All About Space

Black holes’ extreme exoplanets


Planets form from the gravitatio­nal collapse of over-dense areas of protoplane­tary clouds of gas of dust, and supermassi­ve black holes at the heart of active galactic nuclei (AGN) sit at the centre of massive, churning discs of such materials. At the moment there is no evidence that such black-hole-orbiting planets – or ‘blanets’ – actually exist, but recent research modelling the dynamics of these discs of gas and dust suggests that under certain conditions planet formation should occur in such regions. Should such processes occur, blanets would form much farther out from supermassi­ve black holes than most planets do from their parent star – so distant, in fact, that it could take a million years for such a world to complete an orbit.

Radiation from the AGN could help provide a constant supply of fresh material for blanet formation, and the result of this could be runaway formation, meaning blanets could reach sizes much more titanic than ‘regular’ exoplanets. Blanets would be less likely to share similariti­es with the planets of the

Solar System, with whole new classes of astronomic­al objects beyond gas giants and terrestria­l worlds to investigat­e.

With the nearest AGN existing beyond the limits of current exoplanet investigat­ions, the potential discovery of blanets may have to wait. Until then astronomy will provide a cavalcade of exoplanet discoverie­s that challenge our growing understand­ing of the universe and redefine our place within it.

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