Welcome back!

I hope all of you are safe at home and are doing well. The circumstances are hard for everyone, especially for you doctors and nurses out there: you have my respect. Keep going! You have the support of all of us! 

I decided to write this week’s blog post based on one of my favorite quotes. And though it may seem frivolous, it is from a popular series of children’s novels.

“Happiness can be found in the darkest of times if one only remembers to turn on the light.”

Given the constant reminder of the dark times that we are in, I thought it might be nice to take a refreshing break from all the horrors and delve into what are undoubtedly some of the most beautiful astronomical objects in the universe: nebulae.

So take a break from these trying times. They are dark, but read this, and turn on a light.

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Nebulae are, in simple terms, enormous clouds of dust and gas floating around in space. They can take many shapes. Some of the most famous nebulae include the following:

The Pillars of Creation (Eagle Nebula) 

Credit: NASA

Horsehead Nebula  

Credit: NASA

Crab Nebula

Credit: NASA | Hubble

War and Peace Nebula

Credit: NASA

Cat’s Paw Nebula

Credit: NASA 

The list could go on and on, but these are some of the most well-known astronomy images out there. The beauty of these nebulae can be seen just through the pictures—can you imagine how thrilling it must’ve been to actually discover one through a telescope! 

The observational history of nebulae can be traced back to the Greek astronomer Ptolemy (you can find more information about him in the History of Astronomy section of my website). In 150 AD, while under Roman rule, he observed some stars that appeared to be “nebulous”. Indeed, the word nebula is literally Latin for mist. (And nebulous also means misty or unformed!)

Throughout the Middle Ages, there were limited astronomical activities. However, in the centuries following the Renaissance and Enlightenment, astronomy was definitively on the upswing, and nebulae became a reality once more.

The first major catalog of nebulae was made by the combined efforts of William Herschel and his sister, Caroline Hershel—who, incidentally, is an often overlooked astronomer with as many contributions as her more famous brother. 

Before astronomers really understood what nebulae were, they classified any object in the night sky that was “nebulous”, or, in easier terms, fuzzy, as a nebula. As a result, for some time, the Andromeda galaxy was classified as a nebula. 

However, when astronomers began to analyze the spectra from nebulae (for more information, see my blog post entitled Light) they realized not only what their composition was, but what their role was in the universe.

“What is this role?” you may ask. 

Well, nebulae are, essentially, stellar nurseries. They are the birthplace of stars. 

But how does this work? 

I will not be delving into the entirety of the stellar life cycle in the blog post; that’s a story that we’ll save for later. But we can go into the basics of how the stars actually form in a nebula.

As I’m sure that you know at this point, nebulae are clouds of dust and gas. And, as you can see in the pictures that I’ve posted above, some areas of the nebula are denser than others; you can see this as thicker areas of dust and gas.

And when these denser areas of dust and gas increase in size, they end up collapsing in on themselves as gravity increases. And as more and more material begins to aggregate in that one area, the gravity continues to increase. 

In time, the gravity is so high, the particles begin to experience tremendous friction. Now, when there’s a lot of friction, the situation tends to heat up. I’m sure you’ve all experienced this by rubbing your hands together on a cold winter morning in order to bring some feeling into your fingers.

And, eventually, the temperature soars, more material is aggregated, and the first hydrogen atoms are smashed together and fused to form helium. A star is formed!

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Just a quick disclaimer: I’ve simplified the process considerably and excluded some steps. I’ll be explaining the star-forming process in more detail when we discuss stars. So stay tuned for that

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Now, there are various types of nebulae; I’m going to break them down so they’re easier to understand. 

The first kind are diffuse nebulae. These nebulae are large, sprawling, and, well, diffuse! They have no specific borders or boundaries and tend to spread out across a vast region in space. There are a few types of diffuse nebulae, also known as emission nebulae, reflection nebulae, and dark nebulae.

Emission nebulae are significant because they are the only types of nebulae that actively radiate spectral radiation. These nebulae will show up brightly in certain wavelengths of light. One of the best examples of an emission nebula is the Dragonfish Nebula, which shows up brilliantly in infrared.

Reflection nebulae, while identifiable by spectra, do not produce any radiation of their own. Instead, as in the name, they reflect the light of stars around them. One of the best examples of a reflection nebula is NGC 1999, which NASA took a picture of from Orion.

Although the name might suggest otherwise, dark nebulae are not terrifying manifestations of a fantasy dimension. They are just extremely dense nebulae that absorb the light or surrounding stars, making them dark. One of the best examples of dark nebulae is the Coalsack Nebula, which is a vivid dark patch against a brilliant starlit sky.

The second kind are planetary nebulae. These are formed near the end of the life of Sun-sized stars. And yes, our Sun is going to spawn one, too. Essentially, after the Red Giant stage, Sun-sized stars push their outer layers into space, forming an ionized cloud of dust and gas, or a planetary nebula! A good example of a planetary nebula is the Helix Nebula, quite near the Sun.

The third, and last, kind of nebulae are supernova remnants. As is the name, they are just the remnants of supernova explosions! When a star undergoes a supernova, the material that it ejects sometimes stays around the area, forming what we call a supernova remnant. A great example of a supernova remnant is Cassiopeia A, a beautiful remnant from a Type 1a Supernova. 

And those are the nebulae! Thank you all for reading, I hope you enjoyed, and make sure to comment if you have questions or just something to share. Stay safe, and take care.

Clear skies!