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Active Black Hole in Compact

Based on observations by the space telescope, Hubble, an international study led by IRFU has shown that, in the sample under scrutiny, the galaxies that host an active supermassive black hole are on average more compact than others. This discovery sheds new light on the growth of black holes in the heart of distant galaxies.
Published on 10 July 2017
​The widespread paradigm is that all galaxies host a black hole, which may weigh up to several billion solar masses. When surrounding matter "falls" into the black hole, it forms an accretion disk emitting characteristic X-rays—a signature of the galaxy's nuclear activity. In this case, the black hole is called an "active galactic nucleus".

The researchers wanted to compare the shape of galaxies with and without an active nucleus during the "peak" of structure formation in the universe (8 billion years ago), with identical star formation rate and stellar masses. Active nuclei that were hidden behind giant dust clouds were selected so that their visible counterpart would not distort the image of the host galaxy. In this case the nuclei are easily identified in both infrared and X-rays.

The team found that the galaxies hosting active nuclei are significantly smaller and more compact than others. The astrophysicists therefore deduced that the gas masses needed for the growth of the supermassive black hole could be channeled towards the central region due to violent gravitational instabilities inside the disk formed by the stars of the galaxy. These instabilities would trigger an important contraction of the galaxy, hence its ultra-compact morphology.

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