Astronomers have generally thought that massive black holes at the centers of galaxies expel gas in jets of material only during their formative years, when the central black hole is gobbling up gas and stars and producing lots of radiation. This makes them stand out as what astronomers call active galactic nuclei (AGN), or quasars.

If, as the new study suggests, the ionized hydrogen halo around galaxies is more diffuse, but also more extensive, than thought, this implies that the central black holes may actually become active at other times in their lives.

I love how we keep finding more and more about the role that black holes play in our universe.