It’s A Doughnut! Black Holes & Other Mysteries

Astronomy has just had a breakthrough, and that is the photographing of Sagittarius A*, the supermassive black hole at the Galactic Center of our Milky Way Galaxy. But what are black holes anyway? Let’s dive right into this hole in physics.

If you haven’t heard of a black hole before, it’s, as the name suggests, a giant black hole. However, never underestimate this hole because it has strong gravity. Sagittarius A* (abbreviated as Sgr A*) is the black hole that holds the Milky Way together, and our galaxy is estimated by NASA at 100,000 light-years across. One light-year is the distance light (regarded as the universal speed limit at 299,792.458 kilometers per second) travels in a year, which is pretty far. When you multiply that by 100,000, you get some big numbers. So how do these gigantic holes form?

These black holes form when a star collapses due to its weight. If the remaining mass after the collapse is more than 2.8 times the mass of the Sun, it collapses into a point of infinite density, known as the singularity. Now is when escape velocity comes into play. Escape velocity is the speed required to escape a mass’ gravity. Earth’s escape velocity is 11km per second. But the black hole’s gravity is so strong that the escape velocity is faster than light speed. So nothing, including light, can escape a black hole. Therefore, there is no light to illuminate it, and that’s why black holes are black. Once you venture beyond what is known as the event horizon, there is no turning back. Everything it sucks in gets compressed into the singularity, never to be seen again.

There are four types of black holes, but today we’ll only be covering two. The first kind is stellar black holes, typically ranging from 10 to 20 solar masses (one solar mass equals the mass of our Sun). The biggest stars collapse into stellar black holes. If you were to be sucked into one foot first, you would get stretched into a spaghetti. Your feet would feel millions of times the gravity felt by your head. This phenomenon gets called, and I’m not kidding: Spaghettification.

The second type is the supermassive black holes, and scientists believe that there is one of these in each galaxy in the universe. One of the largest has a mass equal to 140 million Suns. As for Sgr A*, its mass is 4.3 million times that of our Sun. If you fall into one of these, you wouldn’t feel as much difference because your body length doesn’t matter compared to the black hole’s mass. So gravity acts virtually the same at both ends. In each case, gravity would act differently on your body.

Anyways, moving on. In the beginning, I mentioned that a black hole sort of punctured a hole in physics. We need to look at Albert Einstein and his Theory of Relativity to explain that. Gravity, Einstein says, makes a curvature in the fabric of the universe known as space-time. However, since a curved route (the curvature caused by gravity) for light to travel on is longer than a straight line (with no gravity acting on it), but light speed is constant, it wouldn’t work. So, Einstein found a work-around. He hypothesized that time would slow down to account for the longer distance light needs to travel in curved space-time. It turns out (as Einstein usually was) that he was right. That meant that the clocks on Earth were slightly faster than those on the International Space Station (ISS) and was proven to be true. It’s accounted for when using GPS navigation. If not, the maps would give you incorrect info. Even though Einstein has explained how gravity works, it doesn’t explain how gravity gets formed, and that is still something astronomers are pondering.

So when black holes come into this picture, something weird starts to happen. Because the gravity of a black hole is so strong, it curves space-time so much that time virtually stops. If you were to fall into a black hole to an observer outside the event horizon, you would be falling toward the black hole and then stop. It would seem that you never crossed the event horizon and gradually faded away. Of course, from your perspective, you would get sucked into the singularity. Why the fading? It’s due to time slowing down. You would seem to be hanging in mid-air until the light illuminating you would also get sucked in, that you fade into nothing. So that’s how a black hole could break physics.

Depending on your perspective, Sgr A*, 26,000 light-years from Earth, could be close or far away. It has always been a challenge for astronomers to photograph the black hole with high resolution since Sgr A* is located in the Galactic Center of the Milky Way. Even with its giant mass, photographing one in the night sky is like trying to photograph a doughnut on the moon. Speaking of doughnuts, the picture of Sgr A* looks quite like one, a red doughnut with empty darkness surrounding it. But we should keep in mind that the photograph in question is the “shadow” because we can’t see the event horizon; All the light gets sucked in. No optical telescope on Earth could photograph such a tiny spot in the vast sky. That’s why we need another kind of telescope. Meet the radio telescope.

It works like a radio dish, which scans the sky and picks up radio waves. The black hole emits radio waves, which travel to Earth, bouncing off the radio dish and into the receiver at the end. Since the distance each wave traveled and bounced off at the same angle and speed, the receiver would receive them at the same time, and with troughs lining with troughs and peaks with peaks, they constructively interfere and form a bright spot in the image. But if you want to see the doughnut, Sgr A*, you need a higher resolution or a sharper focus point. There are two ways you could accomplish this. The first is to detect shorter wavelength radio waves. The problem is that the waves get blocked by the matter surrounding the black hole or our atmosphere.

So astronomers came up with a second solution, which sounds quite silly: Increase the radio dish’s diameter. Running the calculations, you would find that this dish needs to be the size of the Earth (meaning the dish’s diameter is the same as that of Earth’s) to get the high resolution to photograph Sgr A*. Astronomers and scientists alike found a way to do that. Instead of one big dish, why not break it up into several smaller radio dishes (or radio telescopes) across the Continents? It would be the same as creating one giant radio dish. The only problem with that solution was that you couldn’t build a receiver to receive and add up all the info in real-time to create the image of Sgr A*. So the only option was to let each telescope store its information and then transport the petabytes of data generated on hard disks to a central location where it could get analyzed (which is the fastest way). The bright spots in all the different telescopes’ memories would get lined up, and since each telescope has a different position, we could create the image of Sgr A*. The series of telescopes required to do this job has an interesting name: The Event Horizon Telescope Collaboration.

I should also say here that the photographing of Sgr A* isn’t the first time we have photographed a black hole; That was

back in 2019 when we photographed the supermassive black hole at the center of the galaxy M87, which is about 55 million light-years from Earth. Why did we get to photograph a black hole that far away in a different galaxy? It was presumably because the M87’s black hole is much more stable than Sgr A*. Sgr A* could change every few minutes, making it harder to photograph.

So far, we’ve been talking about black holes and their mysterious properties. But when talking about black holes, maybe we should also cover a bit about its neglected twin, the white hole. White holes are the exact opposite of black holes. A white hole “burps,” and its event horizon is the “point of no admission”; You can’t enter a white hole. Even though we know some of its properties, how white holes form is still a mystery, just like those of black holes. Some theorize that white holes get formed when black holes die, and they burp out the matter that they had sucked in in their past life as black holes. If that’s the case, then maybe we were wrong all along, and black holes didn’t have this “point of infinite density” that is the singularity. If the white hole theory was true, black holes were just another passage to some other world that we don’t know yet. And don’t you think that it’s weird, considering that the Big Bang flung out particles and matter, which is also the property of white holes?

The things we have covered, dear reader, are only things in the observable universe. Our universe has been expanding since the Big Bang and the beginning of time (as far as we could tell) 13.8 billion years ago. But some things are so far away that the light from those objects has yet to reach us, meaning we can’t see those objects. The diameter of the observable universe is about 46 billion light-years. However, there are still things beyond that, that we may never get to see. Like it or not, we still have much more to learn about the universe and maybe also to photograph. That’s the end of this production from the New News Newsminute. Thank you for reading, and tune in next time for more.