The super wind that sweeps Galaxy

The international team of astronomers led by Emanuele Nardini and INAF studied the properties of the mighty wind emitted by the supermassive black hole at the center of a galaxy by measuring, for the first time, the intensity and also revealing the spreading of the black hole in all directions. The work is published in the latest issue of the journal Science.
A mighty wind coming out incessantly from the supermassive black hole in a galaxy, a quasar called PDS 456. The researchers measured for the first time, thanks to the data collected by space telescopes XMM-Newton and NASA’s NuSTAR, the intensity of this wind, revealing the spreading of the black hole in all directions. A phenomenon long suspected but which had never before been tried with safety, and able to decisively influence the evolution of the galaxy that hosts the huge black hole.


Credit: NASA/JPL-Caltech

“We know that black holes at the center of galaxies can swallow huge amounts of material, but can also spread away some form of powerful winds, which can control the growth of the same host galaxies,” says Emanuele Nardini. “Knowing the distribution and extent of these winds allows us to understand how intense they are.” So intense that, every second, carrying ten billion billion times more energy than the sun releases in the same second with its solar wind, as it is clear from the results of the study, published in the latest issue of the journal Science. A phenomenon so intense as to decisively influence throughout the galaxy and its ability to form new stars.
PDS 456, even if it located 2.4 billion light-years away, is a relatively nearby quasar than the majority of the objects of this type. A unique opportunity for astronomers to observe in the local phenomena typical of the Age of quasars, which occurred about 10 billion years ago when the supermassive black holes and their dangerous winds were much more common. “For an astronomer, studying PDS 456 is like having a camera on the past,” says Valentina Braito. “We can understand the physical processes that accompany these systems with a level of detail impossible to obtain for similar items typically found at distances much greater.”
“Now we know that the winds produced by quasars contribute significantly to the loss of mass in a galaxy, reducing its stocks of gas, which are the main ingredient for star formation,” adds Risaliti.
NuStar and XMM-Newton have focused their instruments together towards PDS 456 in 5 different periods between 2013 and 2014. The joint observations have proved successful because each of space telescopes can observe a different portion of the radiation X wind leaving the quasar: XMM that of lowest energy, NuSTAR the highest.


Credit: NASA/JPL-Caltech/Keele University

In particular, the researchers were looking for signals related to the issue of iron, one of the chemical elements present in the wind ejected by the black hole. Past observations, including those made by the XMM-Newton, had already identified the presence of iron in front of a black hole. The atoms of iron shield the light from the nearby black hole, creating what is called an absorption profile in the spectrum of its radiation. But this only indicates that the iron atoms, and the winds that carry them, are spreading along our line of sight, but they cannot tell us if they do well in all other directions.
To clarify this, the researchers observed the radiation emitted directly from the iron. This track could only come from the side areas of the black hole and not just those facing us. The vision obtained by adding to the information XMM those NuStar showed that precisely this issue X Iron has finally confirmed this scenario.
Having thus reconstructed the geometric structure and the speed of the wind emitted by the black hole, the researchers were thus able to give an estimate of its power and its possible effect in preventing the formation of new stars. The search now continues to identify observationally the effects of wind on this large-scale structure of the host galaxy. In particular, it is possible, and expected, that the clash of this super-fast wind with the interstellar medium in the galaxy of producing large flows of gas and dust is characterized by speed very minor but by masses much greater. Even for these components to the study of an object “special” as PDS 456 will prove invaluable, in particular through future observations with ALMA observatory large antennas.

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