Black holes are an oft-discussed element of astronomy. That is to say that most people understand them as a dramatic, dark emptiness in space. It’s likely, though, that many of these people can’t explain how black holes work or what their implications are. Black holes are anything but “empty space,” for example. It's not so simple.
Let’s begin with a basic definition of black holes. A black hole is a region of space where gravity wins out over, well, everything -- even light. That's where we get the “black” concept. Humans can't actually see black holes.
Get too close to a black hole, and nothing can escape its gravity. The point that defines “too close” is called the event horizon. Cross this threshold, and there's no escaping. The escape velocity equals the speed of light.
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| A visual explanation of the different features of a black hole region. Image Credit: made myself! |
Another critical point is the range of black holes. Black holes are not all huge as we understand it. Some can be as small as about 10 km in radius. Even at this size though, it's vital to understand that a black hole is still always massive.
The Schwarzschild radius is the radius of the event horizon of a black hole, found by equating escape velocity to the speed of light). Larger mass stars create larger black holes, but stars as small as ~25x the mass of the Sun can also become black holes. Some theorize that black holes can be created from sources other than stars or can be even smaller, but there is no evidence for any of this yet, so they remain theories.
The Schwarzschild radius is the radius of the event horizon of a black hole, found by equating escape velocity to the speed of light). Larger mass stars create larger black holes, but stars as small as ~25x the mass of the Sun can also become black holes. Some theorize that black holes can be created from sources other than stars or can be even smaller, but there is no evidence for any of this yet, so they remain theories.
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| The above image is a computer-simulated rendering of a supermassive black hole found at the center of a galaxy. You can see in the image the way the black hole’s intense gravity distorts a ring of space around it. |
Image credit: NASA
A computer-generated video of a star being ripped apart the tidal forces around a black hole.
Video Credit: NASA
So what are the implications of black holes? The video above depicts the interaction of a star with a black hole. If a star gets too close to the gravitational pull of a black hole, it will be torn apart by tidal forces. Tidal forces refer to a difference in the gravitational strength between two points. This same concept causes the tides on Earth. When it comes to black holes, however, tidal forces are a whole different story.
Black holes literally crush matter out of existence, which can be a difficult concept to understand or visualize. The terms "noodle effect" or "spaghettification" are attempts to clarify just how brutal it would be to slip inside the event horizon of a black hole (if that wasn't already clear from the video above).
What is a singularity?
Once something collapses into a black hole, we can't know exactly what happens. Scientists predict, based on the laws of physics, that "the matter that forms a black hole should ultimately be crushed to an infinitely tiny and dense point in the black hole's center. We call this point a singularity" (Essential Cosmic Perspective 368).
Once something collapses into a black hole, we can't know exactly what happens. Scientists predict, based on the laws of physics, that "the matter that forms a black hole should ultimately be crushed to an infinitely tiny and dense point in the black hole's center. We call this point a singularity" (Essential Cosmic Perspective 368).
As I mentioned earlier when discussing the size of black holes, it can be difficult to understand black holes because there’s still a lot that has either yet to be discovered or will remain undiscoverable about them for the foreseeable future (or forever). Scientists are still actively studying black holes, and there's so much we still don't know. It's also, simply put, really really hard to think about what goes on in black holes. To understand what happens inside a black hole, we need both quantam mechanic and gravity, and these areas of astronomy don't exactly coincide perfectly. Quantam mechanics is concerned with the small scale: atomic level interactions. On the other hand, gravity depends on mass. So black holes are a perfect nightmare -- a miniscule point in space but also so, so massive. No simple scenario for even the most advanced astronomers.
To refine your understanding of stellar remnants in general, and also black holes, check out Natalie's post here.
Thanks for reading!
Kylie
Bibliography
Bennett, Jeffrey O., Megan O. Donahue, Nicholas Schneider, and Mark Voit. The Essential Cosmic Perspective. 7th ed. Boston: Addison-Wesley, 2012. Print.
Clark, Stuart. "What Is a Black Hole?" The Guardian. Guardian News and Media, 1 Feb. 2016. Web. 14 Nov. 2016.
Wheeler, J. Craig. Cosmic Catastrophes: Exploding Stars, Black Holes, and Mapping the Universe. Cambridge: Cambridge UP, 2007. Print.
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