Making Pasta in Space: A Journey Into A Black Hole Brad Koplitz Black holes are one of the most intriguing what that would be like. So, let’s take a and mysterious objects in our universe. journey, not to the closest but the biggest They have captured the attention of black hole in our galaxy. I’ll explain why astrophysicists ever since they were on our 150 million-billion-mile trip to the predicted to be sources of extreme gravity center of the Milky Way! by Einstein’s General Theory of Relativity You might be asking yourself, “If black in 1915.[1] For a refresher on gravity, check holes have such strong gravity, why would out [2]. These monsters have most recently we want to go to the biggest one in the captured the attention of the world when the neighborhood?” This is a reasonable first picture of a supermassive black hole question with a simple answer. It turns out, was taken.[3] when the black hole is much larger than you, the amount of gravity your toes feel will be almost the same as your head (just like on Earth). When you try to enter a ‘smaller’ black hole (ones around a couple times the mass of our sun) your toes will be stretched away from your head in a Figure 1: First image of the supermassive black hole process called spaghettification, which we at the center of the galaxy Messier 87. Credit: NASA, will get to experience later. If we’re going Event Horizon Telescope collaboration et al.[4] inside a black hole, we want it to be as big Roughly 6 million-billion miles from us is as possible. the closest known black hole, and though no We’ll also assume that we’re approaching one has ever been close enough to a black hole that’s as simple as possible; experience it, we have a good idea as to that is, it doesn’t have any electric charge mass of our sun, and nearly 28 million and it isn’t rotating. These are referred to, miles in diameter of pure emptiness. The by physicists, as Schwarzschild black holes. darkest black you have ever seen. We can For an overview of the different types, see see what surrounds the beast as we get [6]. A Schwarzschild black hole is defined closer: swarms of gas in orbit, unable to entirely by its mass and something called escape the pull of Sag A*. Even closer in, the event horizon, which is often considered light is being bent in circles around the the point of no return. It is the point in space black hole. Should we continue? We have at which you can’t escape the gravitational no choice. pull of a black hole, regardless of how fast The gravity of Sag A* becomes more you move. Renderings of black holes often extreme the closer we get. We begin to fall makes it seem as if the event horizon is a faster and faster towards the black hole, physical barrier, which it isn’t, see Figure 2. though everything around us appears to be It’s about what happens to light at this point, acting normally. but we’re getting ahead of ourselves. But what would someone safely away from the black hole see? As we begin approaching, everything is normal to them. But not long after, they will see our clock ticking slower. After a little bit more time, we begin to look redder. Soon the person’s eyes won’t be able see us, they’d need a Figure 2: Artist rendering of a black hole. Credit: way to see radio waves. Assuming they Forbes Magazine.[7] do, our clock will appear to stop as we As we begin to approach, we see stars approach the event horizon, but to us, it’s whipping around what appears to be ticking just fine. What’s going on here? nothing, some traveling at millions of miles The light coming from us is being per hour. But what are they going around? stretched by the immense gravity of the What could possibly move these stars so black hole, this known as gravitational fast without us seeing it? Astronomers call it redshift. As we cross the event horizon, Sagittarius A*, known as Sag A* to its the light is stretched to the point that it friends, and it’s around 4 million times the becomes undetectable to those outside, happens next. Some people, though, have which is why they’re black at all. But what come up with some possibilities. is it like to us as we cross the point of no The math of Einstein’s General Theory of return? Relativity says that everything that falls As we cross the event horizon, we wouldn’t into a black hole gets squished into a point notice anything weird. Time seems to be of infinite density, called a singularity. running at the same rate as before and we Physicists tend to not like it when the certainly don’t look redder to us. But as we answer is infinity, so they have continued try to look at our surroundings, things get to work on the question. Maybe if you weird. No matter which way you look, enter a black hole, you exit whatever the you’re always heading towards the heart of opposite is. This is a white hole. While the black hole. Even if we could travel at the they haven’t been seen in the universe, speed of light, we wouldn’t be able to make they continue to show up in the math, it back to the other side of the event horizon. leading to some wild ideas. Any light that we try to send out would get A white hole, mathematically, can be bent towards the center of the black hole. thought of as a time reverse black hole. If Eventually, we will get far enough inside nothing can escape a black hole, nothing that the force of gravity on our toes is much can enter a white hole’s event horizon. If stronger than on our head. At this point, it the gravity of a black hole pulls everything begins to stretch us like we’re on a medieval towards it, a white hole pushes everything torture device. Soon we’ll be as thin as a away, something called negative or spaghetti noodle, hence the technical term repulsive gravity. ‘spaghettification’. It doesn’t stop there. We My favorite perspective solution, however, keep stretching, thinner and thinner, until is that black holes are gateways to other we are nothing but a string of atoms that the universes. In theory, the way to do this is black hole will eventually break down. to dip into the event horizon while What’s left of us will get pulled deeper and traveling at the speed of light. When you deeper into the black hole. Here is where we come back out, you’ll find yourself in a hit the biggest hurdle of our journey: parallel universe. This may sound familiar physics doesn’t have a consensus on what to you. These are commonly referred to as wormholes, the fancy term is Einstein- Newsletter: Spring-Summer 2020. Rosen bridge. There is debate as to whether http://depts.washington.edu/astron/outre ach/jacobsen-observatory/ this would lead to an entirely new universe or to a different part of ours. In either case, [3] Dohrward, Priscilla – A Shot in the Dark: The First Image of a Black Hole. going faster than light is not allowed by the Theodor Jacobsen Observatory known laws of physics, but being bound by Newsletter: Spring-Summer 2019. these laws are so boring. http://depts.washington.edu/astron/outre ach/jacobsen-observatory/ Science allows us to contemplate the insane, [4] NASA.gov – Black Hole Image Makes imagine the unphysical, and explore the History; NASA Telescopes CoorDinateD unattainable. It strives for truth regardless of Observations. https://www.nasa.gov/mission_pages/chan biases and allows us to explain much of the dra/news/black-hole-image-makes-history world around us. It pushes us to do better [5] SPACE.com – Newfound black hole is and without it, society would not be what it the closest one to Earth we've ever is today. Thanks to Einstein’s General found. https://www.space.com/closest- Theory of Relativity, we were able to black-hole-to-earth-discovery.html journey from our humble homes to the [6] HOWSTUFFWORKS.com – How center of our galaxy and to other universes. Black Holes Work. https://science.howstuffworks.com/diction For an excellent video resource on black ary/astronomy-terms/black-hole.htm holes, I recommend the YouTube channel [7] FORBES.com – Discovery of PBS Space Time.[8] Enormous Stellar Mass Black Hole Perplexes Astronomers. https://www.forbes.com/sites/drdonlincol Sources Cited n/2019/11/29/discovery-of-enormous- stellar-mass-black-hole-perplexes- [1] WIKIPEDIA.org – General Theory of astronomers/#7fad1fa62816 Relativity. https://en.wikipedia.org/wiki/General_relati [8] PBS Space Time – Black Holes vity https://www.youtube.com/playlist?list=PL sPUh22kYmNBl4h0i4mI5zDflExXJMo_x [2] Matt, Cayenne – We are all Space Benders. Theodor Jacobsen Observatory .