University Place

Origins of Magnetic Fields in the Universe

[Jim Lattis, Director of UW-Madison Space Place]
Well, good evening, and welcome to UW Space Place.

Tonight is our monthly guest speaker night, and I’m very pleased to introduce Anna Williams of the UW-Madison, ah, Astronomy Department.

Anna came to us, ah, from well, she did her undergraduate work at Wesleyan ah, and then, um, via Bloomington, Indiana, she was telling me she came to Madison, where she’s, ah, now been doing some, ah, research on magnetic fields in the universe. And so, I asked her to give a talk here tonight that, ah, will cover some, ah, broad territory.

So, she’s going to tell us tonight about Fridge Magnets to Galaxies: Origins of Magnetic Fields in the Universe, Anna.

[applause]

[Anna Williams]
Thank you.

I think the mic is on now, all right, great.

Yes, so I’m Anna Williams. I am a graduate student at Madison- right up the road and I do most of my research with, ah, Eric Wilcots and Ellen Zweibel, they’re my two advisors, um, both at Madison, and then, ah, luckily, since I’ve been here, I’ve also been able to form some collaborations internationally.

So, some of the work that I’ll be talking about, ah, towards the end, um, I’m doing with, ah, Ann Mao, who used to be a post-doc here, but is now, ah, in Germany; and then also, um, George Heald, who is in Perth, Australia. So, um, I feel very fortunate to have been able to gain such a large connection, um, with such a wide variety of people. But, without further ado, I’d like to tell you a little bit about, um, magnetic fields in the universe.

Um, I’d like to start out with just introducing what magnetic fields are, um, get you familiar with this idea, using our refrigerator, refrigerator magnets: What are magnetic fields? Where did they come from?

And then, hopefully once you have a good understanding of what the magnetic fields are, ah, we’re gonna move out into extragalactic space and talk about how astronomers measure magnetic fields; why astronomers are interested in magnetic fields; um, and then how do we know what these magnetic fields are like besides those that keep our mail stuck to our refrigerators.

Um, and then, towards the end, um, I’ll talk about, um, our current search for understanding the origin of magnetic fields in the universe. So, we’re not sure how magnetic fields, um, originated, ah, but we’re doing a lot of work to try to understand that question. Um, and then, I’ll point you towards some new surveys that will be happening that hopefully help with this.

But, anyways, let’s talk about what magnetic fields are to begin with. So, most people are familiar with magnetic fields; um, if you think about navigation, compasses are really useful. They use the Earth’s magnetic field. They also have a little magnet within them, um, that aligns with the Earth’s magnetic field.

Um, I mentioned before, ah, refrigerators. A lot of people have magnets on their refrigerators. Um, I’ve been posting a lot of save-the-dates lately. Ah, so, you can tell what stage of my life I’m in right now. Um, but, ah, I also use it for grocery lists and, um, whatnot.

And then there’s also, ah, a lot of really fun toys out there that involve magnets. So, um, the Wooly Willy: where you can move little iron filings around and draw mustaches or different hairstyles on a the character in the background. And then, also, these, ah, magnets; these, ah, small magnets, ah, became popular a couple years ago. Um, I have some on my desk that help when I’m thinking. Um, I like to play around with those. So, um, we’re familiar with these magnets. These are all examples of permanent magnets. So, in this case, um, it’s due to, ah, the material, um, of these objects that, ah, creates this magnetic field.

But what is a magnetic field?

Um, so, it is this invisible force field that exists around, um, in this case, a permanent magnet. So, um, right now, this is a dipole magnet with a north and a south pole that you can see here. And the iron filings um, these little gray specks, um, around here form, ah, a structure that follows the magnetic field lines that are permeating around this magnet. And because this is a force field, the iron filings are forced, um, to follow these field lines.

So, I mentioned before that we have permanent magnets: those are what we use are used to seeing in, ah, our daily lives. And this has to do with the atomic structure and the, um, crystalline structure of the object or the material, um, in the magnet.

Um, but you can also have also form magnetic fields in another way using electromagnets. So, here, if we have a current, if this we just consider this blue line here is a wire with a current going up, um, it will generate a magnetic field that curls around the wire, which is shown with these red lines, um right here.

Likewise, we can form a magnetic field that looks very similar to the dipole magnet that’s shown in this permanent structure here by having a coil of magnets, or, excuse me, a coil of wire, um, that has a current going through it. And in that case, we can also have, um, magnetic fields, ah, that are generated around those, um, current loops.

Ah, so, magnetic fields and electricity are very closely intertwined; um, and it turns out that it just depends on your reference frame, whether or not you’re observing an electric field or a magnetic field.

So, um, the thing that I want you to take away from this, um, interaction here is, um, in this, ah, little video. It’s showing a copper tube, and someone is dropping a permanent magnet, or a dipole magnet, through that cube or through that tube. And you can see that it slowly goes down that tube. Um, it doesn’t fall as quickly as you would expect just due to gravity.

And that’s because as the magnet moves through that copper tube it generates a current, and then, as we talked about in the previous slide, a current then generates a magnetic field, so it’s ending up generating an opposite force that’s sort of slowing down the magnet and competing against gravity as it falls down. And so, um, this is an example of just how all of these moving objects can, um, create different sorts of forces and different sorts of movements, um, than you would usually anticipate with, um, our usual interactions with, um, objects and just gravity.

So, magnetic fields, both, um, electromagnets and permanent magnets are, um, everywhere in, um, our lives as well. So, bullet trains are generated off of these, um, magnetic forces, electromagnetic forces. Um, your earbuds or headphones, um, work as well. Um, there’s a When your, um, headphones are plugged into your device, they send up an electrical current that then goes through a coil and generates that magnetic field. It oscillates a different magnetic field that then interacts with a permanent magnet to create the vibrations that you then hear. So even your daily devices, like your headphones, um, rely on these sorts of forces.

Um, also, if you have, ah, certain types of flashlights, um, have little dynamos, magnetic dynamos in them; so, when you crank the wheel, youre creating um, you end up creating a current that then can light the, um, your flashlight.

And, similarly, ah, there’s talk of windmills as well. Um, the motion of the wind going through the turbine, causing the turbine can turbine to move, can, will, um, move a magnet that then generates a current and creates electricity.

So, these are all very important features of magnets that we experience in our daily lives.

So, why are astronomers interested in magnetic fields?
Um, so, it turns out, if you look at the Milky Way um, which we have an image here that was done with the Wisconsin H-Alpha Mapper so, this is a telescope that, um, has been surveying the entire sky, led by astronomers here in Madison. And what they’re looking at is ionized gas.

So, wherever you see these bright features here, it’s showing, um, where there is a lot of hydrogen that has been ionized. So, the electron has been, um, removed from the, the proton nucleus, um, and then, ah, because of very energetic processes so, there’s a lot of, um, very high energy photons cruising around causing that ionization process and then when that electron recombines, or when it, um, reconnects with that proton, it’ll emit a photon. And so that’s what we’re seeing here.

So, this is tracing a lot of the ionized gas in the Milky Way. You can see that it’s spread out all over. So, this would be the disk of the Milky Way here. Um, and, as you go above, you’re looking out of what we call the mid-plane of the disk. So, you’re looking more, um, you’re not probing as much material because, um, there isn’t as much material outside of the disk of the Milky Way.
Um, but the interesting thing about this image and the ionized gas is that, um, if we look at the total mass of the Milky Way, which is about four times 10 to the 11 solar masses. So, this symbol here, um, this M with this little circle and a dot in it, um, represents the mass of the sun.

So, when we talk about, ah, masses in the universe, we usually reference solar masses because everything is, I mean, as you can see here, this is a very large number; but if we look at the mass of the sun, it’s 10 to the 30 kilograms, which is something you might be a little bit more familiar with.

The total mass of the galaxy is about four times 10 to 11 solar masses, but only about 10% of this gas is, um, or 10% of this mass, excuse me, is gas. So, the rest of it is composed of stars and dark matter. But I’m only really interested in the, the gas for this presentation tonight.

Um, and then, if you look at, um, the amount of gas, so of this 10%, about a quarter of that is ionized. So, um, this is only a small percentage of the mass of the Milky Way that is composed of ionized gas, but it fills up almost 50% of, um, the volume of the galaxy.

So, if we have ionized gas, which is something, um, that can generate a current, which is then something that can generate a magnetic field, um, there is a lot of potential for the presence of magnetic fields in galaxies here.

Additionally, if we look at the stars, um, they’re very, very hot, um, very, very dense material, and most of the gas that is in a star is ionized as well. So, um, 99.9% of the material in a star is ionized. So, this is also another, um, location where you can have the potential of a lot of currents moving because you’ve got a lot of charged particles moving, um, and thus generating magnetic fields. So, there’s a lot of potential, um, interactions between the, um, material in galaxies and stars and magnetic fields. So that’s one of the reasons why, um, astronomers are very interested in what magnetic fields are and how they exist in the universe.

Additionally, there’s a lot of different processes that go on in galaxies. So, here, um, is a picture of the system M81 and M82. So, these two galaxies here. Um, and if we were to zoom in onto one of these spiral arms, um, right here so you can see this is a nice spiral galaxy, it’s got these spiral features in that spiral arm, you’ll have star formation occurring.

So, in this, um, region, you’ll have a gas cloud, a star-forming gas cloud that collapses, um, and then forms a star. And then, um, during this process, your cloud, um, will become ionized as the star ignites and emits, um, a lot of very high energy hot photons. Um, so that’s gonna create, um, more ionized gas, and then during the star’s formation or during the star’s lifetime, you’re also going to have, um, a lot of motion of material within the star, so you’re gonna have different sorts of dynamo processes, is what we call them. So, when we have gas motion, um, and current motion, um, being converted into magnetic energy and magnetic forces, um, we call those dynamos.

So, within these star-forming regions, we can have dynamos generated within the gas that the stars form, um, within the stars themselves. And then, when the stars reach the end of their lifetimes, um, and they if it’s a low-mass star like the sun it’ll end as a planetary nebula where it just blows off its outer shells, and if there’s any sort of magnetic field in those outer layers, they will also be, um, put back into the interstellar medium, back into these gas clouds.

And then, also, if we have a more massive star, so, say, something that’s like 10 times the mass of the sun, when it reaches the end of its lifetime, it will go and erupt in a supernova, and then, depending on its mass, if it’s slightly lower, it could be a neutron star, if it’s slightly more massive, it could turn into a black hole. And then magnetic fields also will play an important role in the life cycles, um, of these final stages as well.

So, I’ll talk about, towards the end, neutron stars or, shortly, what neutron stars look like with their magnetic fields, and also, um, trying to understand how black holes spin, um, how theyre and whether or not there’s magnetic fields that are around those structures can affect, um, our understanding or our ability to estimate the masses of black holes.

So, um, there’s a lot of motion and dynamics that occur within galaxies due to star formation that can, um, cause magnetic fields to be generated, cause magnetic fields to be strengthened, , um, and also cause them, um, to have interesting shapes and features.

And then, if we move outside of the galaxy so, this is, um, a zoomed in image of the galaxy that we saw down here in the lower right if we look at some galaxies, we see these outflowing structures.

So here, um, in the red, is tracing, again, that H-alpha emission, or that, that same emission that was traced by the WHAM survey that I showed initially of the Milky Way.

So, um, here we can see that there’s hot ionized gas that’s being, um, driven out of the galaxy. And so here we can see that there are there’s a potential that, um, galaxies can put magnetic fields out into the medium between galaxies. And we call that the intergalactic medium. So, um, there’s another location in the universe that we can try to look for magnetic fields, um, in the intergalactic medium and in the intracluster medium. So, if we have a bunch of galaxies all together and they’re in a cluster, there’s a possibility of magnetic fields existing between those galaxies.

And then, you know, there’s just a lot of galaxies in the universe. So, if we want to understand how these structures form, how stars form, um, how they go through their life cycles, we can see that, you know, magnetic fields are gonna have the potential to be present in all of these things. And as you can see with this video here, when you drop a magnet through that, you can see that the motion is different than what you would expect. So it doesn’t fall straight down.

Similarly, when gas clouds are collapsing to form stars, how do they change if there’s a presence of the magnetic field? Do they collapse in a straight, easy, easy line, or do we need to try to get rid of some of those magnetic field features in order for that, um, gas to collapse?

So, because there are so many galaxies in the universe and so many processes that can be affected by magnetic fields, it’s really important that we understand where they came from and how they were generated.

Um, just pause at this picture because I love this picture. Um, it’s of the Hubble Ultra Deep Field. And one of my favorite features of it is that there are only three stars that I could see from our own galaxy. Otherwise every other dot that you see in this image is a distant galaxy.

So, um, one of the examples is here, where you see these starburst-type features, that’s due to, um, photons being reflected off of the, the telescope. And that happens when you have something that’s very, very bright. So, we’ve got one star here, one star here, one star there, otherwise, all of these other teeny-tiny little dots are galaxies. So, this is just an example of how vast the universe is and how much material there is out there that, um, we still don’t understand. Ah, and so, ah, it’s pretty amazing that, you know, we can try to untangle some of these, these mysteries.

So, how do astronomers go about studying magnetic fields then?

Um, one of the complications about being an astronomer but still being a scientist is when you try to design an experiment, you can’t go into a lab and poke and prod, or, you know, investigate the material that youre, you’re interested in. Ah, astronomers are left with their observations.

We can’t go out into space very easily. although, we’re getting there. We have a lot of spacecrafts that are going out, um to Pluto. We’ve got a lot of satellites going around the sun that are taking lots of interesting observations for us. But, as it stands right now, we can’t go to other galaxies. We can’t even see our own galaxy from above. So, um, we have to get creative.

Luckily, there is a broad spectrum of electromagnetic radiation, or a broad spectrum of light that we can use. And all of those different wavelengths can give us, um, different information about the objects that we’re looking at.

And so, when we’re looking at magnetic fields, the primary tools that we use are going to be, um, radio telescopes. That’s what I use primarily.
So, this is an image of the Very Large Array down near Socorro, New Mexico. Um, and this is a radio observatory. Ah, if you saw the movie, Contact, ah, it’s referenced in that. So, it’s the big radio dish that, ah, Jodie Foster has her headphones plugged into. Um, I’ve never done that. I don’t believe that they have any sort of feature available for you to do that, ah, with the radio telescope down there.

But then other ways that we can probe magnetic fields will be using, um, infrared emission, which we can do with, um, optical or infrared telescopes. Um, we have a near-infrared, ah, re receiver, or, um, CCD, on this WIYN Telescope, which is something that, ah, the University of Wisconsin has, ah, a big share in, and so a lot of observations in our department come from there.

And then, also, um, space telescopes like HST can also help us, um, because the Earth’s atmosphere can be troublesome when we’re trying to take observations. So, if we send, ah, space telescopes, um, beyond the Earth’s atmosphere, it helps our observations a lot.

But, as I mentioned earlier, magnetic fields are invisible. So, we can’t directly look at magnetic fields. So, we have to use, um, indirect tools. Um, we have to observe how the magnetic fields affect light and the matter that they’re, um, surrounded by.

So, one of the main, um, emission mechanisms that we use to observe magnetic fields is called synchrotron emission. So, if you have a very high energy electron so, if you’ve got a fast-moving electron and it encounters a magnetic field, because the electron has a charge, um, it will gyrate around that magnetic field.

Um, so, here I’ll start using B to represent magnetic field. Um, so here we’ve got, um, the electron gyrating around the magnetic field. And as the electron is accelerated because it’s changing direction, so that’s an acceleration it will emit a photon. And that photon, we can observe in the radio. And so that’s one way we can observe magnetic fields.

We can get these high energy electrons through processes like supernova explosions. So, here, um, this diffuse bluish light back in the background of this the Crab Nebula, um, Supernova remnant here, is the synchrotron emissions. So, you can see that there’s a lot of emission going on throughout this entire region. Um, so there must be quite a few magnetic fields throughout this supernova explosion. Um, so this is a very a much smaller scale. So, this is something that we would observe within our own galaxy.

If we look beyond our own galaxy and we look at a radio quasar, um, we can also see synchrotron emission. So, this is a, um, radio image taken with the Very Large Array. And what you can see here is a quasar. So this is, um where the mouse is currently pointing is basically the center of is basically a galaxy that has a supermassive black hole that is creating a ton of material, and as that material falls into the, ah, supermassive black hole, ah, it heats up and it ends up sending these huge jets outside of the galaxy.

So, here we’re looking at something that is this dot is probably larger than our Milky Way and it is sending out jets, um, all the way out to these very distant regions. Um, and so this is along out here is synchrotron emission. So, out here we can see that there must be some sort of magnetic field present. Um, very high energy electrons, um, gyrating around those magnetic fields and creating that synchrotron emission.

So, we can observe magnetic fields and synchrotron emission on very small scales, um, within our own galaxy, but then, also, into the intergalactic medium, um, out to these far reaches away from, um, galaxies.

So, that’s one of the methods, synchrotron emission.

Another way that we can look at magnetic fields locally is by using polarized dust emission. So, if we have a star, um, represented here, that’s emitting light so here we can see different, um, orientations of photons so they have their, um, vectors are pointing in different directions. When they encounter some dust grains here represented in yellow um, that are aligned with the magnetic field so dust grains will have, um, their own dipole moment; they’re not necessarily perfectly symmetrical or, um, perfectly neutral, so because they have a dipole moment, they will feel that force of the magnetic fields in the interstellar medium, and that will cause them to orient themselves in a certain direction.

And so then, if this light that encounters it, that is unpolarized so, it has a bunch of different directions, or the vectors are pointing in a bunch of different directions as that light interacts with the dust and is re-scattered off of that dust, it will become polarized. So, this is one way, um, that we can look for magnetic fields in the interstellar medium.

So, down here Im just showing an example, um this is to show, excuse me, the electromagnetic wave. So, it has an electric field. And as it propagates through space, if your photons are unpolarized, um, these vectors can point in all sorts of different directions, but if it’s polarized because it is they’re all scattered off of these grains that are pointing in certain directions, a line direction then your incoming photons will have a, a certain alignment with their vectors, um, and that’s when something is polarized.

As an example locally, um, ah, of light becoming polarized, if you have, um, light that’s reflected off of something, like water, um, it will become polarized. So, if you use polarized filter or polarized glasses to look at water, for example, you’ll be able to see into the water because it’s blocking those photons that are polarized that are being reflected off of the water.

So, um, on the left here, is an, ah it’s an unfiltered image. So, there is no, um, polarization that’s being blocked out. But in this case, it is blocking the polarization, so you’re able to see into the water. So that’s just an example locally of what it means to have polarized light.

So, if we look in space, here is a star-forming region. This is a dark cloud called a brick. It’s a dark cloud, and we say this is close to a star-forming region because it’s very dense and it’s blocking the light behind it. So, we can see all of this bright emission, um, back here. So, this is probably, um, going to collapse and form stars in the near future.

So, if we look at this region, um, in the infrared and in polarization and with a polarization a polarized filter, excuse me, um, you can see that we can detect the alignment of the magnetic fields in this region. So, we can see in star-forming regions, um, as the gas is collapsing, that magnetic fields, um, are probably helping, may be helping to add some pressure support against the collapse of gravity. So, it might help keep the gas, um, pushed up against gravity.

Um, otherwise, another thing that, ah, we can infer from this image is, um, that the gas is collapsing and might be collapsing more strongly in a direction perpendicular to the magnetic field. And so, you’re also squeezing, you could be squeezing and compressing, um, the magnetic fields in this region.

So that’s dust polarization.
Um, another way that we can look at magnetic fields is with the Zeeman effect. This is one of the most powerful methods and one of the most powerful tools that we have for measuring magnetic fields because if we can measure the Zeeman effect, we can immediately get its the strength of the magnetic field and the direction of the magnetic field.

The previous two methods, you have to know a lot more about the gas and you have to make assumptions about the dust material, or the material that’s making up the dust, or the composition of the gas, in order to infer very much information about the strength of the magnetic field. The Zeeman effect is great because you can get that, um, strength and direction immediately.

So, what is the Zeeman effect?

So, here, on the left, we’ve got a zoomed in picture of a sunspot. So, um, this dark region is, ah, where there are strong magnetic fields, um, coming out of the sun, and then these lighter regions are where the magnetic field is weaker.

So, if we take a spectrum, there’s a black line that goes down here, which represents the slit of a spectrum. So, what you can imagine here is at every point along this line, your incoming light is being split into its separate wavelength components.

So, um, if we had white light and we put it through a prism, we would get, um, all of the colors of the rainbow. That’s why we see rainbows. The, the water droplets in the air act as prisms. But here, if we put the slit along this line, then we can imagine that if we look horizontally here, along this direction, um, each, ah, point along this direction is like a different color here. So, it’s being split.

So, if we look at this point here, then the spectrum is a line going across here. But if we look in this darker region, um, where the magnetic field is strong, then we see these lines here, and then this top would be like this is all of, this line here is the spectrum that’s being emitted from that region.

So, the main thing that we see here is when we go into this region of the magnetic field, strong magnetic field, we see these additional dark features. We see these three separate lines here where, in this region where we don’t have magnetic fields, we just see, like, one strong line here. And so, the reason for that is the atomic structure, um, of the element producing this, producing this, um, feature is being altered by that presence of the magnetic field.

And so that’s called the Zeeman effect.

And so, we can, if we have a strong magnetic field, we can observe this line splitting, and based on this line splitting, um, we can get information, ah, about the magnetic field.

So, we can do this across the entire surface of the sun using, um, the Helioseismic and Magnetic Imager. Um, and so, here, on the left, I took these images, ah, today. So, these are up-to-date images of the surface of the sun. There’s not too much activity going on, um, but this where you see dark regions versus light regions um, that’s a change in your magnetic field strength. Here are regions where there would be sunspots, and if you look over here, there’s some little sunspots that are visible. Similarly, this sunspot here corresponds to these magnetic field features. So, we’re able to use the Zeeman effect to map out, um, the strength of the magnetic field across the surface of the sun.

And the last, ah, tool that we have in our toolbox for observing magnetic fields in the universe is called Faraday Rotation.

Um, so again, if we take this idea of a spectrum that we talked about previously. So, if were if we can split the light into different wavelengths, and then if we also, ah, think about the idea of polarized light, um, we can combine these two features to get the Faraday Rotation Effect.

If you have a source of polarized light, so that’s what this guy is on the far right, um, here. That’s our source of polarized light. If it emits light that passes through a region that has some magnetized material so it has some density of electrons, so some amount of electrons, some amount of magnetic field, and at some length it will cause the different wavelengths so, again, remember that we can split the light into different wavelengths here it will cause different wavelengths to rotate a different amount.

So, if we imagine each one of those wavelengths initially starts with the same, um, linear polarization here and then it passes through that magnetized material, the red wavelengths, or the lower energy wavelengths, are gonna be rotated more than the blue or higher energy wavelengths. So, if we take a spectrum and we look at the polarization features of the spectrum at different wavelengths, we can determine, um, the magnetic fields along the line of sight. And that’s called the Faraday Rotation Effect.

Um, and so, this map down here, ah, is actually a map of the Milky Way in Faraday rotation. So, where you see blue, you’re seeing, um, a negative Faraday rotation measure, versus red, you’re seeing a positive Faraday Rotation measure. And what that means is, um, the magnetic field is either pointing towards or away from you. So, it does give us some information about the direction, but again we have to know what that electron density is and what that path length is, is to get the exact strength.

So, um, this is just a summary of all those features or all of those tools that we have for observing. Again, synchrotron, we do in the radio. Um, polarized dust emission, we do in the infrared and submillimeter wavelength regime. Zeeman effect, um, we can do in the radio and submillimeter as well. And then Faraday rotation is all done in the radio.

So, using these different methods, what have we learned about, ah, magnetic fields and the universe around us?
Well, let’s start on the Earth. Um, if we look at the Earth’s magnetic field, it has a strength of about 0.5 Gauss, so about half a Gauss. Um, the Gauss, a Gauss stands for, um, it’s just a unit of strength for a magnetic field. It’s a CGS unit. And if we look at the structure of the magnetic field on the Earth, we see that it looks like a dipole. So, it’s like those dipole magnets that we see.

But it’s not a true dipole. What we think is actually going on in the inside the Earth to generate these magnetic fields is that there’s a hot molten iron core. And so, as this, um, metallic material moves around, um, in the center of the Earth, it’s generating currents that then generate a magnetic field. So, it’s more like this current loop example of the magnetic field generation.

And the Earth’s magnetic fields are super important for us. Um, they make beautiful aurora borealis when the sun sends us a bunch a a bunch of cosmic rays during its, ah, solar cycle. Um, but it’s thought that without the Earth’s magnetic field, early life would not have been able to evolve, um, into the current state that it is because we all of those really energetic electrons and protons and, ah, particles would have messed up the early forms of DNA. So, because we have the Earth’s magnetic field, um, that redirects those charged particles from outer space, life was able to, um, to evolve on the Earth. And, as I mentioned earlier on, um, it does play a big role, and helps us with navigation around the Earth as well.

If we take a step further away from the Earth and look at the sun, um, we can measure, or we’ve measured the sun’s magnetic field to be about twice that as the Earth this is on the surface of the sun it’s about one Gauss. Um, it also looks like a dipole, very similar to the Earth. But it does this interesting thing where it flips every 11 years.

Um, so down here, ah, this is showing the occurrence of sunspots, um, and the directions and the I guess its showing the occurrence of sunspots but also the strength of the, um, magnetic field and the direction. So, where its yellow, you have a positive magnetic field so, you can think of it as pointing towards you versus negative it could be pointing away from you.

Um, and you can see that, ah, after eleven years, where youve got this blue area now turns yellow. So, this is, like, down by the south pole of the sun versus the north pole. So, you can see that every eleven years it does this thing where it flips, um, its orientation.

Again, within the Sun, we think that theres, ah, a similar sort of dynamo process that is going on in the Earth. It doesnt have, um, an iron core a molten iron core instead this is mostly hydrogen within, um, the core of the Sun, um, that would be, ah, the main source of your electrons and protons that are generating your currents. But, um, this is another example of how we can use our tools to observe magnetic fields, um, and learn a bit more about the universe.

And if we take a step further away from the Sun and we go back to that crab nebula and we can look at the Crab Pulsar here. Um, so, this is a neutron star, um, that is left over after a supernova explosion that occurred and, so, um, a neutron star is about the mass of the Sun, but its diameter is about the size of Madison.

So, its very, very massive, um, but in a very, very small region, so very, very dense excuse me, I should say its very, very dense um, and its mostly just made up of neutrons. So, it was so massive, and it didnt have any way of combatting gravity that basically protons and electrons were forced to occupy the same space and, um, squished together to form neutrons.

Um, and, so, all that youve got in this, um, this center central region here is a neutron, a neutron star. Um, and then when that collapse happened it pulled in all of its magnetic fields that it had as well. And, so, um, they were all forced into this teeny, tiny little area. And, so, um, the magnetic field strength grew hugely.

So, um, when we look at neutron stars, um, and pulsars, these objects have magnetic fields that are on the order of ten to the fourteen or ten to the fifteen Gauss. Um, so many, many, many orders of magnitude stronger than what we have, um, on Earth or in the Sun. So, these are very, very intense magnetic fields around these regions.

And because they have these magnetic fields they can also form, um, really strong jets of material, um, that then will pulsate, so we call them pulsars because if we look at them in the radio theyll sort of blink at us and thats because these jets, um, that are generated by these magnetic fields coming out of the neutron star, um, are pointing at us and its spinning rapidly. And so, whenever that jet looks at us, we see we get a little blip. Um, and, so, then we also get a lot of synchrotron emission from these sources because of those magnetic fields.

And then if we take even larger step away from, um, the, um, neutron stars and pulsars and look at the entire scales of of a galaxy, we can see very large magnetic field features. So, up here on the right, is a spiral galaxy. Um, its called NGC 6946. Um, and in the greyscale what you can see is the star-forming regions.

So, this is tracing H-Alpha emission. So, this is the same as that map that we had of the Milky Way that we had to start the presentation. So, its tracing the star forming regions. And what we can see when we look at spiral galaxies and this is a common feature, um, when we look at spiral galaxies is that they have magnetic fields that seem to be all aligned but they dont like to be where the star formation is happening.

So, we see them in-between these star-forming or what we also call optical arms because thats where the stars are emitting most of the light. So, we see these strong, large magnetic field features, um, in-between the star-forming arms.

And one of the reasons that might be happening is, because where we have star formation we have a lot of motion going on so large scale structures cant survive when youve got all this gas moving around and if you have magnetic fields that are being thrown around as the gas is moving around you cant maintain large structures. Um, but when you get into these quieter regions here, its possible that these larger, um, features can form.

And if we look at, um, these galaxies edge-on instead, um this is a galaxy that we can see face-on here is a galaxy that we see edge-on. Here the, ah, vectors or these line segments are again showing the orientation and the alignment of the magnetic field.

And so, what we can see is that they sort of form this X shape here. Um, we’re not sure why the magnetic fields are in an X shape. One idea is that you’ve either got some sort of large-scale dynamo process that’s pulling these magnetic fields, um, as the galaxy is rotating around.

Another way is that if you have those outflows, like we saw, um, in the M82 image, ah, they could also be pulling the magnetic fields out of the galaxies and causing large-scale structures as well.

And so, we see these, um, what we call large-scale structures in, um, nearby galaxies, but when we measure the strengths of these magnetic fields we get them we measure them to be on the order of a few micro Gauss. So that’s about one to the minus six Gauss. So, compared to those neutron stars, we’re twenty orders of magnitude away from the strengths that we get in those neutron stars.

Um, and then, ah, as I mentioned before, these large-scale structures are on the order of a few kiloparsec. So, that’s hundreds to thousands of light years that they seem to be aligned, um. But then, in galaxies where we’ve got this gas, we also have another component to the magnetic field that we call the turbulent component.

So, this is a smaller scale magnetic field, and it tends to be stronger. So, tens of micro Gauss, instead of a single micro Gauss. So, it’s still very, very weak compared to the neutron stars and our own, our own our Earth’s own magnetic field. Um, and then these features are, um this turbulent feature is coherent, or they seem to be aligned on on the order of, um, hundreds of parsecs or hundreds of light years.

So, just for some context I threw a lot of numbers out at you there, um but when we’re talking about length scales, um, the Milky Way galaxy this is an artist’s rendition, this isn’t an actual image because, you know, we can’t get out of our Milky Way. That would be take too long so, the Milky Way is about a hundred thousand light years across in diameter. And this is about thirty thousand parsecs. We are eight light minutes from the sun.

That kind of gives you, ah, the scale because light travels at a finite, um, speed that it takes light eight minutes to get from the sun to us. If we were to emit a photon on this side of the galaxy and start a timer and wait to see how long it got um, it took to get to this side of the galaxy, it would take a hundred thousand years, approximately.

So, these magnetic fields that we’re talking about in galaxies are it’s kind of amazing that we can see features that are, ah, coherent on these these sorts of scales.

And then, going back to the strengths of magnetic fields, your refrigerator magnets are about 50 Gauss. Um, so, you know, that’s about a hundred times, or, a hundred times stronger than the Earth’s magnetic field. Um, so that’s why if you put your, um, magnet on your fridge, it stays there; it doesn’t align with the magnetic field, um, of the Earth.

And, also, MRIs. So, if, um, you’ve ever had to have an MRI I hope you haven’t um, they’re very loud machines. Um, they have magnetic fields on the order of a thousand to a hundred thousand Gauss. So, theyre not we’re not quite getting up to the strength of neutron stars inside these machines, um, but they’re much stronger than what the the Sun has and, um, what the Earth has and what is in the the gas, the interstellar medium surrounding us.

So, yeah. All right, so we’ve measured all of these things about magnetic fields, but there’s still a lot of information that we still we still don’t know about them.

So, we still don’t know their origin: how did they begin in the universe? We don’t know how they’ve gotten to those scales. So, those large-scale features is still a mystery.

The dynamics: What do they do when stars are forming? How do they affect how stars form?

And then beyond galaxies: We have can see hints that magnetic fields could be removed from galaxies, but how? And what happens when they leave those galaxies?

So, one of the things that I’m working on is trying to help build a timeline of cosmic magnetism. So, we have this beautiful picture, um, that describes how the universe has evolved over time, where we start with the Big Bang. We’ve got some inflation where the universe all the sudden grows a ton. So, it increases in size very, very rapidly. Um, and then we’ve got this dark ages where stars haven’t started to form, and then once your stars and galaxies start forming, you you, um, light up the universe again. Um, and then, you know, we get stars and planets forming later on. And we’re somewhere along here, um.

But if we try to put magnetic fields on this, we are really good at stuff really close by. But then as we go back in time, as we look at more distant objects, we have a hard time, um, measuring those magnetic fields, and we don’t know, um, how they’ve gotten to be the strengths that they are today.

So, there are some theories that have predictions for primordial magnetic fields, but we need to know what goes on in here because we can observe that in order to backtrack and try to understand what’s going on.

So, one way we can do that is by using this rotation measure effect that I mentioned before. Um, and so I mentioned, we have to be creative with our experiments since we cant manipulate anything. So, one thing that Im doing, ah, is looking at a control sample of objects and then a target sample of objects.
So, my control sample: Im trying to just observe what the magnetic fields are like in a quasar so, its like that that one little dot that had those big jets coming out of it, um, that radio image that I showed earlier. So, looking at how much Faraday rotation goes on in this sort of a source and then comparing a big sample of those objects to a sample that has an intervening galaxy.

So, the idea would be that if we can measure the rotation measure of, um, these sorts of objects and compare it to the rotation measure of these sorts of sight lines, excuse me, um, if we see a difference then that difference we might be able and we hope can contribute attribute that to the presence of these magnetic fields existing in these intervening galaxies.

So, the cool thing about astronomy is that the further away that we look on an object, the younger it is in cosmic time. So, because it takes time for light to get to us, if we look at something thats a hundred million light years away that means were looking at it when it was a hundred million years younger than it is today than it would be today.

Um, so, what we try to do is oh, did I mention, yes, this is the Faraday Rotation Effect that we hope we would detect within these objects. So, what we want to do is look at objects at different times along, um, the cosmic IBEX to see how magnetic fields change.

So, how do we pick these sorts of objects here? How do we know if theres a galaxy along our sight line?

One way that we try to find these is using Magnesium Two absorption. If we have a quasar here, and we take a spectrum and then we see these sorts of features in the spectrum that are called Magnesium Two Absorptions. So, if theres an object here, like a galaxy or a gas cloud around a galaxy, or an outflow from a galaxy, or a dwarf galaxy thats orbiting another larger galaxy, um, that has magnesium in it, it can create this absorption line feature. And, so, this is how we select our objects for our target sample.

And, when you do this sort of a thing, um, previous work has found that if you look at Magnesium Two absorbers between a red shift of point three nine and one point five two, which, um, has an average age of about one or or an average red shift of about one so, were looking at the universe when it was about five point nine billions years old instead of today where were about thirteen point seven billion years old um, we being the universe that we measure magnetic fields that are about tens of micro Gauss.

So, this is suggesting that, you know, there hasnt been too much like, the magnetic fields that we observe today are probably pretty similar to what was going on about halfway through the lifetime of the universe. So, thats interesting, um, cause it can help theorists, um, backtrack what their original magnetic field strengths you would need.

But if we look at another survey, um, that does a similar sort of a thing, um, and they measure their magnetic field strengths, they get something that is about five times smaller. Um, when they are looking at, um, something about the same age. Ah, so, we have some conflicting data right now about what sorts of strengths of magnetic fields we would expect at about half the age of the universe.

And, so, what I am doing is looking in at a much larger sample within a much smaller red shift range. What I am doing is measuring the magnetic field strengths, um, using, um, the Very Large Array um, this is just an image of a quasar and then one of the magnesium tubes absorbers that I am looking at.

And, so, this is an example image of my data. And, so, what I can do, I can get a lot of interesting morphological structure. Here, were looking at a jet. So, this is a much more much smaller, much more compact jet but its a quasar. And I can measure the rotation measure across this source and the magnetic field across this source.

So, this is all very preliminary. I have a lot more objects to look at. These are some of the more interesting objects that have popped up, um, in my data. And, so, this is just teaser, but theres going to be a lot more of this thing to come within the, um, research that is going on in Madison.

But, then also there are going to be these fantastic surveys, um, the VLA Sky Survey, which is basically like my data except, um, that its gonna be much deeper and gonna look at much more area in the sky. So, instead of my thirty-eight rotation measures in my target samples and my hundred or so rotation measures in my control sample, theyre going to have thousands. So, this going to be pretty revolutionary in the next five or ten years when it comes to understanding the evolution of magnetic fields in galaxies.

And then also, um, theres this thing thats called the Square Kilometer Array that, um, is being built in Australia and South Africa, where theyre trying where the goal is to have a total collecting area of one square kilometer with all of these dishes. So, this is a, um, an artists depiction of what it could look like, um, when youve got all these tiny, tiny little dishes, um, that are all collecting photons at the same place to help you, um, detect super, super faint objects.

So, this is going to be great for discovering things we weve never seen before. And here were going to get hundreds of thousands of rotation measures. So, this will be very interesting, um, when it comes to, ah, trying to understand the the evolution of magnetic fields throughout the universe.

And I will stop there and take questions.
[Applause]