2026 September 11 - M83: The Southern Pinwheel

Greetings and welcome to the Astronomy Picture of the Day podcast. Today's picture is titled M83, the Southern Pinwheel. So, what do we see here? Well, here we see a relatively nearby spiral galaxy known as M83, only about 12 billion light years away. And as galaxies go, that's right in our own backyard. This is a very beautiful face-on spiral, so we're looking down on it, seeing the great spiral structure. And the way we see a galaxy really just happens to depend on how it is oriented relative to us in space. Some we see like this and can see the distinct swirling spiral arms. Others are tilted and the spiral galaxy is relatively flat, so we see just the edge-on view without the direct spiral arms. Now, this galaxy is also known as the Thousand Ruby Galaxy, and you can maybe see why because of all the red glow along those spiral arms. And in fact, those are all star-forming regions. Star-forming regions are, as you might expect, regions where stars are currently forming, but we see them in red, and that's because the hot stars that form are emitting a lot of ultraviolet light. Now, the ultraviolet light itself would not be something we can see directly, but it energizes the hydrogen gas around it. It excites the electrons and causes those atoms to glow. When hydrogen glows, it gives off a very distinct red color. So, all those star-forming regions, all those young stars that have formed are going to have this red glow to them because of that star formation that is going on. Around them, we can also see the blue glow of the clusters of stars. These are more clusters that have formed and are glowing with the blue light. Now, as I said, these primarily give off ultraviolet light, but our eyes are not sensitive to that, so we're going to see the closest wavelengths to that, which are the bluish color that our eyes see here. And ultraviolet is not the only type of light that we cannot see. In fact, the core of this galaxy is very bright in the x-rays, and that means that there are likely a high concentration of neutron stars and black holes present at the center, and may signify a recent burst of star formation. That can often happen when galaxies interact with one another, and their gravitational fields affect clouds of gas and dust, compressing them and causing star formation to begin. So, some of the reasons that we see a lot of blue stars and red star-forming regions here, more so than we would see in a typical spiral galaxy, could be due to an interaction in the past with another galaxy. So, that was our picture of the day, titled M83, the Southern Pinwheel. We'll be back again tomorrow for the next picture, previewed to be Lunar Suncatcher. So, we'll see what that is about tomorrow, and until then, have a great day everyone, and I will see you in class.