Meet the planetary nebula, one of the universe’s most gorgeous phenomena.
If you’ve ever looked through a telescope, you may have seen one of these before. Through a small telescope, one might look like a little planet—hence the name. But make no mistake, these nebulae have nothing to do with planets, and everything to do with stars.
Then, as the star runs out of helium fuel in its core, it expands into a giant a second time. This is the last time a medium-mass star will expand. It’s also the end of the line for the fuel in its core, since it can’t get hot enough to fuse carbon.
At this point, the star is so big that gravity at the surface is too weak to hold onto its atmosphere, especially in the face of the superwind of radiation pressure from the still-collapsing core.
The result is a planetary nebula…but what exactly is a planetary nebula? What is it made of? Why does it look the way it does?
It might, or it might not. If it does, you might recognize it as the periodic table of the elements—more often known as simply the “periodic table.” It’s an ingenious way to organize elements that has worked for scientists for quite some time.
To fully appreciate the ingenuity of the periodic table, I’d have to take you through a few chemistry lessons. Never fear, I have every intention of doing so—later. For now, though, I just want to address enough of the world of atoms to talk about stellar spectra.
That just means the spectrums we get from stars, by the way. (Spectra is plural for spectrum.) And that means…well…we’ll talk about it later. Let’s talk about the different types of atoms first.
This is the periodic table, and it’s pretty much the most important table in all of chemistry.
All the little boxes on this “table” are elements, the simplest form of matter. You literally can’t break these down further. What’s the difference between an element and a substance, you ask?
Okay, well, think of it this way. In my post on matter and its forms, I used water as an example of a substance. Water has its own physical and chemical properties, it’s not a mixture of anything, and no matter how many times you divide it up, you’ll still have the same thing.