Dark Matter | Wisconsin Public Television

Dark Matter

Dark Matter

Record date: Oct 18, 2017

Carsten Rott, Associate Professor in the Department of Physics at Sungkyunkwan University, discusses how researchers are searching for dark matter particles. Rott focuses on the work being done with the IceCube Neutrino Telescope.

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Episode Transcript

 - Welcome everyone,

Wednesday Nite at the Lab,

I'm Tom Zinnen, I work

here at the UW-Madison

Biotechnology Center.

I also work for UW-Extension

Cooperative Extension,

and on behalf of those folks

and our other co-organizers,

Wisconsin Public Television,

The Wisconsin

Alumni Association,

and the UW-Madison

Science Alliance,

thanks again for coming to

Wednesday Nite at The Lab.

We do this every Wednesday

night, 50 times a year.

Tonight it's my pleasure to introduce to you, Carsten Rott.

He's with the Wisconsin IceCube

Particle Astrophysics Center

and was born in

Hannover, Germany

and went to Gymnasium

in Hannover,

and got his undergraduate degree

at the University of Hannover,

Bachelor, or excuse me,

Master's Degree at

Purdue University and

his PhD at Purdue.

Of course I always have

to point out that Purdue

is the French past

participle for lost.

(laughter)

He also did for

his work at Purdue,

he worked at the Fermilab,

which is the French

participle for closed.

(laughter)

Then he went on to Penn

State where he joined IceCube

and then went to Ohio State

and then he's gone on to

creative university that

he will pronounce for us.

And now he's back here at

UW Madison on a sabbatical.

So I think he has

covered four of the--

Are there 12 universities

in the Big 10, 14?

14, that's why it's

called the Big 10, Tom.

So I hope you're

here to enjoying your

time here in Madison.

The lake will freeze over

in a couple of months.

You can go ice fishing.

His talk tonight

is on dark matter,

"Don't Be Afraid of the Dark,"

and the cool thing is,

the folks that are doing

dark matter research

are inviting us to consider

October 31st every year

not just as Halloween,

but as Dark Matter Day,

or as I would like to call

it, Dark Matter Night.

And so I think it's

great to have you here.

I know nothing

about dark matter.

Let's let Carsten

tell us all about it.

Please join me in

welcoming Carsten Rott.

(applause)

- Okay, thank you for

the nice introduction and

it's great to see such a

large crowd here to come out,

to know what dark matter is.

And I think I have to

disappoint you because

even after this talk, you will

not know what dark matter is.

(laughter) And the reason is that we don't know yet

what dark matter is.

But the question about

dark matter is actually

one of the most

fundamental questions

that we are trying to answer.

So since the early

ages of humanity,

people have been trying

to answer the question

what is the world made out of?

And we have come a long way.

So nowadays we know that

everything in this room,

pretty much, is

made out of atoms.

So, and we can also,

we know that the atoms,

we can decompose them

in smaller particles

so they're made out of protons

and neutrons and electrons.

And even if you use a

particle accelerator,

you can break protons and

you can find that protons

are actually made out of quarks,

which are the

constituents that made up,

that make up

neutrons and protons.

Now as we have built ever

more powerful telescopes,

we also started to observe

the universe and we wondered

what is the universe

made out of?

Is the universe also made

out of the same matter

that we have here,

which we sometimes call

the ordinary matter?

So ordinary matter are

the protons, neutrons and

electrons and everything

that we know about.

So is the universe also made

out of this ordinary matter?

Now as we observed the

universe, we came along evidence

that actually the majority

of matter in the universe

is not the ordinary

matter that we know of,

but it's dark matter.

And that's actually why it

is so important to answer

the question "What

is this dark matter?"

Because in order to

understand the universe,

and to answer the question,

"What is the world

made out of?",

we have to understand

what is dark matter.

And we have actually plenty

of evidence for dark matter,

and I will, during this

talk, explain to you

what, how do we know

about dark matter,

what do we know

about dark matter.

And then I will come

to the question,

"How can we identify the

properties of this dark matter?"

And since this series is called

Wednesday Nite at the Lab,

I've actually brought

a picture of my lab,

which is the IceCube

Neutrino Telescope,

located at the

geographic South Pole,

and this is actually the

laboratory that I work with,

I mean not at,

but I've been there a few times,

but that's only a few

special occasions when

we get to go there.

And during this talk I

will also explain you

why we can use the

IceCube Neutrino Telescope

to look for dark

matter and how we have

searched for dark

matter with IceCube.

So now, let me

begin with my talk

and let me give

you the overview.

So this is basically

what I'm gonna cover

during the next hour here,

so this is basically what

I will suggest towards you.

So let's start with

the first question,

"What do we know

about dark matter?"

So we know from observations

that the mass energy

content of the universe,

which is actually shown

on the top right there,

that the universe is

made out of roughly

five per cent ordinary matter,

so these are the protons,

neutrons and electrons,

27 per cent dark matter,

and then 69 per cent

dark energy.

And I'm not going to talk

about dark energy today,

but that's also definitely

a very interesting question.

So what we know

about dark matter

is namely that dark matter

could be a new particle

and basically all that we know

so far about dark matter

comes from the gravitational

interaction that it has.

And maybe if you're

a fan of Star Wars,

then you maybe remember

this scene where Obi-Wan is

trying to find a missing

planet in the star charts.

And basically he--

He finds that the

gravitational pull

is pulling everything in this

spot but there's no star.

So he concludes that, well,

if the gravitational

pull is there,

then also a mass must be there.

And this kind of resembles also

what we know about dark matter.

We know, everything that

we know about dark matter

comes basically from its

gravitational interaction.

So let's go through

some of the evidence

that we have for dark matter and

let's start with rotation curves

or reviewing, actually,

the gravitational law.

So you can see the picture

here of Isaac Newton

and his famous

gravitational law,

which is shown here, which

basically shows that

F, the force, that's exerted

between two masses,

so in this case, the

apple and the Earth,

is given by the two masses

and divided by the

distanced squared

times a constant G, which

is a gravitational constant.

So with this gravitational

law, we can also,

we can basically describe

all the phenomena

in our solar system

and we can also

use this gravitational

law to predict

how fast a planet has to

move around the sun to stay

on a circular orbit, and this

is actually the plot here

on the right side, and--

Yeah, so you can basically

see that all the planets

follow this gravitational,

or the prediction from the

gravitational law.

Maybe you think of Pluto,

that Pluto is not

a planet anymore,

but of course, also the

asteroids and everything else

or dwarf planets

in our solar system

follow the same

gravitational law.

Now, now we can actually ask,

"Is this gravitational

law universally true?"

So if it works well

in our solar system,

does it actually work well

also to describe the motion

of stars in galaxies.

So on the bottom right, you

see a picture of a galaxy,

so this is a large

spiral galaxy,

and this galaxy consists

out of billions of stars.

And in the middle

you have basically

a large mass concentrations

and the stars are moving

around this galactic center, basically.

And the question we want

to ask well, are the stars

in the system following

the gravitational law?

So some of the, or the

pioneering work on this

actually has been

done by Vera Rubin,

Rubin,

and she actually measured the

rotational velocities

of stars in in galaxies.

She unfortunately passed

away just about a year ago,

which it was very

unfortunate because,

I mean, of course,

it's very unfortunate,

but her, she did very, a

lot of the pioneering work

on this and also

found a lot of the

evidence for dark matter

and she was also considered

for the Nobel Prize

and in particular,

given that there are very

few women who have won

the Nobel Prize it

would have been nice if

she also received it.

So actually let's have a look

at her work to honor her.

Now she tried to measure

galactic rotation curves.

And to measure galactic

rotation curves,

she used the Doppler Effect.

So we know the Doppler

Effect basically

from everyday life when you have

a source of sound, for example.

So, let's take this

firetruck here.

If the firetruck is

moving towards you,

the sound pitch will change then

compared to when it's

moving away from you.

And the same effect is

actually present in light.

So we know that

light is also waves,

and these waves

actually get shifted,

if the source is

moving away from us

or it's moving towards us.

And on the bottom here you

can see an optical spectrum

and you can see some

absorption lines in there.

And depending if the source

is moving away or towards you,

you will see that these

absorption lines are shifting.

And so basically if a source

is moving away from you,

it shifts more towards the red

and if it's moving towards you, it shifts towards the blue.

So then on the right

side you can see

that she looked at

galaxies for which we had

basically an edge-on view

and she then measured

basically the color or

she actually looked at

specific spectral

lines, so H-Alpha line,

from hydrogen and

she then basically

could see how much the

spectral lines are shifted.

So out of this

then she can derive

what are actually the rotational

velocities in this galaxy.

So this is a result

that she found.

She actually looked at

many different systems

but this is just one example.

So on the right side you can see

as function of the distance

from this galactic center,

the rotational velocity of the

gas and stars in the system.

And red is actually

what you predict

based on the gravitational law.

And white is actually

what she measured.

So you can see that

this gravitational curve

actually stays pretty much flat.

Which basically indicates

that there's more matter there

than the luminous matter that

we can see in this galaxy.

And she did this

measurement actually for

many different galaxies,

this is just some example of,

yeah, some of the

measurements that she did.

So this is one case where

we have found evidence

for additional matter

that we cannot see.

There's also other

evidence, for example,

through gravitational lensing.

So if you observe large

clusters of galaxies,

as I've shown here, and in

the back you might have--

You look at the distant

galaxies behind that,

you can see that the

image can be lensed.

And you can see this sort of--

Let me see, where

is the pointer?

Okay, maybe it

doesn't appear, but--

But you can sort of see

this sort of ring shape,

and these are actually galaxies

behind this galaxy cluster

and they get distorted and

this distortion basically

is based on the

bending of the light

due to the matter in between.

And then we can actually

check how much matter

do we expect to be in between

and how much bending

do we actually see?

And also from this

you can derive

that there is additional matter.

Further evidence for

dark matter and the,

actually one of its

fundamental properties,

can be derived from an example

which is called

the bullet cluster.

So this is actually a

very beautiful image,

but it's actually

a composite image

that is kind of false colors,

but let me just explain

what you are seeing here.

So this is an example

where two galaxy clusters,

so two clusters of

galaxies are colliding

and they-- so they are

collided and actually pass

through each other.

And what you can see on

here in blue is actually

where the mass is distributed.

So this is actually from

gravitational lensing,

you can obtain a distribution where the mass is located.

And the red you can actually

see where the hot gas is.

So this is the ordinary matter.

So when these galaxy

clusters collided,

actually a lot of the

gas was stripped out

and this is left in between, while the--

most of the galaxies basically

pass through each other.

And the matter is

basically located

at this blue region.

Now this actually tells us

something about dark matter.

Because we can see

from this image that

dark matter did not

collide with each other,

but just passed

through each other.

So from this we

can actually derive

this conclusion, at the

bottom, that dark matter

does not interact very

strongly with matter

and also not very

strongly with itself.

Other evidence for

dark matter...

comes actually from the

structure in the universe.

You can actually see a

movie up here which is

a simulation of our universe

and you can actually see

how the structure in the universe is forming.

So actually these

distributions basically

shows the distribution

of the galaxies and matter

in the universe

and you can see that you

basically get these filaments.

So now-- Let me actually

move on to the next slide.

I mean this actually

goes on for quite a bit,

the simulation.

But if we actually look at the distribution of the galaxies

in our universe we can

actually find a structure

that looks like

this on the right.

And on the left actually I

have put different simulations

of dark matter.

And I labeled these--

Well, I used different names:

Cold, Warm and Hot Dark Matter.

So DM stands for

dark matter here.

It actually describes how

fast the dark matter particles

are moving, so for example,

if I think of a very fast-

moving particle like a photon

or light, which moves

with the speed of light,

then I would be in this

regime of Hot Dark Matter.

And you see that the

structure is very smeared out

which means that dark

matter cannot be hot

and also cannot be

warm but it's cold

and cold basically means

that the dark matter

is moving very slowly or

the dark matter particles

are moving very slowly.

Okay, so then there's further

evidence for dark matter.

Actually from imprints to the

cosmic microwave background,

maybe let me go quick on this.

So this is actually

radiation that's emitted

at the very beginning

of the universe and

this has been precisely

measured actually

with the Planck

satellite and from this

we can actually derive

how much dark matter

there is in the universe.

Now let me move on.

So one of the last evidence that I want to mention here

for dark matter before I go to

how we search for dark matter

is actually evidence

that comes from

the clusters of galaxies.

So in this image here, is the

Coma Galaxy Cluster is shown.

So each of these objects here

is basically a galaxy and

we can also, again, using

this method from Vera Rubin,

when she looks at the

red shift or blue shift

of these objects, we can

look at the velocity,

distribution of this object.

And if you assume

there's more matter here

than the velocity

distribution of these galaxies

will be increased, so they

will be moving faster.

This is just basically

what follows from gravity.

Now this is actually when,

in the 1930s,

actually Fritz Zwicky, who

was a famous astronomer

from Switzerland who worked

most of the time at Cal Tech,

he actually observed this Coma

Galaxy Cluster and he found

basically the first

evidence for this

missing matter or how he called

it, actually, dark matter,

or he spoke German so

he said Dunkle Materie,

so the dark matter.

So this is a picture of him

and the Coma Cluster.

So since these early days

of Zwicky actually we have

learned quite a lot

about dark matter.

So there's conclusive, or

there's overwhelming evidence

for dark matter on all

scales in our universe

as I have shown you, but

the big question is still,

what is this dark matter?

So we have seen dark matter

through its

gravitational effect,

but we want to know what

is this dark matter.

So let's go try to

answer the question,

what is dark matter?

Now from these observational

evidence that I showed you,

we can basically derive

the following properties.

So dark matter is

cold, which means it's,

relative, the particles are

relatively slowly moving.

It's neutral which means

it's not interacting through

electromagnetic interactions.

So it doesn't absorb

or emit light,

because if it would emit

light or absorb light

then we would have

easily seen it.

And it's also not very

strongly interacting

with the ordinary matter.

So this for example, we

have seen in this example

of the bullet cluster, where

the two galaxy clusters

are colliding.

And also there's this,

this new particle has to be

stable because if it decays,

then it's not around anymore.

So these are basically the--

everything that we

know about dark matter.

So then we can ask the question,

well, is there any

particle that we know of

that has these properties?

So now here I show

a table of all the

particles that we know of.

So this is actually the Standard

Model of Particle Physics,

so this is basically

what you can find

or what has been derived based

on years and years of studies

at particle accelerators

and colliders.

And these are all the

particles that we know of.

And as you see on the top right,

the Higgs Boson this

was basically the

last missing particle

in this Standard Model

of Particle Physics

and we think now that this

is basically complete.

So we know all the particles

that we have expected,

we have observed.

And we can ask the question,

well, is any

particle in here,

does it have the properties

of dark matter?

Well so first we have

to ask the question

are those particles stable?

Or do they decay?

And we can cross out

actually a lot of them

because most of them actually

are very short-lived.

So you can only produce

them at the collider

for a very short time and

then they decay immediately.

Also we said that

dark matter does not

emit or absorb light,

so it's not what we say

electromagnetically interacting.

So we can ask, okay,

which of these particles

are electromagnetically

interacting

so we can cross those out.

So then with this,

now we are only

with three particles left,

which are neutrinos but

neutrinos are actually

relativistic particles,

so they move with

the speed of light.

So also we said dark matter

should not be relativistic,

because it should be cold.

So we can also cross these

out and there's nothing left.

So the only conclusion

that we can draw,

dark matter has to

be a new particle, and--

Well, it's actually

not so bad, I mean,

to have a new particle,

it just enlarges our horizon,

maybe makes the world

more interesting

if there is a new particle

and there are actually

plenty of theoretical

physicists who have cooked up

models that predict, for

example, new particles and

just one of them is

super symmetry which you

might have heard about but--

And people are looking for that.

But there are also

many other theories

that predict new particles.

So now how can we actually

look for this new particle?

There are basically

three different ways how we

can search for dark matter.

The first one is we can

try to produce dark matter.

So this is basically recreating

the conditions that were

present at the very early

universe when it was

very hot and dense, when

we expect that dark matter

was actually created, so.

And we can do this actually

at particle accelerator,

so this is, or collider.

So in this case we

collide two particles with

very high energy and produce,

we can produce new particles.

The second way how we

can look for dark matter

is actually through

the scattering of

the dark matter particle

with ordinary matter.

So this is the idea

is basically like

you're playing pool,

if you have an atom and you

have a dark matter particle

coming in, it could hit

the atom in rare cases

and maybe give

some nuclear recoil

and we can try to

detect this interaction

of dark matter particles

scattering on an atom.

And the last way we can

look for dark matter,

what you call dark

matter annihilations.

So when dark matter

interact with each other,

it could produce maybe

standard model particles

which we then can observe.

So now's let's have a quick

look at these examples.

The first one, which

we call Make It!

So the idea here is that we

use two standard model

particles that we collide

at very high kinetic

energies and then use

this energy to

produce new particles.

Now this is being done at

the Large Hadron Collider

at CERN, near

Geneva, Switzerland.

And which is basically,

yeah, 2.7,

27-ring circular accelerator

in which we collide

two protons and these

protons are basically

moving with the speed of

light and are colliding

and when such a

collision happens

this is basically shown

on the top right here,

many particles are created and

out of these many particles

that are created, we are

trying to find a new particle.

And at the bottom right

is, or bottom left,

is kind of such an example

from kind of a theoretical

prediction for

some new particles

that might be produced there.

So analyzing all this data is

incredibly difficult job

and these experiments,

which is for example,

shown here, the CMS Detector,

there are really thousands

of people working on this

and sorting through

all this data.

And after sorting

through all the data,

they have found basically no

evidence for a new particle.

I mean, they have

found the Higgs boson,

so there's something, but

there is no dark matter,

or no physics beyond the

standard model as we said.

Now the second way how we

can look for dark matter

is to look for an

interaction of dark matter

with ordinary matter and

this is what I call here

Shake It!, so basically we

shake the ordinary matter.

And actually outside

here you can find

a booth actually by

Kim Palladino,

so she's sitting over there,

and later on she can--

Since she's working on this

dark matter direct

detection, she can later

also explain you

more about this.

But here I just want to

give you the basic idea.

So the basic idea is

that this new particle

which I noted by this

Greek letter Xx (chi) here,

is just hitting an ordinary atom

and depositing some energy.

We are trying to detect this

small energy deposition.

This is incredibly

difficult to do because

we know that dark matter

is very rarely interacting

so to run these experiments

you actually have to go

deep underground to be

away from any background.

So yeah, later on please

check out the booth outside.

Okay and then the last way,

and this is actually

the way that

I mostly look for dark matter,

is through indirect

searches for dark matter.

So in this case we assume

that two dark matter particles

hit each other and

in this process,

standard model

particles are created

and those particles we

then are trying to observe.

This is actually

the basic idea here.

On the top left here you can see

these two dark matter

particles, or we call this

WIMP dark matter here, weakly

interacting massive particle,

are hitting each other

and then are producing

some standard model

particles and at the end

you go through some decay

chains, but at the end

basically we can find

stable particles

that we can observe

like light, or,

yeah, neutrinos

or some antimatter.

And there are different

experiments that

are trying to look

for this, or indirectly

search for these signals.

Now let me-- I cannot go over

all of them so let me just

pick the experiments

that I'm working on,

which is the IceCube

Neutrino Telescope.

So this is actually a picture

taken at the South Pole,

so this is actually the

counting house where

all our electronics are

located for this experiment.

Now why have we

constructed an experiment

at the South Pole?

Now, IceCube is a neutrino

telescope and in order to

detect neutrinos we need to make

use of an effect which is called

"shrink of light,"

so this is actually

when a neutrino interacts

it produces some

relativistic particles

which then send out

some shrink of light.

And this is actually a

picture of shrink of light.

This is actually taken

in a nuclear reactor.

And in a nuclear reactor,

you have also some

relativistic particles produced

that pass through the water

and when they pass

out through the water

they send out his

shrink of light.

And basically we are trying

to detect the same light

but when a neutrino

interacts with the ice.

Now the--

Now in order to

detect this light,

we need a detector

medium that has very good

optical properties so

that's why actually

we decided to build the

detector at the South Pole.

Because we can, at the

geographic South Pole,

the ice is roughly

two miles thick

and has very good

optical properties,

so that's why we decided to

build a neutrino detector there.

So then the idea to

detect neutrinos through

the shrink of light

emission can be explained

in this following cartoon here.

So you have a neutrino

and that's coming in

on the bottom right

here, it's interacting,

producing a particle

which I call a muon here.

And this muon is basically

like a heavy electron.

And when these

neutrinos interact,

in particular high

energy neutrino,

it produces a very

energetic muon and this muon

can actually travel

several miles.

And when it travels through

the ice it sends out

a cone of this shrink of light

so all that we need now is a

precisely-timed

optical sensor array

and with this precisely-

timed optical sensor array

we can then detect

this shrink of light

and reconstruct where

the neutrino came from.

Now this is a simulation here

that actually shows this effect.

So this, what you can see

here are different strings,

different strings of

optical sensor modules

and this, an energetic muon

passing through this detector.

Let me actually show this again.

And as it passes

through the detector,

you see this shrink of

light that's emitted

and whenever this light

gets detected by one of the

optical sensor modules we

mark this by one of these

colored balls here which

basically indicates

the time actually when the

optical module was hit.

And the size of these

blobs basically indicate

how much light was detected.

Now this IceCube Neutrino

Telescope is actually a

multipurpose experiment.

It basically serves

many different

science or physics cases

and basically we are trying

to look for neutrinos

of astrophysical origin.

We're trying to

study cosmic rays,

atmospheric neutrinos,

even glaciology, trying

to understand the ice

and also look for dark matter.

And of course, IceCube is headquartered here

at UW-Madison, so maybe

some of you know already

a bit about it, so it's

very exciting experiment.

And it's actually a very large

international collaboration.

Also so there are about 300

people working on the experiment

from all around the world.

From 12 different countries

and all the countries

are shown here.

This is actually

a picture of the

South Pole where our

experiment is located.

This is actually the

South Pole marker.

This marker actually

stands where the

geographic South

Pole is and you can--

If you read on there, you

can actually read this

January 1st, 2008,

so this is actually

at the time when I was there,

so I took that picture.

This is actually, some

image of me there.

So at that time, the

gray in the beard

is actually frost,

(laughter)

but now it became real

so time has passed on, so.

Okay so then the detector

is located very close to

the geographic South Pole.

You can see basically

on the top right there,

a map of Antarctica and where

the geographic South Pole

is located and on the--

Yeah, basically you

can see there where the

geographic South

Pole is and also

where the Amundsen-Scott

South Pole Station is.

So this is actually where

the scientists live.

Then there's a Skiway,

this is actually where we

used to, where planes come

in to bring in supplies

and scientists to work there.

And then very close to this

station is actually where the

IceCube Neutrino Telescope

is located.

And on the top left

you can see actually

a temperature

chart and I haven't

seen any winters here in

Madison yet, but I hear that

during this time

here in November, December,

we go to yeah, maybe minus

30 degrees at the South Pole

so maybe we'll reach this

temperature here also.

But you can see from this

temperature profile then in

the austral summer, or austral

winter period actually

goes down to minus 70 or

so, or even below that.

And the IceCube detector

was actually constructed

during this period from

November to February,

so that's actually when the

South Pole is accessible.

So after that, the

station basically

is not accessible

and only a few people

stay behind to keep

the detector running.

This was actually,

on this picture here,

the guy in the middle, tech,

he was actually one of our

Winterovers who stayed there

one entire year to keep

the detector running,

so they are doing a

tremendous job, actually.

Okay, so on the, yeah,

bottom right you can see kind

of this footprint where the

IceCube Neutrino

Telescope is located.

Now let's actually

go below the surface

to see how the

detector looks like.

And you can see here

in the schematic view how

the detector looks like.

So first of all,

the ice is roughly

three kilometers deep and

we have used a hot water

drill to drill holes

into this ice to a

depth of 2.5 kilometers

and then deployed

optical sensor modules.

So in the bottom right

you can see actually

such an optical sensor module.

So it's basically, kind of this basketball-sized module

that contains a

PMT or photomultiplier

to basically a

large light sensor,

and with that, we want

to detect the light

from the neutrinos that

are interacting in the ice.

Then this detector was

built over a period

of seven years and has

been taking data

since 2011, ever since.

Actually already during the construction period

we obtained many very

useful science data.

Okay.

This is how the detector

would look

like if you could

float through the ice.

These are actually the

optical sensor modules.

So it's basically at the

bottom you can see this

large optical or this large

PMT and then also the top,

it's basically just

some electronics

that digitizes the

signal that's received

by this optical sensor module.

Okay, so then how do

we look for dark matter

with this neutrino telescope?

Well one of the most

spectacular ways

actually how to

look for dark matter

with IceCube or very unique ways

is actually to look for

dark matter that's captured

in the sun.

This is actually-- It

sounds at the beginning,

quite out of this world

that this would be possible

but it's actually

a very reliable way

to look for dark matter.

And the idea is

here that you have

dark matter particles from the galactic dark matter halo,

so as we said earlier,

the galaxies are engulfed

in dark matter and so

these individual particles

could scatter eventually

on or with the hydrogen

atom in the sun.

When this scattering happens,

they can lose some energy

and they can become

gravitationally

bound to the sun.

And this is basically what's

shown here in this pink line.

So you have a particle

that's bound to

the sun and, or this dark

matter particle and it will

maybe this orbit brings

it through the sun

and it has a higher chance

of interacting again.

It will lose more energy

and eventually sink

to the center of the sun.

So if this process happens

over millions of years,

we basically accumulate

in the center of the sun

dark matter.

And when you have an enriched

region of dark matter,

eventually it will also

interact with each other

and when it interacts,

it can produce the

standard model particles.

Now from all these

particles that are produced

in the center of the sun,

they are basically no particles

that could make it out,

only neutrinos, are the

only particles that can

make it out of the sun.

So neutrino, I should

have also mentioned

also called the Ghost

Particles because they

interact so rarely, so they

can make it out of the sun

and then come to the Earth.

And if we detect such

a neutrino with the

IceCube Detector and see

that the signal points back

to the center of the

sun, then this is a

smoking gun signal

for dark matter.

Now we have performed

such a search,

actually several searches.

This is actually some

results from the scientific

papers that we have

written on this.

Basically on the bottom

left, you can see

we are basically counting

the number of neutrinos

that we observe in

direction of the sun.

And this is actually what's

shown in these black dots here

and this gray band is actually,

maybe just look at

one of the--

yeah, one of this

bottom region here, so.

And this gray band

is actually what

we expect from a

background from

neutrinos that are

naturally produced

in the Earth's atmosphere.

And you can see that this

gray band which is kind of

the natural background

is basically flat and

the dots that we observe

are pretty much just scattered

around it which means

we don't see any excess

of events or any

additional neutrinos coming

from the center of the sun,

so which is unfortunate,

which means we have not

seen any dark matter

that's captured in the sun.

Otherwise, also if we

would have seen it,

for sure you would have

heard about it already so. (laughter)

And then on the bottom right,

is actually the results plot,

so this actually shows,

and on the X axis, so

on the horizontal axis,

you have the math of

the dark matter particle

and on the vertical

axis is basically the

interaction cross-section

or how strong this

dark matter particle would

interact with ordinary matter.

And, this red line

at the bottom,

this is actually

the result from the

IceCube Neutrino Telescope,

so it actually shows

that the IceCube results

are very relevant.

So also on there are shown

some other experiments

and you can see that IceCube

actually has some of the

strongest bounds

on dark matter,

so we have not found dark

matter, but we can still

exclude some parameters space,

which is then important

for theorists, who are creating models for dark matter.

To know kind of where

there is no dark matter.

So these searches are

actually very important.

There are many other ways

also of how we have searched

for, indirectly for dark matter.

So we have looked for

dark matter annihilation

in our galaxy, in

the galactic center,

in small galaxies,

in galaxy clusters.

In all those we

have not found any,

any evidence for dark matter.

And similar, also other

observatories observing

with gamma rays, they

have not found any,

any evidence for dark matter.

Now one of the things

that we have, however,

seen with IceCube

recently is we observed

very high-energy neutrinos.

This is actually following

this and also the

completion of the IceCube

Neutrino Telescope,

we have also won this

Breakthrough of the Year

from Physics World and

this is actually a very

big or important discovery

because for the first time

we have observed

energetic neutrinos from,

yeah from,

of extraterrestrial origin.

So they are from somewhere

from outer space.

And we still don't know

where these neutrinos

are coming from.

So these neutrinos have

humongous energies.

So they actually have

energies much higher

than the energies that

are created, for example,

at the LHC, at the

particle accelerator.

Basically a thousand

times higher in energy

are these neutrinos

or some of the neutrinos

that we have observed.

And the big question is

where are these

neutrinos coming from?

So there are some natural

astrophysical sources,

source candidates

like gamma ray bursts,

active galactic nuclei.

But also people

have suggested maybe

there's some new physics.

So it could also be, and

so we are also looking if

these high energy

neutrino flux has any

exotic origin or origin

from dark matter so.

Okay so, with that,

actually I'm come to the end

and so let me conclude.

So first of all,

we know that most

of the universe is

made out of dark matter.

So there's overwhelming

evidence for the existence

of dark matter and I've

showed you at the beginning

of this talk the different

ways how we have found

the evidence for the

existence of dark matter.

So for example in large scale

structure of the universe,

the galactic rotation curves,

through gravitational lensing,

cosmic microwave

background and so on.

So there's overwhelming

evidence for the existence

of dark matter on all

scales in the universe.

And we tend to believe

that this dark matter

is a new type of

matter that we have--

Yeah, a new type of

matter and we have found

or we have identified

certain properties of it.

So it has to be stable,

it's non-barionic,

not very strongly

interacting and it's also not

absorbing or emitting

light and yeah.

It's stable and not decaying.

And to understand

the universe, really,

we have to understand

or we have to learn

what dark matter is and

that's why it's such important,

such, yeah, that's why

it's so important to look

for dark matter and all these--

They're intensive

efforts now ongoing,

by searches

at particle accelerators

indirectly through looking

for the annihilation of

dark matter and directly

looking for the scattering

of dark matter with nuclei

and with, through all

these searches we have--

We were able to already

exclude some of the models

that have been proposed

to explain dark matter

but there's still plenty of

parameter space out there

to explore and really we

have to find dark matter

to understand the universe

and to answer the most,

one of our most

fundamental questions,

what is the world made out of?

And so I hope you enjoyed

this talk and also

please remember October

31st, Halloween, no.

No, it's Dark Matter Day,

so that time

you can learn more

about dark matter so.

Thank you for your attention.

(applause)

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