For decades, astronomers have faced a frustrating puzzle when studying star formation in our Galaxy. They know that most stars are born inside clouds of cold molecular hydrogen gas, but this hydrogen is all but invisible to telescopes because it doesn't emit light that can easily be detected. To find these stellar nurseries, researchers have relied on carbon monoxide as a tracer molecule, find the marker and thats where molecular clouds exist. However, there's been a problem with this approach, substantial amounts of star forming gas simply don't light up in carbon monoxide observations, remaining hidden from view.
This invisible material, aptly named CO-dark molecular gas, represents a gap in our understanding of how galaxies build stars. Without being able to see this dark gas, astronomers have been missing crucial pieces of the star formation story, like trying to understand a city's traffic patterns while only seeing half the roads.
A team led by Kimberly Emig from the National Radio Astronomy Observatory has now started to unveil the mystery. Using the Green Bank Telescope in West Virginia, they mapped CO-dark gas across the Cygnus X region, one of the Milky Way's most prolific and well known star forming neighbourhoods located about 5,000 light years from Earth. The survey covered an area more than 100 times the size of the full Moon, representing the first large scale view of this material.
The key to their success lay in observing Carbon Radio Recombination Lines, faint radio signals produced when carbon atoms recombine with electrons. These signals, detected at very low radio frequencies, revealed what carbon monoxide observations had been missing all along. The resulting map shows a fine level architecture of arcs, ridges, and webs of dark gas threading through Cygnus X, structures that were completely invisible in previous surveys.
The observations show that the carbon tracers flow and shift with surprisingly high velocities, creating turbulent conditions that directly influence how quickly new stars can form. The research also demonstrated that the brightness of the carbon signals correlates with the intensity of starlight bathing each region, highlighting how radiation from existing stars plays a powerful role in the ongoing cycle of stellar birth and death.
The dark gas the team have studied represents an intermediate stage in the recycling process, the transitional material between simple diffuse atoms and the dense molecular clouds where stars ultimately coalesce. By making the invisible visible, astronomers can now trace the complete pathway from raw atomic matter to complex molecular structures.
Source : Astronomers Map Mysterious “Dark” Gas in the Milky Way