Ep. 642: Is the Sun… Normal? (1)
Fraser: Astronomy Cast, episode 642: Is the sun normal? Welcome to Astronomy Cast, your weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. I'm Professor Cain, publisher of Universe Today. With me, as always, is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute, and the director of CosmoQuest. Hey, Pamela, how are you doing?
Dr. Gay: I am doing well. It is exciting times around here. My hair and my camera have both decided it is time to celebrate the 80s and glitch in proper Max Headroom and frizzy, curly style –and I think this works. So, we're gonna go with it.
Fraser: You have hot humidity working on both of them at the same time.
Dr. Gay: It's true.
Fraser: Just recking cameras in here.
Dr. Gay: Yes.
Fraser: So, before we get into this week's episode, I just wanna do a rare, shameless self-promotion for something that we're doing on Universe Today. So, as you probably know – well, maybe people don't know this, but –
Dr. Gay: No, tell them.
Fraser: – when you support the Patreon for Astronomy Cast, you're not actually supporting me or Pamela. You are supporting the team that maintains Astronomy Cast week after week after week. Our editors, our produces, everybody, the server hosting fees, all of that. But actually, we don't take a salary from this. It's a nonprofit. But we both have Patreons.
So, for the Universe Today Patreon, which support the work I do with all of the –with all of the –giant team of writers that we have on Universe Today, all of that, the video editors, auto-editing, and so on, we've been hovering under the sort of 800 and 900-mark, and people have been asking me to do some kind of book club. And so, we decided we'll do that if we can reach 1,000 patrons for Universe Today.
So, if you go to patreon.com/universetoday, join as a patron, help us reach that 1,000-mark. And it's a bit of a race. We've mentioned this on our channel. We're gonna try and hit 1,000 patrons before either Space Launch System or the SpaceX Starship launch. Can you help us? Just show that we're the real rocket ship here. Pamela?
Dr. Gay: That is amazing. And I – yeah. We, over at CosmoQuest, we are in the process of doing our final push, just like Astronomy Cast, through to mid-July, and that hiatus, and we're in the process, right now, of planning out this year's CosmoQuest-a-Con. Normally, we do CosmoQuest-a-Con in July, but no lies, I have no air conditioning in my house, and I like my team. So, we are not going to do CosmoQuest-a-Con in July because I like my team.
So, instead, we're doing in October, but our goal is to have everything planned out by July and to sell enough tickets that we don't have to do a Hangout-a-Thon this year. So, we're selling tickets. Links are over at CosmoQuest.O-R-G for our October event. It's themed, Rockets and Robots, and we have an amazing slate of people. So, go get your tickets today.
Fraser: Awesome. All right. So, we've always assumed that we lived in a perfectly normal start system with a normal star, normal planets. It's all normal. But with our modern understanding of billions of stars, just how normal is our sun anyway? All right. Are we normal?
Dr. Gay: No.
Fraser: What?
Dr. Gay: But would we want to be?
Fraser: Yeah –I guess it doesn't –Yes. You know what? I've decided that, yes, we would want to be normal because then that would mean that all of the other yellow dwarf stars that we see out there probably have planets. All the planets probably have the same distribution as we have in our solar system. Probably a rocky world orbiting in the habitable zone, and that means that there's gonna life everywhere. Yes, please. Yes. We wanna be normal. This should be the template for what the universe should be like. Everywhere you go, it's just solar systems everywhere.
Dr. Gay: All right.
Fraser: But that's not real.
Dr. Gay: No. No. And I suspect the Fermi Paradox wouldn't be a thing if your version of normal was a thing.
Fraser: That's true. True. True. All right. So, I guess, do you wanna start with –what's some of the interesting characteristics about our sun and then start to compare that and how we know? So, I guess –let's define our sun, for a second.
Dr. Gay: All right. So, our sun is –a 10 to the 33-gram star. I don't know why we measure these things in grams. We do.
Fraser: Well, you can do 10 to the 33 kilograms, if you like.
Dr. Gay: It's true. It's true.
Fraser: Yeah.
Dr. Gay: It –glows a yellowy-white color. If we were seeing it without our atmosphere, our eyeballs would see it as much more white than it sees it as yellow, simply because our atmosphere is scattering out some of that blue light. So, our sky lies to us. Temperature-wise, it's more of a yellowy hue, so those old incandescent bulbs that we should no longer have in our house – houses, those were more solar temperature than the blue LEDs that we're dealing with. Our sun is about 1.3 percent metals which is anything other than hydrogen and helium, and it's just out there combining atoms to end up with light shining our way and a variety of neutrinos coming out of those reactions.
It's only in comparison that our sun get interesting. Really. It's kinda boring to just look at it by itself.
Fraser: But boring says normal, but you're gonna tell us that it's not normal, therefore, it's all interesting. Game, set, match.
Dr. Gay: So, in the Gaussian distribution, there is interesting on one side, there is completely boring on the other side, and there is average in the middle. So, I would say being boring is actually not normal.
Fraser: I don't think that it's boring. You know what? You're gonna have – you're – we're gonna have to go through this episode and I will judge in the end whether or not it's boring.
Dr. Gay: All right. All right.
Fraser: But right now, my instincts say, not boring.
Dr. Gay: Okay, fine.
Fraser: But let's take apart some of these things. So, you described the temperature.
Dr. Gay: Yeah.
Fraser: You described the mass.
Dr. Gay: Yeah.
Fraser: You mention the metallicity.
Dr. Gay: Yeah.
Fraser: The color.
Dr. Gay: It's also –it's five-ish billion years old, depending on the model you use.
Fraser: The age –Yep. Sure. So, let's pick one of those, and let's set that in comparison to what we see across the universe. So, let's talk about mass.
Dr. Gay: So, in terms of mass, if you simply assume there is one star in every possible mass bin, we're in the middle of the distribution, but the issue is that the universe doesn't have an even distribution of stars. The vast majority of the stars out there are much, much smaller. And so, this puts us up towards the top end of the by-count distribution on size with the majority of the stars being smaller. But then all those stars that are bigger than us, they live much more interesting lives.
So, in terms of the kind of evolution that we get, based on our mass, we're just another star that's going to end up as a white dwarf surrounded by a planetary nebula. So, we're not going to have an interesting supernova, we don't have a companion, so, we're not gonna end up with a different kind of interesting supernova. We're just gonna piddle out eventually.
Fraser: So, give us a sense because –I mean, when you think about it, when you stand outside and you look at the sky, you're seeing bright stars.
Dr. Gay: Yes.
Fraser: You're not actually seeing what is the vast majority of the Milky Way, which are the red dwarfs.
Dr. Gay: Exactly. It's –estimated that no fewer than 80 percent of the stars out there are red dwarfs and smaller, and the reason that we say no fewer is because we're still tracking down all those brown dwarfs out there. We're still tracking down what is the difference in distribution of red dwarfs between different populations. So, in some areas, you're going to get a higher fraction of red dwarfs formed, in some you're gonna get a lower fraction of red dwarfs formed, but no fewer than 80 percent of the stars out there are smaller red dwarfs, and brown dwarfs.
Fraser: It's interesting that we –because they're so dim and because they're relatively small and of low mass, we actually don't know how –where the bottom is.
Dr. Gay: Right.
Fraser: Like, we can see the bright stars. We can see the stars as they explode –billions of light-years away, but it's really hard to even figure out how many of the smaller brown dwarfs there are within a few dozen light-years of us. They're just so hard to see.
Dr. Gay: And this is where we're also suffering from the lack of infrared survey scopes. WISE did a really good job trying to look for them with its surveys, and, unfortunately, JWST –or fortunately, depending on which side of the observing proposal you're on, it's not gonna be used to just scan the skies looking to see what's there, it's going to be looking at specific targets of opportunity. And since these smaller stars give off the bulk of their light in the redder wavelengths –and they're so faint, you really have to be looking in these colors of light that don't really make it to the surface of our planet to be able to find them.
So, we wait, and we hope that eventually we get a good old survey scope up there to just crawl across the sky and infrared the way LSST is going to be crawling across the sky in visible wavelengths.
Fraser: We do need an infrared LSST in space.
Dr. Gay: We really, really do.
Fraser: Yeah. Yeah. Nancy Grace Roman is gonna split the difference, but it's gonna – it has a much wider field of view than Hubble than James Webb is in infrared, not in the same way that WISE is –was.
Dr. Gay: Correct.
Fraser: So, having that and – 'cause that's how you find the asteroid. That's how you find the comet. That's how you find the brown dwarfs, the rogue planets.
Dr. Gay: Yeah.
Fraser: There's a lot of really interesting things that are moving –Let's get that into the decadal survey for next time. Okay. So, we talked about size, mass. I guess size and mass are tied up with each other. Let's talk about –
Dr. Gay: But not really.
Fraser: Oh. Uh-oh. Okay.
Dr. Gay: So, this is where stars get weird, as you have to look at, what is the energy generation mechanism in their core? And you balance out, what is the mass? How are they generating energy in their core? And that tells you the size. ‘Cause, you're constantly balancing the light pressure outwards against gravity inwards. Right now, our star is a main sequence star and that actually makes it fairly average for where we are in the galaxy because stars linger on the main sequence longer than they linger anywhere else in the H-R Diagram, and the main part of our galaxy, while the majority of the stars are older than us, we still see plenty of stars hanging out on the main sequence.
Fraser: So, right now, our sun is a main sequence star. And so, that's what the whole term, main sequence.
