Author: Cindy Hu
From: West Orange, NJ, USA
Once upon a time, there was a beautiful princess called Snow White. She was so beautiful that her stepmother grew jealous and secretly plotted her murder. Luckily, Snow White escaped to a safe corner of the universe, where she made friends with 7 dwarfs: Red, Yellow, Orange, Blue, Brown, White, and Black.
Okay, okay, I know that isn’t actually how the story goes. The “dwarfs” I mentioned above are actually astronomical terms, somewhat related to stars. But I genuinely think that the scientist who came up with these color-coded names was a Disney fan who couldn’t remember the names of Snow White’s companions.
Today we’re discussing these celestial dwarfs! This article will just focus on the first three: red, white, and black. The others are also quite interesting, but for the sake of time, I’ll have to leave them out. (Perhaps I can write a future article about them?)
But before I launch into a discussion about multicolored dwarfs, I have to explain what a star exactly is. They’re much more than just twinkling lights in the night sky, although that is one way to think about it. A star is essentially a ball of gas held together by gravity. An example is our own sun, which is actually the closest star to Earth. (Never mind that it’s over 93 million miles away. Although this should give you a sense of how spread out our universe is.)
Stars undergo a process known as nuclear fusion to generate energy. This is a process that joins hydrogen molecules in groups of four to form helium nuclei. When hydrogen runs out, stars start fusing helium into even larger molecules. Because of this, a star’s composition is constantly changing. They generally all start out as 75% hydrogen and 25% helium, by mass, but this won’t be true for long.
Side note: the term “star” is very broad and is often used to encompass objects that are about to become stars as well as objects that once were stars. For the purpose of this article, we will use the broad definition.
Red dwarfs are among the smallest, coolest, and most common kind of star. They’re red because of their low surface temperatures, and they have lifespans of trillions of years. An example is Proxima Centauri, which is the closest known star to our sun.
Like all other stars, red dwarfs fuse hydrogen into helium. Once the hydrogen runs out, they collapse and become white dwarfs:
Scientists often use Hertzsprung-Russell diagrams to organize star-related information. While this may sound scary, it’s actually just a simple graph. The x-axis represents surface temperature and decreases from left to right. The y-axis represents stellar luminosity, which is a measure of how bright the star is.
White dwarfs lie on the bottom left corner of H-R diagrams, meaning that they have high surface temperatures but low luminosities. They also generally have small radii - hence the name “dwarf.”
As we mentioned earlier, stars produce energy through nuclear fusion, a process that fuses together certain molecules into larger ones. Evidently, a star will eventually run out of molecules to fuse. Stars with masses close to that of our Sun’s will eject their outer layers, leaving behind only a small core. This core is a white dwarf - the “dead” corpse of the star that’s approximately the size of Earth and is no longer undergoing nuclear fusion.
Because they were once the centers of active stars, white dwarfs are extremely hot. However, they are dim because they’re no longer producing any new heat; they’re only radiating what’s been left over.
White dwarfs are extremely massive (not as in “big” but as in “has a lot of mass.”) One teaspoon of white dwarf material has about as much mass as a car! A white dwarf’s surface gravity is also so high, it would instantly crush you into a pancake if you ever tried to land on one.
On that happy note, we move on to black dwarfs. These are formed when a white dwarf cools down, a process that takes trillions of years. If you thought white-dwarf star corpses were depressing, black dwarfs are no better: black dwarfs are so dark they can barely be seen and so cold they approach the coldest possible temperature in the universe. There is absolutely no hope for life on a black dwarf, and the universe itself will be nearing death at this point.
Because it takes so long for black dwarfs to be created, their existence is merely a theory. Currently, no black dwarfs have been confirmed in our universe. But if you’re patient enough to wait 10 trillion years, you just may be able to find one.
Red, white, and black dwarfs comprise only a small sample of what the universe has to offer. As mentioned earlier, there are also yellow, orange, brown, and blue dwarfs, as well as many other interesting celestial bodies not classified as dwarfs. But even with our current knowledge, much of the universe remains unknown.
Who knows, maybe someday we’ll discover an 8th kind of celestial dwarf. What colors are still available, again?
Author: Cindy Hu
Cindy is a high school junior in NJ who loves math, physics, and biology, among many other subjects. Her hobbies include reading, playing the piano, and learning to crochet.
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