The heart of our Galaxy displays a paradox that intrigues astronomers. While this region concentrates immense quantities of gas and dust, the birth of massive stars there appears to be slowed, contradicting scientists' expectations.
An international team led by James De Buizer from the SETI Institute and Wanggi Lim from Caltech has scrutinized three stellar nurseries located at the galactic center: Sgr B1, Sgr B2 and Sgr C. Their study, published in
The Astrophysical Journal, is based on infrared observations made by NASA's flying observatory SOFIA. These data reveal that despite seemingly ideal conditions, the formation of stars more massive than eight solar masses there is significantly slower than in the rest of the Milky Way.
Detailed infrared view of the galactic center region of our Milky Way Galaxy. These images reveal massive stars in formation and emission from cold regions of dust and gas orbiting the central supermassive black hole.
Credit: J. De Buizer (SETI) / SOFIA / Spitzer / Herschel The researchers compared these central regions with similarly sized areas located farther from the galactic center, including near our solar neighborhood. Their analysis confirms that the star formation rate near the galactic center remains below the galactic average. James De Buizer emphasizes that unlike some previous studies, massive stars continue to form in these regions, but at a particularly moderate pace.
The likely explanation for this phenomenon lies in the extreme conditions prevailing at the galactic center. These regions orbit rapidly around the central black hole, interacting with older stars and possibly with other material falling toward the black hole. These violent interactions would prevent gas clouds from maintaining themselves long enough to initiate sustained star formation, thus limiting the production of massive stars.
Among the three regions studied, Sgr B2 presents an interesting particularity. Although its current rate of massive star formation is low, it appears to have retained significant reserves of gas and dust. This characteristic suggests the possibility that a future stellar cluster could emerge from this region, unlike Sgr B1 and Sgr C which seem to have exhausted their resources.
This study challenges the traditional classification of giant H II regions. Wanggi Lim explains that these central regions, although similar in appearance to stellar nurseries in calmer galactic regions, produce less massive stars and in reduced quantities. Their inability to maintain material reserves for successive cycles of star formation indicates they might represent a distinct category of stellar nurseries.
Giant H II regions
H II regions constitute cosmic zones where interstellar gas, primarily hydrogen, is ionized by the intense radiation from young, massive stars. Traditionally, astronomers considered these regions as active cradles housing stellar clusters still embedded in their natal clouds. Their study helps us understand the formation mechanisms of the most massive stars in our Galaxy.
These regions are characterized by their characteristic emission in the spectral domain of ionized hydrogen. Their size can extend over hundreds of light-years, containing enough matter to form thousands of stars. Observing these zones requires instruments sensitive to infrared wavelengths, capable of piercing the thick veil of dust that obscures them.
The classification of H II regions has evolved with observational advances. Recent research suggests they might exhibit greater diversity than expected, with properties varying according to their position in the Galaxy. This complexity challenges some established paradigms concerning their star formation cycle.
The study of galactic central H II regions opens new perspectives on stellar evolution. Their particular behavior could reveal physical processes specific to extreme environments, enriching our understanding of the diversity of star formation mechanisms in the Universe.