By definition, black holes themselves remain shut off from direct observation. But astronomers have been able to precisely image the sphere of influence of a black hole – the area in which its gravity is the dominant force. In the case of a supermassive black hole in the interior of a galaxy, this area can be up to 500 light-years across. For comparison, the closest star to the Sun is a good four light-years away.
This imaging was done by the Atacama Large Millimeter/submillimeter Array (ALMA) in the Atacama desert of Chile. NGC 3258, a giant elliptical galaxy about 100 million light-years from Earth was the object being observed. This galaxy is one of about ten percent of galaxies whose core is surrounded by a rotating cloud of cold (non-ionized) gas. These clouds contain, among other things, carbon monoxide (CO), which can be observed in the submillimeter range, ALMA’s specialty.