Inside a Black Hole Millions of Lightyears Away

On April 10, the collaboration of world-spanning telescopes called the Event Horizon Telescope announced that they had taken the first ever image of a black hole. Though previously thought impossible to do, we can now see the unseeable.

Black holes are areas in space from which nothing can escape due to their infinite density and gravitational pull. They are pitch black to our eyes because not even light can escape the pull of gravity at a black hole.

The center of a black hole is what general relativists call a singularity. It is a single point in spacetime that has a mathematically calculated mass of infinity, making the gravitational pull also infinite. In astrophysical and cosmological terms, a singularity is understood to be the universe’s earliest state during the Big Bang. The quantitative reasoning behind a singularity is still unclear to scientists, and many people have lost themselves trying to find the answers to the universe’s biggest questions, including this one: what is inside a black hole?

We’ve calculated that at the center of a black hole there is a point so dense it stops anything from pulling away from it, including light. But because of this lack of light, we can’t see anything that might be “inside” a black hole. There is a certain point with every black hole at which we cannot see anything further. This point is called the event horizon (after which these telescopes were named). The event horizon marks the point of no return. If anyone were to cross the event horizon, there would be no way to get back out. It is at the event horizon that gravity starts to pull faster than light can move, and light is the fastest thing in the universe.

The perhaps more interesting (and more difficult to understand) thing about black holes is their effect on time. The trick to thinking about the universe is to keep in mind that space and time are much more entangled than we typically realize. Large bodies of mass (like a black hole) have strong gravitational pull, and this pull affects everything. The sun, for example, has enough gravity to keep all of the planets in our solar system in orbit. If there were a comet zooming past our sun, it would get pulled in too. But black holes have a mass millions of times of that of our sun, and can thus pull in a lot more stuff, including spacetime. Spacetime warps near black holes, and if you were to observe from afar somebody crossing the event horizon, their time would appear to slow so much until it looks like it isn’t moving at all. They would appear to move slower and slower to you. To them, though, their time is going the same speed as always because while time is accelerating and being pulled into the singularity, they are too. Time is relative.

For easy visualization, picture a skyscraper on Earth. On the first floor, it takes one minute for a person to move x distance around the axis of the Earth as the planet rotates. On the 20th floor, it takes one minute for a person to move more than x distance, let’s call it y distance. The closer you are to the axis we rotate on, the less you actually have to travel. If that’s still too hard for you to visualize, think of an oval race track. If everyone started and finished their race at the same line, those who are on the outer rings of the track have to actually run a good deal more than those who are closer to the inside of the track. The circumference of the inside of the track is smaller than the circumference of the outside of the track. If the runners were moving at the same pace, the person on the inside would win every race because they have less distance to cover.

The same concept happens with clocks. A clock on the first floor of the skyscraper is ticking along at its normal rate. However, a clock on the top floor has to travel more distance in the same amount of time. This means that on the first floor, one minute equals x distance, and on the 20th floor, one minute equals y distance, where y is greater than x. So how can one minute equal both x and y if light travels at the same speed no matter where you are?

The answer is, it can’t. Time is relative to where you are. After enough rotation of the Earth, the clock on the top floor will read something other than the clock on the first floor. It will tick slower than the other clock. This concept is called time dilation. Anyone on the first floor would say that it took one minute to travel x distance, and anyone on the top floor would say that it took one minute to travel y distance. And they would both be right, because time is going at two different speeds. 

Of course, this skyscraper situation doesn’t happen to an immense scale. On the 20th floor of the building, it’s probably noon at the same time as on the first floor. But stars, galaxies, time itself, those are all on larger scales. What are pretty big numbers for us to use on a daily basis don’t even begin to reach the sheer amount of spacetime of our universe. Our solar system is part of a cluster of stars that revolve around a center black hole. It takes us 250 million Earth years to make one single galactic year in the Milky Way. The closest neighboring galaxy is 200,000 light years away, meaning that even if we could travel at the speed of light, we would still only get there after 200 thousand Earth years of traveling at that constant speed.

As you can understand, it’s easy to get lost in the world of cosmology, and it’s definitely not for everyone. (And, if you’re now more interested, the Frostburg physics department is a great place to start.) We’re still discovering new things all the time.

Though these ideas and many more are what make up the most fundamental laws of our universe, there is much we don’t know, and many more questions that will arise upon ever finding the answers. But back to what this article was really all about: we actually have an image of the inside of a black hole!

The global telescopes that make up the Event Horizon Telescope are placed in different spots around the globe. The image is of the black hole at the center of the Messier 87 galaxy, about 55 million light-years away. These telescopes have been collecting data for more than a decade.

The photo is of a slightly lopsided, fiery orange ring. At the center is black. This area is the event horizon. The orange is all of the light that is being bent around the black hole. The shape of it is circular, just as Einstein predicted.

The image was actually taken from radio waves that are emitted from the black hole. We can only see a certain amount of light called visible light. Above the visible color spectrum are UV rays, and just below them are infrared. Infrared rays are manifested as heat, which our eyes can’t pick up as color, but which certain devices can change into something we can perceive. Infrared lenses take invisible infrared rays and make them visible. The same idea can be applied to these telescopes, that pick up radio waves and translate them into visible color.

More images like this will allow us to discover more and more about our universe. Black holes are one of the universe’s biggest mysteries. We’ve never really understood them. According to mathematical equations, there is nothing we can do to ever understand them completely. But we just got a step closer and achieved something recently thought impossible.