Astronomers have discovered over 33,000 hydrogen gas halos surrounding galaxies, far more than the previously known 3,000, according to a new study published in the Astrophysical Journal. The findings may help explain where the universe's 'missing' hydrogen has been hiding, particularly from the era known as 'cosmic noon' 10 to 12 billion years ago when star formation peaked.
Hydrogen, the primary fuel for star formation, does not emit light on its own and is typically detected when illuminated by ultraviolet-emitting stars. Until now, only the brightest halos were observable due to the need for sensitive instruments and long observation times.
The team used the Hobby-Eberly Telescope at the McDonald Observatory in Texas, analysing nearly half a petabyte of data. They identified halos ranging from tens of thousands to hundreds of thousands of light-years across, with shapes varying from simple football-like clouds around single galaxies to irregular structures resembling 'giant amoebas with tendrils' containing multiple galaxies.
Lead author Erin Mentuch Cooper noted that these irregular halos are particularly intriguing. The researchers hope to study them in detail to refine models of galaxy formation and evolution. 'Now we can focus on individual halos and see at a greater detail the physics and mechanics of what's going on,' said Dustin Davis, a postdoctoral researcher at the University of Texas at Austin.
