Tuesday, September 13, 2016

What Color Are Black Holes?

     Black holes - the only object that can stop light. The same light that travels 186,000 miles per second. Black holes are so unique, the laws of physics don’t apply inside of them, and once you fall in, you can't climb back out. As the saying goes, “what happens in the black hole, stays in the black hole.” When it comes to black holes we tend to think of large, black circles that road trip through the universe and suck up everything, but there is much more to it than that. There are many misconceptions about black holes, from their size, formation, behavior, and color. Are they really black? I am going to pick those misconceptions apart, and deliver the truth about the mighty black hole.
The primary force of black holes is gravity. We all know what gravity is. If an object has mass, it experiences gravity. Supermassive black holes have the strongest gravitational pull in the universe. So much matter is packed and squeezed into a black hole, it’s unfathomable. While we can’t fathom the density, we can analogize it. According to NASA, a star ten times more massive than our already massive Sun squeezed into a sphere the diameter of New York City would create a gravitational field so strong, it would qualify as a black hole. That is a lot of matter in a ridiculously small space. The Sun is already 864,000 miles across. Now imagine that times 10, packed into an area of just 468 square miles. When it comes to black holes, density rules.
Black holes began forming after the birth of the universe. These black holes are thought to reside in the center of galaxies, including our own Milky Way. Yes, we may orbit one massive black hole. Today, black holes are formed from supernovas. Large stars collapse under their own gravity when they die, causing a supernova. The material from the supernova becomes tightly trapped, creating a strong gravitation pull, and there you have it, a black hole is born. 
According to Dr. Chris Fragile, an old professor of mine, black holes range from as small as five times the mass of our Sun to over billions of times the mass of our Sun. Black holes range from the size of a mid-sized city to as big as our solar system. That is a quite a big range. Thanks to science fiction, it is believed that if you put a black hole near an object, that object is a goner. Black holes have even been referred to as “cosmic vacuum cleaners." This isn't true. It all goes back to mass. A black holes gravitational pull is equal to its mass. If the Sun were replaced by a black hole and its mass was equal to the mass of the Sun, Earth would orbit as normal. If the Moon were replaced by a black hole of equal mass, tides would see the same effect as they do now. This is why our galaxy hasn’t been sucked into the black hole at the center. Since that black hole has kept the same mass since the beginning, the orbits of the stars have not and will not change, keeping the residents of the Milky Way safely positioned.
While black holes can and do swallow everything, you would have to be really close to the event horizon to feel the gravitational effect. The event horizon is the “black” part of the black hole. It is still not certain what exactly happens inside of the event horizon, but one thing that is certain is that nothing can escape it. The flat, swirling disk that is typically seen in pictures is not the actual “black hole” itself, but the accretion disk. This disk is debris, gas, light, and other space particles that are swirled inwards towards the event horizon, but have not fallen in. Because of the intense speed, the particles become incredibly hot and the accretion disk glows and emits radiation. Think of the event horizon as Saturn, and the accretion disk as Saturn’s rings. The pull of the black hole is the same concept as a tornado. If you’re standing a mile away from a tornado, it’s not really a big deal, but if you’re standing next to a tornado, well good luck. The edge of the tornado is the event horizon and the debris flying around is the accretion disk. So black holes are not “cosmic vacuum cleaners.” While they can pick apart objects of the universe, it all depends on the mass of the black hole and how close you foolishly are to it. 
While the popular term “black hole” has been in use since 1967, it is not the most accurate. Black holes are technically not black. That’s right, we’ve all seen pictures of black holes and there’s always a black center, but they technically are not black. You see, it all goes back to light. The radiation that stars and galaxies give off comprises the electromagnetic spectrum. The visible light wavelengths are the only wavelengths that human eyes can see. Since black holes suck in light, there is no visible light, making them invisible.
So if they are invisible, how do we know they are there? Well, scientists have special equipment and telescopes that allow them to see all the wavelengths around the black hole. The accretion disk and the cosmic object that is being consumed emit large amounts of radiation and light. Scientists can study the matter and motion of the objects and determine if a black hole is likely present. Scientists believe that a supermassive black hole is at the center of our galaxy because it has been discovered that inner galaxy stars orbit a lot faster than outer galaxy stars, meaning there is something at the center with a huge gravitational pull, likely a black hole. And as long as we've been studying black holes, scientists may have just witnessed a star collapsing into one for the first time in real time.
There are plenty of theories on what would happen if you fall into a black hole, but nothing is universally accepted. One theory is that black holes could be used to time travel. The 2014 sci-fi film Interstellar played on this. The classic theory of “spaghettification” states that your body would experience tidal forces and be stretched thin like spaghetti and snap apart, and this process would keep repeating until there is nothing left. And of course, you die. Newer theories suggest you would instantly catch on fire, and die. Other theories suggest a mix of both. According to Amanda Gefter of BBC, reality would split in two. You would fall unharmed in one reality and be incinerated instantly in the other, and you would fall forever because of the singularity. So while there is not a current agreement on the fate of black hole victims, it is pretty safe to assume it's not an experience you’ll be able to tell your friends about afterwards. There's even now a theory that black holes don't have an "inside", so you can't fall in (but you would still die).
So can a black hole travel to our orbit and suck up Earth? The answer is no. Black holes cannot randomly appear, and there are none near our solar system.
You will likely never be able to take a tour bus to the nearest black hole and snap dazzling pictures for your Instagram account, but at least you now understand the truths. You'll never have to be afraid of waking up one morning and seeing a black hole in the sky ready to ruin your day.

*Chris Fragile, Amanda Gefter, NASA, BBC, Mother Nature Network, NPR, Physics of the Universe

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