A galactic bar is the approximately linear structure of stars and gas that stretches across the inner regions of some galaxies. The bar stretches from one inner spiral arm, across the nuclear region, to an arm on the other side. Found in about half of spiral galaxies, including the Milky Way, bars are thought to funnel large amounts of gas into the nuclear regions, with profound consequences for the region including bursts of star formation and the rapid growth of the supermassive black hole at the center. Quasars, for example, have been suggested as one result of this kind of activity. Eventually, however, feedback from such energetic events (supernovae, for example) terminates the inflow and stalls the black hole’s growth. How bars and gas inflows form and evolve are not well understood—galaxy mergers are thought to play a role—nor are the physical properties of galactic nuclei that are still actively accumulating gas. A serious difficulty is that dust in the dense material around the nucleus is opaque to optical radiation and, depending in part on the geometry, can obscure observations. Infrared and submillimeter wavelength measurements that can peer through the dust offer the best way forward.
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Source: Phys.org