Molecular clouds reveal the secrets of star formation in the galactic outskirts
The process of star formation inside galaxies is well understood, but until now little was known about how newborn stars arise and develop on the outskirts of galaxies. On January 8, at the 243rd meeting of the American Astronomical Society, astronomers announced that they had observed for the first time the molecular clouds that give rise to star formation in these distant regions.
About 18 years ago, the GALEX satellite discovered many newborn stars on the outskirts of galaxies, which was an unexpected discovery. Astronomers began to wonder about the conditions for this star formation and searched for molecular clouds that are the source of star formation, but were unable to detect them in distant regions until recently.
Typically, star formation begins with the attraction of tenuous atomic gas, which begins to compress over time. As the gas density increases, atoms begin to form molecules, and the molecular gas becomes a medium capable of giving birth to stars.
When the GALEX satellite discovered newborn stars on the outskirts of the M83 galaxy in 2005, researchers were unable to detect accompanying molecular clouds, which raised eyebrows.
Using a variety of instruments, including the Atacama Large Millimeter/submillimeter Array (ALMA), Very Large Array (VLA), Green Bank Telescope (GBT), and Subaru Telescope, researchers made additional observations to unravel this phenomenon. They found that the outer shells of molecular clouds on the outskirts of the M83 galaxy were invisible, and observations could only recognize small «hearts» these clouds.
A team of astronomers has discovered 23 individual molecular clouds in small regions of the M83 galaxy. This confirms the presence of star forming regions on the outskirts of galaxies, although they look completely different compared to the inner regions of galaxies.
Scientists believe these new observations solve an 18-year-long puzzle related to the process of star formation on the outskirts of galaxies. However, this study also raised new questions. In the area where the molecular clouds were discovered, the researchers were able to detect an unusually high concentration of atomic gas, which does not correspond to the observed amount of molecular gas. This necessitates new research to understand the causes of this anomalous phenomenon.