Artist's impression of galaxy with outflow
This illustration shows a galaxy in the early Universe that is releasing material via two symmetric outflows triggered by the supermassive black hole hosted at its centre.
The effects of supermassive black holes on their host galaxies pose a tricky puzzle: numerical simulations suggest that star formation in early galaxies might be suppressed by the activity of the supermassive black holes at their centres. In some galaxies, the central black hole accretes matter at extraordinarily high rates, giving rise to very bright emission across the electromagnetic spectrum; these galaxies are said to host an active galactic nucleus (AGN). The accretion process is accompanied by the outflow of material and, if it is powerful enough, this may eventually drain the galaxy's reservoir of gas, halting its star-forming activity.