Chanda Prescod-Weinstein
Appearances
Short Wave
Could This Particle 'Clean Up' A Cosmic Mystery?
We want it to be something that doesn't interact very strongly with light, if at all. So we want it to be effectively transparent, effectively invisible. And we also want it to be relatively slow moving. So if it's fast moving, then it won't clump together under gravity. It will escape gravity and then you won't form galaxies.
Short Wave
Could This Particle 'Clean Up' A Cosmic Mystery?
Frank Wilczak, who named the axion, named it after the laundry detergent.
Short Wave
Could This Particle 'Clean Up' A Cosmic Mystery?
So axions are essentially a class of models that all look kind of similar. So they tend to be lighter in mass. And they also have these very interesting properties that they behave more like a wave than like a particle, depending on the situation you are looking at, the physical scenario you're looking at.
Short Wave
Could This Particle 'Clean Up' A Cosmic Mystery?
I mean, don't we all? Because it really challenges us to rethink our intuition about what constitutes normal in the universe. Like I always think about in that context, the axion is actually one of these dark matter candidates that challenges us to rethink, oh, it's just a different type of particle.
Short Wave
Could This Particle 'Clean Up' A Cosmic Mystery?
Because in our head, when we think about particles, we tend to think of them as like maybe little billiard balls bouncing off of each other or something like that. And the axion really requires us to think it's not that because it does behave like a wave in key physical scenarios that are of interest to us for the purposes of dark matter.
Short Wave
Could This Particle 'Clean Up' A Cosmic Mystery?
And this makes it distinct from other dark matter candidates. And this is actually one of the reasons that I got into the axion as a dark matter candidate is I was like, oh, I like this wave stuff. And in particular, I liked that it potentially formed... A state of matter known as a Bose-Einstein condensate.
Short Wave
Could This Particle 'Clean Up' A Cosmic Mystery?
Yeah. So Bose-Einstein condensate is a state of matter that can only be formed by bosons. So all types of matter are either bosons or fermions. So what's the difference? So I like to think of fermions as stacking particles. They don't all like to be in the same place, in the same status, the same energetic state at the same time. Whereas bosons are like the pep squad.
Short Wave
Could This Particle 'Clean Up' A Cosmic Mystery?
They will go and do everything together, a large number of people all doing the exact same thing at the exact same time. It's the flash mob all the time. Yes, flash mob particles. That's like essentially what a Bose-Einstein condensate is. It's like a flash mob of particles that have all committed to doing the same thing at the same time. And they love it. They love it.
Short Wave
Could This Particle 'Clean Up' A Cosmic Mystery?
One of the things I love about axions is they're like the flash mob dark matter candidate, right? It's an awesome characteristic. And so the thing that I have been most concerned about in my research, particularly over the last decade, is what are the implications of this particular aspect of axion properties that they do this Bose-Einstein condensate flash mob thing.
Short Wave
Could This Particle 'Clean Up' A Cosmic Mystery?
And what are the implications for the nature of galaxies and how galaxies evolve if dark matter does in fact behave like this on very large scales?
Short Wave
Could This Particle 'Clean Up' A Cosmic Mystery?
So the short answer is this is not a particle that you go looking for by smashing things together. And there's a little bit of potential there, but because of how this particle... So let me think about how we would say this. So the way that we would say this is... in physicist speak, is that the particle doesn't couple very strongly to standard model particles.
Short Wave
Could This Particle 'Clean Up' A Cosmic Mystery?
And so when you are colliding particles together and looking for other particles, that assumes that there is such a strong relationship between those particles and whatever you're trying to create that it will pop out when you smash them together. But if that relationship doesn't really exist in the first place, there's no amount of smashing together that's going to that's going to make it happen.
Short Wave
Could This Particle 'Clean Up' A Cosmic Mystery?
It's not going to work. You're not going to make fetch happen. That's so you just like you don't make axions happen that way. She doesn't even go here. She doesn't even go here. That's exactly it. She doesn't even go here.
Short Wave
Could This Particle 'Clean Up' A Cosmic Mystery?
So this is where computation can be really useful. And so you can imagine a scenario where there are two galaxies that are maybe colliding with each other and basically collided them to see what would happen. And then we tweaked the properties of the axion-like particle to see if the collision happened differently depending on how we tweaked the properties.
Short Wave
Could This Particle 'Clean Up' A Cosmic Mystery?
And so this is an example of why you would call it, for example, particle cosmology, because this is one where we're making changes to the characteristics of a very small object. But then we're looking at large scale astrophysical implications for those very small changes that we make. Oh, that's so cool.
Short Wave
Could This Particle 'Clean Up' A Cosmic Mystery?
Yeah, so neutron stars, just to back up a little bit, neutron stars are stellar remnants. So they are objects that are formed when a massive star reaches the end of its life, goes through a supernova experience, and neutron star is potentially left over on the other end. So this is not well understood, but neutron stars often have a magnetic field associated with them.
Short Wave
Could This Particle 'Clean Up' A Cosmic Mystery?
And when I say it's not well understood, we don't really understand where the magnetic field comes from. There are good models for it, but this is actually still an active area of research. So I made this claim that dark matter doesn't really interact with light, but axions do actually have a very mild, tiny, tiny, tiny interaction with light.
Short Wave
Could This Particle 'Clean Up' A Cosmic Mystery?
So you can have a situation where an axion is traveling over long distances through a galactic magnetic field and converts into a photon, so a little particle of light.
Short Wave
Could This Particle 'Clean Up' A Cosmic Mystery?
you can have axions going through a neutron star's magnetic field and turn into a photon. And then potentially we can see that photon. And so this is an active area of research. People also look for these kinds of interactions around white dwarfs, which are another possible outcome for a star at the end of its life. For much smaller stars. Much smaller stars, yes.
Short Wave
Could This Particle 'Clean Up' A Cosmic Mystery?
So at this point, I think the way we've been thinking about both white dwarfs and neutron stars in this kind of scenario is that it allows us to rule out axions with certain properties because we go looking for evidence that there was this phenomenon happening. And we don't see it. And so then we can say, okay, this axion with this kind of characteristic is not out there.
Short Wave
Could This Particle 'Clean Up' A Cosmic Mystery?
So one of the data sets that I've been interested in is from the Gaia Space Telescope. This was a European Space Agency mission. And what they did is they characterized the motions of stars. And they characterized the motions of a lot of stars.
Short Wave
Could This Particle 'Clean Up' A Cosmic Mystery?
And so this allows us to get into these questions of if there is this flash mob core thing happening and it's affecting how the stars move in a way that's unique to the axion scenario, can we look for evidence of that in the stars?
Short Wave
Could This Particle 'Clean Up' A Cosmic Mystery?
I mean, obviously we should find one. That would be good. So one thing I didn't talk about is that people do have these ground-based experiments. And this is actually a lot of the global investment is actually in trying to look for an axion using the exact same mechanism that that we might use to look for axions around neutron stars.
Short Wave
Could This Particle 'Clean Up' A Cosmic Mystery?
So they basically take a microwave cavity, they turn on a giant magnetic field inside of it, and then hope an axion will fly through and become a photon. And yeah, so this is the biggest type of experiment like this in the United States is the Axion dark matter experiment, which is housed at the University of Washington. But there are experiments that are similar to this around the world.
Short Wave
Could This Particle 'Clean Up' A Cosmic Mystery?
And so there is some possibility that we will actually what we would call directly detect one. So instead of looking for how it impacts how structures form, that we would actually see evidence that one went through our laboratory. So that would be awesome. Yeah, that would be very exciting.
Short Wave
Could This Particle 'Clean Up' A Cosmic Mystery?
Thank you for having me. And maybe next time we can talk about axion laundry detergent and other weird axion paraphernalia that I know about.
Short Wave
Could This Particle 'Clean Up' A Cosmic Mystery?
When we look at how stars move in galaxies, they move as if there is a lot of matter there that we can't see.
Short Wave
Could This Particle 'Clean Up' A Cosmic Mystery?
And she says that this missing matter... It's actually most of the matter in the universe. And it is not visible. And when we say it's not visible, we mean it doesn't interact with light in any way that we've so far detected.