#14: Star types in a movie theater
TRANSCRIPT
Moiya McTier
Welcome to pale blue pod the astronomy podcast for people who are overwhelmed by the universe but want to be its friend.
Corinne Caputo
Mhm I'm Corinne Caputo, a writer and comedian and friend to the universe. Yes.
Moiya McTier
And also friend to me. Hi, I'm Moiya McTier. I'm an astrophysicist and a folklorist and I have had a complicated but mostly loving relationship with the universe for for a long time. And Corinne Where are we right now?
Corinne Caputo
We are in a place I've had a complicated but loving relationship with which is the movie theater I worked at in high school. And they've really upgraded since I worked here. So now there's even more snacks even more drinks. And guess what stadium seating with reclining chairs.
Moiya McTier
Oh, you're getting fancy
Corinne Caputo
uh huh, And they are letting us after we grab the snacks. They're gonna let us record in this theater. And then we can go watch a movie.
Moiya McTier
Nice. Are we are we going to record in the projector room? I've always wanted to see a projector room
Corinne Caputo
we should just sneak in.
Moiya McTier
Yeah, let's just sneak in and then and then record our episode up there. And we can watch the movie at the same time.
Corinne Caputo
Perfect.
Moiya McTier
Well, I don't know what movie we're going to be catching glimpses of. But I do know that we're going to be whispering up here about stellar classification schemes, which I get very well.
Corinne Caputo
I have no idea.
Moiya McTier
I am such a fucking nerd. I'm over here. Like, Oh, I love schema for classifying stellar types and, and other people are like, Oh, you mean that sequence of letters that people use to describe stars? I'm like, Yeah, that's the shit.
Corinne Caputo
Yeah, that.
Moiya McTier
I really like thinking about how we classify things in astronomy, because astronomy is fundamentally an observational science, meaning we aren't running experiments on the things we study, we aren't creating our own control groups in a lab, we have to go look at stuff in space and put them into groups ourselves so that we can have large enough populations to actually do our studies on which means we have to be good at putting things into groups of similar characteristics. So classifying is such a huge part of astronomy, but it often creates these hilarious hijinks. There are misnomers. There are bad classifications there are there are beefs between different schools of astronomers who prefer one scheme over another like it's fun in the way that nerds can be and have fun.
Corinne Caputo
That's very sweet. And I can't wait to learn about it so I can be a part of it. But I have no idea.
Moiya McTier
Although I will say you saying that sweet sound in my head a lot like oh, are you lovable dork?
Corinne Caputo
Oh you weirdos.
Moiya McTier
Yes, I am. I am I am a lovable dork. I'll own up to it. But I do want to talk to you a bit about how we have classified stars throughout history, and run by you some of the highlights of like the modern stellar types, like the big three types of stars that people think about today.
Corinne Caputo
The big three.
Moiya McTier
The big three, yes, but we're going to start with historical classification schemes. And for this, like most things with the history of astronomy, we're going to go back to ancient Greece, I do want to take a moment to say that ancient Greeks did not invent astronomy, the Egyptians and the Babylonians, they were doing some very cool astronomy stuff, they were measuring the motion of stars, they were predicting eclipses, they were predicting the positions of the planets in the sky at different times of the year. So like, older societies, were doing cool astronomy. But the ancient Greeks did really ramp it up. Through a confluence of factors, they were a society that really valued learning, they also happen to be around at the right time, when there were instruments and they were concepts that made it easier for people to start thinking about astronomy as a science, as opposed to some like mystical interpretation of the messages from the gods, which is what a lot of astronomy was before. So we're starting with Ancient Greece. And one of the first people to classify stars into different types was the ancient Greek astronomer, I guess, named Hipparchus. And now we have a telescope named after Hipparchus. And it's going around mapping stars, or at least it was mapping stars. It was the precursor to the really beautiful and high achieving Gaia telescope that is mapping the Milky Way right now. But back to Hipparchus. Hipparchus in 129 BCE, started labeling stars based on their brightness. So like, how bright how shiny did they appear to be? They didn't know what stars were, they didn't know what stars were made of. They didn't understand how light from a source gets dimmer as that source is farther away, like they didn't understand any of that stuff. But Hipparchus was still taking meticulous notes about how bright all of these stars were, and classifying them by their luminosity or their apparent luminosity.
Corinne Caputo
Yeah, that makes sense. That's a good instinct.
Moiya McTier
I agree. Because one thing we know about stars is that they 'gon shine. So why not classify them based on how much they shine?
Corinne Caputo
Yes.
Moiya McTier
That's the catchphrase of today's episode, stars. They gon shine.
Corinne Caputo
They gon shine.That's That's so true. That's what they do and are famous for.
Moiya McTier
So Hipparchus made this list of stars, and he called the brightest ones that he could see first magnitude stars, like he was, like, these are the brightest, these are the pinnacle, they are the first magnitude. And these would be stars like Spica, or Sirius or even Vega. Like those are the very bright stars. And then he put the stars into six groups, with the sixth group being the dimmest stars that he could see with his naked eye. And he called those sixth magnitude stars, which, which created this precedent for a system where a low number means a brighter star. And we have kept that system today with with a little tweak.
Corinne Caputo
Oh, I see. Okay.
Moiya McTier
You know, intuitively, you would expect that the brightest star has the higher magnitude number.
Corinne Caputo
Like the classic scale of one to 10.
Moiya McTier
Exactly. Nope, we can't make it that easy.
Corinne Caputo
I'm just getting so overwhelmed thinking about this. I'm like, he just used his naked eye and looked at the sky and wrote down. How I just feel like I've looked at the sky. And I've, you know, the longer you look, the more you might see like, it just feels like a task. That's overwhelming.
Moiya McTier
Yeah, that's why people devoted their entire lives to doing this before there were telescopes.
Corinne Caputo
Yeah.
Moiya McTier
Telescopes weren't invented until like the 1600s. So...
Corinne Caputo
Wow.
Moiya McTier
...people were looking with their naked eyes and doing really great work. Like they also didn't have the light pollution we had so they could see a lot more stars. And they would just every single night go out and take meticulous notes about where those stars looked to be in the sky.
Corinne Caputo
Wow.
Moiya McTier
I know. Wild to think about.
Corinne Caputo
That's a lot of work.
Moiya McTier
I could never I could not have been an astronaut and astronomer No. 2000 years ago couldn't be me. No, thank you. My memory is shit. Like if I was rich enough to have paper and writing implements, great but if I was doing it just based on memory alone, no, nothing. No,
Corinne Caputo
no, I don't know what I would have liked to do back then. But definitely not that
Moiya McTier
no if I'm being totally honest, in today's world, given the option between sex work and astrophysics, I choose astrophysics. in that world 2000 years ago, I'm choosing sex work every single time. Every time.
Corinne Caputo
I think that it probably wasn't incredible job. And and yeah, and can be still.
Moiya McTier
We're talking about sex work not astronomy, right?
Corinne Caputo
Astronomy can be a good job if you let it.
Moiya McTier
But you know, just like this podcast is coming down firmly pro Union, we are also firmly pro sex or hell yeah. You know, in a safe way led by the sex workers.
Corinne Caputo
Yes,Yes, absolutely.
Moiya McTier
Okay, so the magnitude system,
Corinne Caputo
tell me about it
Moiya McTier
back to the magnitude system. So Hipparchus
had this six group system, flash forward, like 1700 years. And now Galileo is able to look at stars through telescopes. And he's seeing for the first time stars that are dimmer than the dimmest stars that Hipparchus
saw. And we need to come up with new numbers for them. So he continued in the direction that her parkas went, and he was like, Oh, I see a star that is too faint to see what the human eye let's call that magnitude seven. And it just kept going that way. They also eventually started seeing stars that were brighter. So they had to go into negative number. Yeah.
Corinne Caputo
How do you do that?
Moiya McTier
Yeah, negative numbers.
Corinne Caputo
I don't know guys, I don't know about I know you put a lot of work into this. It's the sunk cost fallacy of like, we can just start over and we're not going to lose much.
Moiya McTier
Oh, my God, it totally is the sunk cost fallacy. That's exactly what's happening here. Because so young astronomers in training in modern day, they have to learn about the magnitude system. And I remember it being one of the more confusing concepts that I learned in an introductory astronomy class, simply because it goes backwards than how I expected it to.
Corinne Caputo
Yeah.
Moiya McTier
And, and I know that sounds like a small thing to let like, get in my way. But it really made a difference. I was so confused about the magnitude system for a solid semester.
Corinne Caputo
Yeah and that makes complete sense, especially if no one's being explicit with you of like, this is weird and bad. And like it's not instinctual.
Moiya McTier
Yeah, just the acknowledgement that something isn't sitting. Obvious. Yeah, that helps a lot. Okay, so Galileo, he continued this magnitude system in the 1600s. And this unstandardized. Chaos continued until the 1850s, when a scientist named Norman Pogson.
Corinne Caputo
Okay.
Moiya McTier
This is a fun name.
Corinne Caputo
It's way more fun than we usually get.
Moiya McTier
Yes, Norman Pogson. He suggested rather, I think, like with common sense, it says he sent sickly suggested that a star's magnitude should be based on its inherent flux, or its inherent luminosity, its inherent brightness. And so he looked back at hypothesis catalog, and measured the brightnesses of those stars, which we can still see with equipment that was modern to his day in 1850s. And he noticed that Hipparchus
's first magnitude star was about 100 times brighter than the six magnitude star. So Pogson decided to keep that proportion, where every time you go down by five magnitudes, you get 100 times brighter
Corinne Caputo
okay
Moiya McTier
Which means, which gives us this equation called the distance modulus that I'm not going to go into here. But that means that a magnitude five star is two and a half times brighter than a magnitude six star. So anytime you have a difference in magnitude of one, the difference in brightness is about two and a half.
Corinne Caputo
Okay.
Moiya McTier
And that works because like 2.5 to the fifth power is about 100. So if you multiply 2.5 by 2.5 by 2.5 by 2.5. By 2.5, I think that's five of them, you get the proportion of 100 times brightness between the first magnitude and six magnitude star.
Corinne Caputo
Okay, I get that.
Moiya McTier
Cool. So now, astronomers use this magnitude system, and the distance modulus, which I mentioned but will not explain with the star Vega as a reference point. Vega is a really bright star, we say it has a magnitude of zero, and then we can scale up and down from there. So
Hipparchus
labeled them or classified stars by their brightness, but in the 1860s, we had this newfangled technology called a spectrograph. The spectrograph let us look at stars. Take the light from them, split that light into its component wavelengths, and get a sense for what types of Elements were in that stars atmosphere with like the the absorption and emission lines that you would see in the spectra, they would see the absorption and emission lines. And they didn't understand what that meant back in the 1800s. But they knew that it could be used to classify these stars, they knew that it was in some way related to an inherent property of the star. So they used it to classify them. One of the first people to use spectra to classify stars was I, I'm not going to assume I was going to assume Italian, but I'm not going to assume the scientist named Angelo Secchi.
Corinne Caputo
Hey I'm Italian, and I have no idea.
Moiya McTier
He took advantage of this newfangled technology and studied the spectra of stars. So the telescope would collect the light from the star, it would pass that light to the spectrograph, which would split it up into all of its wavelengths. And then a picture of that spectra would be saved on a giant photographic plate, back then they were made out of glass. But I've also seen plates that are made out of aluminum, one of the professor's in my grad school, had one of these aluminum plates turned into a table.
Corinne Caputo
That's cool.
Moiya McTier
Yeah, it's like three feet wide, there are these these giant circular dishes that depending on what you use it for, might have different holes and different shapes in it. So the one that my professor had, that was a more modern one, and it had a bunch of holes in it, where people essentially poked wires through the plate that represented the positions of different stars. So you can study these plates to see the positions of stars on the sky at different times of the year. And there are hundreds of 1000s of these plates. The biggest collection of them is at the Harvard College observatory, and there are 500,000 of these plates. Right now there's a project to digitize all of these plates called DASH, which is it stands for Digital Access to a sky century at Harvard. And they are, they should be pretty much done digitizing most of these plates by now.
Corinne Caputo
Wow, that's so many.
Moiya McTier
I know, some Oh, because this guy is really big career. I
Corinne Caputo
know, this is again, I'm not that can't be my job.
Moiya McTier
I wouldn't have wanted this job either. But the plates that Angelo Secchi was using, instead of having the holes poked in them, the picture of the stars Spectrum was essentially just like printed onto a glass plate. Because otherwise you have to look at the spectra through the telescope, and then just draw it in your notebook, which, you know, you can imagine brings in some error. Yeah, I
Corinne Caputo
Yeah, I don't know about that. I can barely draw like a person for I mean, who can draw a person but I can't draw like an apple from memory.
Moiya McTier
From memory, you're like you're looking at? Yeah, it's like drawing a Phoenix that's sitting right in front of you. But it's still really fucking hard.
Corinne Caputo
I was just reading about this woman who drew like a lot of textbook images before pictures. Were laying. Of course, I can't remember her name or what she did. But I thought it was like, Oh, that was such an industry of like, kind of drawing and relaying information via illustration, when we didn't have like photos, or the technology to like, capture something so far away.
Moiya McTier
I think all the time about the fact that scientists used to have to be better at drawing.
Corinne Caputo
Yeah.
Moiya McTier
like, there was this exhibit at the at one of the museums at Harvard when I was there, have these beautiful botanical drawings of old flowers, and then glass recreations of these flowers based on the drawings. And when I think back to all of the naturalist drawings of things in nature, like animals and stuff like I could I couldn't do that. There are so many reasons I couldn't have been a scientist 200 years ago.
Corinne Caputo
Same.
Moiya McTier
Yeah, both of us we would we would not be here. 300 years ago, you would not be hearing our voices way. No, no, sorry, Bob. I haven't said that in a decade
Corinne Caputo
I was thinking like, when did I last hear that? That's a good one. We're bringing that back.
Moiya McTier
Bringing it back. Okay, so Angelo Secchi, after studying the spectra of these stars, split them up into five different classes. And it's essentially based on their color, and generally what spectral features they have. So the first class is white and blue stars with really broad hydrogen absorption lines. And absorption line in a spectra looks like a black line, it looks like the absence of light because it is that the light at that wavelength has been absorbed by whatever you're observing. So an absorption line looks like a black spot, a black line, and a hydrogen line is at a certain wavelength so they can tell what what element lines they're looking at me spectra. The second class was yellow stars with some hydrogen absorption lines, and a good amount of metallic absorption lines. And remember that for an astronomer, anything heavier than helium is considered a metal. So these metallic lines would be like carbon lines and oxygen lines and nitrogen lines. The third class was orange to red stars with an eye quote, complex band spectrum, which I think just means like, there's a lot of junk in that storm.
Corinne Caputo
Yeah.
Moiya McTier
The fourth class were red stars with significant carbon bands, and lines. And then the fifth class was just a catch all it was stars that instead of having absorption lines have a lot of emission lines. Okay, so we're an absorption line looks like a just like a black emptiness. And the admission line would look like a like a bright spot. So that was in the 1860s. Like 20-30 years later, in the late 1800s, a scientist at Harvard named Edward Pickering, whose name I don't even like saying, conducted a survey of stellar spectra with data on more than 100,000 stars, I think he had like 250, or something thousand stars that he took spectra on with these plates.
Whoa.
And the data on those plates was all analyzed by the team of women, collectively known as the Harvard computers, or Pickering's harem. One of the like, the leaders of these computers, these women at Harvard was named Willamina Fleming, and she classified the features of more than 10,000 stars on her own. Whoa, by looking at these plates, by looking at the picture of a spectra that has been printed onto these glass plates, and just analyzing the features of the spectrum, putting them into groups, all by eye.
Corinne Caputo
I don't know. Now, I'm sounding like this is a job I do want. I love little organizing tasks.
Moiya McTier
There you go. That could be nice. Yeah, um, we now do this with very advanced computers.
Corinne Caputo
Of course, I've been replaced already.
Moiya McTier
Well, back then you would have you would have been a computer Corinne
Corinne Caputo
could have been me
Moiya McTier
So we now do this with advanced computer algorithms that can look through this, this like forest of spectral lines, and pick out the strong ones and pick out the absorption and emission lines and compare it to databases that tell you exactly what wavelength or what element you're supposed to be looking at. And we now have more data to comb through. So it's harder in that way. And we have to be more careful and more rigorous with our work. But in a lot of ways, it's so much easier to study these spectra than it was for Willamina Fleming. So she took those 10,000 stars that she was classifying that she was studying. And she split them up into more groups than Angelo Secchi had and instead of using Roman numerals, like the, his scheme went from one to five, instead of doing that she used letters from from our alphabet A through Q. And this was called the Draper classification scheme, named after a man who took a picture of one of the first spectra of a star. And those classes went from A to P. There were there were a lot of different groups. And then there was a Q group, which was just a catch all miscellaneous category. Okay, yeah, why not? So Annie Jump Cannon, is considered by most people today, to be the person who came up with a modern stellar classification system. So she took Willamina Fleming's Draper scheme, and simplified it, taking the letters A through P, and instead just going with seven different groups, taking letters from each of those groups, so and then like rearranging them, so her scheme, which is today called the Harvard classification scheme, split stars up into seven different groups, each assigned a letter, and those letters are O,B,A,F,G, K, and M. There are seven of them.
Corinne Caputo
Okay.
Moiya McTier
So that was in like the late 1800s, very early 1900s. And then in 1943, three people at Yerkes Observatory in Wisconsin and their names are WW Morgan, Philip Childs Kenan and Edith Marie Kelman. So together this this new scheme is called M K K or use really just MK because they leave out EF Kalman, of course, they leave out the woman. But together, these three decided that you should add more information to the classification scheme. Because the Harvard classification scheme that Annie Jump Cannon made, that only tells you about the stars, spectra or its temperature, they also wanted additional information about the stars brightness, or luminosity. So in addition to the letter, you can also have a Roman numeral that tells you basically, how bright the star is within its given category.
Corinne Caputo
Yeah, that makes sense.
Moiya McTier
So now we have this classification scheme from hottest to coolest, which is also brightest to dimmest which is also shortest lived to longest lived, the stars are OB a FGKM.
Corinne Caputo
Okay
Moiya McTier
it's important for me to state that this is only the scheme, for stars on the main sequence. So this is only the way that we can classify stars that are actively fusing hydrogen in their cores, for and after they are fusing hydrogen they're on a different path. And they have different words and different classifications to describe them.
Corinne Caputo
Okay
Moiya McTier
So we're only talking about the main sequence, which is stars that are burning hydrogen in their course. I'm going to focus on three types of stars for the rest of the episode. The least massive stars are called M dwarfs or M types. Then in the middle, we have sun-like stars, those are G type stars. And then all the way at the massive end of this, classification scheme. We'd have the Oh stars, those are very hot, very bright, very blue.
Corinne Caputo
Cool.
Moiya McTier
Hey, friends, it's Moiya. And you know the deal. I am here to give a shout out to our amazing patrons who are supporting this podcast and keeping us going. First, I want to start off by thanking our latest pre main sequence stars, Ashley Ellis, Jason minich and Leilani lumen. Y'all are awesome. One day you are going to glow just as bright as Rigel and Bill juice and all the other main sequence stars. Don't be ashamed just because you haven't started fusing helium in your course. Next I want to thank our latest red dwarf stars JB and pinky panna Tierra. I'm loving all of the alliteration in this week's new patrons. So thank you so much. And as always, thank you to our sun-like stars Sharn Llewellyn Finn and Ian Williams. I don't know what else to say you're amazing your sun-like, you are not just stellar, you are solar. So thank you all. And you too, can support us you can hear your name on this podcast. And you can make it to our patrons star chart, which I made a brand new Python code to generate every single week. So you want to be on our patrons star chart. And you can do all of that by supporting us on Patreon. You can find that star chart our Patreon info and more at our website pale blue pod.com. Or you can go right to patreon.com/pale blue pod for just $5 a month, you get access to our director's commentary slash research notes for each episode, and you get to hear your name on this pod. So again, that's patreon.com/pale blue pod. We will love you forever.
Corinne Caputo
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Moiya McTier
I love spooky things. And I love history. And I love myths and folklore that people have been using to explain the natural world from all over the globe. And I love to laugh and I love to feel like I'm with friends. And you know what there's just one podcast where I can go to get all of those things and it's called spirits. Spirits is another show on the multitude collective and it's a history and comedy podcast focused on everything folklore, mythology and the occult, but told through the lens of feminism queerness and modern adulthood. The two hosts are Julia Schifini and her childhood best friend Amanda McLaughlin, and together they get To learn about a different story from mythology and folklore, over drinks, so the name is a pun get it and its spirits like spooky stuff, but also spirits like the stuff that'll get you crunk. So they'll cover things like the mythological origins of major franchises like Lord of the Rings and Wonder Woman, but they'll also cover modern urban legends from listeners. And they'll do a roundup of like werewolf stories from around the world, you can start listening to their more than 300 episodes that they've released over the last six years, wherever you get your podcasts or by going to spirits. podcast.com spirits is actually one of the only podcasts that I listen to every single week when it comes out. So you can join me in listening to spirits every single Wednesday. Again, that's spirits Sp ir it s podcast.com. Or just go to your favorite podcast app and search spirits.
So I'll start with M dwarfs and then move up.
Corinne Caputo
Yeah.
Moiya McTier
And I'll tell you just just some fun facts about each of these stellar types. And then you can you can ask any questions or whatever you want.
Corinne Caputo
I can't wait.
Moiya McTier
Okay, so first, we're going to start with the M dwarfs. Astronomers have studied the mass distribution of newly formed stars. So like if you have a group of stars that form from a giant molecular cloud, that's, that's what we call them. Those will form like thousands of stars at once from a single cloud of gas. Well, astronomers have studied those newborn clouds of stars and also like existing clouds of stars to see is it even across all the masses, or is one type of storm more common than the other. And they can explain this in an equation. That equation is called the initial mass function, and it just tells you like, for a given stellar mass, what fraction of a new stellar population will have that mass.
Corinne Caputo
Okay.
Moiya McTier
The initial mass function is another thing that really confused me when I was in my astronomy classes, because there's, there's more than just one, like different scientists have made these observations and fit their own curves to them, essentially. And so there are different initial mass functions. Astronomers are right now still actively trying to figure out if the initial mass function in the Milky Way is the same as for the rest of the universe, like we don't know if the IMF is universal, or if it changes over time. Well, we think it does change over time, but we don't know how much Another fun fact about the IMF, the most popular IMF is the saltpeter. IMF, it's named after an astronomer whose last name was saltpeter. I was very good friends with his grandson in college.
Corinne Caputo
Oh my god, how fun.
Moiya McTier
I know. And so I was in my astronomy classes, learning about the IMF. And then later that night, I was hanging out with my friends doing my homework, and I was describing to my friend what I was trying to do, and he was like, oh, saltpeter that's my grandpa. And I was like, fuck you, Caleb. Like, you can't just casually drop the fact that I'm learning. Your grandfather's like, cool.
Corinne Caputo
Was he also an astronomer?
Moiya McTier
No, not one bit.
Corinne Caputo
That's so funny that you cross paths. I love that you did.
Moiya McTier
We just happen to live in the same freshman dorm. And then we're friends for most of college.
Corinne Caputo
That's so cool.
Moiya McTier
I know. But according to this IMF, and according to our observations of different populations of stars, and dwarfs are by far the most common. Do you have any, any any guests for like, what percentage of stars in the Milky Way are M dwarfs?
Corinne Caputo
Oh my gosh. My gut is to say not many because they're small. But I don't know if that's right.
Moiya McTier
Well, this isn't like what fraction of stellar mass? Of course, this is just like, by pure number of all the stars. Yeah. And I'll tell you like they are the most common.
Corinne Caputo
um 60%.
Moiya McTier
Pretty close. It's somewhere between 70 and 75% of all the stars in the galaxy. Are these M dwarfs.
Corinne Caputo
Yeah.
Moiya McTier
And it should probably be pretty similar in the rest of the universe to we think,
Corinne Caputo
wow,that's really cool.
Moiya McTier
And so 75% of stars are m dwarfs, and yet, I'm pretty sure we can't see any M dwarfs with our naked eye. Like when we look out at the sky. Oh, all of the stars we can see without a telescope are more massive, brighter stars.
Corinne Caputo
So most of the stars we can see.
Moiya McTier
Exactly. We are not seeing a representative sample of stars with our unaided eyes.
Corinne Caputo
Yeah. Wow. Okay.
Moiya McTier
So these M dwarfs, they are the lowest mass stars. They have less than 10% the size of the Sun that's both mass and radius. So they're they are small. They are light, they are dim, they are cool. Their temperature is less than 3800 Kelvin. And as a comparison, our sun has a temperature of like five something 1000 Kelvin.
Corinne Caputo
Yeah. Okay.
Moiya McTier
So they're they're much cooler than our sun. They make up for it, though, by being very magnetically active.
Corinne Caputo
I was gonna say with their sunglasses.
They're the coolest stars. We know
Moiya McTier
I like to think that other types of stars would boycott sunglasses, because they're like, I don't need this. That's, why are you making G type stars so special? I bet they'd feel left out.
Yeah, I buy that.
Um, tours are very magnetically active, which leads to has led to a lot of discussion about whether or not an a planet around an M dwarf star would be a good candidate for having life. Okay. Because if you have a lot of magnetic activity, it might affect evolution on a world it might affect the atmosphere of that world. Although I think most astronomers now would agree that M stars and then they're they're slightly more massive companions, K stars, I think most astronomers would agree that that's actually the best chance for finding extraterrestrial life out in the in the galaxy, because they're just so many of them. Yeah, these M dwarfs are cool. They are literally cool. Like they have a low temperature. But they're interesting, in that they transfer all of their energy from the core to the surface through convection, which we talked about in the fluid dynamics episode we did. So convection, very important in the energy and heat transfer and stars. But different types of stars have have different mechanisms that they use. And M dwarfs are unique in that they are completely convective with no, no part of their stellar body is dominated by radiation. So cool. They also in the book, in the autobiography book that I wrote, The Milky Way describes M dwarfs as the most selfish stars. Because they don't make heavy elements. They they will make helium and they are very good at turning hydrogen into helium. But because they're fully convective, they're also very good at like cycling or mixing that helium throughout the entire star. So they just get there the vacation. Yeah, so they like they can't start the next stage of turning helium into carbon, because the temperature and pressure like doesn't really get high enough to start the carbon burning. So they don't make heavy elements. And they live for a very long time. These M dwarfs can spend more than 100 billion years, fusing hydrogen in their interiors. The my universe has not been around long enough for any M dwarf to die. We have not seen this,
Corinne Caputo
oh my God.
Moiya McTier
, when we talk about the end stages of an M type star. We are basing this off of models and our understanding of physics, like we have not observed this. And we never will
Corinne Caputo
That's so cool.
Moiya McTier
Because the universe is only 14 billion years old. Or we're babies and these M stars are like, I'm gonna be here forever. Yeah. So the Milky Way calls them selfish, because they they hoard a lot of gas for a very long time. And they don't make heavier elements that can be used in future generations of stars. After those 100 billion years, we're pretty sure that an M dwarf that has stopped fusing hydrogen in its core will just turn off. It will, it will radiate away all of its heat from the surface of the star. And it'll get dimmer and dimmer until it is a white dwarf star. So instead of being supported by pressure from nuclear fusion in their cores, a white dwarf is supported by what we call electron degeneracy pressure, where essentially, the electrons have so much energy and they're packed so tightly together, that they they create like a solid lattice to support the weight of the white dwarf. Cool. So you have this like crystal and structure that supports this almost dead and dying star.
Corinne Caputo
Oh, comfy home.
Moiya McTier
And I wanted for each of these to come up with an example of a famous member of this stellar type. And for me, when I was thinking, what are the what's the most famous M dwarf? It was no question. then for me it has to be TRAPPIST one. So back in. In early 2017, astronomers announced the discovery of a seven planet system called TRAPPIST one. Three or four of these seven planets are in the habitable zone of their system, meaning they are close enough. They're like the right distance from their star to have liquid water on their surfaces, maybe. But that star that they're orbiting is an M dwarf star about 10% the size of our Sun. So they are all much closer in fact, the entire TRAPPIST one system can fit well within the orbit of of earth around the sun. Oh, well. So these are these are tiny, but like I said before, M dwarfs are a good candidate for life out there. And the TRAPPIST one system was a really exciting one because there were so many habitable worlds.
Corinne Caputo
I know TRAPPIST one because of those, like kind of retro JPL posters that came out and there's a Trappist one that I looking up now and I'll put on the Instagram when this episode comes out. But I mean, the posters are all of those posters are so fun. I agree.
Moiya McTier
I love the like we were kind of inspired by that for our cover art
Another notable M dwarf, at least in my heart is Kepler 186. Have a poster to it. Kepler 186 F. Absolutely. Yes, that one. Yes. Kepler 186 F is an earth ish sized planet in the habitable zone of this M dwarf star. I studied it in one of my projects in undergrad. And it's my favorite planet.
Corinne Caputo
I love that.
Moiya McTier
Yeah, the poster is sick. I had a t shirt of that poster. And then I grew too big for the T shirts. So my mom put it into the t shirt quilt. She made me when I graduated college.
Corinne Caputo
I love that. That's so sweet.
Moiya McTier
That's very cute. Okay, any questions about m dwarfs?
Corinne Caputo
I didn't realize how many there were I had no idea that most of the stars were this and also that I've never really seen one with my naked eye.
Moiya McTier
Your eyes when they look at it space, they are lying to you. They
Corinne Caputo
really are. It's very freaky. I'm like, what else is right in front of me that I'm not seeing?
Moiya McTier
I actually think that there's there's like a comforting message in here. Or at least, like an encouraging message. Like, you know how people always say, Oh, well, the pictures that you take of the moon always look shitty, even though you know, the moon is beautiful. So don't get upset about pictures you take for yourself. I feel like there's something similar here where it's like, the most common type of star isn't even visible to us. So, but we know it's there. So maybe something about like, something that you love about yourself and others, it doesn't mean it's not there, like exactly,
Corinne Caputo
it just might not be visible in this moment. But that doesn't mean it's gone. Yeah, I totally agree.
Moiya McTier
People just need stronger telescopes to see the M dwarf of your personality. That's great. I'm just trying to make inspirational posters here. Okay, so the next of the big three that we're going to talk about is sunlight stars, or G type stars if you don't want to be as solar centric, as most humans are, and most astronomers most astronomers would say a sun like star, the Milky Way in the book really, really didn't like that. It says call them G type stars. Your your sun isn't special. So these are specially compared to M dwarfs not very common in the universe. So what what percentage do you think? Are the are the G type stars?
Corinne Caputo
Well, I want to think that there's a ton of them because we have one that I've always just like, Could it be true that things are this special and rare? Um, but I don't know. Maybe we just learned 75%. I don't think this is the full 25% remaining. But maybe like 10? Lower lower five? Yeah,
Moiya McTier
it's like five or six.
Corinne Caputo
Oh, wow.
Moiya McTier
So about five or 6% of stars in the galaxy are like our Sun, which means they they're pretty average. In terms of in terms of everything. They're like the middle of the road for a star. So a G type star will have a temperature between like 5006 1000 Kelvin, and I did the size and mass comparison and for the M dwarfs relative to the sun. So now I just have to give you actual numbers. So the the mass of the Sun is two times 10 to the 30th power kilograms. I'm telling you it in kilograms, because I cannot tell you in pounds because pounds is actually a unit of weight that is specific to Earth. It's like, it's like your mass times the acceleration due to gravity of the earth. So since it's impossible for the sun to be sitting on the earth, it's impossible for the sun to have a weight in pounds. But it does have a mass in kilograms. And that mass is more than 300,000 times the mass of the Earth. So it's quite heavy. How many earths Do you think you could fit into the sun?
Corinne Caputo
Well, I know that the sun is like, like, if you took all the mass of our solar system, the sun is like 99%.
Moiya McTier
Yeah, we're talking about volume
Corinne Caputo
volume. Okay. Yeah.
Moiya McTier
How many Earth? Could you physically fit into the sun?
Corinne Caputo
I'm imagining the sun opening up like a Pokeball?
Or it's or hopping in?
Moiya McTier
Any Gotta Catch. Catch all the earth's? It's got to be like a million. Yes. Really? Yes.
Corinne Caputo
Not bad. Not bad. I'm kind of saying that number in like a hyperbolic way. It's gonna be like a million, like
Moiya McTier
a million. I know. I know. You're right. So it's about 1.3 million. Wow, could fit in. By volume. Yeah, it is. And then Jupiter is in between. So you can fit like 1000 Earths into Jupiter. And you can fit like 1000 Jupiter's into the sun.
Corinne Caputo
Wow, Jupiter is so big.
Moiya McTier
And so 1000 times 1000 is like a million. Yeah. So the M star had fully convective heat transfer, the sunlight star, the G type stars, they have a radiative core surrounded by a convective layer. And that is because the inner cores density gradient, which is like the the rate at which the density changes, it's actually too steep for convection to work close to the core of an of a G type star, because convection works by a blob of material having less density than the material around it, so it rises and vice versa is also true. But the gradient for a G type star is so steep that any blob of material would rise and find that it is still denser than the material immediately surrounding it. So it drops back down. So the only way that you can get heat and energy from the center of a G type star is through radiation. So it's generating a lot of photons. And then once you get to the outer layers, the density gradient isn't as steep. So convection works. So you get convection carrying heat from like, halfway to the edge of the star to the edge. Does that make sense? Yes.
Corinne Caputo
picturing the lava lamp that we talked about. So
Moiya McTier
an M dwarf star, it's all lava lamp. But a G type star, it's only a lava lamp on the outer half. A G type star, unlike the M dwarfs can make heavier elements. So they'll make elements like carbon and nitrogen and oxygen, but not really heavier than that. And they will fuse for about 10 billion years. So our son is four and a half billion years old. Ish. It's middle aged. Yeah, we have a middle age sun,
Corinne Caputo
middle age is the new young.
Moiya McTier
It is yeah. After those 10 billion years, G type star will puff up into a red giant. So it'll get really big, and the temperature will will decrease. Like it looks red. We're still trying to figure out how big the sun will get. But most estimates say it's going to eat Earth, like the Red Giant phase of the Sun will pop out to our orbit.
Corinne Caputo
Not if we eat the sun first. I've been saying it and saying it.
Moiya McTier
Eat the sun so it doesn't eat us. So it'll puff up into the red giant. And I like to say that like after it does that it gets so hot that it starts taking off, it's close, because it will start to shed the outer layers of material. So you get these beautiful nebulae. And like 200 years ago, or 100 years ago, astronomers thought that these nebulae that we were seeing out in space like the beautiful, colorful clouds, they thought that that's where stars were born. That's actually where stars are dying. That is that is stars. The graveyard. Yeah, it's like the you know how when humans when we freeze to death, we get very warm at the end stages and we get naked. So we find a lot of frozen people naked, like stars are doing the same thing at the end of its stages. It's gonna get really warm, it's gonna take off and we're gonna find it naked. Because the thing left behind after that is a white dwarf just like what the M dwarfs will become. And our Sun is kind of right below the mass cut off for an end that is more interesting than a white dwarf. So any star It is more massive than our Sun probably will not end in a white dwarf. And instead they get they get fun Nova or supernova explosion.
Corinne Caputo
I love that word.
Moiya McTier
I'm doing. I'm doing a supernova supernova. It's actually like you can tell it's a supernova dance because I'm using my hands and I'm like, exploding away from my body.
Corinne Caputo
Yeah, I do think of supernovas as like, these kind of eruption, not even an eruption, but like a wiped out like in a movie when suddenly everything Yes,
Moiya McTier
yeah, a single supernova explosion in a day generates more energy than our sun will over its 10 billion year lifespan, they are very bright, they're very energetic,
Corinne Caputo
that's a lot of energy.
Moiya McTier
And they are able to have that much energy because they come from the most massive stars, which brings us to Blue giants, like Oh, np type stars. I'm not gonna make you guess. It's, it's tiny. It is, according to the source that I found, and you know, people are still trying to constrain these measurements. But an O type star accounts for 0.00003% of stars in the galaxy, oh, my gosh, that is so tiny. There really aren't a lot of these things. So an O type star is any star that is heavier than 15 times the mass of our Sun, they have temperatures higher than 40,000 degrees Kelvin, they give off really high levels of ultraviolet and gamma ray radiation. So like dangerous, dangerous radiation that our bodies wouldn't be able to handle, which is why people usually don't consider them for habitability searches. But there's another reason that people don't really consider them. And it's because they are so short lived. And oh star will fuse through all of its hydrogen in just about 10 million years, which is actually less time than it takes most planets to form.
Corinne Caputo
Yeah, we have at least 1,000,000,010 billion behind us.
Moiya McTier
So these are very short lived stars. The Milky Way in the book calls them like they're the giving stars, they are the least selfish, because they don't live very long. So they're recycling gas quickly. But they also in their cores can make the heavier elements all the way up to iron. And they have this this fun like backwards stacking thing where by the end of an O star's life, it's not hydrogen in the middle, and then iron on the outer layer, it's flipped. So that hydrogen is on the outside. Because the hydrogen gets fused into helium gets fused into carbon gets fused into nitrogen and oxygen, and it goes up in the layers, just fusing heavier and heavier elements in the core until eventually the core is is made of iron. And when that happens when there is no longer fusion happening in the center, and remember from our last episode on the fundamental forces, the strong nuclear force that makes fusion happen, it doesn't operate on scales larger than the iron atom. So once you stop fusing iron, the hydrostatic equilibrium of the star breaks. This was one of my favorite phrases in astronomy, hydrostatic equilibrium. So during the main sequence, stage of a star when it's fusing in its core, the star keeps its shape, because there's gravity pushing in, and there is pressure from the fusion reaction pushing out. But when you start fusing, you lose that outward pressure, so gravity can dominate and make the star implode. And that's what happens. The star implodes, but then it hits that, that iron core, there's so much density and so much pressure and temperature that it rebounds, and it explodes. And that's a supernova. Where's the supernova explosion that is so powerful, and so fast that it will actually move through space at supersonic speeds faster than the speed of light. So we talked about shocks in our fluid dynamics episode. Those shocks happen because the supernova explosion like all the the outer layers of the star, they get basically shot away from the star at very high speeds. After the supernova happens, there will be a core a remnant left of the star, and the nature of that core depends on the mass of the star that died. So if it's heavier than the sun, but less than 30 ish solar masses, then the core leftover is going to be A neutron star, and neutron stars are held together by instead of electron degeneracy pressure like a white dwarf. They are held together by neutron degeneracy pressure. These are some of the densest objects in the universe. Imagine something with the mass of our Sun squeezed into like something the size of Manhattan. Oh my gosh, they are incredibly dense. They are so dense that the electrons on the outside of an atom get squished into the nucleus, and they combine with protons to become neutrons pretty much. So you have an entire star and entire crystal lattice made out of neutrons. Wow. Oh, so cool. So dense. And if you have a star that is heavier than 30 solar masses, the the core that's left behind is the only thing denser than a neutron star. Do you have any idea what that could be? Corinne?
Corinne Caputo
I don't think I know.
Moiya McTier
I think you do know what is the densest thing...
Corinne Caputo
a black hole?
Moiya McTier
a black hole!
Corinne Caputo
That's what I was thinking when you were talking about how dense I was like, wow, black hole.
Moiya McTier
Yeah, so only the most massive stars will end their lives as a black hole. Wow. And then I couldn't really find any notable O type stars because they don't live very long and there aren't a lot of them. But the star Rigel in the Orion constellation, which is just like opposite Beetlejuice. That star is a very massive B type star, which is almost an O type star.
Corinne Caputo
Close enough.
Moiya McTier
It's close enough. Yes. So those are the types of stars that can form. But that's not the entire picture. Because there are actually generations of stars that have slightly different properties. So the first stars in the universe were formed from primordial hydrogen and helium, like the first elements that were created after the Big Bang, those stars would have been very bright, and hot and short lived, very similar to an O star that we would find today. And they would live for for just like 10 million years or even shorter, before they seated the the space between them with the elements that they fused in their cores. And then those heavier elements would get used up in the next generation of stars. And this happens over and over and over again. Until eventually you have stars that we see now that have heavier elements in their bodies already from the time they form. And this is again, we started this episode, with a confusingly backwards number system with magnitudes, remember, well, we're going to end the same way. Because we have named these different generations of stars. And the stars that we see now that have a lot of heavy elements in them. We call them population one stars.
Okay.
The first stars in the universe that didn't have heavy elements in them any elements heavier than helium. We call those population, three stars.
Corinne Caputo
Guys, come on.
Moiya McTier
I know. I know. It sucks. So subsequent generations of stars had more metals. And now the stars, the population, one stars that we see are very contaminated. We actually haven't been able to find any pure population, three stars, we think probably because they lived such short lives. But also, maybe there are some left. But as they float through the galaxy, they pick up heavier elements that get incorporated into their outer layers. So maybe these population three stars are like hiding under their metallic trench coats.
Corinne Caputo
Yeah, I love that image,
Moiya McTier
Me too. And the metallicity of a star, which is like basically the fraction of elements in that star that are heavier than helium. So a high metallicity star has like a lot of iron and stuff in it.
I don't think I've ever heard that word metallicity before.
Oh we use it all the time. I don't
Corinne Caputo
Felicity the name, but metal,
Moiya McTier
math, no metal metallicity. It actually does affect stellar properties. And so astronomers today have to be very careful about teasing apart different factors of a star like you can't just study its temperature, you have to study its temperature and its brightness, and its metallicity. And its met like you have to study these together. One I did like a quick search for the effects of metallicity on Stellar behavior. One of the cooler ones I found in my three minute Google search was that stars with lower metallicity these stars that don't have a lot of heavy elements in them, they tend to spin more rapidly He at the end of their lives, then a high metal star. And that is because stars do spin, they rotate. That rotation slows down over time. But if you have a lot of metals in your star, then you essentially slow down faster. So even if you have two stars that start at the same rotation speed, but one of them has a lot more metals, the metal rich one, which is how we say it, the metal rich one will spin down more quickly. So it will have a slower speed at the end of its lifecycle than the metal poor stuff.
Corinne Caputo
Ooh, cool.
Moiya McTier
That's stars. Wow. That's a lot. I know. It was a lot. But you can you can hear?
Corinne Caputo
I think I'm most surprised by like I said before, how many endorsers there are?
Moiya McTier
And how we can't see them?
Corinne Caputo
Yeah, yeah, I think that's what's not sitting well with me.
Moiya McTier
Yeah, oh, that's a good question. Is there anything else that's sitting uneasy with you about stars?
Corinne Caputo
I like knowing the things I don't know. Which obviously, like can't be done, but I think I'm like, Okay, I don't know a ton about astronomy, but like, I hate knowing something so specific. I'm like, Oh, my God, I
know what, they're all just looking at me all the time. And can they see me?
Moiya McTier
Yes, but the M stars canonically have the best vision of all.
Corinne Caputo
But this is so fun. And I love. I love thinking about how huge our son is and like how kind of being reminded the perfect set of circumstances have happened to to lead to this.
Moiya McTier
Yeah, and I think it is. Maybe maybe people will take some comfort knowing that we are kind of an oddity. Yeah, we are around a kind of rare type of star. And it's even rarer in that it doesn't have any sort of stellar companion most stars exist in binaries or like triplets. You know, twins like me, like like Korean. Yes, our son is is unlike Korean, and that is not a twin. But, but like Korean, in that, you know, for humans, twins are rare. So you and the son have that in common. Being a twin for a son is rare. Good. Good. Yeah. You're you're both unique. You're both special. Everyone is special.
Corinne Caputo
I think it would be fun to quickly think of a pneumonic for that start letters, which as a reminder to everyone are OBAFGKM
Yes.
Moiya McTier
So the the mnemonic that I learned in school, which I don't want other people to use, was O B f fine, girl. Kiss me. Okay, so let's let's I hate it. I hate it so much. Oh, be a fine girl and kiss me. No, no, no. Be a fine girl and refuse to kiss me if that's what you want. Yeah, so we're gonna we're gonna come up with a better a couple better. Do you do you have any?
Corinne Caputo
I have one. Okay, that I just thought of. It's very silly. It goes. Okay, baby. Frogs gotta kick me.
Moiya McTier
They do. It's to keep their legs, their leg muscles strong.
Corinne Caputo
They gotta stay strong. We need all the frogs in the room to get up and give me a kick. Okay,
Moiya McTier
baby. Okay, mine is over by a frigid Glen. Koalas mate. I
Corinne Caputo
love that one.
Moiya McTier
What's up Glenn? This is like a little cute little woodsy area. Yeah, you're right Glen of the woods. Yeah. Over by a frigid Glen koalas mate. We could do that we could do the back and forth one hears
Corinne Caputo
them wait only brothers are finding a way to forgot the letter G
Speaker 2
Okay, you want to start with only only pitches are finding gold I'm gold. carats that's no that's what the seat that's what the snow carat like 14 karat gold is that's a C
Corinne Caputo
14k is
the abbreviation? No, it's
not. It's okay.
Speaker 2
It's okay. Okay, we want gold carats mom. Only bitches are finding gold carrots mom. This isn't a face yeah, Okay, I'll open box away from generous. Oh, I don't want it to be open box away from generous klepto maniac I almost almost knocked my computer over.
Corinne Caputo
Generous. It's so funny. If you're a Gen that's like Robin Hood, I guess it's like stealing and giving. And
Moiya McTier
I don't know why you want to only open the box away from them, but it's
Corinne Caputo
a present for them. Oh, yeah.
Moiya McTier
I like that. Yes. Open boxes away from generous kleptomaniacs. Please let us know which of these pnemonics is your new favorite?
Corinne Caputo
I can't wait to hear them. You guys came up with great ones for the planet. I think these are gonna be even better. And I think our movie is starting where I think we're gonna see em three gun, which is what I call the movie Megan. That's
Moiya McTier
what everyone should call it. What everyone should have three games. These were long previews.
Corinne Caputo
I know they really were they're just getting longer these days. They're trying to anything to keep you in the movie.
Moiya McTier
I'm here for it. That worked. But
Corinne Caputo
wherever you are, I hope you remember that you are space by
Moiya McTier
pale blue pod was created by Moiya McTier and Corinne Caputo with help from the multitude productions team. Our theme music is by Evan Johnston and our cover art is by Shea McMullen. Our audio editing is handled by the incomparable Misha Stanton.
Corinne Caputo
Stay in touch with us and the universe by following at pale blue pod on Twitter and Instagram or check on our website pale blue pod.com were a member of multitude and independent podcast collective and production studio. If you like pale blue pod you will love the other shows that live on our website at multitude dot productions.
Moiya McTier
If you want to support pale blue pod financially, join our community over at patreon.com/pale blue pod for just about $1 per episode, you get a shout out on one of our shows and access to director's commentary for each episode. The very best way though, to help pale blue pod grow is to share it with your friends. So send this episode this link to one person who you think will like it and we will appreciate you for forever.
Corinne Caputo
Thanks for listening to pale blue pod. You'll hear us again next week. Bye.