Shocked molecular hydrogen emission from the centre of the Galaxy

• Published in: Monthly notices of the Royal Astronomical Society 1984-10, Vol.210 (3), p.565-575
• Main Authors: Gatley, Ian, Jones, T. J., Hyland, A. R., Beattie, D. H., Lee, T. J.
• Format: Article
• Language: English
• Subjects: Astronomy; Characteristics and properties of the milky way; Earth, ocean, space; Exact sciences and technology; Stellar systems. Galactic and extragalactic objects and systems. The universe
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/210.3.565

Observations of molecular hydrogen emission lines near 2 µm show that the nucleus of the Galaxy is encircled by a ring of shocked gas; this ring has a radius of 2 parsecs, lies in the plane of the Galaxy, is symmetric about the centre of mass, and rotates in the sense of Galactic rotation. Gas is being shocked at a rate of $\gt 10^{-2} M_\odot \enspace \text {yr}^{-1}$ to a temperature about 2000 K, in a region of mean molecular density $5 \times 10^3 \text {cm}^{-3}$. The momentum needed to shock the gas cannot be provided radiatively. Mass loss from the nucleus can account naturally for the central density minimum and for the shocked gas; a mass loss rate of $3 \times 10^{-3} M_\odot \enspace \text {yr}^{-1}$ is required. Simple time-scale arguments suggest that observable molecular hydrogen emission from the Galactic centre may be a long-lived phenomenon. A model involving a single central engine is suggested.