Ever heard the term ‘champagne flow?’ I’m not talking about a celebration, it’s actually a term in astronomy. When a cluster of massive stars form and ionize the surrounding hydrogen cloud, the hot gas propels itself through the layers of cooler gas at the cluster outskirts. When the hot gas finally bursts through to the vacuum of space, it flows rapidly like a newly opened bottle of champagne. This is exactly what’s happening in the cluster RCW 34, a young, gaseous cluster in the southern constellation Vela.
The interesting thing about this cluster is that its nearly invisible in optical wavelengths (the ones human eyes can see). It is obscured by a huge amount of foreground dust. But when we look at it in infrared wavelengths it becomes clearly visible and reveals its structure.
The infrared emission is caused by the formation of stars in the cluster. They output ultraviolet light that strips hydrogen atoms of their electrons near the star. As one moves further from the star the UV output is lower, and eventually you reach a point where the electrons and protons recombine into Hydrogen. This recombination releases an infrared photon which can be seen from Earth and used to find where stars are forming throughout the sky. The amazing this is that by measuring the amount of infrared radiation, we can work backward and find the amount of UV radiation released from the stars, which we can use to estimate the number and mass of stars that have formed in the cloud.
The interesting thing about this cluster is that if we look at the stars, we notice a lot of younger stars in the outskirts, with more massive aged stars in the centre. This distribution suggests that the cluster has undergone several episodes of star formation, with the massive central stars forming first and then triggering the formation of the less massive stars later.
Understanding and quantifying star formation in galaxies gives us clues to the evolution of those galaxies and the broader universe. By tracing the formation of stars in the present and past, we see a timeline of galactic evolution that leads us to the universe we see today.