Why is the black hole image so fuzzy? Do black holes really look like lopsided donuts? Why does this matter? Everyday Einstein, Dr. Sabrina Stierwalt, explains the significance of this monumental scientific achievement.
Last week we witnessed an incredible first: the first ever image taken of a black hole. If you turned on a computer, opened a newspaper, or turned on the television, you saw the orange, glowing donut. We discussed here on the Everyday Einstein podcast, two years ago when the observations were first taken, what kind of telescope—or rather a globe-spanning combination of telescopes—was needed to take such an image.
So what do we make of the image now that it’s finally here? What exactly are we looking at? Is it what we expected? And what’s next?
Here are 5 facts about the first ever image taken of a black hole:
Why is this the first image we’ve ever taken of a black hole?
Supermassive black holes like to lurk in centers of massive galaxies like our Milky Way, but despite being so common, before last Wednesday, we had never actually seen one. Astronomers had only been able to infer their presence based on the motions of stars that orbit them or the energetic radiation that gets emitted as the matter being gobbled up by the black hole heats up. The problem, of course, is that black holes are so dense that their gravity becomes so strong that not even light—massless, fast-traveling light—can escape. Black holes are, by definition, black.
Humanity got our first look at a black hole last week, however, thanks to the use of radio waves and an observational trick called interferometry. In an interferometer, multiple telescopes are used together to mimic one larger telescope and thus observe with finer detail than would be possible on their own. Such observations are only now possible thanks to world class radio telescopes, the invention of the algorithms required to analyze their data, and, of course, a team daring enough to try it.
The black spot at the center of the image encompasses the black hole itself, including its event horizon, the point of no return for any matter and light, as well as the shadow it casts on its surroundings.
Why is the black hole shaped like a lopsided donut?
The black spot at the center of the image encompasses the black hole itself, including its event horizon, the point of no return for any matter and light, as well as the shadow it casts on its surroundings. This “shadow” reveals where light traveling close enough to the event horizon gets bent inward and lost forever to the singularity. So our black hole looks like, well a black hole in the image.
But what about the light traveling by the black hole that just narrowly grazes the event horizon enough to miss it and not be consumed by the incredible density of the black hole? That light continues its travels and gets sent back out into space. But space is bent around dense objects, like black holes, where gravity is strong so the path that light travels is not a straight line but a curved one around the black hole. So that light gets essentially slingshot around the black hole to form a glowing round shell called a photon sphere that shows up as the orange ring in the image.