Thanks to its suite of of instruments operating at far-infrared wavelengths, Herschel the largest telescope ever launched to space, has been able to peer through the dust, affording the scientists the chance to study the turbulent innermost region of our Galaxy in great detail.
Super massive black holes probably lie at the center of most galaxies, and are a contributing factor to their evolution. The one at the centre of the Milky Way, in the region of Sagittarius A*, is a particularly fascinating object, since it is hundreds of times closer than those of the neighbouring active galaxies whose nucleus can be scrutinised in detail. This black hole is situated in the center of a cluster of young, hot and massive stars surrounded by dust grains heated by the ultra-violet radiation from these stars.
Located 26 000 light years from the Earth, hidden behind thick and opaque clouds of dust, the central region of our galaxy, the Milky Way, hide mysteries that have puzzled astronomers for many years. A franco-german team, including scientists from the LESIA [2] of Observatoire de Paris, already recently managed to detect, in the near infra-red, with the help of the adaptive optics of the Very Large Telescope in Chile, the motions of stars influenced by the gravitation of a central, massive but invisible object : very probably a black hole.
Rich and hot medium
The last observations made by Herschel space telescope, following proposal of a team including LERMA researchers, at Observatoire de Paris, brings new light on the subject in the relatively unexplored yet field of low energy radiation. The result shows that currents of ionized gas orbit or fall onto the central black hole. A rich variety of simple molecules (carbon monoxide CO, water vapour H2O, hydrogen cyanide HCN as well as OH, OH+, H2O+, H3O+, CH+, HF, CH and NH) have been detected. Detailed analysis of the carbon monoxide radiation indicates that a part of the molecular gas is very hot, with temperatures reaching 700 °C (1000 K) ; this is surprising, in view of the fact that ordinary interstellar clouds are on the contrary extremely cold, typically in the range -260 to – 220 °C. The explanation invokes vigorous heating mechanisms. These involve intense ultraviolet radiation, high speed shocks arising from violent collisions between the clouds, and powerful stellar winds coming from the massive stars in the stellar cluster.
Herschel and the associated scientific teams, which include Maryvonne Gerin, CNRS research director, Massimo de Luca, post-doctoral scientist, and Pierre Encrenaz, professor of the Université Pierre et Marie Curie and member of French Academy of Sciences, at the Laboratoire d’Etudes du Rayonnement et de la Matière en Astrophysique LERMA of the Observatoire de Paris, have thus added another brick to our understanding of the complex phenomena taking place in the environment around massive black holes at the centre of Galaxies.
[1] The Laboratoire d’Étude du Rayonnement et de la Matière en Astrophysique LERMA is a science department of Observatoire de Paris. It runs in association with CNRS, Université de Cergy-Pontoise, Université Pierre et Marie Curie, and Ecole Normale Supérieure.
[2] The Laboratoire d’Études Spatiales et d’Instrumentation en Astrophysique LESIA is a science department of Observatoire de Paris. It runs in association with CNRS, with Université Pierre and Marie Curie, and Université Paris Diderot.