Original subtitles

(ambient music)

- [Narrator] Black holes, where time and space converge

under gravity's immutable power.

These extremes of nature, once considered improbable,

are now giving up their secret.

In fact, scientists have been able

to imagine the impossible,

the black hole at the center of our galaxy.

We can now peer into the abyss.

(dramatic upbeat music)

(spacecraft whooshing)

(satellite whooshing)

(rocket rumbling)

(particles hissing)

(graphic whooshing)

(graphic whooshing)

(dramatic music)

The concept of black holes was first proposed

by the German astronomer and physicist Karl Schwarzschild,

barely a year after Albert Einstein had published his works

on the field equations of gravitation in 1915.

Schwarzschild wrote to Einstein from the German trenches

of the First World War, detailing his mathematical results

of his gravitational equations.

Sadly, the brilliant scientist later succumbed to a skin

disease he contracted in the trenches at the age of 42.

The existence of these so-called frozen stars was written

about and debated for 50 years.

In 1967, physicist John Wheeler coined the term

black hole to describe these impossible objects

and the conditions that would create them.

New Zealander Roy Kerr advanced the concept

by publishing a solution to the equations

which would require that black hole spin,

like all other astronomical bodies.

Then Stephen Hawking and Roger Penrose

theorized that black holes could emit radiation,

now called Hawking radiation.

The theory; if a black hole had no material to absorb

and grow, then a black hole could evaporate,

effectively shrink, and die.

All scientists had to do was find one to study.

Quasars, the tremendously bright distant objects,

were factored in as a strong case for black hole accretion,

the only imaginable energy source

capable of such incredible luminosity.

In 1964 astronomers discovered one of the brightest

X-ray sources in the sky,

in the constellation Cygnus, and labeled Cygnus X-1.

The powerful source didn't coincide with

any bright optical (rumbling)

or radio source, leaving it in the mystery basket

of observations.

Before long, with advancements in computers and space-based

telescopes like Hubble, black holes were eventually

detected, or their effect on their surrounds were detected,

as black holes, by their nature, can't be seen.

- Black holes are these incredibly fascinating

but mysterious objects, we know they sit at the hearts

of galaxies, and they drive how those galaxies grow,

and how those galaxies die.

They swallow gas and stars up.

They're also these incredibly enigmatic and mysterious

objects that live at the boundary between our two great

theories of physics; general relativity,

which describes gravity, and quantum mechanics,

which describes the smallest things in the world.

- Black holes are literally gravity run amok,

they are purely gravitational objects predicted

by Einstein's theory of general relativity.

And their most notable and terrifying feature is

that things go in and they never come back out.

- Wonder comes to my mind first.

Such objects were never expected

to exist in nature until very recently.

As a matter of fact, I was a complete skeptic

about black holes as recently as 20 years ago.

- Black holes are places where Einstein's theory

of general relativity is the whole story,

not merely a perturbation on top of Newton's theory,

which explains the dynamics of planets in our solar system.

As a result, black holes provide a unique environment

in which to probe general relativity, specifically,

and strong gravity, generally,

and its implications across the cosmos.

- If you want to make a test of the fundamental theories

of the universe, you want to go to the most extreme

laboratories in the universe, and a black hole is that.

- Seeing a black hole actually allows us to

not only know they exist,

and not only know an event horizon exists,

it also allows us to test some of the very basic predictions

of the theory of general relativity of Albert Einstein,

which really describes space and time

in its completeness, and that has never been tested before.

- If you like Einstein's theory of gravity,

then black holes are, you know,

one of the most interesting examples of this theory,

and this is my role within this project,

I am a theorist, I work with, you know,

equations and simulations, and my role is to

try and understand whether the image that we produce

corresponds to the predictions of Einstein's theory,

or maybe to something else.

- From the physics side

I find that more an interesting question, that this is

basically some kind of rent or terror, maybe, in space time,

and a place where we don't understand the physics and

have a lot of serious questions about information theory.

- I was very excited the first time I saw the first image.

For a long time this was purely theoretical.

We were predicting that we would see certain features

in the image, but we didn't really know was it really there,

and now we know.

And it was exciting that all of that uncertainty

collapsed in that moment.

(dramatic music)

- So as the magnetized gas is falling onto the black hole,

it heats up, and therefore generates the light

that we then see.

Now, from our daily experience, we expect that light travels

on straight paths and straight trajectories,

we call them rays.

Here, the situation is very different,

we have a black hole sitting right there.

So what the black hole is doing,

it is deflecting and bending the light rays away from the

straight paths that we understand in our daily life.

(particles fizzing)

And in fact, it can be so strong

that we can see things that are behind the black hole

that we thought are obstructed by it,

just because the black hole is bending the light rays

into our line of sight.

(dramatic music)

- [Narrator] Scientists began running

simulations on supercomputers.

Multiple computational models were visualized

to better understand what they might find

in the data collected from their observations.

- After we computed the radiative signature

of our simulations

we have to compare them to the observations,

and this can be imagined as you are in a stadium

during a football match, and you have an image,

and you want to figure out if this person, or whatever

is on this image, is among the spectators in the stadium,

so what you do is, you take this image and try to match it

with all the 60,000 spectators in the stadium,

and you do this while you rotate it, you scale it,

you increase the contrast, and you try to figure out first

what is on your image;

is it a person, is it a cat, or whatever?

And try to match this to the spectators.

And this seems trivial, but it's not.

It's a highly computational, demanding process.

So we need a super computer, which we have in Frankfurt,

and we developed a so-called genetic algorithm,

which is a very smart way running through these images

and try to adjust them.

And this takes roughly a month.

And after this calculation time

we have maybe 10 of those spectators which match your image.

And this is very similar to what we do in the EHD.

So we try to compare and match our observations

with the theoretical predictions.

- So what is most surprising of this experience

is that we managed to get a very good image the first time

we tried to synchronize all of these telescope

at the same time.

It is not so surprising that we obtained the image

that we had predicted through simulations,

because while we believe our simulations are correct,

and because we believe that the theory

of Einstein's general relativity is the correct one.

(dramatic music)

- In 2019, they achieved their result,

an image of the shadow of a massive black hole

in the distant M87 galaxy.

It was a world first achievement

celebrated around the globe.

- I think we had been extremely lucky.

I'd expected that we have to work for years and years

through many observations until we get a final image.

And then we look at our first source and we see that ring,

we see the event horizon, and we see that shadow,

that dark region, and you know immediately,

we are looking at an event horizon,

at a black hole from all sides at once in this thing,

we see at a region where time stops.

This is very different part of the universe

that we're seeing for the very first time.

- We want you to take an image of a black hole.

And the problem with black holes is

that they are very small.

So you want to take a very big black hole,

which unfortunately is very far of away from us,

and so you need a big telescope.

This telescope is a hundred meter in diameter,

but is not enough, you want a bigger telescope,

and of course it's impossible to build.

But you can create a virtual telescope

by joining different telescope in different locations.

And so you can build a telescope

which is as big as the Earth.

And in fact, that's exactly what we've done,

we joined telescope like this

with telescope on the United States,

and in one even in the South Pole

to get a very sharp image.

Actually, an image is comparable

to seeing an orange on the moon.

(dramatic music)

Black holes tell you that are regions inside them

that cannot be explored.

And for a physicist, this is very disturbing

and attractive at the same time because,

you know, we don't like to have doors which we cannot cross.

And in particular, inside black holes,

physics is even expected to to fail completely.

And so, this even adds fascination to these objects.

- The future of the project will hopefully going towards a

new understanding of more fundamental questions in physics.

If this is true, that black holes are the extreme objects

where we can study gravity,

and we know that general relativity,

which describes black holes in the outer part,

up to the event horizon, breaks down at the event horizon.

So the big hope is that with more data we might be be able

to study the physics beyond general relativity.

So maybe there might be quantum physics ruling

beyond the event horizon, or the combination

of quantum physics and general relativity,

which would be the theory of quantum gravity,

which is nonexistent at the moment,

but we might learn more about this

with the help of studying black holes.

(people chattering)

- Our experiments are like an arctic expedition; we have to

plan for months, and months, and months in advance,

gather our equipment, and then we have this great migration

of people to observatories all around the world.

We stay up all night, we run our telescopes,

and then we have this terrible period of waiting

where we don't know if it's all worked.

We send all of our data together,

and only when it's truly combined do we know if it's worked.

And then the even harder part begins of analyzing

that data, and being very, very careful,

doing all the checks and balances

to know that we got it right.

(dramatic music)

- Data analysis, imaging black holes,

and doing simulations is very exciting,

it's also very difficult and requires a lot of patience,

it's a very long process,

but seeing the final product is very satisfying.

- The Event Horizon Telescope Collaboration

is this amazing group of fantastic people

from all around the world, Americans, Europeans,

people from Asia, who've come together

with all their technical expertise and scientific expertise

to make this image of a ring around the black hole.

(people chattering)

The future of this project is amazing, because now that

we've seen what we're after, we have so many more questions

to ask about it, to push into the regime of,

can we decide, is Einstein right?

Can we study how gas really gets swallowed

by the black hole?

Can we see a giant eruption of radiation,

of particles coming out of the system?

So many things to do, we've really only just begun.

- Now we wanna make the first movie.

Now we want to understand how spacetime

rotates around the black hole.

We'll do that by putting more telescopes around the world

to make our virtual lens even better.

- It was a fantastic way

of combining talent from different people

in a way that otherwise would have not been possible.

In order to take this picture you need the cooperation,

the simultaneous observations,

of many radio telescopes across the planet.

You need to have the largest possible network

of telescopes taking the same image at the same time.

(dramatic music)

- [Narrator] New goals for the Event Horizon Telescope

were quickly set.

The M87 massive black hole is far away from earth.

Scientists wanted to get a closer look,

and decided to image another black hole

at the center of a galaxy, one much closer,

but also much smaller, and shrouded in gas and dust.

(dramatic music continues)

- So if you try to look into the center of galaxies

it's usually blocked from you by dust and other stuff,

and the radio you can look through.

Like here, today we can look through rain,

you can look through clouds, and we can look through dust.

And with combining radio telescope like this together

with other telescopes in the world,

you can peer right into the center of the galaxy

and see this black hole.

(dramatic music)

- The science result, it's just one point in time,

in the project, and we are always learning more

about how the instrument works, how people work,

how new theories come about.

And so this is an evolution, in my perspective.

It's not just one point

in time where you say, "This is it, that's done."

It always continues.

- So we still have a lot of mysteries to be solved,

you know, problems to be tackled.

There are still many questions about black holes.

So I would like to study farther in the black holes.

(dramatic music continues)

- [Narrator] The Event Horizon Telescope targeted

the black hole in Sagittarius A, which is the location

of the center of our very own Milky Way galaxy.

- The long term future of experiments like

the Event Horizon Telescope is moving this kind

of instrument into space and starting imaging black holes

from space, which improves a lot this kind of observation,

because it allows us to have even higher angular resolution

than what we have now.

So we will be able, maybe in 20 years, 30 years,

make a very accurate images

of the event horizon of a black hole.

(ethereal music)

- Not only did scientists image the black hole,

they sampled the radio emissions

from the surrounding hot gases

giving us an audio impression; the sounds of a black hole.

(black hole whirring)

(dramatic music)

- So far we've been looking at

the closest massive black hole,

but quasars, they are very distant from us.

With gravity, we can see the motion of gas,

and resolve the sizes of these regions,

and thereby measure then the mass precisely.

So if you can do this for many, many quasars,

many distant objects, then you can solve perhaps the riddle

how massive black holes play the role

in the evolution of galaxies.

We now know that basically every galaxy has at its center

a massive black hole of different masses.

We'd like to understand that in detail.

There is, if you like, a symbiosis

between these black holes and galaxies,

and we need to understand that in order to understand

the evolution of the universe.

(eerie music)

- Studying the data from the Event Horizon Telescope

continues to reveal more detail.

In this case, X-ray emissions reveal

magnetic lines of force through the orbiting gas clouds.

Further study of the X-ray emissions is currently underway

with a new space based X-ray observatory,

the imaging X-ray polar imagery explorer, or IXPE.

(IXPE whirring)

Launched in 2021, IXPE is designed to observe

extreme cosmic objects, like pulsars, neutron stars,

and black holes.

This satellite is able to study X-ray radiation

which is polarized or oscillating in a particular direction.

This reveals more detail of the physics

of these high temperature environments,

particularly around black holes.

- But there are two other parameters that we could

look at if we only had the tools to do that,

and those have to do with the polarization,

the degree of polarization, and the position angle,

the angle associated with the polarization.

So by doing this mission, we're opening up

two more degrees of freedom to be able to try to understand

how are the X-rays produced, what are the models

we have to be able to predict

the polarization that we will turn out to measure.

So it's really exciting.

Our science working group has studied it all.

We have seven different teams studying different classes.

So for example, the the radio pulsars,

supernova remnants, et cetera.

And so we have, we're gonna be looking at seven different

classes, and several examples of those classes,

so that we get a good preliminary survey

of what polarization is out there.

(upbeat music)

(star whirring)

(star exploding)

- [Narrator] The extreme environments created by black holes

are an opportunity to study many other phenomena.

Neutrinos, the most abundant particles in the universe,

have almost no mass, and very rarely interact with matter.

They seem to be generated in extreme objects

like exploding stars and the fast particle jets

ejected by super massive black holes.

(jets hissing)

Colliding black holes are another event closely watched,

as they generate gravity waves

that ripple through space time

and can be detected here on Earth.

Another recent event detected, was the flipping

of the magnetic field surrounding a massive black hole.

The reversing polarity caused the visual brightening

of the material surrounding the black hole,

and the reduction of its X-ray emissions,

during this time, the X-ray corona disappeared,

and only when the flipped magnetic field gained strength

did the X-ray's emissions recover.

Another black hole has been observed devouring

a star that wandered too close,

(black hole crackling)

The ejected super fast jets of material

interacting with nearby dust clouds,

and aiding to form planets within the material.

These singularities appear to be an intrinsic part

of both the destruction and creation of stars and planets.

While we don't have all the answers

discoveries like this one set us on a path

to understanding more about the universe.

(spacecraft whirring)

(graphic whooshing)