A magnetic field at the centre of our galaxy may be keeping a supermassive black hole at bay.
Supermassive black holes exist at the centre of most galaxies, and our Milky Way is no exception.
But many other galaxies have highly active black holes, meaning a lot of material is falling into them, emitting high-energy radiation in this "feeding" process.
By comparison, the Milky Way's central black hole, known as Sagittarius A*, is relatively quiet.
Scientists at NASA believe this is because of the strong magnetic field at the centre of the Milky Way, which is strong enough to constrain the turbulent motions of gas.
"If the magnetic field channels the gas so it flows into the black hole itself, the black hole is active, because it is eating a lot of gas," NASA explains.
"However, if the magnetic field channels the gas so it flows into an orbit around the black hole, then the black hole is quiet because it's not ingesting any gas that would otherwise eventually form new stars."
NASA scientists have used a new instrument known as a High-resolution Airborne Wideband Camera-Plus (HAWC+) to visualise this magnetic field for the first time.
Magnetic fields are invisible forces, so they cannot be imaged directly, but the HAWC+ instrument detects polarised far-infrared light emitted by celestial dust grains. These grains align perpendicular to magnetic fields.
From the results, astronomers can map the shape and infer the strength of the otherwise invisible magnetic field, helping to visualise this fundamental force of nature.
"The spiral shape of the magnetic field channels the gas into an orbit around the black hole," said Darren Dowell, a scientist at NASA's Jet Propulsion Laboratory, principal investigator for the HAWC+ instrument, and lead author of the study.
"This could explain why our black hole is quiet while others are active."
