Black Holes Should Be Surrounded by Light

One of the main things black holes are known for is, erm, being black. They are not colorless per se, they just do not allow light to bounce of them, and therefore determine a color. All materials that absorb photons are generally considered to be black, but now astronomers say that the supermassive behemoths at the cores of large galaxies may in fact be surrounded by rings of light. Though it may seem a bit counterintuitive at first, the idea is actually not that far-fetched, Technology Review reports.

One could argue that the knowledge of light rings around black holes is of no use to us, given that light cannot escape the structure's gravitational pull. This may be true, but astronomers have recently had a great deal of success in imaging black holes using very long baseline interferometry, a measuring technique that for instance allowed them to gain more insight into the supermassive black hole at the core of our galaxy, the Milky Way. It is generally agreed upon that, in the very near future, advanced observational method will be made available. This method would arguably be able to penetrate the black hole until they get very close to the event horizon.

According to theoretical predictions, the light rings, made up of photons that the black hole absorbed and trapped, but which did not pass through the event horizon, should be located just outside of this horizon. They should also have diameters several times larger than that of the structure they are circling, which would render them visible for future imaging methods. One of the most important things astronomers hope to find using these techniques is a way of directly measuring the mass of the structure. This would help, for example, with establishing clearly that theories regarding other aspects of black holes, such as their influence on the environment, or their birth process, are true or false.

Astronomers are now happy for two reasons. For starters, they will soon be able to look at a black hole directly, and secondly, they will be able to detect these hypothesized rings of light very close to home. They say that the black hole at the core of our galaxy could be a prime target for observations. “The black hole in the center of the Milky Way, is the ideal candidate for a test of the no-hair theorem [that black hole's properties should only depend on mass and spin] due to its high brightness, large angular size, and relatively unimpeded observational accessibility,” say University of Arizona in Tucson experts Tim Johannsen and Dimitrios Psaltis.