DUSTDEVILS · The Dust Devils in Galaxy Centres

The Dust Devils in Galaxy Centres

The vast majority of the universe is empty thanks to the cosmological expansion of space itself. Gravitation led to the formation of islands within this tremendous emptiness. These are called galaxies and they consist billions of suns dancing in grand design patterns around the galaxy centres bound in a cosmic cycle of birth and destruction to the material they are born from and resolve in, gas and dust. But apart from the stars, gas and dust, there is something else lurking in the very centre of the galactic gravitational well, something that swallows all matter alike, a supermassive black hole. While it is established by now that at least all big galaxies host supermassive black holes in their centres, it is far less clear how, where and when they were born, and how they grew to their spectacular masses of up to 10^10 solar masses! Furthermore, it seems that these objects are not just an isolated curiosity of nature but they seem to even play an important role in the evolution of the galaxies by blowing material from the inner regions outwards, sometimes even out of the galaxy. This in turn can suppress (or amplify) the star formation within the galaxy and thus influence the further evolution of the whole system. Therefore, the study of the galactic black holes is well motivated as one of the pieces required for understanding the universe. This project focuses on the growth and feedback phase of the galactic black holes during which large amounts of radiation are released throughout all the electromagnetic spectrum. The nuclei of these galaxies will shine many times brighter than all the rest of the galaxy together. They are visible even over cosmic distances and are called active galactic nuclei (AGN). The powerful emission is primarily generated by an accretion disk forming as a results of the gravitational pull of the black hole and angular momentum conservation from gas and dust that somehow crossed into the gravitational sphere of influence of the black, either as a result of a galaxy merger, or a secular process like galactic disk or bar instabilities. A large part of the in-falling matter is actually not consumed by the black hole. Instead, it is lifted up from the swirling accretion disk and taken up in vertical direction, like a dust devil in the desert. Of course, the underlying physics of such vertical, or polar, outflows are fundamentally different from dust devils, but recent results indicate that the former are, in fact, surprisingly dusty, and they extend out to kiloparsec scale, way beyond the sphere of influence of the black hole. Thus, here we see the black hole feedback onto the galaxy in action! The polar dusty outflows have only recently been discovered, and they are have the potential to significantly advance our understanding of the AGN structure. Their base together with the accretion disk could give rise to the angle dependent obscuration that is required by the AGN unification models, and thus replace the so far canonical but purely phenomenological torus scenario. Therefore, polar dusty outflows are the subject of this research action.

Текст от CORDIS, на английски · Данни: CORDIS, © Европейски съюз