Widespread Turbulence is Upsetting Star Formation in Stephan's Quintet

The movement of star-forming gas in galaxies is a fundamental research question in astronomy. Galaxies are huge interacting systems where molecular hydrogen is subjected to multiple forces. It's stretched out into streams between galaxies, and compressed in shock fronts elsewhere. It's diffuse and spread out in some places, and densely packed in others. It's dark and cold, or lit up with radiation.

Unfortunately, molecular hydrogen is not easy to observe, even though it's by far the most abundant molecule in giant molecular clouds . Instead, astronomers map carbon monoxide (CO), which is only a trace species in star-forming clouds. Despite making up only a tiny fraction of the volume, CO is widespread in clouds, and responds more readily to energy changes, making it a reliable proxy for molecular hydrogen.