For those of you who are not signed up for my newsletter, I’m sorry I’ve been away forever—life happened. It’s been a very rough three months. I hope you’re all doing well in light of the COVID-19 pandemic. I know it’s pretty tough right now, but we’ll pull through. Hang in there! 🙂
And now, for some long-awaited astronomy…
Meet Betelgeuse, a bright star in the winter constellation Orion.
Betelgeuse is a cool red supergiant that we’ll talk about a lot more in just a couple weeks, when we cover variable stars. Not too long ago, it was the height of excitement among astronomers. No one was sure why it…well…appeared to be dimming.
Yeah. Like a lightbulb. It was literally getting fainter—considerably fainter.
It’s pretty normal for Betelgeuse, like any other variable star, to fluctuate in brightness over time, but it was doing something downright weird. We’ll explore what was going on with it soon enough.
For now, let’s take a look at why Betelgeuse, as a supergiant, is so darn big.
As with most questions in astronomy, the answer to that is not definitive. But stellar models can give us a pretty good idea.
Mathematical models of stars tell us that their life—or, to use a less personifying term, function—depends on the balance between two opposing forces: internal pressure and gravity.
Stars produce energy to function. They don’t just do this to light up our skies and provide for life on their orbiting worlds. They need to produce energy to constantly support the weight of their own mass.
The more massive stars are, the more energy they need to produce—and the reverse is true too. There has to be a balance.
But is there a limit? Is there a point where balance is impossible?
Ask any climate scientist how we should power our world without fossil fuels, and they’re bound to tell you about wind and solar power.
You might be surprised to know that both of these come from the sun. Solar panels collect the sun’s energy directly, but we wouldn’t even have wind if not for the sun.
Why? Because in order to move, you need energy. And not just you. I’m talking about every speck of material on Planet Earth that shifts an inch. It’s because it has energy.
That energy can come from a lot of places. Earth is still a dynamic world with a hot interior, but it’s not hot enough to sustain all the life and other movement on its surface. A lot of our planet’s energy comes from the sun.
But here’s the big question. How the heck does it get here?
Take a wild guess: how much energy do you think the sun generates?
Think about it. It definitely generates enough energy to power a world.
Humans depend on the photosynthesis of plants, which converts sunlight into energy. And that’s not all. Without energy from the sun, our atmosphere would behave very differently, and so would our oceans.
Everything that moves on Planet Earth does so because it has energy. And a lot of that energy comes from the sun. It doesn’t even stop there—obviously, the sun has plenty of energy to spare, if the recent influx of solar power means anything.
The sun is incredibly powerful. And it’s powerful enough to keep generating that kind of massive energy supply for billions of years.
Meet the sun: a G2 class star towards the middle of its lifespan.
Wait a second…G2? What does that even mean?
It’s all part of a way astronomers break down the billions of stars in the sky and organize them by temperature. They can use a star’s spectrum to figure out what it’s made of, and that helps them figure out how hot it is.
But really…being able to read stellar spectra (plural for spectrum) is only so helpful. There are billions. It helps to have an organizational system.
That way, if an astronomer sees a stellar spectrum that looks a certain way, they can know immediately that it’s a certain class of star.