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Quasar puzzle solved

01 June 2015
Quasar: galaxy with an ultraluminous nucleus and a double radio source straddling it

Using the Herschel Space Observatory, an international group of astronomers led by Pece Podigachoski and Peter Barthel of the Kapteyn Institute at the University of Groningen (Netherlands) have found strong new evidence that quasars are in fact radio galaxies, observed under a favourable angle. Barthel proposed this unification model in 1989, on the basis of observations with optical and radio telescopes. The model found considerable support but also criticism. New observations in the far-infrared with Herschel provide strong evidence in its favour. The results of this research will appear shortly in The Astrophysical Journal Letters.

Quasars and radio galaxies are active phases in the life of a galaxy. Massive galaxies (ten to hundred times more massive than our galaxy, the Milky Way) harbour massive black holes in their nucleus. When such black holes become active by accreting matter, their immediate surroundings become very hot and the galaxy nucleus radiates an intense luminosity. Under certain conditions, a gigantic double radio source develops, straddling the galaxy. Barthel’s unification model states that the angle under which these radio-bright active galaxies are being observed is of crucial importance. An opaque dust ring surrounding the nucleus blocks its bright radiation in some directions but not in others. The Herschel observations in the far-infrared are in excellent agreement with the predictions of the model concerning the dust radiation in the active galaxies, both from their nuclear and larger scales.

The astronomers also report that combination of measurements in the infrared wavelength range indicate in a simple way if a galaxy has an active black hole or not. Moreover, the relative importance of the nuclear activity to the total energy output of the galaxy can in this way be assessed. This is an important diagnostic in future research concerning the growth of galaxies and their black holes in the early universe.


‘The unication of powerful quasars and radio galaxies and their relation to other massive galaxies’ will be published soon in The Astrophysical Jounal Letters.

Pece Podigachoski & Peter Barthel, Kapteyn Instituut, Rijksuniversiteit Groningen; Martin Haas, Ruhr-Universität Bochum, Duitsland; Christian Leipski, Max-Planck Institut für Astronomie, Heidelberg, Duitsland; Belinda Wilkes, Smithsonian Astrophysical Observatory, Harvard University, Cambridge, USA


More information

Peter Barthel, Kapteyn Instituut, Rijksuniversiteit Groningen
Mobile: +31 6 1139 1826

Last modified:02 June 2015 10.09 a.m.
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