In this episode we talk about globular clusters and how they help us work out the age of stars, and then return to our neighbourhood to investigate the rumour of an undiscovered planet in the Solar System.

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Chris

Welcome back to a brand new episode of The Astroholic, I am producer Chris,

Alfredo

And I’m Alfredo, the Astroholic.

Chris

Today, we have a couple of new fan questions, which is very exciting because people are writing in and sending us questions left, right and center

Alfredo

It is very exciting because then Chris doesn’t have to think about thew questions.

Chris

It’s good. It is good in that respect as well.

Alfredo

Now, we’re very grateful that you’re curious about space, and that we can satisfy your curiosity.

Chris

Yeah, it’s it’s all good. But before we start, you may remember in the last episode, I very haphazardly ventured to guess as how people may have injured themselves or worse on board the International Space Station.

Alfredo

Yeah, you said that they might have tripped because you forgot about gravity.

Chris

I didn’t forget about gravity. I thought that would be like some sort of fake gravity. I just didn’t realize that that was science fiction, not reality!

Alfredo

To be honest and actually I forgot to mention this in the episode, you can create gravity by making a spinning spacecraft.

Chris

Maybe that’s a topic for a future discussion

Alfredo

That may be the topic for future discussion and there you can sort of trip but I think it gets a little more complicated, so let’s not dwell too much on to it.

Chris

Right. So I found out that some people have been injured.

Alfredo

Okay,

Chris

I tell a lie. Some people have died in space.

Alfredo

Okay.

Chris

Three people, in fact, have died in space. I did my research on it. And apparently, these were three cosmonauts, who were onboard the Soyuz 11 in 1971. On their reentry towards Earth, a valve burst and they were exposed to the vacuum of space. And from what I can tell, I believe they suffocated when they opened up the craft, they were blue, but still warm and were tried to be resuscitated, but they were dead. Very, very dead. So people haven’t died onboard the ISS, but there are some nasty things that have happened. Anyway, on to much, much much cheerier topics.

Alfredo

Let’s start the episode.

Chris

Let’s start the episode. The first question comes from Jediknitter on Instagram and Twitter, who asks, What is a globular cluster and how do we work out how old they are?

Alfredo

Very very interesting question.

Chris

I have zero idea what a globular cluster is.

Alfredo

Never heard of it?

Chris

I mean, I could venture a guess.

Alfredo

Okay, you venture a guess

Chris

I’m gonna venture the guess that a globular cluster is a nebula, a big gassy cloud in space. Just sounds, you know, cluster makes it sound like there’s lots of stuff going on. Like maybe… Okay, no. If it’s cluster then maybe it’s like a small galaxy. But globular is a very…

Alfredo

You’re closer to the truth with small galaxy.

Chris

Okay, small galaxy. But again, globular, maybe it’s an uneven galaxy. Globular, like it’s patchy. There’s a lot of stuff going on in different bits. I don’t know why globular for me is very overly descriptive. And it makes it sound like there’s just blobs of stuff happening. No?

Alfredo

No.

Chris

Okay, so then..

Alfredo

We’re going to get there. Anything that sounds a little bit like globular that you might have heard of?

Chris

Blobular?

Alfredo

Blobular??!! That’s why you’re thinking that it’s all sorts of patches! It’s not flubber!

Chris

Globulus? Lobular?

Alfredo

It doesn’t have to rhyme. Look at the beginning of the word.. Glob?

Chris

Global! Lots of globes, lots of spherical objects in this galaxy. Oh, a cluster of spheres in space: globes!

Alfredo

We’re getting really close a cluster of spheres in space. Okay, good.

Chris

Solar Systems?

Alfredo

No, but we’re gonna get there. So what are..

Chris

Planets? stars?

Alfredo

Stars!

Chris

Yeeeeeah! So it’s just a regular galaxy?

Alfredo

No, but good attempt. Very good attempt, you’re getting a gold star!

Chris

I deserve a cake for this.

Alfredo

So, a globular cluster is a spherical collection of stars. So, the globular refers to the shape of the cluster, and it orbits a galactic core as a satellite. So they’re just collections of stars that orbit the galaxy. And there is some interesting stuff. They’re found in the halo of the galaxy.

Chris

What does that mean?

Alfredo

Okay, let’s think of a traditional picture of a galaxy. So you have the spiral. So the spiral, if you see it in 3D…

Chris

It should be quite flat.

Alfredo

Exactly. So imagine that you have this, the flat part is where the spiral is and that is the thin disk. Some galaxies can have a thicker disk. Around that, you can imagine there is this spherical region and that is the Halo.

Chris

Okay.

Alfredo

So some stars in the galaxy can be there and that’s where we find the globular clusters. They think they formed when some interactions with other galaxies, smaller galaxies, or sometimes even from bigger galaxies, throws material around and…

Chris

Basically is it just like the loose bits?

Alfredo

It is loose bits,

Chris

okay.

Alfredo

And it’s very interesting because they are good places to do some interesting astrophysics and studying things. And Jediknitter, very interestingly points out the age of stars and that is something that is very important when it comes to globular clusters. So these globular clusters can have tens of thousands of stars. I think the biggest is maybe pushing a few million. So they’re still very small compared to even the smallest galaxy, but they’re sort of in-betweens.

Chris

Okay.

Alfredo

But what is fascinating when it comes to aging, we think they either form in a single burst, so all the stars in the public cluster have the same age, or maybe they form in a couple of bursts.

Chris

Okay.

Alfredo

So there is something is called a bimodal population. And then it’s very good because they allow us to test certain theories about how we expect stars to change with age, but also our models of how can we recognize that the age of the stars is correct.

Chris

Before we carry on, I want to quick aside, can you very briefly explain how we tell the ages of stars in general? And is that the same as aging globular clusters?

Alfredo

So, actually, the globular clusters are our best bet to work out the age of stars. Because usually, we cannot tell how old a single star is. So stars change throughout their lives and often is very difficult to pinpoint the specific characteristics that would age a star. And there are some stars that might appear much younger while they’re actually much older. So when you have a globular cluster, you just have this assumption that you were going to have a good population of many different stars. So you’re going to have some stars that formed quite small, so they evolve very slowly. You’re gonna have some stars that they were very massive at the very beginning and they evolve very quickly.

And by sort of estimating how massive this globular cluster is you can work out how many of each group of stars you should have, and by working out “this many have evolved, these may have not evolved, these are looking like this, etc.” you can have a good statistical approach on how old the entire cluster is.

Chris

Wow.

Alfredo

How can we work it out for other stars? It becomes a little bit more complicated. You might have heard of red giants or supergiants, so you know that those are evolved. They move beyond the main sequence. Stars, after they come into adulthood, they’re in the main sequence and…

Chris

The retired celebrity era stars

Alfredo

No, the main sequence is when they’re getting all the roles and then they move on something called the horizontal branch in which they getting redder and redder, and then something happens so so they can become red giants, red super giants eventually, and some go supernova and some become white dwarfs. So there is quite a variety. You can sort of estimate the stars ages with that.

You can estimate star ages with… if they are in a region where they saw stars forming, you can work out if it’s millions of years, in the tens if not hundreds, millions of years. So those are ways to get a ballpark figures. With globular clusters, we tend to have quite good estimates simply because with the assumption that if we believe that that specific cluster form in a single go, then we expect the population to be in a certain way. But even if you have a couple or a few star formation events, even with us, it’s very easy to model. Then when you put in an entire galaxy with a hundred billion stars, and many things going at once, then it becomes a lot more complicated.

Chris

Well, it’s really interesting. I hope, Jediknitter has learned something new today.

Alfredo

Well, I hope that answered the question. He has some pretty good background and astronomy.

Chris

Well, maybe he knew already and he was just testing your knowledge.

Alfredo

Did I pass the test?

Chris

Okay, we’re gonna move on to the next question, now. The next question is from an anonymous source. I mean I know who they are but they wish to remain anonymous.

Alfredo

Stay tuned we are about to get some information

Chris

No, not a ‘source’ in that respect!

Alfredo

Did you misspeak by saying ‘source’?

Chris

No, I think a source also works. “This is from a source” would prefer to remain anonymous..

Alfredo

All right [laughs]

Chris

Not in a source of information but rather a source: a location, a person, a place!

Alfredo

What does Deep Throat want?

Chris

I hate that name

Alfredo

What? Codename giraffe?

Chris

I’ve completely forgotten how he started the sentence. So, so so so so, the anonymous person asks “Planet Nine, is it real?”

Alfredo

Good question. And I was hoping that you would tell me who has good information about existence for nine. So what is Planet Nine?

Chris

They didn’t tell me they did at least

Alfredo

Okay, what is Planet Nine?

Chris

Not Pluto

Alfredo

No, not Pluto. So Pluto is not classified as a planet. It is classified as a dwarf planet. If we want to argue about this,

Chris

We’ll have a brand new series of spin-off episodes.

Alfredo

And we can have it in another episode

Chris

Alfredo vs. Pluto.

Alfredo

No, I don’t mind that. I feel that the conversation needs to be more nuanced, but seriously, bother me with this for season two.

Chris

Okay, I will jump in with what I think I know about planet nine.

Alfredo

Yes. So let’s do a little quiz on how much Chris knows about Planet Nine

Chris

I may be mistaken Planet Nine, or is it referred to as Planet X? I don’t know if they are one and the same because maybe Planet X is what Planet Nine was referred to when Pluto was still a planet? As in planet Roman numeral x Planet 10.

Alfredo

Yes.

Chris

So they, being scientists, believe that the evidence for Planet Nine being a thing is that our solar system is whacked out of shape, maybe or just bent or something.

Alfredo

Okay, yes, that’s good.

Chris

Something, a big source of gravity, has moved through the region and warped everything at some point in the past. That it’s only something that a planet could do, but where is the planet? Oh, maybe it’s on the other side of the solar system. We can’t see it yet. Or it’s really far out!

Alfredo

I wish this wasn’t an audio medium because you just miss Chris being very pointy up and down a while describing all of that. So some good stuff there. Let’s refine it a little bit. There are some weird things in our solar system. The first key evidence that points to the presence of a yet-to-be-discovered planet, and it is yet to be discovered, it’s the fact that a lot of smaller objects beyond the orbit of Neptune, called Kuiper Belt Objects, to which Pluto belongs, all seem to be pointing in the same direction. An orbit of planet or object around the star is going to be elliptical. So Earth’s orbit around the Sun is more or less like a circle, but you can have very eccentric orbits.

Chris

So in this respect, it will be an oval. So it would come very close to us to the sun, but then go very far away and then come back very close, but then carry on going very far away.

Alfredo

Yeah, in this oval shape. And the aphelion, the furthest point from the Sun, of a lot of these objects all point more or less in the same direction, which it’s quite peculiar.

Chris

Is that suggesting that something has made them do that?

Alfredo

Yes, and that suggestion is a large planet, I think it was between 10 and 20 times the mass of the Earth. So bigger than Earth but smaller than Neptune, orbiting between 200 and 700 times the Earth-Sun distance. Pluto is around 30 Sun-Earth distance

Chris

Wow! so it’s really far out if it’s there.

Alfredo

Really, really, really far out!

Chris

With that, if it’s ever discovered, would it basically make our solar system hundreds of times bigger than we thought it was?

Alfredo

No, we know that there are objects gravitationally bound to the Sun such as comets that have enormous orbits. There is the Oort cloud. It is this region of material, very, very dispersed, that probably stretches to maybe up to like a light-year away.

Chris

Okay, it wouldn’t make our solar system bigger than we thought it would, basically

Alfredo

No, but it would really give us some interesting things to think about. Like, for example, could this object be moving at some point through and beyond the Heliosphere? So the Voyager probes, both left the solar system, they’re moving at a speed that is high enough for them to not be gravitation trapped by the Sun, and they are now in the region of space in which the solar wind and the particles produced by the sun are more than balanced out from the particles coming from the rest of the galaxy.

It also depends on the shape of the orbit. Could this planet sort of be far enough away to move through? And actually, we might be able to work that out already. I actually don’t know the answer. It just popped into my head. And I’m gonna look it up later if we can work it out. Or if we know that if it’s beyond or not, but it’s fascinating. And it would also expand our definition of what our system is. We had in the previous episode, the question from Laurie about solar systems, then if they look like ours, and one thing that other systems have, that we don’t is Super-Earths and sub-Neptune planets. We don’t have anything that is quite in between. We have terrestrial and then we have giant ice giants. And so it would be nice to have one of them not really around the corner.

Chris

Brand new buddy planet.

Alfredo

So it would be, I think, very, very interesting. We don’t have any direct observation or direct evidence, there is a lot of circumstantial evidence. And obviously the team that proposed this claims that the evidence is now making the case against this very, very unlikely. With some things, I tend to agree. They make some very good cases, but as always, extraordinary claims require extraordinary evidence.

Chris

Cool. I’m gonna throw one more quick question at you.

Alfredo

Hit me.

Chris

Is it likely to be filled with aliens who are hell-bent on reaping all of the gold from our planet to fix their own atmosphere, is this Nibiru?

Alfredo

Ahhhh. Ok. No,

Chris

Just “No”. “No” on its own?

Alfredo

Yeah, just ‘no’ on it’s own. The only thing I would say about Planet Nine is, if it exists, and we discover it, it should be obviously called something starting with the letter P, so all the kids can remember the..

Chris

The old mnemonic: My Very Efficient Memory Just Stores Up Nine Planets.

Alfredo

Yes. And with that you need P. and we can there’s only one.

Chris

Yeah, it’s Persephone.

Alfredo

It’s got to be Persephone. And I would say, I know that is the Greek name and not the Latin name like for all the other planets, but literally screw it. Persephone is the name for it. And it’s perfect. We expect it to be on a quite eccentric orbit so it comes for half of it quite close to the sun. Like Persephone coming out of the underworld… Seriously make it happen. Planet Nine be out there and we’re going to call you Persephone!

Chris

It’s the perfect name.

Alfredo

Perfect name.

Chris

Awesome. Thank you very much for answering the questions today. And we will be back next time with some brand new ones.

Alfredo

See you then.

Chris

Do you have any burning questions for the Astroholic? If so send them to me, @illucifer on Twitter, and I will spring them on him in an upcoming episode. See you next time!

Image Credit: The Messier 80 globular cluster. NASA, The Hubble Heritage Team, STScI, AURA