the black hole, the speeds are so high and the friction is so strong, that the disk reaches more than 10 million degrees (2000 times hotter than the surface of our Sun!!), emitting
all the energy in X-rays. It is the information transmitted in those X-rays that, similarly to a ``feel Box'' game, astronomers use to comprehend and test the complex theoretical models which describe the exotic properties of black holes.
My research uses today's best X-ray telescopes, together with today's largest radio antennas and most sensitive optical telescope, i.e., those systems which are engulfing their accretion disks at the highest rate allowed by physical laws. The rate is actually so high, that these systems find themselves in a bottleneck, which in turn produces remarkable effects, such as extraordinary variations in their X-rays brightness and, hurricane-like disk winds which have never been seen
before in others systems.
Interests and expertise (Subject groups)