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The Black holes – The existence of warm absorbers


Here is the identikit of the so-called “warm absorbers”, the layers of ionized plasma remotest among those issued, in galaxies to active nucleus, the central black hole.
What could be simpler than a black hole? It is an object so uniform that describing it should be like a walk. But if the black hole in question is one of those supermassive, heart and engine of the galaxy that hosts it, the matter becomes much more complex. Its interactions with the environment – or rather, what it surrounds – are in fact so intricate to take a real ecosystem. An ecosystem which Francesco Tombesi, researcher at NASA, and the international team led by him – who also includes two researchers of: Massimo Cappi IASF Bologna and Valentina Braito Astronomical Observatory of Brera – are gradually revealing some mechanisms long remained obscure. Last year touched UFOs, acronym for ultra-fast outflows, of which we have realized here on Media INAF. Today, with an article published in Monthly Notices, it is the turn of warm absorbers, layers of ionized gas present from the outermost regions of the host galaxy.
What Tombesi and colleagues found is that ultra-fast outflows and warm absorbers, as apparently diverse and far between thousands of light years, are manifestations of the same phenomenon: the wind of the matter from the central black hole. Wind on which the same black hole exerts its influence over a very wide spatial range: up to eight orders of magnitude, in fact, the distance separating – compared to the black hole – the very near ultra-fast outflows and remote warm absorbers. “It’s a bit like saying that the flutter of a butterfly can cause a hurricane on the other side of the world,” says Tombesi. But here the “world” is as large as an entire galaxy.

AGN_winds_unification

Credit: ESA/AOES Medialab

The existence of warm absorbers, which we could translate as “lukewarm absorbers” (the name is due to what of them scientists can observe, that the absorption lines), has long been known for high energy astrophysics. Compared to the ultra-fast outflows, highly ionized components with velocities close to one third of that of light, the warm absorbers are decidedly more moderate: while being also constituted by plasma, their speed is in the order of a few hundred km per second, as well as to temperature and ionization level of the values involved are far less extreme. To date, however, no one had a clear idea of their nature and their dynamics. To lift the veil of uncertainty that enveloped them, Tombesi and the team led by him have examined the same sample of AGN (active nucleus galaxies) that had enabled them to identify the UFO, and have crossed the features with data collected by the instruments with higher energy resolution among those on board the space telescopes XMM-Newton and Chandra.
“In so doing, we have succeeded for the first time to unify the different absorbers, observed in the X-ray spectra of various AGN, as part of the same wind on a large scale observed at different distances along the line of sight, from the immediate vicinity of the central supermassive black holes to the edges of the host galaxy, at distances of the order of thousands of parsecs, “says Tombesi. “We have also had confirmation that these winds, especially UFOs, are in fact so powerful that they can exert a feedback effect on their host galaxies. And, then, of influencing the evolution. “

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