1,512 words · auto-generated from the episode video
1:18:49it in different directions and that 1420 MHz would be a little bit redshifted or a little bit blues shifted depending on where you were looking and what you could do. I mean, there's a lot of error, right? Because you don't know exactly where you're pointing. It's kind of a, you know, old disc that they were like, "Okay, let let the undergrads, [laughter] you know, use it for their lab." Um, so you don't know where it's pointing and the frequency resolution is not that great. But you could actually like I remember calculating the rotation curve, which is depending on how far away I am from the galactic center, um, how fast is the stuff moving. And you could actually chart out the galactic rotation curve and you could see that the galactic rotation curve
1:19:31plateaued. Now, okay, this is not as good as the data that I got. The data that I got had massive error bars [laughter] and only like eight data points, but what you could see is that it would rise and then it would plateau. And this is characteristic of dark matter. Vera Rubin the astronomer actually used these galactic rotation curves to calculate dark matter because if you think about it the farther away you get from a galaxy center the slower >> yes >> you should be moving >> right >> because Newton's laws inverse square law but >> here the farther you get away >> you're still moving at the same rate the only way this is possible is if there's a bunch of invisible matter that's actually pulling on you >> that's creating this gravitational force
1:20:12>> that's the stain that creates that plate to sustained uh uh speed because otherwise like there's no other external factor that could be >> Yeah. because we don't see any stars. And yet you're telling me that there's a bunch of new mass that's pulling on you >> because you're farther and farther away and your speed has not changed. Yeah. >> Even though it should now be slower because you're farther away from the gravitational center. >> Exactly. >> So that gravitational force that must come from has come from something. >> And that's where sort of Okay. Yeah. Dark matter. It makes sense. There's a lot of other avenues of research that actually point to dark matter, but this is one of the really cool ways of showing. Yeah, it's got there's got to be something there that we're not seeing. >> And it's also rel like even for someone who's not as deep in this, it can be relatively intuitive.
1:20:53>> Yeah. Yeah. And it's something that an undergrad can figure out, you know, using um a shitty radio dish [laughter] on the roof of Jadwin Hall. Um that that was one of my favorite like two weeks was actually doing this experiment and then writing the report. Okay, so now let's get back to the story. How do we find these? Well, we look at the 121 cm line, right? And the fast radio telescope, which is the 500 meter aperture spherical telescope. In 2023, it found a region of space that looked kind of weird. This is the radio telescope. It's out in Guijou, China, just north of Vietnam. It looks kind of like Aerosibo, which was out in Puerto Rico. It got damaged by the hurricane
1:21:34and is no longer in operation. But now China has something that's even better. >> That pronunciation was a pretty pretty good. And where did you learn that from? >> I I looked it up. [laughter] I I looked it up earlier. >> Yeah. So, um, they've got this telescope, the fast radio telescope. In 2023, it spots this object. Okay. >> Yes. >> And the this object has a bunch of 21 cm 1420 hertz coming through. >> And from all of the previous surveys, there's nothing starry there. >> Right. >> Okay. Okay. So, it's it's a patch of sky where we're getting a bunch of >> hydrogen emission, but there's no real stars there. It's right next to another
1:22:14galaxy, the M94 group. And the recession velocity of this gas. So, if you were to look at the red shift of this gas, it's very similar to the recession velocity of 304 km/s >> of the galaxy. So, it's associated to that galaxy because they're both moving away from us at the same speed and they're both right next to each other. So they've got to be sort of tied together, right? Okay. So that's the first observational signature, right? >> The second observational signature comes from the VA, the very large array. >> Yes, >> this is very recent. I think it came out last year. It shows that the broadening of that Halpha, that hydrogen line
1:22:55is very close to what we would expect if that hydrogen was thermalized to that UV radiation that I was talking about in the reionization epoch. Because imagine, right, I've got a cloud of hydrogen. It's hot and the temperature is right about at 10 4 Kelvin, which is what we calculate the UV radiation to be back then. And if the temperature is around that, then there's going to be some gas particles that are moving away from us, some gas particle moving towards us. And the spread of that thermal radiation is going to be right around 12 km/s if you calculate what the thermal radiation should be. And that's exactly what we see. The VA looks at that thing and sees that the spread is about 12 km/s. >> Mhm.
1:23:35>> So again, okay, this is thermalized radiation from that reunization epoch. >> Okay, very good. >> Very good. >> Very good. Also, if you look at rotating dwarf galaxies, those dwarf galaxies have a thermal radiation of like 30 to 50 km/s, much faster than what we see. And this is where we get to the astrophysical journal letters paper that we're going to talk about. The main story is this paper that came out very recently, the first relic question mark. They're asking, >> is this Cloud9 that we've been looking at for the past 2 or 3 years? Is this finally the thing that we had hypothesized in 2017? And actually, some of the authors of this paper
1:24:16>> were the authors on that original paper that hypothesized the relic. So, this guy's been chasing after a relic for like 3 or 4 years now, and and he's finally trying to figure out, is this it? And what he's done is use the Hubble Space Telescope to point it at that thing and say, there are no stars here. >> You're right. >> Okay. >> Unequivocally, cuz before we have like surveys and they might have missed something, but here we've got a Hubble Space Telescope mission that is looking at this thing for a very long time. Okay, almost 5 hours total. So, it had two 9,000 second exposures at that spot in the sky, and
1:24:56it's looking at it with two different filters. And those filters are optimized so that it looks for red giant branch stars because if there's a dwarf galaxy in there, that dwarf galaxy is probably going to be old and metal poor. So, the brightest stars in there are going to be red giants. Okay? And the amount of exposure time that these guys used was enough to see stars that are much fainter than those red giants. So, we're not going to miss it. >> Right? >> That's the point. If there's any there, we're not going to miss it. >> The threshold was high enough that it would have captured it if it's like, "Oh, well, you didn't turn it." >> No, no, no. We stared at this thing for long enough. If there was something there, we would have seen it. And they only observed three sources that they detected in that region. And then they
1:25:37said, "Okay, is three a lot? Maybe those three stars are you know what I can can I say that is that a lot is that a little well this this is something that's very clever and something that people do in science all the time is they try to measure something and then they say what could I see just by chance >> what is my background okay so they looked and they measured the density of sources in blank regions of that image that are far away from cloud9 and what they found was the average background is about 3.7 for this for a similar region so even just by chance. >> Yes. >> The amount of stuff that I would see in something that's not there >> is about 3.7. So, the fact that I'm seeing three is kind of just a roll of the dice. >> You know, there's it's not out of
1:26:20>> it it it it it doesn't it's not out of