Photo Credits: Roen Kelly/Discover
The mystery of what a black hole looks like has puzzled scientists and artists alike for decades.
A black hole is, by definition, unseeable — a region of space with a gravitational pull so intense light cannot travel outward to bring us an image. But, using the laws of physics and our understanding of the cosmos, scientists are able to recreate what a black hole should look like to a reasonable degree of accuracy.
The resulting images depend on a number of factors, for example, whether the black hole is active or not, or whether it's spinning, but they do share a number of features. Where many of these images end up diverging, ultimately, is in how scientifically accurate they actually are.
This image is a quite accurate depiction of what scientists think a black hole with an accretion disk of hot gas and dust around it might look like. The two rings we see are actually just one; gravity bends the light from the rear of the disk around the black hole on both top and bottom so that it appears perpendicular to the real thing.
Because the disk is spinning so quickly from left to right, the Doppler effect comes into play as well. Light on the left side appears brighter as it comes toward us and dimmer as it moves away.
The black hole itself, of course, is the black sphere in the middle, defined by the absence of light. The bright line that divides light from dark on the inner ring demarcates the inner edge of the photon sphere, the innermost region where we can still see particles of light escaping from the black hole's pull.
Photo Credits: NASA/JPL-Caltech
In addition to an accretion disk, some black holes are also surrounded by what appears to be a large donut. The structure is called a torus, and scientists have just recently managed to image one with the ALMA radio telescope array in Chile
This galaxy is known as NGC 1068, and it's located about 50 million light years away. This picture is an artist's representation of what the very heart of the galaxy may look like, a shining accretion disk surrounded by a much larger torus of gas. How the structures form and behave is still largely unknown, and it's a topic of interest for researchers, as it may give new insights into how even larger things like galaxies come to be.
Photo Credits: NASA, ESA, and D. Coe, J. Anderson, and R. van der Marel (STScI)
Yet another conception of a black hole, this time without any material around it and backed by a dense field of stars.
Such objects do exist, in the form of quiet black holes that aren't currently sucking anything in. It's not clear whether such an object would look exactly like this, but the image does capture the way that a black hole would bend any starlight coming from behind it into a circle.
The ring of colorful stars results from light passing near the black hole curving around its gravitational well — the nearer to the black hole, the more the light gets bent.
Photo Credits: NASA/SOFIA/Lynette Cook/UPI
A different vision of a black hole, this time without the gravitational bending of light included. The resulting image doesn't capture relativistic effects, but it does illustrate the sometimes massive clouds of material that can surround the tiny pinprick of space that is a black hole.
This particular back hole is emitting what scientists call a "relativistic jet," a powerful beam of energy some very active black holes will emit as they suck matter inwards. Exactly how these jets are produced isn't quite known, but they can be some of the most powerful phenomena in the universe, sometimes extending for thousands, or even million of light years beyond the black hole.