No matter which origin of life theory you subscribe to, water is a key component. A new pre-print study takes one step beyond to consider how water became so abundant in our galaxy, the Milky Way. The researchers present evidence that the Milky Way’s central supermassive black hole, Sagittarius A*, might have made the Milky Way a much nicer place to live.

When supermassive black holes consume galactic gas and dust, they emit huge amounts of radiation, temporarily becoming active galactic nuclei (AGN). Similar activity in other galaxies appears to correlate with an increased density of water and other organic molecules conducive to life, which occurs as X-rays from the AGN remove electrons from previously neutral atoms and molecules. This release of free electrons can accelerate the creation of organic molecules.

The researchers constructed a computer simulation of a molecular cloud containing dust grains and gaseous chemicals. They tested what would happen if they exposed the cloud to X-ray irradiation, like that from an AGN, for a million years. The AGN was then either switched off or allowed to continue emitting for a further 10 million years. Both these scenarios were compared to a simulated molecular cloud which experienced no X-ray irradiation.

When the AGN kept emitting X-rays, more water formed on the surface of dust grains in the molecular cloud compared to the model without irradiation, and this trend appeared even when the AGN was switched off. The explanation for this is that irradiation can increase the rate at which hydrogen molecules split, speeding up water formation.The simulation experiment also found that too many X-rays could eventually lead to a decrease in gaseous water, which suggests that there is a "sweet spot" for X-ray emissions where water can form and persist.

Computer models like these are complex with assumptions that may not perfectly reflect reality, but they can also be really useful for understanding past events. The study shows that X-ray emissions from an AGN could have a substantial effect on the abundance of water in the Milky Way.