Our galaxy series continues with elliptical galaxies. Unlike other types, these are large, smooth with very few distinguishing features. They’re filled with red and dead stars, a clue to their evolution.
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Show Notes
This episode discusses Elliptical Galaxies, one of the major types of galaxies in the universe. Here are the key points covered:
Elliptical Galaxies
- Large, smooth galaxies with very few distinguishing features.
- Filled with red and dead stars, indicating they are not actively forming new stars.
- Likely the final form of a spiral galaxy after mergers with other galaxies.
Formation
- Giant elliptical galaxies can form through mergers of large spiral galaxies.
- Smaller elliptical galaxies may form from smaller clumps of matter in the early universe.
Characteristics
- Contain enormous numbers of stars – trillions compared to the Milky Way’s 100 billion.
- May have the largest supermassive black holes in their centers.
- Lack the spiral arms of spiral galaxies due to the chaotic nature of mergers.
- Reddened due to a lack of gas and dust for new star formation.
Future of the Milky Way
- The Milky Way is predicted to collide with Andromeda Galaxy in about 5.5 billion years.
- This collision will trigger a massive burst of star formation.
- The Milky Way and Andromeda will eventually merge into a single, giant elliptical galaxy called “Milkdromeda.”
- Our supermassive black hole will likely become more active, but not as bright as a quasar.
The Distant Future
- Over trillions of years, Milkdromeda will eventually run out of fuel for star formation.
- It will become a dead galaxy filled with white dwarfs, red dwarfs, and possibly rogue planets.
- Stellar collisions will become rare events.
Additional Information
- The episode mentions dwarf elliptical galaxies, which were discussed in a previous episode.
- The largest known elliptical galaxy is 16.3 million light-years across, compared to the Milky Way’s 100,000 light-years.
- Early universe galaxies, including some ellipticals, may have formed much faster than previously thought.
Transcript
Human transcription provided by GMR Transcription
Fraser Cain:
Astronomy Cast, episode 720, the galaxy series, elliptical galaxies. Welcome to Astronomy Cast where we take a facts-based journey through the cosmos. We help you understand not only what we know but how we know what we know. I’m Fraser Cain, I’m the publisher of The Universe Today. With me as always is Dr Pamela Gay, a senior scientist for the Planetary Science Institute and the director of Cosmos Quest. Hey Pamela, how are you doing?
Dr Pamela L. Gay:
I am doing well and I – when this podcast goes out, we’ll be getting ready to head to Balticon in Baltimore on the weekend of May 24th. You are going to be in Japan getting ready to come back. And while you’re in Japan you are just doing the vacation thing. You’re doing…
Fraser Cain:
Mm-hmm.
Dr Pamela L. Gay:
The responsible to your soul thing of actually taking time off.
Fraser Cain:
Yes.
Dr Pamela L. Gay:
I’m not that person.
Fraser Cain:
No.
Dr Pamela L. Gay:
So, on May 24th, in Baltimore, I’m going to be doing a Cosmos Quest, meet up, Astronomy Cast, Cosmos Quest meet up at the details are all on our Patrion. Go check it out. May 24th in Baltimore. And then the following week I’m going to be in Orlando. And I’m going to be doing a meet up at the east end market on May 30th. That’s a Thursday. And we are also planning a meet up for San Diego the last week of August. Details are hopefully going to go out before you are getting this in your podcast feed.
Fraser Cain:
Right.
Dr Pamela L. Gay:
So, go check all of the details out on Patrion and RSVP. It’s a public post, so anyone can participate because we want your RSVP numbers.
Fraser Cain:
That sounds great. All right. Our galaxy series continues with elliptical galaxies. Now, unlike the other types, these are large, smooth with very few distinguishing features. And they’re filled with red and dead stars, which is a clue to their evolution. And a terrifying fate of the future of the Milky Way. All right, so we continue on our galaxy series and in this we’re going to talk about giant elliptical galaxies. So, what are they?
Dr Pamela L. Gay:
They are systems generally several times larger than the Milky Way that are probably that big in may cases because galaxies like our own Andromeda have smushed together and because the stars have a variety of different angular momentums, are moving in a variety of different planes, when all of these stars come together and all of the passage to and fro as the galaxies merge is over, you end up with stars in a swarm instead of stars in a disk.
Fraser Cain:
Mm. And so, you say stars in a swarm. So, if I was to – I imagine when I fly out in the universe and I buzz around a spiral galaxy, I’m seeing this big, spinning pizza pie. Right. With spiral arms on it in space. But if I was to fly around one of these giant elliptical galaxies, swarm of angry bees?
Dr Pamela L. Gay:
Swarm of angry bees with their queen in the center.
Fraser Cain:
Yeah.
Dr Pamela L. Gay:
So, they are definitely held on those in the center are moving much, much faster. Those further out are some moving faster than they should because that pesky dark matter. But we do see a velocity curve and we also see that these systems don’t have all their stars necessarily moving in mostly one direction. There’s always exceptions. This is the rule of astronomy. There’s always exceptions. We have stars going the wrong galaxy in the Milky Way.
Fraser Cain:
Right.
Dr Pamela L. Gay:
The number of stars going in the wrong direction goes up and it becomes difficult to find wrong direction as you start looking at elliptical galaxies.
Fraser Cain: And so, I mentioned that, right, that it’s the evolution of these giant spiral galaxies. This is the final form of a galaxy. And…
Dr Pamela L. Gay:
Or the first. This is the scary part.
Fraser Cain:
Okay. Okay. We’ll get there. We’ll get there. But let’s talk about it in the final form version. And so, we take a galaxy like the Milky Way that’s coming in in one direction and then we T-bone it.
Dr Pamela L. Gay:
Yeah.
Fraser Cain:
With another galaxy. And so now you’ve got the, you know, they don’t get this nice simple averaging out of the rotations of the, you know, of the stars that are rotating…
Dr Pamela L. Gay:
Yeah.
Fraser Cain:
Around the common center mass. Now it’s a mess. And so, swarm of angry bees.
Dr Pamela L. Gay:
Yeah.
Fraser Cain:
Like it just loses that spiral structure.
Dr Pamela L. Gay:
And the key is you have to have the right mass ratio and the right angle of attack when they come in. So, t-boning definitely is in your favor. Equal mass is definitely in your favor.
Fraser Cain:
Mm.
Dr Pamela L. Gay:
If you have a large difference in masses then the smaller galaxy’s simply going to inflate the disk of the larger galaxy and lead to something not too different from what we have with our Milky Way. We see other galaxies with even more inflated spiral disks. It’s that t-boning of two things of about the same size that gets you that first elliptical galaxy form through merger. Now these suckers can do all sorts of merging in their history, and they can also form on mass into an elliptical from the start at all sizes, so.
Fraser Cain:
Right.
Dr Pamela L. Gay:
So, we had dwarf ellipticals at the beginning of this series. We have giant ellipticals today. Where do you want to go at this point. We’re at the branching point of the podcast.
Fraser Cain:
Right. I want to talk about the – because the dwarf ellipticals, the stuff that’s early on in the universe, this is a newer discovery. So, I’d rather stick with some of our older understandings first.
Dr Pamela L. Gay:
Okay.
Fraser Cain:
And then we’ll come back around to it. So, let’s just get a sense of the scale of one of these giant elliptical galaxies, because they are enormous.
Dr Pamela L. Gay:
Yeah.
Fraser Cain:
Do you have any sort of ways to wrap your head around how big these things are?
Dr Pamela L. Gay:
So, you have systems that are just like two spirals collided. You end up with the combination. It’s two times bigger. Not a big deal. Who cares.
Fraser Cain:
Right.
Dr Pamela L. Gay:
But in the centers of galaxies, you have these central cluster galaxies. Once upon a time these were called CD galaxies. I don’t know when or why we stopped calling them that. Now it’s just the brightest cluster galaxy. These central galaxies have a very special role. They are where anything that got dragged down too much, ends up colliding.
Fraser Cain:
Mm.
Dr Pamela L. Gay:
And so, over time these central galaxies, they can end up with the entire mass of the local group tied up into one ginormous galaxy.
Fraser Cain:
Right. Just to get a sense of scale, right, the Milky Way has 100 billion stars, these things are going to have trillions of stars.
Dr Pamela L. Gay:
Yeah.
Fraser Cain:
One of the sort of examples, M87 which is the, you know, where the [inaudible] [00:08:05] telescope took those images of the super [inaudible] black hole at the heart of M87. That is a giant elliptical galaxy. It has 15,000 globular clusters surrounding it. Compared to the Milky Way that has a couple hundred.
Dr Pamela L. Gay:
Yeah. So, the largest galaxy ever discovered is in keeping with the theme of how I work around here. I’m going to mispronounce this. I’m so sorry. I should have taken phonics. Children, learn to read right. The alcionious galaxy is 16.3 million light years across.
Fraser Cain:
For scale, the Milky Way is like 120.
Dr Pamela L. Gay:
Eighty thousand.
Fraser Cain:
Yeah.
Dr Pamela L. Gay:
Between 120, 180.
Fraser Cain:
Yeah, yeah.
Dr Pamela L. Gay:
Depends on…
Fraser Cain:
Around 100 thousand.
Dr Pamelia L. Gay:
Yeah.
Fraser Cain:
Light years across. And this thing is, say the number again.
Dr Pamela L. Gay:
16.3 million light years.
Fraser Cain:
Wow.
Dr Pamela L. Gay:
It’s 160 times wider than the Milky Way.
Fraser Cain:
Wow. And yet it doesn’t have structure. It is just this giant swarm of angry bees.
Dr Pamela L. Gay:
Yeah. Yeah. And so, what’s happening is just as galaxies end up with more and more stuff in their nucleus through a variety of interactions, things, their velocities change, they get drugged down, they end up in the core. In globular clusters, where you have the inter cluster medium creating drag, creating friction, slowing the orbits, causing them to spiral in towards the center, you can end up with material just piling up and piling up and this particular system is only four times bigger than the previous record holder which was 3.9 million light years across.
Fraser Cain:
Right, much bigger.
Dr Pamela L. Gay:
So, there are these massive systems just sitting out there as hungry monsters eating their kin. Galaxies are cannibals, people, galaxies are cannibals.
Fraser Cain:
Right. So, give a sense of the evolution of the universe. How we got galaxies that are this big.
Dr Pamela L. Gay:
I mean it’s one of these things where you start out, we don’t know what was step zero for galaxies we see in the modern universe. But presumably, you start out and one of the larger over densities of mass in the universe. That larger over-density collapses down fragments into galaxies. Some of these galaxies are going to be some of the largest galaxies forming in the universe. So, we are starting to see massive clusters forming in the earliest apex of the universe. These massive clusters that form early have time for all of these drag and friction processes that I mentioned to cause things to come in towards the center, merge in the center, merge in the center get bigger and bigger central brightest galaxies.
And then galaxy clusters that form near each other can also merge together getting super clusters. And it’s just constant merger and when your biggest things form early, it gives them a head start on this merger process to just keep building bigger and bigger things through mergers.
Fraser Cain:
And I guess it just follows this distribution curve that we mentioned in a couple of episodes ago that you’re going to have big things and then you’re going to have small things. And there’s going to be something that’s the biggest. And also, big things in the universe are bright and so they’re easier to find. They’re more obvious than the little things. And so.
Dr Pamela L. Gay:
Yeah.
Fraser Cain:
Somewhere out there, there had to be a biggest galaxy cluster and a biggest, most massive galaxy and…
Dr Pamela L. Gay:
Yeah.
Fraser Cain:
Is almost certainly one of these giant elliptical galaxies. So, I mean, we see these giant elliptical galaxies billions of years into the past. And so, is this giving this idea that okay these things are forming quicker than anyone thought?
Dr Pamela L. Gay:
So, they are definitely forming quicker than we thought. It is now clear that within the first 500 million years of our universe there were already galaxies with billions of stars clumped.
Fraser Cain:
Wow.
Dr Pamela L. Gay:
Which is not what anyone expected. GZ9P3 was spotted 510 million years after the big bang, and it already contained several billion stars. We can’t make out its cluster other than it is a fuzzy blob.
Fraser Cain:
Right.
Dr Pamela L. Gay:
But my bet is this fuzzy blob is probably elliptical in nature. I could be totally wrong. That is…
Fraser Cain:
Right.
Dr Pamela L. Gay:
That is simply what I have chosen to guess.
Fraser Cain:
So, what are some are the features. We look at a giant elliptical galaxy, we don’t see the spiral arms but what are some of the features that we do see in these things?
Dr Pamela L. Gay:
So, what I had mentioned in the last episode on spiral galaxies about the size of the bulge, the velocity dispersion of the stars in the bulge is directly related to the size of the super massive black hole in the course of these systems. Well, an elliptical galaxy is just all bulge. So, elliptical galaxies are where you’re going to be finding the biggest super massive black holes.
Fraser Cain:
Mm.
Dr Pamela L. Gay:
So, when we see active supermassive black holes, that is where we start seeing some of the coolest looking jets around. We’re still trying to figure out how to make out the exact morphology of a lot of quasars. It’s hard. The cores are bright, drown out the structure of the fainter surroundings. But if you think about it, with these elliptical galaxies early in the universe when active galaxies were most common, they’re undergoing massive collisions. They have dust and gas in them initially. That initial dust and gas is going to undergo massive amounts of star formation. Ellipticals in the early universe are blue.
Fraser Cain:
Mm.
Dr Pamela L. Gay:
Not what we see today.
Fraser Cain:
Wow.
Dr Pamela L. Gay:
Then all of that star formation gets used up. All of that gas and dust either gets used up or blasted out of the system through super Novi and the solar winds from all of the stars forming. And what’s left behind is a system without enough gas and dust to do more star formation. And so, you just have these stars that shone so amazingly blue in their early universe that are now just going to get old.
Fraser Cain:
Mm.
Dr Pamela L. Gay:
As they get old, they become red giants. They – the red dwarfs they just keep sitting there being red. So, all of your big blue stuff stops being blue. It either goes super nova or becomes a red giant. All your little stuff just sits there staying red and continuing to exist. And so, these systems become red and dead.
Fraser Cain:
Yeah, yeah. And so, this reddening of the galaxy, this just tells you that it’s run out of the reserves of star formation.
Dr Pamela L. Gay:
Yeah.
Fraser Cain:
And it’s run out of the new and active stuff and now it’s just your left with whatever is the longest-lived stars, the red dwarfs.
Dr Pamela L. Gay:
Right.
Fraser Cain:
You see the sum of red dwarfs and white dwarfs. But trillions of them collected together into this old dying galaxy.
Dr Pamela L. Gay:
And with the central brightest galaxies and clusters, by the time galaxies make it all the way down into the core they’ve pretty much lost everything they had to form stars, to ram pressure stripping.
Fraser Cain:
Mm.
Dr Pamela L. Gay:
To galaxy harassment. Galaxies live violent existences, and all these different factors work against them to strip out the loose bits to trigger star formation where it can and to blast out what doesn’t form stars. So, we’re just feeding the leftover bits of these disruptive galaxies or galaxies that have gone through horrible times into these central brightest galaxies.
Fraser Cain:
All right. So, I want to take that other path now.
Dr Pamela L. Gay:
Yes.
Fraser Cain:
I want to take the not gigantic elliptical galaxies, the little elliptical galaxies. What?
Dr Pamela L. Gay: So, so, what I love is we hit on these some in the very first episode in this series. There are when in the early universe the stuff that galaxies are made of fragmented, it fragmented into a few big pieces, a few more middle-sized pieces and a whole lot of little, tiny pieces. And these little, tiny pieces end up gathered around galaxies, gathered up in galaxy clusters and for the most part they didn’t have that much mass in them. They underwent an early epic of star formation, and a lot of the cases are the ones we see in our own local group. These are things that are roughly the same age as the globular clusters that we see.
And the tiny ones only had a single epic of star formation. The bit bigger ones had a few epics of star formation, and we can actually see in the Hertzsprung-Russell diagrams, the color magnitude diagrams those different epics of star formation in a few cases which is really cool to see the multiple turns offs on the main sequence. But when I look at them in the early universe, these are bright blue systems again.
Fraser Cain:
Mm.
Dr Pamela L. Gay:
These are the fireflies that shone bright and they’re still out there and as they go from spherical to elliptical that’s where you start seeing more epics of star formation more likely. More of a history that led to the changing of the structure over time. The universe’s little systems are the building blocks of everything.
Fraser Cain:
And so is it really just that you’re getting these collisions happening perpendicular to each other that you don’t get this smooth spiral evolution because its just its such a chaotic mess and you also get because you’ve got them coming together the gas clouds collide inside the galaxies and you get the furious star formation.
Dr Pamela L. Gay:
Well, it’s also just hard to know when your mass gets that small if it’s a matter of it just doesn’t have enough stuff to start forming a spiral structure. So, if you think about it, globular clusters, spheres. Dwarf galaxies that are tiny, spheres. Open clusters, spheres. And these are all different objects. They all have different formation histories but none of them have that angular momentum that causes them to flatten so whatever slow process caused the mass to collapse down didn’t cause it to also spiral. So, there’s a different angular momentum involved with these.
Fraser Cain:
Mm-hmm, mm-hmm. Now, I want to talk about the future of the Milky Way because…
Dr Pamela L. Gay:
Yes.
Fraser Cain:
A giant elliptical galaxy is in our future. So, let us know how the future of the Milky Way is going to play out. And again, once again, you know, we’re into the – some astronomers think a bit this way, some astronomers think the other way, some think the merger has actually already begun. But what’s the…
Dr Pamela L. Gay:
Yeah.
Fraser Cain:
Sort of mainstream understanding of the future of the Milky Way and Andromeda?
Dr Pamela L. Gay:
So, in general it’s thought that about 5.5 billion years from now, the Milky Way and Andromeda are going to be far enough along in the process of colliding of gravitational emerging into a single Milkdromeda system, Milkdromeda.
Fraser Cain:
Yeah.
Dr Pamela L. Gay:
That we’re going to start to see massive amounts of star formation going off. We are going to see our black holes eventually rotating together, potentially colliding. Colliding’s not quite the right word. Merging over time in a massive gravitational wave release to form a single galaxy. And this is going to be the kind of thing that we see when we look out at the colliding galaxies like the mice where you have two spiral systems that essentially unwind their arms forming amazing tidal tails in the process and leave fragments messily behind that will gravitationally from many of them the pieces will come back in later.
It’s going to be a destructive process and it’s going to light everything up brighter than we can imagine with all the star formation going on. And it’s also going to happen about the same time that our sun either does or does not consume the planet earth.
Fraser Cain:
Right.
Dr Pamela L. Gay:
Coincidence here. Strictly coincidence. And whether or not the earth is consumed in the atmosphere of the sun. The surface of our planet will be not exactly habitable at that point. So, human beings need to find a new home to watch this collision of galaxies in the future.
Fraser Cain:
And do you think that our super massive black hole will become a quasar again?
Dr Pamela L. Gay:
Yes. Well, quasar is a strong word, so.
Fraser Cain:
Active?
Dr Pamela L. Gay:
It will become an active galaxy. So, active galaxies incorporate lots of different systems and quasars refer to things that have a ginormous well quantified amount of energy coming out of their core and they pretty much only exist further back in time than where we are.
Fraser Cain:
And actually, to be technically correct, pointing at a very specific angle compared to the observer.
Dr Pamela L. Gay:
Yeah.
Fraser Cain:
Right.
Dr Pamela L. Gay:
And so, it’s a relationship of what is the total amount of energy coming out of the core of the active nucleus. We probably aren’t going to have that much stuff.
Fraser Cain:
Right.
Dr Pamela L. Gay:
But there is going to be material driven into the black hole and the black hole will become active. There will likely be jets. There will be an accretion disk. So, all the bits and pieces that you see in a quasar will be present. What won’t be there is the tremendous energy that is present in a quasar.
Fraser Cain:
Right. And it’s funny like I get this question from people, they’re like, “Oh, when, if the Milky Way turns into an active galaxy, what will it look like in the sky?” And the answer is absolutely nothing. It’s shrouded by gas and dust, the core and Milky Way and so we couldn’t see it even if it was blazing. But also, it’s still not very bright. You wouldn’t be able to see it with the unaided eye. You’d still need a telescope, preferably an infrared telescope to even see this process happening. It’s just not that bright in the grand scheme of things. You need a telescope.
Dr Pamela L. Gay:
Now what I would love to know, and I haven’t done the calculations on this. I don’t think I’ve seen a paper on this is if the Radia jets would be loud enough to start to interfere with communications.
Fraser Cain:
Mm.
Dr Pamela L. Gay:
I don’t know.
Fraser Cain:
Yeah.
Dr Pamela L. Gay:
I don’t know.
Fraser Cain:
Interesting. So, that is our future and then like the other you know giant elliptical galaxies, we will the young – the hot stars will die, we’ll be left with the red stars and star formation will cease and we will fade away over trillions of years to just a giant galaxy filled with white dwarfs, tiny red dwarfs and rouge planets, I guess.
Dr Pamela L. Gay:
There will be rouge planets. One of my favorite things…
Fraser Cain:
Yeah.
Dr Pamela L. Gay:
That we’ve recently realized is we used to say…
Fraser Cain:
And a couple of black holes.
Dr Pamela L. Gay:
Yeah. But we used to say that galaxies are so empty that you won’t have stars collide and now we know that stars do actually now and then actually collide. So, there could be a few…
Fraser Cain:
Right.
Dr Pamela L. Gay:
Stellar collisions. They’re going to be rare, but yeah. It happens.
Fraser Cain:
Yeah. Every now and then a new, it’ll appear as if a new star is forming in the Milky Way but, or in Milkdromeda, but it’ll be over. Yeah.
Dr Pamela L. Gay:
Yeah.
Fraser Cain:
It’s funny how we can feel anthropomorphic, we feel sad about this future, but you know it’s like we need to worry about our cholesterol, not about the…
Dr Pamela L. Gay:
It’s true.
Fraser Cain:
The death of the Milky Way.
Dr Pamela L. Gay:
But Andromeda is so pretty.
Fraser Cain:
Mm-hmm.
Dr Pamela L. Gay:
And that prettiness is going to go away.
Fraser Cain:
Yeah. But not in our lifetimes.
Dr Pamela L. Gay:
There won’t be any naked eye galaxies at that point for observers on our lack of planet.
Fraser Cain:
Yeah.
Dr Pamela L. Gay:
So, that’s a thing.
Fraser Cain:
Yeah. All right. We may continue the series next week. We may move on to something else. We will, we’ll talk about that. You’ll find out next week.
Dr Pamela L. Gay:
It’s true.
Fraser Cain:
What happened with the series. All right, thanks Pamela.