Five monsters buried in the dust

The space telescope NuStar identified a population of supermassive black holes invisible until now because of the cloud of gas and dust that surrounds them. Already it suspected the existence, but the data say they are much more bright and active than expected.
This time it was not luck. They knew where to look, the team of astronomers – including even researchers of Bologna and Rome – led by Durham University. Among the countless galaxies with a question mark at the center, they had selected nine: good candidates to host each a black hole – supermassive and in full swing, but hidden from the eyes of observers by a thick mantle of gas and dust. And they were right, at least for a good half of the sample: it was actually recorded a signal at very high energy, as only a super black hole can emit, come from five of the nine galaxies.


Credit: Hubble Legacy Archive, NASA, ESA

But if they went so without fail, because there have been noticed before? The suspect was in fact, what was missing was the right tool. The density of the blanket that wraps these frightening machines gobble-matter is such as to absorb even high-energy emissions. Only X-rays more penetrating, those near the border with gamma rays, unable to cross it. None of the satellites for high energy available before but had detectors capable of intercepting them. How long, exactly three years ago, NASA has orbited NuSTAR (Nuclear Spectroscopic Telescope Array), a space telescope with receivers capable of capturing even the most energetic X-rays, up to about 80 keV. Sufficient, therefore, to unmask these holes blacks until now invisible.
“Thanks to NuStar we were able, for the first time, to clearly see these monsters, which we expected to hide there, but buried by sitting continued to elude us,” he said Monday, July 6, 2015 at NAM2015 (the annual meeting of the Royal Astronomical Society) the first author of the study (to be released in The Astrophysical Journal), George Lansbury, postdoctoral researcher at the Centre for Extragalactic Astronomy of Durham University.
And in all probability this is just the appetizer. “Quasars in the study were chosen on the basis of indirect evidence, little more than a suspicion. NuSTAR observations not only confirm the suspicions, but lead to think that there are many more than there could have expected”, says Andrea Comastri, Director INAF Astronomical Observatory of Bologna, one of the co-authors of the study. “The astrophysical implications of this result are relevant sources of this type were already known galaxies in the local Universe, and not very bright, but for the first time, thanks to NuStar, finding these monsters buried has been able to push at greater distances and higher brightness. “

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