Do black holes have magnetic fields?

Daniel and Jorge try to resist the magnetic attraction of the mysteries of black holes, and fail.

See omnystudio.com/listener for privacy information.

Episode Transcript

Speaker 1 (00:07):
Hey, Danie, what do you think makes black holes so interesting?

Speaker 2 (00:11):
You know, I think the mystery, the finality of it,
the weirdness of it.

Speaker 1 (00:16):
For sure, they're like a magnet for fascination.

Speaker 2 (00:21):
They absolutely are for curiosity, for investigation, for dedication.

Speaker 1 (00:27):
And it's not just physicists. Everyone seems to have questions
about black holes.

Speaker 2 (00:31):
Yeah, they seem to be sort of mentally magnetic.

Speaker 1 (00:36):
So black holes attract matter and also questions.

Speaker 2 (00:41):
They definitely attract questions. They seem to repel understanding.

Speaker 1 (00:45):
Or they just repel physicists.

Speaker 2 (00:48):
I'm pretty sure they'd be happy to suck me right in.

Speaker 1 (00:51):
I don't think I want to go down that rabbit hole.
Hi am Hora May Cartoons, an author of Oliver's Great

(01:12):
Big Universe.

Speaker 2 (01:13):
Hi, I'm Daniel. I'm a particle physicist and a professor
at UC Irvine, and I desperately want to know what's
inside those black.

Speaker 1 (01:21):
Holes, if there is even an inside. Right do we
know that they have an inside?

Speaker 2 (01:26):
We don't really know anything beyond the event horizon at all.
In some sense, the interior of a black hole could
be like another universe.

Speaker 1 (01:35):
Whoa like We could be living inside of a black
hole right now, is that possible.

Speaker 2 (01:42):
I think that gives me a mental black hole even
thinking about it.

Speaker 1 (01:47):
I suckered you write in. But anyways, welcome to our
podcast Daniel and Jorge Explain the Universe, a production of iHeartRadio.

Speaker 2 (01:53):
In which we try our best not to give you
a headache while we contemplate the deepest secrets of the universe.
Want to understand everything that's out there, from the tiniest
little bits to the hugest swirling black holes and everything
in between, because we think that it's possible somehow to
make sense of it all, to understand it, to predict it,
and to explain all of it to you.

Speaker 1 (02:15):
Yeah, that's right. We try to be the advil or
tile and all to your understanding of the universe, not
give you a headache about how amazing things are, but
rather try to ease the pain of trying to wrap
your mind around this amazing costmoves we live in. I
think it was as your prescription for physics.

Speaker 2 (02:34):
Well, everybody out there is going to need like another
kind of health insurance now physics health insurance.

Speaker 1 (02:40):
The physicists have special health insurance for you know, headaches
and mind bending.

Speaker 2 (02:46):
We're going to help you cover the cost of understanding
the universe, because while physics has made lots of progress
in understanding the way the universe works, there are still
huge gaps in our knowledge. In fact, we're pretty sure
there's more that we own understand than that we do,
and a lot of those mysteries might have answers waiting
for us beyond the curtain of the event horizon.

Speaker 1 (03:08):
Yeah, as we've talked about, we only know about five
percent of the whole universe. The rest, the other ninety
five percent is a complete mystery. And even within the
five percent there we think we know, there are still
huge holes in our understanding of how things work and
what can happen out there in the universe.

Speaker 2 (03:25):
The best way to unravel some of the open mysteries
is to embrace the unknown, is to dive into our
ignorance and try to reveal something new about the universe.
Often this happens at the extreme points of the universe,
places where things are super duper hot, are super duper dense,
or super duper crazy, because it's that those places that

(03:45):
our understanding breaks down. That's one reason why black holes
are so attractive to physicists, because they are where our
current theories have to break.

Speaker 1 (03:55):
Yeah, it seems like there's no place in the universe
that is more extreme or mysterious and a black hole.
We have so many questions about that. Everyone has questions
about it. It seems that it attracts not just mass
and energy, but also curiosity.

Speaker 2 (04:08):
It does absolutely. I don't know if it sucks in curiosity,
or it's radiating curiosity, or how the whole curiosity field works.

Speaker 1 (04:15):
Talking talking radiation of curiosity exactly.

Speaker 2 (04:19):
Maybe it's consuming anti curiosity while radiating curiosity.

Speaker 1 (04:23):
He knows anti curiosity. Oh, that's an interesting concept, But
what is that?

Speaker 2 (04:28):
I don't know. That's what we're trying to generate on
this podcast. We're trying to satisfy everybody's curiosity or are
we just trying to stoke it. I'm not even sure anymore.

Speaker 1 (04:36):
It sounds like you're trying to annihilate people curiosity.

Speaker 2 (04:41):
No, I guess we're trying to generate anti confusion particles.
How about that?

Speaker 1 (04:44):
Oh, there you go, rock Ons, get it. Tino's exactly
the AHA particles. That's what we're after.

Speaker 2 (04:54):
Yeah, I want to be one with the AHA field.
But there are still very basic questions about how black
holes work, what it means to be near a black hole,
what you would experience, what you might measure with your
devices near a black hole. We've talked about the massive
black holes, we talked about the charge of black holes,
we talked about the spin of black holes. But there
are still even more basic things we can think about

(05:15):
when it comes to black holes.

Speaker 1 (05:17):
So today on the podcast, we'll be tackling the question
do black holes have magnetic fields?

Speaker 2 (05:28):
Like?

Speaker 1 (05:29):
Are they attractive or repulsive? Do they have raised or not?

Speaker 2 (05:34):
Can you use black holes to find lost wedding rings
on the beach? I knew there was a practical application
of my research somewhere.

Speaker 1 (05:41):
Could you use it to detect your wedding ring on
the beach when in it just swallow up the whole beach?

Speaker 2 (05:47):
Then you'd have a good excuse for why you lost
your wedding ring. Look, there was a black hole on
the beach.

Speaker 1 (05:53):
Yeah, and you would technically know where it is. It's
inside the black hole. You just you know you can't
get it.

Speaker 2 (05:59):
Ever, Yeah, exactly. No number of explainingons is going to
get you out of that jam.

Speaker 1 (06:04):
Yeah, But yeah, it's an interesting question. Do black holes
have magnetic field? And I know, we've did a whole
episode on whether black holes have a charge, right, Yeah,
and so this is different. This is more about the
magnetic field.

Speaker 2 (06:17):
Yeah, we did one on charge, we did another one
on spin. There's not that much stuff you can actually
know about black holes, and we know so little, so
I'm always excited to talk more about it.

Speaker 1 (06:27):
Then we do a whole episode on the hairiness of
a black hole.

Speaker 2 (06:31):
That's true, their lack of hairiness actually their smooth shavenness.

Speaker 1 (06:36):
Yeah. Well, this is an interesting question, and so as usual,
we were wondering how many people out there had thought
about whether black holes have magnetic fields, and if they do,
what do they look like or feel like.

Speaker 3 (06:49):
I think it's possible that they do, I think if
I'm not too sure exactly after rationalets, but somehow I
feel like it might be possible for black holes to
have mynetic fields.

Speaker 4 (07:00):
I think they do, if only from the spiraling matter
that's been consumed by the black hole. Whether or not
they are magnetic in their core, whatever their core is,
if you can have a call in a black hole,
I don't know, but by virtue of the whole of
the object that's whorly yes.

Speaker 5 (07:17):
I do not believe so only because I do not
believe there are any charged particles within a black hole. However,
since we do see jets coming from black holes at times,
that could be totally wrong about that.

Speaker 1 (07:27):
I don't really know, but if I had to guess,
I think they would like.

Speaker 2 (07:31):
Something to do with the hawking radiation being magnetized somehow, or.

Speaker 6 (07:36):
So the black hole itself beyond the event horizon. I
don't think we can know that, but the area around
the black hole where the Acresian disk is probably can
have a magnetic field.

Speaker 2 (07:47):
Black Holes have mass, and they have spin, and I
believe they have a charge.

Speaker 6 (07:52):
So if something has a charge, it should also have
a magnetic field, probably a little squirrely with the amount.

Speaker 2 (07:59):
Of gravitational force is going on, but going with yes.

Speaker 7 (08:03):
Yes, I'm pretty sure black holes have magnetic fields because
whenever a particle that's charged enters it, the electric charge
is conserved. So I guess a black hole would need
to have that magnetic field that the particle had.

Speaker 1 (08:13):
I have no idea that.

Speaker 7 (08:15):
As a wild guest, I would say, yes, they have
probably vacuumed app some magnetic vibes along the way.

Speaker 2 (08:22):
Black holes do have magnetic fields.

Speaker 3 (08:24):
I'm pretty sure that the Beatles wrote a song about it,
Magnetic fields forever.

Speaker 6 (08:30):
If a black hole is churning around, does it create
a magnetic field? Is there a north pole to a
black hole? I wonder if magnetism can escape gravity or
is immune to it.

Speaker 2 (08:42):
I think magnetize are neutron stars with a magnetic charge.
I'm not sure about a black hole. Maybe if it's
spinning and has an electric charge.

Speaker 5 (08:50):
I think that if a black hole a bunch of
large stuff with a magnetic field, and the black hole
would get a magnetic field.

Speaker 8 (08:58):
I'm gonna say yes because this one out of three
things that that black hole present so that we can measure.
But I forget one of them. So there are spin, there, mass,
and electromagnetic force. So I'm gonna say yes.

Speaker 1 (09:10):
All right. Interesting answers from a lot of magnetic people.

Speaker 2 (09:16):
Yeah, you could tell a lot of people had not
thought about this question at all. They seem to sort
of come up with their answers on the fly.

Speaker 1 (09:22):
Yeah, it's kind of a polarizing question.

Speaker 2 (09:26):
People either retracted or repelled by it.

Speaker 1 (09:30):
Yeah, Well, it seemed to attract definitely a lot of
ideas about what's going on in the black hole, and
so let's dive right into it. Daniel take us through
the basics of black holes and how they relate to electromagnetism.

Speaker 2 (09:42):
So fundamentally, we don't really know what black holes are
in our actual universe, like the physical things that are
at the center of the galaxy, or they have really
dense stuff orbiting them really closely. We're not really sure
what those things are, but we do have a concept
in our theory general relativity dicks a kind of black
hole that we know. Again, general relativity can't be right,

(10:04):
so this theoretical object can't actually align with what's out
there in the universe, but it gives us something to
dig into, something that play with. And because general relativity
tells us that gravity is not a force between objects
the way Newton described it, but instead a curvature of
space time, there's something weird that can happen when you
get enough mass, enough energy density actually together in one place,

(10:27):
which is that space can curve so much that the
inside is essentially cut off from the outside. There's a
place beyond which space is curved so that it only
points towards the center of the black hole, meaning any
object that falls past, that event horizon will always end
up at the center of the black hole. And so
this is the basic concept of a black hole, sort

(10:49):
of extreme space time curvature that generates this event horizon
past which nothing can escape.

Speaker 1 (10:55):
Right, right, because I feel like that's always one of
the carriats we have to point out is that the
bending of space time, right, it's not just sort of space,
it's also sort of like what happens in the future.

Speaker 2 (11:05):
There are definitely time related effects. Also, mass bends space
and creates this event horizon, it also bends time. So
you are near a black hole, for example, a distant observer,
we'll see your clock go more slowly, and near black holes,
space and time are very confusing, and in fact, the
whole concept of space time is easier to understand in
special relativity when you have flat space. In general relativity,

(11:29):
which direction is space and which direction is time becomes
very very confusing, and in some cases it's not even clear.

Speaker 1 (11:35):
And so, as you said, it's something that physics predicts
is happening out there in the universe because we see
around us and it seems like, you know, the Sun
is bending space around it, the Earth is bending space
around and we're bending space around us. But if you
take it to an extreme, it predicts something called a
black hole.

Speaker 2 (11:52):
Yeah, and a lot of people imagine a black hole
in a sort of Newtonian way. They think, oh, gravity
is so strong that you have to go faster than
the speed of light in order to escape it. But
it's not a question of forces, it's not a question
of a velocity. It's not a Newtonian picture at all.
It really tells you that the story of how gravity
works is very, very different. That you're literally trapped inside

(12:15):
this event horizon. No amount of velocity, no force can
ever escape it because the shape of space itself has changed.
And so if you imagine space is this like emptiness
in which things float, then you need a new idea.
General relativity tells us we could describe it as this
sort of stuff with curvature to it, that we're moving
through that curvature, and that curvature is not sitting inside

(12:38):
some like deeper, larger space that you might be tempted
to imagine. That's all there is, and we are trapped
inside of it, and there's nothing on the outside of
it as far as we.

Speaker 1 (12:47):
Know, right, right, and as usual we also have to
give the cavit that black holds are technically theoretical, right, Like,
we've seen things that sort of behave like black hold
but we haven't sort of been in front of one
or touched it, right.

Speaker 2 (13:01):
That's right. And what we're describing is a prediction of
general relativity, which we know to be very accurate in
most circumstances, except we expect it to break down when
things get very very intense and very very small. And so,
for example, general relativity predicts that at the heart of
one of these black holes is a singularity, a point
of infinite density. This runaway gravity just goes on forever

(13:24):
and you get infinite curvature at the heart of the
black hole. But we don't think that that's really happening
because we know that that's in conflict with quantum mechanics.
And so real black holes, if they exist out there
in the universe, can't align perfectly with this theoretical description
of a general relativity black hole. There has to be
some quantum fuzziness to it, some other version of a
black hole. And we talked recently on the podcast how

(13:47):
quantum black holes probably radiate. They're not perfectly black due
to Hawking radiation, and there must be other changes we
need to make from this general relativity picture of a
black hole to a realistic quantum gravity black hole that
we don't even know how to describe. And you're right
that the things we've seen out there in the universe,
at the heart of our galaxy, etc. We're not even

(14:07):
sure if they actually are black holes because we've not
technically observed an event horizon. All we've seen is that
there are very dense objects, very massive, very small, very compact,
and so we suspect that they are black holes, but
they could be something else. These days, there are quantum
gravity inspired ideas for other things that could fit the data.

(14:29):
Fuzzballs or dark stars, etc. Yeah, all kinds of fun names.

Speaker 1 (14:33):
I wonder if we should maybe start calling black holes
and not black holes then maybe.

Speaker 2 (14:38):
Or maybe just black holes with a question mark black
holes really dark objects rdos.

Speaker 1 (14:45):
All right, So then a big concept in a black
hole is this idea of an event horizon. Now is
the idea of an event horizon also dependent on relativity
and quantum mechanics playing nicely with each other, or does
relativity only break down at the center of a black hole? Like,
is the edge of a black holes safe to talk about?

Speaker 2 (15:08):
The edge of a black hole is really only something
we can talk about in general relativity. We don't know
how quantum mechanics will modify that. It might make it
so that there are no event horizons. These buzzballs, for example,
compact states of strings do not have event horizons at all,
So it could be that there are no event horizons
in the universe. So if we want to talk about this,
really the only thing we can do is talk about

(15:29):
what general relativity predicts, even though we're not exactly sure
it's real.

Speaker 1 (15:35):
So then how do you define the event horizon?

Speaker 2 (15:37):
Then? Well, in general relativity, the event horizon is the
point past which no information can escape, and that's something
we can calculate in general relativity and depends on the
mass of the object, also whether it's spinning, whether it
has charged these kinds of things.

Speaker 1 (15:52):
And it's kind of a very special point in a
black hole because that's the point at which not even information.

Speaker 2 (15:58):
Can escape, right, Yeah, that's right.

Speaker 1 (16:00):
So the sort of limits of the things we can
know about the black hole.

Speaker 2 (16:04):
Yeah, you can't know anything that's going on inside the
black hole, but you can measure some things about the
black hole, like we know, for example, obviously you can
measure the black hole's mass. You can measure its gravitational
effects on things nearby. If you fly near a black hole,
you're going to be drawn towards it because space is curved,
So the effect of the black hole exists outside the

(16:25):
event horizon. You can sort of think of it as
the event horizon itself having a property. The event horizon
is there, it summarizes all the stuff that's inside of it.
The mass of the event horizon or the black hole
itself affects space outside the event horizon. So you can
definitely know that about the black hole, and you can
know a couple of other details as well.

Speaker 1 (16:44):
Like the spin and also the charge of a black hole.

Speaker 2 (16:47):
Right, Yeah, that's right. Those are the three things that
general relativity says we can know about the black hole.
That a black hole can also be spinning, right, Things
that fall into a black hole if they have angler
momentum to keep having angular momentum, because in our universe,
angular momentum is conserved. We're pretty sure same thing with
electric charge. The universe strictly preserves electric charge. We've never

(17:10):
seen that violated. You can create plus and minus particles together,
but the overall charge of the universe has to be
the same. And so if you drop an electron into
a black hole, then the black hole has to have
that charge because it can't just disappear from the universe.
So mass, spin, and charge are the things you can
know about a black hole from the outside. You can't

(17:31):
know like the arrangement of charges or masses or spins
or whatever inside the event horizon, but you don't have
to in order to know the total mass or the
total charge or the total spin from the outside.

Speaker 1 (17:42):
Can you tell if that black hole has a headache
or something?

Speaker 2 (17:47):
Do black holes wear mood rings? I wish they did?
Always black?

Speaker 1 (17:50):
Does that mean do they wear engagement rings? Well, you
said charge, and I'm wondering. You know, that's the electromagnetic charge,
but we also talked about it in this podcast. But
other kinds of charge in the universe, from the weak
fours and the strong force. Can you know those other
charges about a black hole? Can you know the color
of a black hole?

Speaker 2 (18:11):
The color charges are really fun and tricky concept. It's
not something we really understand very well because objects that
have color don't ever exist in the universe. We only
see neutral things, like things that have color, like quarks
are always bound together into neutral states, something with the
opposite color or the other two complementary colors, so they
balance out because there's so much energy in the strong force,

(18:33):
so things can't have their own color charge. You might
want to imagine, like what happens if you have a
quark anti quark pair and they're bound together, but one
of them falls into the black hole. And now you're
doing quantum gravity, because we're talking about bound states of quarks,
and one of them falls into the black hole and
the other one doesn't. We don't know the answers to
those questions because we don't have a theory of quantum gravity.

Speaker 1 (18:55):
But is it possible then maybe they also conserve those
kinds of charges, and you would have to add that
to the list of things you can know about a
black hole.

Speaker 2 (19:03):
It is possible, And it's also possible that there are
other kinds of charges in the universe we've never even discovered,
like dark matter could have all sorts of other forces.
There could be like a dark version of electromagnetism with
dark photons and dark charges, and black holes could have
those dark charges as well.

Speaker 1 (19:20):
Wait, were you saying black holes could have a hidden
charge like a hidden fee?

Speaker 2 (19:26):
Exactly? Check your statements, people.

Speaker 1 (19:28):
When you buy a black hole, read the small print
before you go into a black hole. All right, So
then that's you know, we can tell it it has
a gravitational field and an electric field. And now let's
talk about a magnetic field of a black hole. What
exactly is a magnetic field?

Speaker 2 (19:43):
Magnetic fields are really weird and awesome because they have
lots of really interesting symmetries, symmetries that exist and also
symmetries that are broken. Like in a lot of ways,
the magnetic field is a perfect sister to the electric field,
like light, for example, is a between electric fields and
magnetic field. It's slashing perfectly back and forth between electric

(20:05):
fields and magnetic fields and back. It really tells us
that the distinction we make between electric fields and magnetic
fields is a little bit arbitrary. It's just sort of
like a historical thing. We drew a dotted line between
these two things that are really part of a larger hole.
But there also are important differences between electric fields and
magnetic fields. For example, we have electric charges in the universe,

(20:26):
but we don't have magnetic charges. Like an electron has
a negative charge. You can just create a charged object
by putting an electron on it, right, you can't do
that with a magnetic field. There's nothing with a magnetic charge.
If it existed, this would be called a magnetic monopole.
It'd be like something with just a north or something
with just a south. We've never seen one in the universe.

(20:47):
Physicists don't know why. They think maybe they do exist
out there, or used to exist in the early universe.
But you can't make a magnetic field the same way
you make an electric field by just adding a magnetic
charge to something.

Speaker 1 (20:59):
Well, maybe take a step back here, because you know,
like I'm wondering, how do you even define what a
magnetic field is. You know, like a gravitational field tells
me how much a planet, for example, is pulling on
me at any point in space, or an electric field
tells me how much you know, an electron is repelling
or pushing me or attracting me at any point in space.
What does a magnetic field tell you?

Speaker 2 (21:21):
Yeah, great question. If they were magnetic monopoles, then they
would be affected by magnetic fields. The same way that
electrical charges are affected by electric fields. They would be
accelerated in one way or another. But those don't exist,
so we can't use that to define magnetic fields.

Speaker 1 (21:39):
What do you mean, like when you talk about monopole,
you mean like like an a maact that you have
a north in the south.

Speaker 2 (21:44):
Right in the magnets that we have in our universe,
we have a north in the south. Those are dipole
magnets that create a dipole magnetic field. There's a pair
of a North in the south.

Speaker 1 (21:54):
So are you saying, like, if you had a North
in front of me and I'm the south, it would
tell me how much I'm attracted to the north repel?

Speaker 2 (22:01):
Yeah, exactly. If you have a huge magnet makes a
magnetic field, and then if you put a North in
that field, it would get pushed or pulled in one direction,
and by the strength of that push or pull, you
could measure the magnetic field.

Speaker 1 (22:12):
So there is some sort of charge, Yeah, exactly, Like
what would determine how much of that push and pool?
I feel?

Speaker 2 (22:17):
Well, the north and south are like the plus and minus. Right,
North and south for a magnetic field are plus and
minus for electric charges.

Speaker 1 (22:24):
And I can have like more of it or less fit.

Speaker 2 (22:26):
Yeah, exactly, you've got to bigger magnets or smaller magnets.
You've got to more norths and more souths. We've never
seen a north on its own or a south on
its own the way we have for electric charges. But
in principle they could exist. Nothing in physics says that
they can't. But we've only ever seen them paired together.

Speaker 1 (22:44):
I mean, like, if something has a north, it also
has a south.

Speaker 2 (22:47):
Yeah, and that's because those magnetic fields are actually made
by electric charges. See, there's a very close connection between
electricity and magnetism because if you take an electric charge,
like an electron, and you wiz it around them, it
makes a magnetic field. Any charge in motion, any charge
with velocity, is going to make a magnetic field. And

(23:07):
so every magnetic field that we ever created is actually
made by moving electric charges.

Speaker 1 (23:13):
So if it's made by electric charges, it's made by
the electric field. So why do we even call it
its own field.

Speaker 2 (23:18):
Well, because it's made by electric charges doesn't mean it's
an electric field, right, Yeah, we could just call this electromagnetism.
You might be saying, Hey, the distinction between these two things.
Seems arbitrary. Yes, it's totally arbitrary and historical. Because we
discovered magnets and we discovered lightning. We call them two
separate things. We build two theories, and then boom, one
day a brilliant Scottish dude realized they are actually two

(23:39):
parts of the same thing. Now we call them electromagnetism.
And you might say, let's just call it all electromagnetic fields. Cool,
we can do that, but we do notice that there
are two different charges that are described by this field,
electric charges and magnetic charges, and only one seems to
exist in the universe.

Speaker 1 (23:55):
M all right, So it's deeply connected to electricity, and
if some things just seem to have it or not, right,
things would charge seem to have it or not.

Speaker 2 (24:06):
Yeah. So every magnet we've ever seen in the universe
is either a tiny little object that has quantum spin,
like an electron has quantum spin, and that spin combined
with its charge, makes it a tiny little magnet. But
because it's spinning, it makes two magnets. It makes a
north and a south, so it's a little dipole magnet.
Or you can have current like motion of electrons through

(24:27):
a wire that makes a dipole magnet. So every magnetic
field we've ever seen is made either by tiny little
quantum particles having their own little magnetic fields. That's, for example,
why your refrigerator magnet has a magnetic field. Has all
these little particles with quantum spin oriented in the same
way adding up, or like an electromagnet, like an electric
motor that comes because of current from electricity.

Speaker 1 (24:51):
Interesting, and so I guess now the question is, since
black holes can have an electric charge and also spin,
can they also have a magnetic field. So let's dig
into that. But first let's take a quick break. All right,

(25:17):
we're asking the question can a black hole have a
magnetic field? And what would happen if you put it
on your fridge?

Speaker 2 (25:26):
You would eat everything in your fridge.

Speaker 1 (25:29):
There you go. You can blame that also on a
black hole.

Speaker 2 (25:33):
I don't know who finished the pie, honey, really, I don't.
Maybe it was a black hole in the middle of
the night. Check the camera.

Speaker 1 (25:39):
Yeah me, Rich, I'll put a black hole in the
fridge there.

Speaker 2 (25:43):
The new black hole diet by Daniel Yeah.

Speaker 1 (25:46):
I don't think that sounds it's work.

Speaker 2 (25:49):
I might need to work shop that a bit.

Speaker 1 (25:51):
Yeah, yeah, yeah, yeah, it's more like an excuse for
a bad diet. But yeah, so black holes do they have?
Getting feels like literally, if we have a tiny one,
would it stick to your fridge? That's kind of what
we're asking here today, right, right.

Speaker 2 (26:07):
Yeah, it's a really cool question, and the answer is
it depends why am I not surprised? It depends on
your reference frame, It depends on your velocity. Because we
don't have magnetic monopoles. You can't just like throw a
monopole into a black hole and have it have a
magnetic field, like inherently. The only way for it to

(26:31):
have a magnetic field is for it to do what
electrons do and electric currents do, which is have a
charge and a spin. So take a black hole, spin
it and charge it by shooting like a beam of
electrons right near the event horizon, so it gets some
angular momentum and it gets some charge. In that case,
it will get a magnetic field because now it's spinning

(26:51):
relative to you. So if you have like a magnetometer
or something, you will measure a magnetic field near the event.

Speaker 1 (26:58):
Horizon, sort of in the same way that like an
electron on its own can have an electric field because
it's a charge. It does charge and it has spin.

Speaker 2 (27:07):
Yeah, exactly right.

Speaker 1 (27:08):
Or like if you take a coil of wire and
you spin a bunch of electrons that is those that's
a charge spinning which creates a magnetic field.

Speaker 2 (27:16):
Yeah, exactly. You make a coil of wire and you
run a current through it, that makes the magnetic field
through the coil, right. Or simply if you just have
a single line of wire, not a coil, and you
run electrons through it, then you're going to get a
magnetic field around the wire. But that magnetic field is
frame dependent. It depends on the electrons moving relative to

(27:37):
you through the wire. It only happens because electrons are moving.
It's charges in motion that give us magnetic fields. So
if you have your black hole and it's spinning near you,
you measure magnetic field. Now you get in your ship
and you start orbiting the black hole at exactly the
same rate it's spinning, so that when you look out
of your ship the black hole is not spinning relative

(27:58):
to you, then it no longer has a magnetic field.
The magnetic field is frame dependent.

Speaker 1 (28:04):
Well, meaning that the magnetic field disappears or that you
don't feel it.

Speaker 2 (28:11):
It's not there. I mean, we don't even know if
fields are real anyway, but you can't measure it, and
according to the physics, it isn't there. Like you do
the calculation, there's a prediction of no magnetic field there.
And the thing is the field itself. You like to think
of it as something physical. It's out there in the universe.
But the distinction between electric fields and magnetic fields, like

(28:31):
you were saying earlier, is a little bit arbitrary, and
it turns out to depend on your frame of reference.
And not just for black holes, also for the simple
situation of electron going down a wire. If you jump
in a car and you drive down the wire the
same speed as the electrons, the electrons only have an
electric field. But your buddy who's standing next to the wire,
he measures the electrons going through the wire, they have

(28:52):
a velocity. He will also see a magnetic field. So
magnetic fields are always frame dependent because they depend on velocity.

Speaker 1 (29:00):
Well that's a little bit odd to me, I guess.
So let's say have like a loop of wire and
I run a current through it, and you're saying, if
I sit in the middle of it, on a like
an office chair and I spin myself that I'm not
going to feel the magnetic force.

Speaker 2 (29:15):
Yeah. If you spin at the same rate that those
electrons are moving, so the electrons have no velocity relative
to you, then you will feel no magnetic field. You'll
sense no magnetic field. It's a timely a little bit
more complicated there because now we're spinning, so we have
acceleration and non inertial frames, so it's a little bit
simpler in the straight line case. But yeah, the same

(29:35):
thing applies, right.

Speaker 1 (29:36):
I guess that's what I was trying to get at,
is that you're saying it it depends, but it doesn't
depend on like an inertial frame, which is sort of
like the standard frames of the universe. It's like you
have to make up this weird frame, right, like I
would be feeling other things. I won't feel that electromagnetic field,
but I'm going to feel, for example, uh, this interpretal force.

Speaker 2 (29:57):
Yeah, exactly. And that's sort of the Missy piece because
you might be wondering, like, hold on a second. If
I'm measuring a magnetic field and my friend is not
measuring a magnetic field, how is that possible? If you
dropped a monopole into that situation, would it get pushed
or would it not get pushed? Right, there has to
be like one answer to that question, and the answer
is a little bit subtle but kind of beautiful. What

(30:19):
relativity tells us is that the same laws of physics
apply no matter what your reference frame, but the story
they tell about why things happen doesn't have to agree.
So in one scenario, your friend will say, oh, there's
a magnetic field there and it helps push things around.
The other person will say, no, there's no magnetic field there,
but they will also see the electric field is a

(30:40):
little bit different and that will compensate. So one person
will see a combination of electric and magnetic fields doing
pushes and pulls on charge particles and magnetic monopoles. Somebody
else will see only electric fields and no magnetic fields,
but they'll actually predict the same motion for all the particles.
They'll just have a different reason for why it happened.

Speaker 1 (31:01):
Right. It's sort of like if you're moving with the electricity,
then you won't feel the forces of the electromagnetic field,
but you'll have to push and spin yourself around the wire,
which is sort of equivalent, I think, is what you're saying.

Speaker 2 (31:16):
Yeah, all the differences actually add up to give the
same prediction, which is kind of amazing. And that's one
of the beautiful things about relativity is that it shows
you that all these pieces work together, because really the
distinction between electricity and magnetism is a bit arbitrary, and
it's even frame dependent. You know, people going at different
speeds see electric fields or magnetic fields. But all the

(31:38):
pieces work together, so that even people in different reference frames,
while they tell a different story about why things happen,
like did you have a magnetic field or not, they
will agree in these scenarios about what actually did happen.

Speaker 1 (31:50):
But I wonder if you can just can you just
say the same thing about everything in the universe. You know,
like you could also make gravity disappear if you move
with the grat, or you can make like a charge
disappear if you move with the charges.

Speaker 2 (32:04):
Not everything in the universe is frame dependent. For example,
black holes are not. If there's a black hole, then
everybody agrees there's a black hole. You can't like boost
yourself into some frame in which there is no black hole.
This is why, for example, you can't make a black
hole just by going really really fast. You might think, oh,
black holes are actually happen when you have a lot
of energy, not just mass. So why can't I make

(32:27):
a black hole by taking a particle and zooming it
to really high speeds because that would make a frame
dependent black hole, which doesn't exist in our universe. So
there are some things that are invariant no matter what
frame you're in, inertial or not. But yeah, there are
a lot of things in the universe that are frame dependent,
I think more than people suspect, right.

Speaker 1 (32:46):
I wonder if the analogy is sort of like, you know,
if you jump out of an airplane and you're falling
towards Earth, you can't tell that there's a planet there
blow you right, Like, to you, it's going to feel
like you're floating in space as you plummet to your death.

Speaker 2 (32:58):
Yeah, that's right in that scenario. Actually, in freefall, you're
not doing any accelerating. It's the planet that's accelerating towards you.
The surface of the planet is accelerating towards you. If
you take out a gravitometer or an accelerometer in that scenario,
you'll measure no acceleration, So you need to look out
the window to see a planet rushing towards you to
discover that your life span is going to be very short.

Speaker 1 (33:21):
Right, So in that way, sort of gravity is also
reference dependent, Right, I can make it disappear if I
jump out of an airplane.

Speaker 2 (33:27):
Lots of gravitational effects are frame dependent. Yes, there are
some things that are frame independent, like the existence of
a black hole, but a lot of things are frame dependent, absolutely,
And you're right that this story applies very broadly. There's
lots of situations in physics where people will disagree about
why things happened, even if they apply the same rules,
and they might agree about what happened, they'll tell a

(33:49):
different story about how that happened or why that happened,
even though the outcome is the same.

Speaker 1 (33:55):
But I guess if you stick to what most people
think is normal, which is like an inertial frame or
you know, not spin around at a crazy speed in
an office chair, then you would say that a black
hole does have a magnetic field.

Speaker 2 (34:10):
Yeah, exactly, and it's not special, right. The black hole
has a magnetic field, and exactly the same way a
coil of wire has a magnetic field. You got charge
in there, You've got spin, so you're moving charges, so
you get a magnetic field. The magnetic field of a
black hole is not deficient in any way compared to
the magnetic field from an electromagnetic motor, for example.

Speaker 1 (34:31):
And I guess what that means is that if I
take a compass and I hold it up close to
a black hole, I'm going to see it point in
a specific direction, right, just like it points to a
specific direction here on Earth.

Speaker 2 (34:42):
Yeah, exactly, a black hole have a magnetic field the
way the Earth does. And we think the Earth's magnetic
field probably comes from convection and flow of stuff inside
the Earth, though we don't totally understand. And so yeah,
you could use a compass to navigate near a magnetic
black hole.

Speaker 1 (34:59):
So I mean black holes have a north and south pole.

Speaker 2 (35:01):
Yeah, exactly, they have a north and south pole for
their spin as well. Right, A black hole that doesn't
spin is spherically symmetric, But a spinning black hole has
broken that symmetry because there has to be some axis
around which it's spinning. So that gives it a north
and south spin black hole, because that spin is what
generates the magnetic field. It also then has a north
and south magnetic pole.

Speaker 1 (35:22):
Whoa, And so if I have a tiny spinning black hole,
then it would be attracted to my fridge door.

Speaker 2 (35:28):
Right, Yes, it would be attracted to your fridge door.
Even if its gravity was too weak to hold it there,
its magnetic field might be powerful enough, because remember, magnetic
fields are much more powerful than gravity. So you make
a tiny black hole out of a few electrons, it
might not have very strong gravity, but the magnetic fields
could already be quite powerful.

Speaker 1 (35:48):
Yeah, it's interesting to think that a black hole has
a north and south pole. I hear the north pole
of a black hole is where all the dark elves
hang out.

Speaker 2 (35:59):
Are they making presence for dark Christmas?

Speaker 1 (36:02):
And now they're just making a bunch of coal presents
for everyone? It's the opposite. It's the opposite. Can you
measure the magnetic field of a black hole from a distance?

Speaker 2 (36:13):
In principle, if you were near the black hole, you
can do what we describe, which is used the compass.
We can't go near black holes, unfortunately, but we can
see the effect of black holes on nearby particles. Right,
black holes are almost never on their own. They formed
because they're in the middle of some dense blob of
matter they've been gobbling, so usually there's a lot of
stuff around them. And if you trace the path of

(36:35):
the charged particles near the black hole, then you can
measure something about its magnetic field. But those particles also
will generate a magnetic field. So teasing those two things
apart is quite tricky.

Speaker 5 (36:47):
Mmm.

Speaker 1 (36:48):
Sort of like give you throw a bunch of iron
filings feelings filings at a black hole, they would form
a pattern around the black hole, and that would tell you, Oh,
that's the magnetic field, that's where the north pole is pointing.

Speaker 2 (37:00):
Yeah, it's filings. If it's little pieces of shaved iron,
it's fillings. If they came from people's teeth, which were.

Speaker 1 (37:05):
You imagine both? I guess, I guess both would work.

Speaker 2 (37:12):
I guess if you go near a black hole, it
might pull out your iron fillings. What if you file
some fillings, I'm going to find a complaint with the
black hole division if.

Speaker 1 (37:19):
That happens, another full.

Speaker 2 (37:21):
I think they're filled up already.

Speaker 1 (37:24):
Yeah, all right, So then could we measure it potentially
from Earth? Like if we you know, we have these
pictures now of what we think are black holes. Could
we measure their magnetic feel from here?

Speaker 2 (37:34):
Absolutely, we can and we have we have.

Speaker 1 (37:38):
All right, well let's talk about that, but work, let's
take another quick break. All right, we're talking about the
polarity of a black hole. They're very polarizing black holes.

(38:01):
Some people love them, some people really love them.

Speaker 2 (38:04):
Those are your only two choices.

Speaker 1 (38:06):
Yeah, you either either love it or you don't love it.

Speaker 2 (38:10):
Fill out this survey or what take your iron fillings?

Speaker 1 (38:12):
Well, we talked about how black hole has a magnetic field,
but it's sort of not new information, right, Like it's
it's it's the product of its charge and it's been
so it's not like it has a fourth property that
you can find out about it. It's it's sort of
a derivative of its charge and spin.

Speaker 2 (38:30):
Yeah, exactly, not derivative in the calculus sense, but derivative
in the like, oh you just copied that sense. It
comes out of the other properties. It's not a core
basic quantity of a black hole itself, unless the black
hole had a magnetic monopole in it, and then it
would be a core property. But you're right, it sort
of emerges from the other properties.

Speaker 1 (38:49):
What do you mean if a black hole ada monopole.

Speaker 2 (38:51):
If a black hole aida monopole would be something we
call a dionic black hole, and it would have its
own monopole magnetic field, just like the monopole that fell
into it, Right.

Speaker 1 (39:02):
How would it ever eat a monopole number one?

Speaker 2 (39:04):
A monopole would have to exist in the universe, and
we don't know that they do, but they might, and
then they would have to go near a black hole.
And then gobble gobble.

Speaker 1 (39:12):
Could a black hole split a dipole into a two
monopoles that it eats one and it shoots off the
other one.

Speaker 2 (39:17):
That would be an awesome feature of quantum gravity. Currently
in our predictions, know, you can't split a diepole because like,
where does that come from? It comes from the electron spinning,
So you're going to split the electron somehow, So we
don't know how to do that.

Speaker 1 (39:31):
I don't know in general, can you tell a black
hole what it can or can't do?

Speaker 2 (39:35):
If black holes are listening to this podcast, I apologize
for my presumptuousness.

Speaker 1 (39:40):
They're going to come after your fridge watch out, all right, Well,
so what can we see of a black hole or
what have we seen?

Speaker 2 (39:50):
So we've seen. The black holes have a huge effect
on nearby matter. They don't just suck stuff in, they
also shunt stuff away from themselves. Their magnetic feels can
be so strong that in falling particles can actually follow
those magnetic fields and then escape the black hole, you know,
the same way that like we've seen these aurora. Because
charge particles falling in towards the Earth end up spiraling

(40:11):
around our magnetic fields and then end up in the
North Pole. It's also possible when particles are falling in
towards a black hole. Basically the same thing happens, but
they get so much speed that they then escape the
grip of the black hole and they shoot out up
and down the North and South poles. And we see
these enormous jets from black holes. You see galaxies with

(40:32):
super massive black holes at their center, and then these
huge jets extending thousands of light years up and down,
sort of above and below the plane of the galaxy.
Those are jets from the central black hole, and they're
powered by its magnetic field.

Speaker 1 (40:46):
Whoa wait, wait, wait, wait, hold on, it's not stuff
coming out of the black hole, is it right? It's
not right, because nothing can escape a black hole.

Speaker 2 (40:53):
It's not something escaping a black hole. It's something having
a near miss. It's like fell in and then a
magnetic field outside the black hole, the same way we
have a magnetic field outside the atmosphere of the Earth.
The magnetic field that's outside the black hole guides those
particles towards the north and then they escape, but they
never went inside the event horizon.

Speaker 1 (41:14):
I see now, I wonder if that means that a
black hole looks different to like an electron than it
does to a proton.

Speaker 2 (41:22):
Potentially, they definitely do look a little bit different. I mean,
a proton and an electron have different charges, and so
they're affected differently by those magnetic fields. But all these
particles do see the same event horizon. The event horizon
is the event horizon is the event horizon.

Speaker 1 (41:39):
But wouldn't they like their paths near a black hole
be different, in which case the point at which they
would definitely fall in is different.

Speaker 2 (41:46):
Yeah, the paths near the event horizon are different because
they are affected by magnetic fields differently, and their masses
are different, et cetera, and their charges are different. But
the event horizon is still just the event horizon. That's
a feature of the curvature of space. It's not an
issue of like the forces on the particles. Remember, it's
a product of the black hole itself.

Speaker 1 (42:08):
And that's just from the mcdaide field of the black
hole itself. You mentioned earlier that the stuff swirling around
it can also make mcnad fields.

Speaker 2 (42:15):
Yeah, exactly. There's huge accretion disks surrounding most black holes,
especially the ones at the center of galaxies that have
been feeding on gas and dust, and so there's a
lot of stuff that has fallen close to the black
hole and is still in orbit around it. Remember, things,
unless they fall directly towards the center of the black
hole or towards the event horizon, they're still going to
have some angular momentum. You can orbit a black hole

(42:37):
the same way the Moon orbits the Earth. Black Holes
are not like literally sucking things in. They're just gravity, right,
They're just curvature of space. You could in principle, orbit
a black hole forever and never fall in. But if
you're in this big disc of gas and dust, you're
also going to have friction. You're going to bump up
against each other, and some stuff is going to end
up falling in. But before it does. You know, this

(42:58):
huge disc of gas and tidal forces are heating it up,
so it's really hot and energetic and glowing in the
X ray. And because it's a lot of charged particles
swirling around, it has its own very strong magnetic field.

Speaker 1 (43:12):
Like it adds to the black holes. Is a magnetic
field or it cancels it? Or how does it interact
with the black holes? Is magnetic field itself?

Speaker 2 (43:21):
Yeah, great question, and that's essentially the cutting edge of
our research right now. It's like, what do the black
hole magnetic fields look like? What are the magnetic fields
coming from the disc look like? It depends a lot
on how calm or how turbulent that accretion disc is. Like,
if everything is flowing very nicely, like Saturn's rings, then
all those magnetic fields will add up very nicely and

(43:42):
they'll all contribute in the same direction. But if it's
sort of chaotic, like a big storm, then the magnetic
fields generated by those particles might cancel each other out.
We also don't really know how much of the magnetic
field is coming from the disc and how much is
coming from the black hole itself. We can't separate those
two things very easily.

Speaker 1 (44:00):
We can't because it's just too complicated.

Speaker 2 (44:02):
Yeah, we don't really understand how much magnetic field there
is coming from the accretion disc because it's not something
we've modeled very well. We have lots of competing theories
about what the accretion disc looks like, and so to
separate out the black holes magnetic field you have to
understand the rest of the magnetic field very well. But
we've tried to do that. We've been able to take
these images of the event horizon or images of the

(44:24):
stuff near the event horizon, and recent pictures of that
have used some clever tricks to try to understand what
the magnetic fields look like near the black hole.

Speaker 1 (44:33):
WHOA, how can you do that? Well, first of all,
you can't really see the event horizon, right, You only
see the shadow of the black hole, which is different.

Speaker 2 (44:40):
Yeah, that's exactly right. We're just not seeing photons from
the event horizon or anywhere near it in a way
that lines up really really well with predictions of general relativity.
And so that's an indirect piece of evidence for black holes.
Another frustrating the indirect piece of evidence. But we can
see the stuff the accretion disc nearby it. That's why
these photos look sort of like a big crispy cream donut.

Speaker 3 (45:01):
Right.

Speaker 2 (45:01):
You have the hot gas glowing near the accretion disk,
and those photons that come from the gas that are
emitted from these high speed charged particles. They can give
us some clues about the magnetic field that they're in
because the magnetic fields will polarize these photons. It changes
how the photons wiggle, like are they wiggling this way
or they're wiggling that way. And if the magnetic fields

(45:22):
are all nicely organized, then the polarization of those photons
will be nicely organized. And if the magnetic fields are
all a big hot mess, then the polarizations will all
be scrambled. So they recently reanalyze the image of the
black hole at the heart of the eighty seven galaxy
to try to measure the polarization of these photons, not
just like where's it bright and where's it dim, but

(45:42):
in which direction of those photons wiggling, and that give
them some clues about what might be happening in the
accretion disc.

Speaker 1 (45:49):
WHOA, which would then sort of tell you what's going on, right.

Speaker 2 (45:52):
Yeah, exactly, And it's really fun. They had two models
of black hole accretion disc magnetic fields. One of them
was called sane stable and normal evolution as ANE, and
the other one is called mad magnetically arrested disc. So
it was a big competition between the scene and the
MAD groups.

Speaker 1 (46:14):
They're like, no, I'm saying, no, you're mad.

Speaker 2 (46:17):
I mean, you've heard of crazy astronomical acronyms before, but
this is like dueling crazy acronyms. I'm impressed by their coordination.

Speaker 1 (46:25):
Yeah, so each one of these was invented by a
different group.

Speaker 2 (46:28):
Yeah, exactly. They like competing theories for how the accretion
disc will come together. And basically the difference between them
is how turbulent is it and how coherent is it?
You know, is it basically all scrambled and you don't
get a strong magnetic field, or is it kind of
coherent and well ordered, in which case you do get
a stronger build up of the magnetic fields from the
accretion disc, right right?

Speaker 1 (46:49):
Or are they all just crazy physicists.

Speaker 2 (46:52):
Yeah, And so for a long time people thought that
the same scenario was more natural sort of weaker fields
because everything would be sort of more scrambled. But what
they measured is more consistent with the mad scenario that
things are like nicely organized, so they all add up
to give more powerful magnetic fields than people.

Speaker 1 (47:10):
Suspected, meaning that the black hole is not as chaotic
as we thought it was.

Speaker 2 (47:15):
Yeah, it turns out to be a little bit tidy.

Speaker 1 (47:17):
Wait, the mad scenario is more sane than the same scenario.

Speaker 2 (47:23):
The mad scenario is more like our universe. It's the
one where things are better organized.

Speaker 1 (47:28):
Yeah, it sounds like physicists are just trying to drive
as mad. All right, Well, I think that sort of
answers the question. Black holes do have magnetic fields. I
mean they have Spain in charge, which means they'd have
magnetic fields. You can take a black holes, stick it
on your fridge. You can use it to mess up
your friend's compass. But measuring it might be a little

(47:50):
bit tricky because it's so far away, and there's also
these weird physics and dynamics going on or around outside
of it.

Speaker 2 (47:58):
That's right. We can't know what's going on inside a
black hole, but magnetic fields give us a pretty good
clue as to what's going on near a black hole,
which one day might help us gain some clues about
what's going on past the event horizon.

Speaker 1 (48:11):
Whoa do you think we can use magnets to see
what's inside of a black hole? It's kind of what
you're saying.

Speaker 2 (48:16):
Well, in general relativity we definitely cannot, But in a
quantum version, with quantum gravity, there could be some correlation
between the information on the surface of the event horizon
itself and what's going on inside. There could be some feature,
some hair to the black hole, and that could affect,
for example, the radiation and the magnetic fields. And so eventually,
if we get detailed enough information and better theories of

(48:39):
quantum gravity, we might be able to see what's inside them.

Speaker 1 (48:42):
That would be insane.

Speaker 2 (48:43):
I wouldn't be mad about it.

Speaker 1 (48:46):
Well, you know what they say, wearing magnets can really
help you out.

Speaker 2 (48:49):
Do they say that that sounds like pseudoscience?

Speaker 1 (48:55):
Well, honestly, all this black holes so also sounds a
little bit like sseuiccience.

Speaker 2 (49:00):
Definitely not the final word on how any of this
stuff works. Is just science in progress.

Speaker 1 (49:05):
I see, it's not pseudoscience. It's pre science science, and
it's key. Everything is pre science. Nothing is the proto science.
That sounds better proto.

Speaker 2 (49:16):
Science science in action.

Speaker 1 (49:18):
About that, that's right, you don't want to be a
pre scientist. All right? Well, another reminder about the incredible
mysteries out there in the universe and how they're staring
us right in our telescopes. You can see them, you
can point telescopes, you can measure things about them, but
all you see is pure.

Speaker 2 (49:36):
Unknown and their magnetic personalities.

Speaker 1 (49:39):
That's right, the riz. Well, we hope you enjoyed that.
Thanks for joining us. See you next time.

Speaker 2 (49:49):
For more science and curiosity, come find us on social
media where we answer questions and post videos. We're on Twitter,
disc Org, Instant, and now TikTok. Thanks for listening, and
remember that Daniel and Jorge Explain the Universe is a
production of iHeartRadio. For more podcasts from iHeartRadio, visit the
iHeartRadio app, Apple Podcasts, or wherever you listen to your

(50:11):
favorite shows.