Protoplanetary disks around stars may not be the only site for planet formation in the Universe, according to a team of theoretical astrophysicists from Japan. The researchers propose a new site of planet formation: a dusty torus around supermassive black holes in active galactic nuclei.
Supermassive black holes, millions to billions of times the mass of our Sun, are found at the centers of galaxies.
Many of these enormous objects are hidden within a doughnut-shaped cloud of dust and gas known as a torus.
“A torus can contain as much as a hundred thousand times the mass of the Sun worth of dust. This is a billion times the dust mass of a protoplanetary disk,” said Professor Eiichiro Kokubo from the National Astronomical Observatory of Japan and colleagues.
“In a low temperature region of a protoplanetary disk, dust grains with ice mantles stick together and evolve into fluffy aggregates.”
“A dust disk around a black hole is so dense that the intense radiation from the central region is blocked and low-temperature regions are formed.”
The astrophysicists investigated a growth path from small icy dust particles to Earth-sized planetary bodies in such low-temperature regions, located several light-years from supermassive black holes in low-luminosity active galactic nuclei.
“Our calculations show that tens of thousands of planets with 10 times the mass of the Earth could be formed around 10 light-years from a black hole,” Professor Kokubo said.
“Around black holes there might exist planetary systems of astonishing scale.”
“With the right conditions, planets could be formed even in harsh environments, such as around a black hole,” said Professor Keiichi Wada, from Kagoshima, Ehime and Hokkaido Universities.
Keiichi Wada et al. 2019. Planet Formation around Super Massive Black Holes in the Active Galactic Nuclei. ApJ, in press; arXiv: 1909.06748