Vera Rubin rotation curves (why we know DM is real)

6:03is not large enough to to to explain why they're moving so fast. >> Yeah. And and so there's got to be some stuff there that acts like matter in that it's gravitationally bound and it creates a gravitational potential, gravitational force, but it doesn't act like matter in the sense that there's like no light coming out of it. Right. >> Okay. And that's what's weird. Um there were other observations. Vera Rubin very famously solid solidified the concept in the 1970s with galaxy rotation curves. What you can do is figure out how fast stars are moving >> around a galaxy. Yes. And what you expect is something like the solar system. Again, the farther you are out, the short the smaller your velocity, the

6:45slower you should be going. That's why a year on Jupiter is like 15 years because it takes 15 years to go around the sun. That's not just because the orbit is bigger, like the circle is bigger. It's also that it's moving slower, right? It shouldn't be that long. But it's moving slower. That's why it's that long. If it was moving as fast as the Earth, it would be like 5 years or 3 years. And this is this is a similar graphic we talked about in our our Ver Rubin deep dive. We're looking at a graph now where we see the expected uh the expected path for the visible disc sort of dissipating on the x-axis. >> Yeah. And that would be like if it was it if it was normal if the farther I get away from the galaxy the the slower I

7:25should be moving. What we actually see using starlight and the hydrogen 21 cm line 1420 MHz is that actually you're just getting faster. So there's a bunch of invisible matter that is pulling on you that we have no idea how to see. Okay. >> So >> the question is what what is what is going on? What what is this dark matter? Well, the more and more observations we did, the better we got. In the 1980s, people discovered something called low surface brightness objects. These became known later on in 2015 as ultra diffuse galaxies. Okay. In 2015, we made a discovery using something called the Dragonfly Telephoto Array. Okay. This is

8:07a new array that was built by Yale and the University of Toronto. It's very cool. Actually, you as a camera guy, you're going to love this. So, each of these lenses, so it's in a honeycomb structure, right? And it's called Dragonfly because the dragonfly eye very much looks like this. It's a bunch of like honeycomb lenses. >> Yep. >> Each of these lenses is just the offtheshelf Canon 400 mm f/2.8 lens. >> Really? >> Yeah. It's just >> No way. >> It's there's they just they just bought a bunch of them, put them in a hexagonal array, and then they're compiling the light together >> to create these images. >> That's actually incredible. >> Right. This is something you can get like on Amazon, but they they put a

8:47bunch of them together. Now, the question is, why would you do this, right? >> Yeah. Yeah. Yeah. Traditionally, you never want to use lenses because the bigger the lens is, one thing you get is aberration, which is the idea that the bigger the lens is, the weight of the lens is going to >> deform the lens, >> right? Because glass is not like >> completely metal. So, there's some fluid property to it. So, the larger you make the glass lens, it's going to sort of like deform because of the weight of its own >> gravity or the other way around. And so