Collisions between galaxies, especially ones rich in molecular gas, can trigger bursts of star formation that heat the dust and result in their shining brightly in the infrared. Astronomers think that there is also significant gas inflowing to the central regions of galaxies that can stimulate starburst activity. Inflowing gas, as it collides with the gas in the inner regions, should produce powerful shocks that should make the gas itself glow. Some evidence for gas inflows on galactic scales has been discovered, but there have been few observational confirmations of the effects of the inflowing material in the inner region of the galactic nucleus.