) - 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 Astronomy Department.
Anna came to us from,
well she did her undergraduate work at Wesleyan,
and then via Bloomington, Indiana,
she was telling me she came to Madison,
where she's now been doing some research
on magnetic fields in the universe.
And so I asked her to give a talk here tonight
that will cover some broad territory.
So she's going to tell us tonight about
Fridge Magnets to Galaxies,
Origins of Magnetic Fields in the Universe, Anna.
[applauding]
- 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 Eric Wilcots
and Ellen Zweibel, they're my two advisors,
both at Madison, and then 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
towards the end, I'm doing with Ann Mao,
who used to be a post-doc here,
but is now in Germany, and then also George Heald,
who is in Perth, Australia.
So, I feel very fortunate
to have been able to gain such a large connection
with such a wide variety of people.
But, without further ado,
I'd like to tell you a little bit about
magnetic fields in the universe.
I'd like to start out with just introducing
what magnetic fields are, get you familiar with this idea,
using our 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,
we're gonna move out into extragalactic space
and talk about how astronomers measure magnetic fields,
why astronomers are interested in magnetic fields,
and then how do we know what these magnetic fields are like
besides those that keep our mail stuck to our refrigerators.
And then, towards the end,
I'll talk about our current search
for understanding the origin
of magnetic fields in the universe.
So, we're not sure how magnetic fields originated,
but we're doing a lot of work
to try to understand that question.
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.
If you think about navigation,
compasses are really useful.
They use the Earth's magnetic field.
They also have a little magnet within them
that aligns with the Earth's magnetic field.
I mentioned before refrigerators.
A lot of people have magnets on their refrigerators.
I've been posting a lot of save-the-dates lately.
So you can tell what stage of my life I'm in right now.
But I also use it for grocery lists and whatnot.
And then there's also a lot of really fun toys out there
that involve magnets, so, the Wooly Willy,
where you can move little iron filings around
and draw mustaches or different hairstyles
on the character in the background.
And then, also, these magnets,
these small magnets became popular a couple years ago.
I have some on my desk that help when I'm thinking.
I like to play around with those.
So we're familiar with these magnets.
These are all examples of permanent magnets.
So, in this case, it's due to the material of these objects
that creates this magnetic field.
But what is a magnetic field?
So, it is this invisible force field that exists around,
in this case, a permanent magnet.
So, right now, this is a dipole magnet
with a north and a south pole that you can see here.
And the iron filings, these little gray specks around here,
form 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 to follow these field lines.
So, I mentioned before that we have permanent magnets.
Those are what we are used to seeing in our daily lives.
And this has to do with the atomic structure
and the crystalline structure of the object
or the material in the magnet.
But you can also have, also form magnetic fields
in another way using electromagnets.
So, here, if we have a current,
if we just consider this blue line here is a wire
with a current going up,
it will generate a magnetic field
that curls around the wire,
which is shown with these red lines 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
that has a current going through it.
And in that case, we can also have magnetic fields
that are generated
around those current loops.
So, magnetic fields and electricity
are very closely intertwined, 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, the thing that I want you to take away
from this interaction here is in this 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.
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 this is an example of just how
all of these moving objects
can create different sorts of forces
and different sorts of movements
than you would usually anticipate
with our usual interactions with objects and just gravity.
So, magnetic fields,
both electromagnets and permanent magnets
are everywhere in our lives as well.
So bullet trains are generated off of these magnetic forces,
electromagnetic forces.
Your earbuds or headphones work as well.
There's a--
When your 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,
rely on these sorts of forces.
Also, if you have certain types of flashlights,
have little dynamos, magnetic dynamos in them,
so when you crank the wheel,
you end up creating a current
that then can light your flashlight.
And, similarly, there's talk of windmills as well.
The motion of the wind going through the turbine,
causing the turbine to move, can 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?
So, it turns out, if you look at the Milky Way,
which we have an image here
that was done with the Wisconsin H-Alpha Mapper.
So this is a telescope
that 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 where there is a lot of hydrogen
that has been ionized.
So the electron has been removed from the proton nucleus,
and then, because of very energetic processes,
so there's a lot of very high energy photons cruising around
causing that ionization process,
and then when that electron recombines,
or when it 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.
And, as you go above,
you're looking out of what we call
the mid-plane of the disk.
So you're looking more,
you're not probing as much material
because there isn't as much material
outside of the disk of the Milky Way.
But the interesting thing about this image
and the ionized gas
is that 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,
this M with this little circle and a dot in it,
represents the mass of the sun.
So when we talk about 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,
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 gas
for this presentation tonight.
And then, if you look at the amount of gas,
so of this 10%, about a quarter of that is ionized.
So 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 the volume of the galaxy.
So, if we have ionized gas,
which is something that can generate a current,
which is then something that can generate a magnetic field,
there is a lot of potential
for the presence of magnetic fields
in galaxies here.
Additionally, if we look at the stars,
they're very, very hot, very, very dense material,
and most of the gas that is in a star is ionized as well.
So, 99.9% of the material in a star is ionized.
So this is also another location where you can have
the potential of a lot of currents moving
because you've got a lot of charged particles moving
and thus generating magnetic fields.
So, there's a lot of potential interactions
between the material in galaxies and stars
and magnetic fields.
So that's one of the reasons why 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 is a picture of the system M81 and M82.
So these two galaxies here.
And if we were to zoom in
onto one of these spiral arms 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 region, you'll have a gas cloud,
a star-forming gas cloud that collapses
and then forms a star.
And then, during this process,
your cloud will become ionized as the star ignites
and emits a lot of very high energy hot photons.
So that's gonna create more ionized gas,
and then during the star's formation
or during the star's lifetime,
you're also going to have 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 and current motion
being converted into magnetic energy and magnetic forces,
we call those dynamos.
So, within these star-forming regions,
we can have dynamos generated within the gas
that the stars form within the stars themselves.
And then, when the stars reach the end of their lifetimes,
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 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 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 trying to understand how black holes spin
and whether or not there's magnetic fields
that are around those structures
can affect our understanding
or our ability to estimate the masses of black holes.
So, there's a lot of motion and dynamics
that occur within galaxies due to star formation
that can cause magnetic fields to be generated,
cause magnetic fields to be strengthened,
and also cause them to have interesting shapes and features.
And then, if we move outside of the galaxy,
so this is 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, in the red, is tracing,
again, that H-alpha emission,
or that same emission that was traced by the WHAM survey
that I showed initially of the Milky Way.
So here we can see that there's hot ionized gas
that's being driven out of the galaxy.
And so here we can see that there's a potential
that galaxies can put magnetic fields
out into the medium between galaxies.
And we call that the intergalactic medium.
So, there's another location in the universe
that we can try to look for magnetic fields
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, 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 line,
or do we need to try to get rid of
some of those magnetic field features
in order for that 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.
Just pause at this picture because I love this picture.
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 one of the examples is here,
where you see these starburst-type features,
that's due to photons being reflected off of 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 we still don't understand.
And so it's pretty amazing that, you know,
we can try to untangle some of these mysteries.
So, how do astronomers go about
studying magnetic fields then?
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 you're interested in.
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 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, 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 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 radio telescopes.
That's what I use primarily.
So this is an image of the
Very Large Array down near Socorro, New Mexico.
And this is a radio observatory.
If you saw the movie,Contact, it's referenced in that.
So it's the big radio dish
that Jodie Foster has her headphones plugged into.
I've never done that.
I don't believe that they have any sort of feature available
for you to do that with the radio telescope down there.
But then other ways that we can probe magnetic fields
will be using infrared emission,
which we can do with optical or infrared telescopes.
We have a near-infrared receiver,
or CCD, on this WIYN Telescope,
which is something that the University of Wisconsin
has a big share in,
and so a lot of observations in our department
come from there.
And then, also, space telescopes like HST can also help us
because the Earth's atmosphere can be troublesome
when we're trying to take observations.
So if we send space telescopes
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 indirect tools.
We have to observe how the magnetic fields
affect light and the matter that they're surrounded by.
So one of the main 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,
it will gyrate around that magnetic field.
So, here I'll start using B to represent magnetic field.
So here we've got 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, this diffuse bluish light back in the background
of the Crab Nebula Supernova remnant here
is the synchrotron emissions.
So you can see that there's a lot of emission
going on throughout this entire region.
So there must be quite a few magnetic fields
throughout this supernova explosion.
So this is 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,
we can also see synchrotron emission.
So this is a radio image taken with the Very Large Array.
And what you can see here is a quasar.
So this is, 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 supermassive black hole,
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
all the way out to these very distant regions.
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.
Very high energy electrons gyrating
around those magnetic fields
and creating that synchrotron emission.
So we can observe magnetic fields and synchrotron emission
on very small scales within our own galaxy,
but then, also, into the intergalactic medium,
out to these far reaches away from 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,
represented here, that's emitting light,
so here we can see different orientations of photons.
So they have, their vectors
are pointing in different directions.
When they encounter some dust grains here,
represented in yellow,
that are aligned with the magnetic field,
so dust grains will have their own dipole moment.
They're not necessarily perfectly symmetrical
or 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 rescattered off of that dust,
it will become polarized.
So this is one way that we can look for magnetic fields
in the interstellar medium.
So down here, I'm just showing an example,
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,
these vectors can point
in all sorts of different directions,
but if it's polarized,
because they're all scattered off of these grains
that are pointing in certain directions, a line direction,
then your incoming photons
will have a certain alignment with their vectors,
and that's when something is polarized.
As an example locally of light becoming polarized,
if you have light that's reflected off of something,
like water, 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, on the left here, it's an unfiltered image.
So there is no 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 back here.
So this is probably going to collapse and form stars
in the near future.
So, if we look at this region
in the infrared and in polarization,
or with a polarized filter, excuse me,
you can see that we can detect the alignment
of the magnetic fields in this region.
So we can see in star-forming regions,
as the gas is collapsing,
that magnetic fields are probably helping,
may be helping to add some pressure support
against the collapse of gravity.
So it might help keep the gas pushed up against gravity.
Otherwise, another thing that we can infer from this image
is 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
the magnetic fields in this region.
So that's dust polarization.
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 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
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 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, this dark region is where
there are strong magnetic fields 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, if we had white light and we put it through a prism,
we would get all of the colors of the rainbow.
That's why we see rainbows.
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,
each 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
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
of the element producing this 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,
we can get information about the magnetic field.
So we can do this across the entire surface of the sun
using the Helioseismic and Magnetic Imager.
And so, here, on the left, I took these images today.
So these are up-to-date images of the surface of the sun.
There's not too much activity going on, but this,
where you see dark regions versus light regions,
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 the strength of the magnetic field
across the surface of the sun.
And the last tool that we have in our toolbox
for observing magnetic fields in the universe
is called Faraday Rotation.
So, again, if we take this idea of a spectrum
that we talked about previously,
so if we can split the light into different wavelengths,
and then if we also think about the idea of polarized light,
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 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 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
the magnetic fields along the line of sight.
And that's called the Faraday Rotation Effect.
And so this map down here is actually a map
of the Milky Way in Faraday rotation.
So, where you see blue,
you're seeing a negative Faraday rotation measure,
versus red,
you're seeing a positive Faraday Rotation measure.
And what that means is 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 to get the exact strength.
So, 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.
Polarized dust emission, we do in the infrared
and submillimeter wavelength regime, Zeeman effect,
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 magnetic fields
and the universe around us?
Well, let's start on the Earth.
If we look at the Earth's magnetic field,
it has a strength of about 0.5 gauss, so about half a gauss.
The gauss, a gauss stands for,
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 inside the Earth
to generate these magnetic fields
is that there's a hot molten iron core.
And so as this metallic material moves around
in the center of the Earth, it's generating currents
that then generate a magnetic field.
So it's more like this current example
of the magnetic field generation.
And the Earth's magnetic fields are super important for us.
They make beautiful aurora borealis
when the sun sends us a bunch of cosmic rays
during its solar cycle.
But it's thought that without the Earth's magnetic field,
early life would not have been able to evolve
into the current state that it is
because all of those really energetic electrons and protons
and particles would have messed up the early forms of DNA.
So, because we have the Earth's magnetic field
that redirects those charged particles from outer space,
life was able to evolve on the Earth.
And, as I mentioned earlier on, 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, 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.
It also looks like a dipole, very similar to the Earth.
But it does this interesting thing
where it flips every 11 years.
So down here, this is showing the occurrence of sunspots
and the directions,
I guess it's showing the occurrence of sunspots
but also the strength of the magnetic field
and the direction.
So where it's 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.
And you can see that after 11 years
where you've 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 11 years,
it does this thing where it flips its orientation.
Again, within the sun, we think that there's a similar
sort of a dynamo process that is going on in the Earth.
It doesn't have an iron core, a molten iron core,
instead this is mostly hydrogen within the core of the sun.
That would be the main source of your electrons and protons
that are generating your currents.
But this is another example of how we can use our tools
to observe magnetic fields
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,
so this is a neutron star that is leftover
after a supernova explosion that occurred.
And so a neutron star is about the mass of the sun,
but its diameter is about the size of Madison.
So it's very, very massive but in a very, very small region.
So, very, very dense.
Excuse me, I should have said, it's very, very dense.
And it's mostly just made up of neutrons.
So it was so massive
and it didn't have any way of combating gravity
that basically protons and electrons
were forced to occupy the same space
and squish together to form neutrons.
And so all that you've got in this central region here
is a neutron, a neutron star.
And then when that collapse happened,
it pulled in all of its magnetic fields that it had as well.
And so they were all forced
into this teeny, tiny little area.
And so the magnetic field strength grew hugely.
So when we look at neutron stars and pulsars,
these objects have magnetic fields that are on the order
of 10 to the 14 or 10 to the 15 gauss.
So, many, many, many orders of magnitude stronger
than what we have 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 really strong jets of material
that then will pulsate, so we call them pulsars
because if we look at them in the radio,
they'll sort of blink at us,
and that's because these jets that are generated
by these magnetic fields coming out of the neutron star
are pointing at us and it's spinning rapidly.
And so whenever that jet looks at us,
that's when we see, we get a little blip.
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
the neutron stars and pulsars
and look at the entire scales of a galaxy,
we can see very large magnetic field features.
So, up here on the right is a spiral galaxy.
It's called NGC6946, and in the grayscale,
what you can see is the star-forming region.
So this is tracing the H-alpha emission.
So this is the same as that map that we had of the Milky Way
to start the presentation.
So it's tracing the star-forming regions.
And what we can see when we look at spiral galaxies,
and this is a common feature
when we look at spiral galaxies,
is that they have magnetic fields
that seem to be all aligned, but they don't 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
that's where the stars are emitting most of the light.
So we see these strong, large magnetic field features
in-between the star-forming arms.
And one of the reasons why that might be happening
is because where we have star formation,
we have a lot of motion going on.
So large-scale structures can't survive
when you've got all this gas moving around,
and if you've got magnetic fields that are being
thrown around as the gas is moving around,
you can't maintain large structures.
But when you get into these quieter regions here,
it's possible that these larger features can form.
And if we look at these galaxies edge-on instead,
this is a galaxy that we can see face-on.
Here is a galaxy that we see edge-on.
Here the 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.
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
as the galaxy is rotating around.
Another way is that if you have those outflows,
like we saw in the M82 image,
they could also be pulling the magnetic fields
out of the galaxies
and causing large-scale structures as well.
And so we see these
what we call large-scale structures in 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 microgauss.
So that's about one to the minus six gauss.
So, compared to those neutron stars,
we're 20 orders of magnitude away from the strengths
that we get in those neutron stars.
And then, 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.
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, 10s of microgauss, instead of a single microgauss.
So it's still very, very weak compared to the neutron stars
and our Earth's own magnetic field.
And then these features are,
this turbulent feature is coherent,
or they seem to be aligned on the order of
hundreds of parsecs or hundreds of light years.
So just for some context,
I threw a lot of numbers out at you there,
but when we're talking about length scales,
the Milky Way galaxy,
this is an artist's rendition,
this isn't an actual image
because we can't get out of our Milky Way.
That would take too long.
So the Milky Way is about
100,000 light years across in diameter.
And this is about 30,000 parsecs.
We are eight light minutes from the sun.
That kind of gives you the scale
because light travels at a finite 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 took to get to this side of the galaxy,
it would take 100,000 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 coherent on these sorts of scales.
And then, going back to the strengths of magnetic fields,
your refrigerator magnets are about 50 gauss.
So, you know, that's about 100 times stronger
than the Earth's magnetic field.
So that's why if you put your magnet on your fridge,
it stays there.
It doesn't align with the magnetic field of the Earth.
And also MRIs.
So if you've ever had to have an MRI, I hope you haven't,
they're very loud machines.
They have magnetic fields
on the order of 1,000 to 100,000 gauss.
So we're not quite getting up to
the strength of neutron stars inside these machines,
but they're much stronger than what the sun has
and what the Earth has and what is in 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 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 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
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.
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 light up the universe again.
And then, you know, we get stars
and planets forming later on.
And we're somewhere along here.
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 measuring those magnetic fields,
and we don't know 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, and so I mentioned,
we have to be creative with our experiments
since we can't manipulate anything.
So, one thing that I'm doing
is looking at a control sample of objects
and then a target sample of objects.
So my control sample, I'm trying to just observe
what the magnetic fields are like in a quasar.
So it's like that one little dot
that had those big jets coming out of it,
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 these sorts of objects
and compare it to the rotation measure of,
these sorts of sight lines, excuse me.
If we see a difference,
then that difference we might be able,
and we hope that we can contribute
or attribute that to the presence of magnetic fields
existing in these intervening galaxies.
So the cool thing about astronomy
is that the further away that we look at 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 that's 100 million light years away,
that means we're looking at it when it was
100 million years younger than it would be today.
So what we try to do is, I mentioned,
yes, this is the Faraday Rotation Effect
that we hoped that we would detect within these objects.
So what we want to do is look at objects
at different times along the cosmic IBEX
to see how magnetic fields change.
So, how do we pick these sorts of objects here?
How do we know if there's a galaxy along our sight line?
One way that we try to find these
is using magnesium II 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 II absorptions,
so if there's an object here, like a galaxy
or a gas cloud around a galaxy or an outflow from a galaxy
or a dwarf galaxy that's orbiting another larger galaxy
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,
previous work has found that
if you look at magnesium II absorbers
between a red shift of 0.39 and 1.52,
which has an average age of about one
or average red shift of about one.
So we're looking at the universe
when it was about 5.9 billion years old
instead of today we're about 13.7 billion years old.
We being the universe.
That we measure magnetic fields
that are about 10s of microgauss.
So this is suggesting that there hasn't 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 that's interesting
because it can help theorists backtrack
what their original magnetic field strengths you would need.
But if we look at another survey
that does a similar sort of a thing
and they measure their magnetic field strengths,
they get something that's
about five times smaller
when they're looking at something at about the same age.
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've been doing
is looking at a much larger sample
within a much smaller red shift range.
What I'm doing is measuring the magnetic field strengths
using the Very Large Array.
This is just an image of a quasar
and then one of the magnesium II absorbers
that I'm looking at.
And so this is an example image of my data.
And so what I can do is,
I can get a lot of interesting morphological structures.
So here we're looking at a jet.
So this is a much smaller, much more compact jet,
but it's 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 in my data.
And so this is just a teaser that there's gonna be
a lot more of this sort of thing to come
within research that's going on in Madison.
But then also there are going to be these fantastic surveys,
the VLA Sky Survey, which is basically like my data
except it's gonna be much deeper
and it's gonna look at much more area on the sky.
So instead of my 38 rotation measures in my target sample
and my hundred or so rotation measures in my control sample,
they're gonna have thousands.
So this is gonna be pretty revolutionary
in the next five or 10 years
when it comes to understanding
the evolution of magnetic fields in galaxies.
And then, also, there's this thing called
the Square Kilometer Array
that is being built in Australia and South Africa,
where they're trying--
The goal is to have a total collecting area
of one square kilometer with all of these dishes.
So this is an artist's depiction of what it could look like
when you've got all these tiny, tiny little dishes
that are all collecting photons at the same place
to help you detect super, super faint objects.
So this is going to be great
for discovering things we've never seen before.
And here we're gonna get hundreds of thousands
of rotation measures.
So this will be very interesting when it comes to
trying to understand the evolution of magnetic fields
throughout the universe.
And I will stop there and take questions.
[applauding]