Short Wave - The Mysterious "Great Attractor" Pulling Our Galaxy Off Course

Episode Date: May 1, 2024

No matter what you're doing right now – sitting, standing, walking – you're moving. First, because Earth is spinning around on its axis. This rotation is the reason we have days. Second, because Earth and other planets in our solar system are orbiting the sun. That's why we have years. Third, you're moving because the sun and the rest of our solar system is orbiting the center of the Milky Way galaxy at over 500,000 miles per hour. If all of that isn't nauseating enough, everything in the entire universe is expanding outward. All the time. But in the 1970s, astrophysicists noticed something strange about our galactic neighborhood, or Local Group. The whole clump of neighboring galaxies was being pulled off course at over one million miles per hour, towards something we couldn't see — the "Great Attractor." This Great Attractor sits in the "Zone of Avoidance," an area of space that is blocked from view by the stars and gas of the Milky Way. Today on the show, host Regina G. Barber talks to astrophysicist Jorge Moreno about this mysterious phenomenon: What it might be and what will happen when we eventually reach it. Curious about other cosmic mysteries? Email us at [e-mail]. See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. Regardless of what you're doing right now, sitting, walking, driving, laying in bed, you're moving. First, because Earth is spinning around its axis at a cool 140 miles per hour right now. That's why we have days. Second, because the Earth and the other planets in our solar system are orbiting the sun. Our planet does that at around 67,000 miles per hour. and that's why we have years. Third, you're moving because the sun and the rest of our solar system

is orbiting around the center of the Milky Way galaxy at over 500,000 miles per hour. That's a galactic year. And finally, on top of all this movement, everything in the entire universe is expanding outward. It's only been about 100 years that we've known that almost every other galaxy in the universe is moving away from the Milky Way.

The universe is expanding at ridiculous speeds. Here's the thing. Sometimes there is a misunderstanding because that would imply that we are at the center of the universe. But the reality is that this is happening everywhere in the universe. So if you take an observer in another galaxy, they would observe the same thing. So everybody's moving away from everyone. That's Dr. Jorge Moreno, a computational astrophysicist, cosmologist,

and professor at Pomona College in California. To help his students understand how everything is moving away, from each other, he says. I like to think of a rubber band. So a rubber band or a rubber sheet, but this will be in three dimensions. And this is infinitely big. It's like the universe is an infinite rubber sheet.

And if you stretch that sheet, every point will look like it's stretching away from each other. So sometimes I get the question, what is the universe expanding into? It's expanding into itself because the universe is everything. So everything is expanding outward, roughly equally in all directions.

But in the 70s, astrophysicists noticed that something in our local group, basically our galactic neighborhood, seemed kind of off. This whole clump of neighboring galaxies were being pulled off course towards something at over one million miles per hour. That means since you started listening to this,

you've moved about 55,000 miles through space. And that's the region we call the Great Athlete. But it's really confusing because, unfortunately, that direction coincides with the disk of the galaxy itself, which has a lot of stars and a lot of dust is blocking the direction of the great attractor. Which means scientists can't really see what's pulling us towards it. Today on the show, The Great Attractor, what's pulling us and our neighboring galaxies off course and what will happen when we reach it? I'm Regina Barber, and you're listening to Shorakor. Wave, the science podcast from NPR. Okay, so this great attractor is something that scientists assume is extremely massive, right?

Because the more mass something has, the bigger its gravitational pull, like its ability to yank stuff towards it. And this great attractor, it has a huge gravitational pull on our local group, the Milky Way galaxy we're in and other galaxies around it. But what exactly is the great attractor? Like, it's been kind of this mystery. So why is it so hard to pin down what it is? The reason is because the Milky Way has millions and millions of stars and a lot of dust, which is blocking all that information that we could be measuring in that direction.

So our own galaxy is blocking the great attractor. And all these millions of stars and dust, I read it makes up a region called the Zone of Avoidance. And this is where scientists just can't see anything. Exactly. So people like want to measure galaxies in every direction in the sky. However, because you have the Milky Way blocking the view, you don't get the entire sky. You get like two halves, but there is a region in the middle that you don't get because the Milky Way itself is blocking it. And unfortunately, the great attractor happens to be in that region. Jorge, we know that there's this thing, the great attractor.

And it's like pulling us and our nearby galaxies and its view is blocked by our own galaxy, the Milky Way. But is there a way to like indirectly observe it? Like, how do we know it's there? So what we can do is we can look at, take a step back and look at larger scales. And you can see the flow of galaxies and that can give you information about that great attractor. So imagine you want to, I don't know, measure the size of Los Angeles. But you cannot see downtown LA because there is a lot of smog. Yes.

So what you do is you see how many people are driving on the freeways towards Los Angeles. And that can give you information of how populated that region is, right? Yeah. Okay. And over the years, there's been like a few hypotheses on what this great attractor was, right? So can you tell me like some of the candidates that have come up over the years? I think it's the story of the great attractor is a story of bad luck. It happens to be on this same direction as our own Milky Way galaxy. So it's on the sun of avoidance.

Also Virgo is sort of in that direction, the Virgo cluster. Let's actually take a second though to just break down what the Virgo cluster is. Sure. So the universe is not just composed of galaxies, but it has galaxy clusters. Just like this country, not only does it have houses, but it has cities. It has accumulations of houses. The universe has accumulations of galaxies. So galaxy clusters are collections between 100 and 1,000 galaxies.

So the very cluster is 60 million light years away from us. It's a collection of galaxies. It has around 1,000 galaxies, and they're orbiting each other. And so astronomers thought that maybe the greater tractor was this Virgo cluster because it's in the same direction. And then they thought maybe it's the Shapley super cluster because it's even more massive. It's a much larger cluster of galaxies and it's like also in that direction. But researchers don't think that anymore, right? So what is the candidate now?

Like after thinking about this for decades. So there is another cluster at the center of what we of the grader tractor called the normal cluster. but that's just a, that would be like the downtown of the city, but the city itself, now we call that Lanier. Lani Akiah was discovered by Brentali and collaborators in 2014. And Lani and Akiah are Hawaiian words. So Lani means heaven. Akea means spacious or immeasurable.

So Lani Akea would be immeasurable heaven. So basically scientists generally think we're moving towards the center of this supercluster. Akea. And that supercluster is an area in space that includes a lot of smaller galaxy clusters like Virgo. So the Great Attractor is not just like one of these galaxy clusters. And instead, our local group is kind of on the outskirts. And we're being pulled towards the Great Attractor, which is the center of mass of this region. Exactly. So it encompasses the region we call the Great Attractor and everything that's flowing into that region. Which is 500 million light years wide. Yes. And this

region is approximately 10 to the 17 solar masses, so that's 1 and 17 zeros times the mass of the sun, which corresponds to approximately 100,000 galaxies. Wow. And now we have the James Webb Space Telescope, which is like an infrared telescope, and it can see better into dust and gas. So like it's going to make that zone of avoidance more visible, like less avoidancy, right? So will this telescope help us solve this mystery? Like, is there even more mystery to solve? So I think the regions close to the greater tractor, you can measure the velocities really well. But once you start going to farther away distances, that becomes harder. So I think with James Webb, especially when you're looking in the sun of avoidance, it can really help.

I don't think the dose is completely settled. Pun intended. Yeah, exactly. For example, there was a paper claiming that there is another supercluster in that same general direction called the Villa supercluster. So some people are not sure maybe Lania is a subset of that or not, but that's still not clear. But I think this really connects with a bigger conversation, which is how fast is the universe expanding. Right. And because across all of this, like we're measuring the movement of things in space. So like velocity, which is speed and direction, is really important to pay attention to.

And there are two especially important velocities here. One, the velocity we expect from the universe expanding, and two, the actual velocity of our local group towards this great attractor thing, right? And it's pulling us off course from that, like, regular expansion. Exactly. So by measuring the mass of Lanakia and also the neighbors around Lanakia, we would be able to really get that accurately. So the Milky Way, you know, our local group, this little cul-de-sac in our universe, which we kind of belong to, we're all getting sucked towards the great-attractor. But like, what does that mean for us? Like, what's going to happen? So before I mentioned galaxy clusters like Virgo.

So these are stable systems where the gravitational energy holding it together is bigger than the energy that has to do with motions, right? Lania K is not that yet. But in the future, if we wait billions or trillions of years eventually, that whole system is going to become a galaxy cluster. So it's kind of like the universe is expanding and we're moving away from each other, but gravity ultimately will bring that region together into its own home. So it's like we're going home. Oh, so like all of these clusters are even going to become like a massive, massive cluster. Yes.

Going again back to cities. You can look at LA and San Diego. Those are all separate cities right now. But if we come back in a hundred years, that's going to be a massive city. So we can think of that right now is a super. cluster, but in a hundred years it's going to be just a massive cluster because all of them are going to get connected. But San Francisco is not going to be a part of that. And this might be worrying some of our listeners. Is it something they need to worry about? When is this going to happen?

We shouldn't worry about that because that's going to happen after the sun engulfs Earth. Right. That's what I like to tell people. I'm like, they're like, oh my gosh, Indromeda's going to run into us. And I was like, yeah, but our son will probably be almost dead at that point. So it's fine. It would be cool to be alive. Yeah, I mean, yeah, it would be cool. Like, what does this tell us about our universe more broadly? So I think he tells us this is a story of a coming home. So in the Big Bang, we all separated. And at least those of us who are members of Lanierkega,

we're all kind of coming back together. I was doing a calculation in the back of an envelope last night. And basically, if you take Lanakia and you go back to the beginning of time, all of that was in a region of about three meters in diameter, about the size of this studio. So imagine that, like, in a fraction of a second, something as big as this studio expanded into Lanakia. But now, because of gravity,

because this thing is detaching from the global cosmic expansion, now everybody's going back together. Although the rest of the universe is still accelerating in a way, Lanakia, our home, we can count that it's going to be with us for a long time. And I think when we think about our own humanity, and there is so much division and so much polarization in this world, I think Lana Kia can inspire us to come back together, right?

Oh, that's beautiful. Jorge, thank you so much for talking to us about the great attractor. I've been thinking about it for decades, and now I have an answer. Thank you for having me. This episode was produced and fact-checked by Rachel Carlson and edited by our showrunner Rebecca Ramirez. Maggie Luthor was the audio engineer. Special thanks to our forever PhD advisor, John Blakesley.

Beth Donovan is our senior director and Colin Campbell is our senior vice president of podcasting strategy. I'm Regina Barber. Thank you for listening to Shorewave from NPR.