Crash Course Astronomy: White Dwarfs and Planetary Nebulae

I’ll be honest: Every episode of Crash Course Astronomy has been fun to write, edit, and shoot. They all really have. But the past few episodes, and the next few to come, deal with one of my favorite topics in astronomy: what happens when a star decides to give up the ghost.

When stars die all sorts of fantabulous things happen: They explode, they leave behind bizarre ultradense objects, they fling gas into space that creates amazing and breathtaking shapes and colors.

This week, CCA is about what happens after stars like the Sun die: They become white dwarfs, and in the process blow out a series of winds that become one of the most beautiful sights in the sky: planetary nebulae.

I studied the planetary nebula NGC 6286 for my master’s degree at the University of Virginia, investigating a giant circular halo of gas around it from the star’s original red giant wind. I had to simultaneously learn about planetary nebulae, the physics of interacting colliding winds, how gas radiates light, how the digital detector on the telescope worked (this was when such cameras were brand spanking new, so every thing about them was a learning experience), how to use the telescope, and how to write code to analyze the data. It was … interesting. Very difficult, but in the end I got results that were worth publishing.

My adviser, Noam Soker, is the man I mention in the video. I have never met a harder working astronomer in my life; he published a ridiculous number of papers, covering one small topic very well in each, and then moving on. I remember talking to him about why 6826 had an elliptical inner region, and he suggested it could be from a Jupiter-like planet orbiting the star. The problem was it would have to be very close to the star to be enveloped when the star became a red giant, and I thought that wasn’t possible—our Jupiter, after all, is more than 700 million kilometers from the Sun, way too far to get swallowed up! And you can’t form a planet that big that near a star anyway.

Oh, me. This was five years before the first “hot Jupiter” was found, and now I wish we had emphasized this even more in our paper instead of just adding a single line about it! It turns out they may be quite common; they form farther out from the star and migrate inward over time. I was pretty shocked when 51 Peg b was discovered, and seriously my first thought when it was announced was, “PLANETARY NEBULAE! OF COURSE!”

Yes, I think in all caps sometimes. It’s very funny to me that planets and planetary nebulae are in fact connected, especially since, despite their names, they are very, very different objects. But in science you find that everything’s connected in one way or another. It’s a tapestry, and every thread counts.