I got completely absorbed in my novel-in-progress and wrote 3 chapters in the time I planned to write one. But everything else I planned to do on those weekends got squeezed out.
Unfortunately, I’m not coming back right away. I’ve decided I need to focus on building an independent income stream this coming weekend (Tues and Wed, for me) so that I can break free of my 9-5 and have time for my life.
We’ll be back to our regularly scheduled programming ASAP. And hopefully, by this time next year, I’ll be free and I’ll have a lot more time for the things I love, like this blog.
Next up—hopefully just a week or two away—is the diameter and luminosity of galaxies! And I hope you guys continue to enjoy the rest of the blog in the meantime.
Last week, I teased you with the idea that it’s actually easy to estimate distances to galaxies.
I do mean estimate–and distance indicators are still important.
The Hubble Law is named for Edwin Hubble, the astronomer who was first able to settle the debate over what galaxies were–using the new Hale Telescope, the largest in the world at the time. But the Hubble Law is undoubtedly what he’s most famous for.
In order to understand the Hubble Law, though, we first need a little review of the Doppler effect…
Well, I’ll give you a spoiler: they’re ridiculously far away.
Let’s consider for a moment what a light-year actually means. It sounds like a unit of time, but it’s actually the distance that light travels in one Earth year.
Think of it this way: if your name is Bob, and you can travel a certain distance in one year, that distance could be called a Bob-year.
I know it’s strange to think of light traveling at a certain speed. When you flip a light switch, the room immediately brightens. When you shine a flashlight, its beam immediately falls across the nearest surface.
But that just goes to show how insanely fast light travels. If it takes 2 million years for light to get from one object to another…imagine how far apart those objects are?
Well, that’s the case for our home galaxy, the Milky Way, and our nearest galactic neighbor, the Andromeda Galaxy.
By now, we’ve spent a heck of a lot of time exploring spiral galaxies.
It makes sense–they’re certainly the most photogenic. Seriously. Do me a favor and do a quick Google search for galaxies. When I did, nearly all the results were spirals…even though spirals are not the most common galaxies in the universe.
There is, of course, another reason we’re so familiar with spirals right now. We dipped our toes in the waters of studying galaxies by exploring our own home galaxy–a reasonable starting point. Our Milky Way just happens to be a spiral.
Well…it doesn’t “just happen” to be a spiral. But we’ll get to the reasons for that…
For now, let’s take a dive into all the different types of galaxies.
Alright, people…time to finish off our exploration of the Milky Way Galaxy, our home in the cosmos!
For the past nine weeks, we’ve covered everything from how our galaxy was “discovered” to how it may have formed. But there’s so much more to explore–and, starting next week, we’ll begin covering the vast universe of galaxies beyond our own!
But before we do that…I want to wrap up our discussion of our own galaxy with an overview to tie the last nine posts together.
(By the way, has anyone noticed I actually managed to chug out a post a week for the entire Milky Way “module”? I’m a bit impressed with myself for that!)
Over the course of my last eight posts, we’ve covered just about everything there is to cover about our home galaxy–or, well, at least the basics.
We’ve explored how astronomers first discovered what that incredible, milky stream of dust across the night sky actually is. We’ve followed astronomers like the Herschels and Harlow Shapley as they tried to measure the size of our galaxy.
We’ve covered its structure–a thin disk of spiral arms, surrounded by an enormous, diffuse halo–and how truly massive this great wheel is.
Most recently, we delved into the composition of the Milky Way–that is, how much heavy elements its stars contain. We discovered that stellar compositions hint at how old certain parts of the galaxy are.
But there’s one question we haven’t answered yet, and it’s quite possibly the most important one of all.
How did the Milky Way actually become what it is today?
We could even build on that, and say that the thin disk is where all the youngest stars are found. We could say that within the thin disk are spiral arms, where the star formation actually happens. We could say that the oldest stars are found in the central bulge and the halo, where there is very little dust and gas to make new stars.
But…what about its chemical composition? If we could explore our galaxy and bring home test tubes of “star stuff,” what would we find? And what can that tell us about our galaxy’s history?
Here is an edge-on illustration of our Milky Way Galaxy. (Keep in mind that the disk actually stretches quite a bit farther out from the budge than is apparent in this illustration. Proportionally, its full diameter makes its thickness less than that of a pizza crust.)
What if I asked you to imagine what that central bulge would look like to us–lifeforms living inside the galaxy? What would you imagine?
Perhaps you’d imagine looking inwards toward a glowing ball of light. Perhaps you’d imagine a region of our sky unusually thick with stars and interstellar clouds. Or perhaps you’d imagine something entirely different.
Probably the most spectacular feature of our Milky Way galaxy is its spiral arms.
We can’t get a probe far enough out yet to take a galactic selfie, but astronomers arereasonably sure that we live in a spiral galaxy. Observations of other spiral galaxies offer clues to what kind of objects can help us trace out the shapes of spiral arms, called spiral tracers. Using those spiral tracers, we’ve been able to map out patterns within our own galaxy that appear to be spiral arms.
Over the years, astronomers have tested the spiral arm hypothesis against the evidence again and again, and there is now a great deal of confidence that the Milky Way is a spiral galaxy.
More than that–star formation, which we know is limited to the disk of the galaxy (rather than its central bulge or halo), appears to be specifically found in the spiral arms.
But why? And for that matter…what even are spiral arms?