If you are eager to study an image of a black hole, you will, unfortunately, be disappointed. There are none. They can’t be seen or imaged. Nevertheless, science tells us that they do, indeed, exist. The most sophisticated technologies and techniques in existence are unable to directly sense them. Physics associated with black holes fall far outside common, every-day experience.

Fortunately, black holes reveal their presence in indirect ways, much as how in a completely dark room, you will not see a friend standing just a few feet away, but the sound of your friend’s voice is strong evidence that you are not alone.

Black holes are not really holes by the common definition of a hole. A tremendous amount of mass exists within them. That mass produces a gravitational field like any other, and the force affects other nearby masses. This means that the motions of comparatively close objects betray the presence of that “hole’s” gigantic mass. According to Einstein’s model, gravity, as we usually think of it, results from the warping of space caused by mass. Light itself must follow the created curvature, generating some bizarre effects. Strange arcs of light are created by this kind of gravitational lensing. Light from an object behind a black hole — a star for example — can skim past just outside the hole, making the star’s light visible when under normal circumstances, it would have been obscured.

Gravitational lensing such as this can even be created by masses smaller than that of a black hole. The reason electromagnetic radiation, including visible light, can’t escape from the boundary of a black hole (called its event horizon) is that a hole’s escape velocity is greater than the speed of light. Escape velocity is the speed that must be attained to “escape” from a gravitational field.

Media have sometimes helped to create myths concerning black holes. They are not cosmic vacuum cleaners. Fortunately, their reach is constrained. If this fact were not the case, stars in large galaxies would all fall together into super black holes at galactic centers.

— Kent Fairfield is a volunteer with Pine Mountain Observatory and a lifelong amateur astronomer. He can be reached at kent.fairfield@gmail.com. Other PMO volunteers also contributed to this article.