it's a kind of a neat piece of physics
it ends up with a truly enormously
ridiculously big number um but mainly i
want to talk about it because it gives
me an excuse to show you this so this is
a composite of an optical picture so the
kind of the gray bits of stars and a
radio picture so the pinky stuff is what
you see if you had radio eyes and the
gray stuff is what you see with normal
optical eyes and as you say there is
this kind of tight jet of material
coming out and you can see so this is a
whole galaxy a large galaxy in the
middle and you can see the radio
emission is way way bigger
than even the whole extent of the
galaxy's enormous scale that's going on
here in fact you can trace back because
you can see these little lines where
it's coming from it actually originates
clearly near the middle of the galaxy
and as we know
strange things look at the center of
galaxies and therefore it's probably
even though it's on an enormous scale
it's probably somehow intimately tied to
what's going on right in the middle of
the galaxy this must be a very different
galaxy to live in that we're something
this dynamics coming out of the center
like if something like that was coming
out the center of our galaxy that feels
like it would be a game changer
that's an interesting question i'm not
sure it would unless you happen to be
you know unlucky and getting right in
the way of where these jets are headed
because it's so tightly collimated
actually it doesn't have much impact on
most of what's going on in the galaxy it
really is only if you're unlucky enough
to get in the way
but one one interesting question and the
thing that we're going to be able to
answer with this synchrotron minimum
energy stuff is how important is it in
the sense that is this just kind of big
and showy or is there actually a lot of
energy associated with it a lot of
energetic processes and is it really
kind of something we have to worry about
in terms of how it interacts with the
galaxy the effect it might have on the
galaxy we have to talk about where this
ora this emission comes from what causes
it and then that will allow us to then
unpack the
how much energy there is packed away in
these radio jets and hence whether it's
actually an important structure or just
something that looks pretty so the
process that emits these radio waves is
a process called synchrotron emission
which is where you have a magnetic field
and a bunch of charged particles and
when you've got a magnetic field and a
bunch of charged particles the charged
particles interact with the magnetic
field they sort of spiral around it
and because they're now not traveling in
a straight line anymore that means
they're being accelerated and whenever
you take a charged particle and
accelerate it it emits radiation and in
this particular case it's the the
energies of the particles are such that
it'll emit that radiation in the radio
part of the spectrum so the physical
process that's leading to this emission
is just basically you've got the
magnetic fields associated somehow with
these structures and charged particles
and the combination of the two the
charged particles traveling around
orbiting around the magnetic field lines
then produced this synchrotron emission
in this particular case what's the
source of our magnetic field and what's
the source of our charged particle so
almost certainly both you can trace back
again just following the line back to
the middle it's something to do with
what's going on in the middle here and
whatever it is is tangling up magnetic
field lines which will create stronger
and stronger magnetic fields but also
producing these particles which then get
accelerated out along the jets and the
synchrotron just means the reason so
there's another kind of radio emission
you get from electrons traveling in
magnetic fields called cyclotron the
difference between synchrotron and
cyclotron is it's called synchrotron
when the electrons are traveling at
relativistic speeds so we know these
electrons are being shot along at
incredibly high speeds and producing
this radio emission because of that
initially you were saying charged
particles now you're saying electrons
they are electrons i mean they have to
be protons as well because you can't
have you have to have a kind of a charge
balance in this process so the protons
being shot along as well but the
electrons are the one that give their
presence away by producing the the
strong radio waves that we see
fundamentally we don't know why you see
this phenomenon in some galaxies in
other galaxies you tend to see these
kind of big radio jets where there's a
big elliptical galaxy for example but
not all large elliptical galaxies
produce these radio jets so there's
something that makes some galaxies
produce them and others not or that
maybe all galaxies do it but they just
switch on and switch off and we catch
some in the end but not others so
there's obviously a very strong magnetic
field far away from this galaxy actually
it turns out it's not strong at all
it's actually a very weak magnetic field
but it's very very large that's the
thing there's a lot of magnetic field
there but actually the field strength at
any given place is actually quite small
so it turns out when you calculate it
it's actually a very tiny magnetic field
what would be creating a magnetic field
at all around the galaxy like that so
the whole of space is permeating with
magnetic fields as a kind of primordial
magnetic field out there in space and
presumably what's happening here is that
some process is sort of concentrating
that many fields are making it stronger
so it's still very weak but actually you
know stronger than it used to be some
again something to do with the black
hole in the middle pulling material in
and strength pulling the magnetic field
lines in and creating a stronger
magnetic field so now we have to get to
the the crux of the matter is does it
matter right is it just all for show or
is there actually much energy associated
with this and so we actually have to
worry about it on an astrophysical scale
and this takes us back to the 1950s when
this was first figured out by a guy
called jeffrey burbidge who came up with
a very elegant way of showing quite how
much energy that has to be associated
with these jets we know there are
relativistic particles in the jets and
there's clearly this energy associated
with those relativistic particles
because it's kind of the kinetic energy
of the particles themselves
and we sort of have some handle on how
much energy that actually is because we
can see how much radio machine there is
and obviously the more
rapidly moving particles there are the
more radio emission you'll see so the
mass goes something like
luminosity you see is proportional to
the energy stored in the electrons
times the magnetic field strength to the
three halves power it turns out this is
just basically saying that the way that
the the you get stronger luminosity
coming out if either there's more high
energy particles or if there's more
magnetic field so we could rearrange
this because we can measure the
luminosity and the thing we want to know
is how much energy is there stored in
there we could rearrange this to say
that the energy we store is proportional
to that luminosity
goes over b to the three halves power
that means that we measure the
luminosity and so we want to know what
this energy stored in the uh the
electrons is but unfortunately we don't
know what the magnetic field is we can
guess but we don't actually know what it
is but we can say okay so we don't
actually know what it is but we could
plot how much energy there is stored if
we just allow that magnetic field to
change okay and so as this magnetic
field goes up
the energy store goes down because
that's in the denominator so it's going
to do something like that
and we know we're somewhere along that
curve we don't know what the magnetic
field is but we know you know if the
magnetic field with this value then that
would be what the energy was stored but
it turns out that's not the only source
of energy in these jets because there's
also energy stored in the magnetic
fields themselves if you've ever taken
two magnets and tried to push their
poles together
you know that they push each other apart
and actually when you push them together
you store some energy so the stronger
you make a magnetic field the more
energy there is actually stored in the
magnetic field itself so it's the second
term we need to worry about energy
stored in the magnetic field and it
turns out that that's proportional to
the magnetic field squared right as you
crank up the magnetic field there's more
and more energy stored in the magnetic
field similarly as you push two magnets
closer and closer together there's more
and more energy stored because you've
got a stronger and stronger magnetic
field so if we were to plot this
contribution
that one goes the other way right
actually as as b increases the magnetic
the energy stored in the magnetic field
goes up
so it's going to do something like that
and of course the total energy is just
the sum of these two terms it's the sum
of the energy stored in the electrons
the relativistic particles which goes
down with magnetic field and the energy
stored in the magnetic field itself
which goes up with the magnetic field
and the total energy is just the sum of
the two which is going to do
something like that when we add the two
together so again we still don't know
what the answer is because actually we
don't know what the magnetic field is
still and we just know that tells us
that the total energy lies somewhere
along that line
but we have a minimum we have a minimum
indeed so we know that the energy has to
be stored that is stored in there has to
be at least that much we know that
there's some minimum energy stored when
you go through the calculations which is
what burbidge first did in the 1950s it
turns out that amount of energy is a
ridiculously huge amount of energy i
mean this is a galaxy i'm not
everything's huge when you deal with
galaxies okay this even by galaxy
standards this is huge so the amount of
energy you typically get for a galaxy
like this system like this it works out
that the energy stored in these radio
jets at the minimum energy remember it
could always be more than that is about
10 to the 52 joules
that's one with 52 zeros after it duels
and again you're right every number is
beginning astronomy so let's put that in
a little bit of perspective
the sun gives out quite a lot of energy
and one of the things that people will
think about in terms of very advanced
civilizations this idea of these things
called dyson spheres where you could
actually take all the energy of the sun
and use it to bend it to your will do
what you want with it
so if we were to build a dyson seer
around the sun
and in fact if we were to build a dyson
sphere around every star in the milky
way
then if we wanted to get that much
energy the amount of energy stored in
these radio lobes we'd have to take all
the energy from all the stars in the
milky way for hundreds of millions of
years
and that really is a ludicrously large
amount of energy and it tells you
immediately that actually this is a very
energetic process that's going on in
these jets we're always told energy
can't be created or destroyed yes like
this energy that's living in this lobes
which is dyeing our minds
didn't just like come from nowhere nope
it started somewhere else where did it
come from so and they said well there's
the clue right that you can see where
the jets come from they come from right
in the middle of the galaxy
and we know at the center of every
galaxy there's a super massive black
hole and we know that one of the most
efficient ways there is of liberating
energy is to drop things into a black
hole you basically remember the if
you've got some mass m the total amount
of energy associated with it is via
einstein's famous equation m c squared
and it turns out you actually if you
drop something of mass m into a black
hole you liberate some large fraction of
m c squared in the process so it's an
immensely efficient way of liberating
energy and if you were to power these
radio lobes by dropping matter into the
black hole in the middle it works out
you'd have to drop about 100 000 times
the mass of the sun into that black hole
which is sounds like a big number but
actually the black hole is probably
several hundred million solar masses in
size so actually it's a small fraction
of the total mass of that black hole but
by feeding the black hole in the middle
you can generate these huge amounts of
energy you need to create these radio
loads if you'd like to see even more
about synchrotron radiation in
particular how it's used by scientists
here on earth well i've made a lot of
videos about that you can check them out
i'll put links on the screen and in the
video description
and if just huge objects in space like
this galaxy fascinate you you really
need to be checking out deep sky videos
which is our dedicated astronomy channel
and each video is about a different
galaxy or cluster of stars telling you
amazing things about them it's really
worth checking out again links on the
screen and the description also a
reminder you can support 60 symbols on
patreon like these people here
and as always thank you for watching