A Science Hack’s Guide To Black Holes

In the 1930s, physicist John Wheeler coined the term “Black Holes” to describe a particularly massive object in the cosmos. Yet curiously, I think Wheeler may also have been quite the practical joker, because a black hole is almost certainly comically misnamed, or at least misleading in its name.

First off, I say “almost certainly” because there’s a big problem with black holes. Science is essentially the way you answer questions about things you observe in the natural world, and this is where the first problem lies.

Artist's Rendering of what a Black Hole Might "Look" like. Click for full size image
Artist’s Rendering of what a Black Hole Might “Look” like.
Click for full size image

We can’t directly observe a black hole—at least, not currently.

To understand this, we must first understand how we use sight to observe anything.

When you observe something with your eyes, you’re seeing light (formally known as electromagnetic radiation) from an energy source such as the sun, or simple light bulbs and Light-Emitting Diodes (LEDs) either directly hitting your eyes, or bouncing off an object. For instance, if you look at a green plant, it’s absorbing all light except green light, which it reflects, and that’s why it appears green to you.

Most people know there’s a speed of light, this speed is 299,792,458 meters per second, or approximately 671 million miles per hour. This is the speed at which all things move unless they have mass slowing them down.

Electricity, gravity waves, light, radio waves, and any other massless objects all move constantly at this breakneck pace. But what is often forgotten in that fact, is that this is only true in a vacuum like the emptiness of space—well, sort of.

When light enters Earth’s atmosphere, passes through water, or interacts with any other matter, it imparts a small force on whatever it strikes. This is the principle behind using solar sails like this one from LightSail™ as a means of propulsion.

Artist’s concept of LightSail backdropped by the Milky Way galaxy. Credit: The Planetary Society
Artist’s concept of LightSail backdropped by the Milky Way galaxy. Credit: The Planetary Society

If this is true, when you account for Isaac’s 3rd law of motion which states that for every action (force) in nature there is an equal and opposite reaction, this means that whatever force light photons impart, that bit of mass will impart an equal force back on the light photon.

At first you might think that because light photons have no mass, they can’t impart such a force, but they do have energy and momentum, as explained here.

This reactionary force is often said to slow down the light. But it’s not actually slowing down because massless things travel at the speed of light always, it’s just taking a longer jagged route on its way from Point A to Point B as it bounces off of all the matter in its way, instead of taking the shorter straight line it would in a vacuum.

You can observe the results of this phenomenon by sticking a straight object in water and wondering why the %$#& it appears to be bending.

Click image for a more detailed explanation of this refraction
Click image for a more detailed explanation of this refraction

Black holes are masses significantly larger than our sun, which as you know, is pretty damn big.

It was often believed that a mass about 25 times larger than our sun would have the gravity it takes to form a black hole, however this star was observed and believed to be nearly 40 times as large, yet didn’t form one. So we’ll leave that in the “unknown” column for the moment.

We often think of gravity as a force that pulls a mass towards a larger mass, but Einstein understood gravity as a  wave bending space-time which simply forces things together. Because a black hole has so much mass, it bends space-time in such a profound way that light cannot make it back out, instead it just keeps bouncing around inside it, never making its way to our telescopes or eyes.

blackhole_gravity[1]

So pretty much all we know (or think we know) is based on calculations, understanding of physics we do know, and observations of effects in space that we think are most likely attributed to black holes.

As a result, most of what everyone reports about black holes, especially this post, are largely conjecture. As always, I often simplify things a bit as well. Sometimes because try to appeal to a general audience, other times because it’s simply all the better I understand the subject.

Nonetheless, any physicists or otherwise knowledgeable people on the matter, your comments, clarifications, or corrections are most certainly welcome below, this post is called A Hack’s Guide after all, so expert opinion is welcome.

At the beginning of this, I mentioned that I feel it’s comically misnamed. The whole point of explaining the light issue is to explain that a black hole is almost certainly not black in a traditional sense. There’s a lot of energy there, as this article from John’s Hopkins points out, “light is nature’s way of transferring energy through space.” Look no further than our sun for evidence of this.

So it’s most certainly emitting some light, even if it’s not in our visible spectrum, which therefore means it wouldn’t technically be black. It’s only that the light can’t escape its gravity, so you cannot observe its color and thus see no light (black) in the place in space it exists.

Some might argue that all things that are pure black absorb all light. For better or worse, I draw a distinction because those things are merely absorbing light hitting them, not emitting light on their own which simply can’t escape.

Now that we’ve covered why I believe it shouldn’t necessarily be called black, I’m going to address why it shouldn’t be called a hole, either.

Asteroids, such as Itokawa, pictured here, are thought to be more like piles of rubble loosely clung together, than solid chunks of rock. Credit: ISAS/JAXA (Click for more info)
Asteroids, such as Itokawa, pictured here, are thought to be more like piles of rubble loosely clung together, than solid chunks of rock.
Credit: ISAS/JAXA
(Click for more info)

If you were to put groups of celestial matter into categories by size that are big enough to be seen from the ground, you would have smaller objects like asteroids (meteors if they’re fixin’ to smash into Earth), which can be any random sort of shape for the most part.

Once they get about 200 kilometers in diameter however, the gravity of their own mass will start to pull them into a spherical shape, because it wants to start equalizing, or making sure that everything is equidistant from the center. That 200 kilometer number is rather interestingly called the Potato Radius, because celestial bodies below that size, often look like a potato.

Such large celestial bodies aren’t just asteroids, they can be dwarf planets like Pluto or full-fledged planets like Earth if they revolve around a star like our sun in a solar system. They can also be moons that revolve around planets.

This synthetic perspective view of Pluto, based on the latest high-resolution images to be downlinked from NASA’s New Horizons spacecraft, shows what you would see if you were approximately 1,100 miles (1,800 kilometers) above Pluto’s equatorial area, looking northeast over the dark, cratered, informally named Cthulhu Regio toward the bright, smooth, expanse of icy plains informally called Sputnik Planum. The entire expanse of terrain seen in this image is 1,100 miles (1,800 kilometers) across. The images were taken as New Horizons flew past Pluto on July 14, 2015, from a distance of 50,000 miles (80,000 kilometers). Credits: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
This synthetic perspective view of Pluto, based on the latest high-resolution images to be downlinked from NASA’s New Horizons spacecraft, shows what you would see if you were approximately 1,100 miles (1,800 kilometers) above Pluto’s equatorial area, looking northeast over the dark, cratered, informally named Cthulhu Regio toward the bright, smooth, expanse of icy plains informally called Sputnik Planum. The entire expanse of terrain seen in this image is 1,100 miles (1,800 kilometers) across. The images were taken as New Horizons flew past Pluto on July 14, 2015, from a distance of 50,000 miles (80,000 kilometers).
Credits: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

As they grow and gain mass, the pressure created from their massive gravity can start to heat up their core, where the gravity’s pressure is greatest (like Earth’s core), but if they get enough mass, it can eventually trigger nuclear fusion at their core, which can then make them become a star.

Our own solar system would tell you that this size would be somewhere between our own sun, which is a constant fusion reaction, and Jupiter, our solar system’s largest planet. But it’s a little fuzzy as to how much more massive Jupiter would have to become for this to happen.

From there, if a star continues to gain significantly more mass, it can go supernova and essentially blow up, form a neutron star, or if it’s mass is even greater, form a black hole.

Gumby
Gumby

So a black hole is not a hole (a nothingness) at all, it’s a huge mass. Despite Hollywood conjecture, things wouldn’t travel through it like they would an actual hole, they’d be slammed into it and become part of it with a monumental splat. Imagine it would be something like falling to Earth from an airplane without a parachute, but you’d be travelling way WAY faster and be stretched out like a cosmic Gumby as the part of you closest to it gets pulled harder than the part of you furthest from it—a process called spaghettification, for reasons I hope I don’t have to explain. A prospect that sounds generally unpleasant.

A black hole is also almost assuredly not flat like you’d think of when you think of a hole. Instead, it would likely be a perfect sphere since it is far greater than the aforementioned Potato Radius and thus its gravity would pull on everything equally from all sides towards the center keeping it round.

So what do I think it should be called instead? Something like Supermass or Megamass would have been much more appropriate to me. But nearly a hundred years after the phrase was coined, just like the largely misnamed football (Specifically American football, which is rarely kicked; not to mention the other football already existed) I doubt this movement would gain much traction at this point. So black holes it is…dammit.

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