If you wanted insights about the origins of life in the universe, supermassive black holes are probably one of the last places you’d expect to find them.
Not only do these gigantic punctures in spacetime consume anything that passes their borders, they also enjoy belching out galaxy-coring blasts of radiation, which seems like bad news for cosmic hospitality. Yet, in a counterintuitive way, those same energetic explosions might have enriched our galaxy, the Milky Way, with organic molecules and water—the main ingredients for life on Earth.
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This premise is applied to the Milky Way’s own supermassive black hole, known as Sagittarius A* (Sgr A*) , in a new study published on the preprint server arXiv, which has not yet been peer-reviewed.
Sgr A* is located at the center of the Milky Way and is in a relatively sleepy phase right now. But there’s evidence that a few million years ago it was an active galactic nucleus (AGN) that was blasting out high-energy X-rays. If you were a lifeform within a few thousand light years of the AGN, odds are you’d die either from radiation or because your planet’s atmosphere got blown off, according to a 2017 study in Scientific Reports.
But some scientists have wondered if AGNs may have beneficial effects on habitability over longer distances and timescales. That’s why the new study, co-authored by Xian Chen, an astrophysicist at Peking University, simulated the effects of high-energy radiation over a distance of about 26,000 light years and a duration of 10 million years.
The team’s models predicted galactic abundances of water and two organic molecules, methanol and formaldehyde, both with and without the blasts of an AGN phase. The simulations were informed in part by observations of organic compounds created in other actively flaring galaxies.
The models showed that the AGN increased the abundance of organic molecules by orders of magnitude, both on the surface of galactic dust grains and in a gas state. Moreover, these life-nourishing molecules sustained those higher levels for millions of years. The effects on water were less pronounced, especially in the gas phase, but the simulations did show that more water would have formed on the surface of dust grains due to the AGN.
This long-term enrichment of the Milky Way with organic molecules and water may even have reached our corner of the galaxy. “Our solar system is exactly 8 kiloparsecs (26,000 light years) away from the supermassive black hole,” Chen said in an email. “So the gas environment in which the solar system formed could have been affected by the irradiation from the Sgr A*.”
It’s still “too early to say” whether Sgr A* has had a net positive effect on the Milky Way’s habitability, noted Chen. “From these simple molecules to life is a big leap, and many works need to be done before we can fill in that gap,” he explained. “Personally, I’d like to simulate the formation (or destruction) of more complex molecules during X-ray irradiation,” such as amino acids.
Advances in radio astronomy may also help scientists identify the molecular signatures of the Milky Way’s recent AGN phase in the clouds surrounding Sgr A*. “The imprint in the chemical abundance is visible even several million years after the AGN turns off,” the team notes in the study.
“The potential impact on the origin and evolution of organic and prebiotic molecules in the Milky Way deserves further investigation.”
