There are 100 billion stars
in our galaxy, the Milky way,
or maybe there are 200 billion or maybe 400 billion.
No one really knows.
In the universe there are 100 billion galaxies.
And as technology improves,
that number could increase to 200 billion galaxies.
No one is certain.
At the start of the 20th century
there was only one galaxy, our own.
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Clearly over the past hundred years,
our knowledge of the universe has expanded,
but there's still a long way to go.
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After more than 40 years, Voyager 1
has left the influence of the solar wind
and is heading for interstellar space.
Most of its instruments have been switched off
and its nuclear battery is running low.
It will be many thousands of years before it reaches
anything other than interstellar debris.
By then, the craft will be long dead.
Cosmic distances are so vast
that sending a probe to investigate anything
beyond our solar system is not practical.
The only realistic way we have of exploring the universe
beyond our neighborhood
is by examining the light that reaches us.
The telescope is the main tool
we have for this investigation.
And for centuries, astronomers have been building
ever larger instruments to see deeper into the cosmos.
In the 20th century, conventional telescope design
reached its limit.
Past eight meters in diameter the curved primary mirror
becomes so heavy that it will sag.
As it is aimed at different targets
its precise curve is distorted by the effects of gravity.
In addition, any extra resolution gained
by the larger mirror is not delivered
because of atmospheric distortion.
One way to solve both these problems
is to put a telescope in space.
The Hubble Space Telescope is the best known example.
While the absence of atmospheric distortion
was a breakthrough producing very sharp images,
both operational and maintenance costs are considerable.
And there are launch constraints on the size of a telescope
that can be delivered to orbit.
But engineers have developed a new generation
of earth-based telescopes with segmented mirrors
that overcome the limits to size and can nullify
much of the distortion caused by the atmosphere.
The twin Keck telescopes on Mauna Kea in Hawaii
were early adopters of this technique.
Both have 10 meter mirrors each in 36 hexagonal segments.
Sensors monitor the mirrors shape
and actuators behind each segment
continually correct for any distortions to the curve.
The system is called active optics.
A similar system that works at a more rapid rate
monitors the stability of a bright guide star
or an artificial guide star generated by a laser.
The adaptive optic system reads wave front changes
in the atmosphere then adjusts the mirror's shape
to minimize any distortion.
This image of Jupiter using adaptive optics
rivals those captured by an orbiting telescope.
Observatories are located at high altitude
where the air is dry
and there is no light pollution from nearby cities.
The European Southern Observatory has clusters of telescopes
at several sites high in Chile's Atacama desert.
At Paranal, four identical large telescopes
each have 8.2 meter mirrors.
They can combine their light using interferometry.
In addition, four auxiliary 1.8 meter telescopes
can link into the cluster.
Collectively they are the Very Large Telescope
Interferometer or VLTI.
Visible light is just a small part
of the electromagnetic spectrum.
ESO has another facility northeast of Paranal
on the Chajnantor Plateau.
Here, an array of 66 radio dishes
observe in millimeter and sub-millimeter wavelengths.
They are linked and also function as an interferometer.
Observing in the microwave part of the spectrum
is particularly useful as these frequencies
penetrate gas and dust clouds
that remain opaque to higher energy signals.
The more widely the telescopes are separated,
the better the angular resolution they can deliver.
This property led radio astronomers
around the globe on a unique collaboration.
If radio telescopes around the world could link up,
perhaps they could see the un-seeable.
General relativity predicted bodies so massive
with such strong gravitation
that not even light could escape from them.
They were called black holes.
And at first they were regarded as a mathematical anomaly,
but evidence mounted suggesting that black holes
were more than just a theoretical curiosity.
At the center of some galaxies light far more intense
than could be expected from stars has been detected.
Massive bodies, such as young stars, attract diffuse matter,
which begins swirling and flattens
into what's called an accretion disk.
Just as planets orbit stars, it's now accepted
that galaxies orbit super-massive black holes.
The very bright light comes from the accretion disk
surrounding the black hole.
Matter in the accretion disk is accelerated
to incredible speeds, generating intense heat.
Along the axis of rotation, jets of ionized material
are ejected at close to the speed of light.
Computer modeling indicated that the vast energy generated
by a black hole's interaction with material
in the accretion disk could be detected.
The silhouette is the event horizon.
The boundary beyond which light cannot escape.
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.
Astrophysicists knew that by linking
widely separated radio telescopes, the resolving power
of the combined instruments would increase dramatically.
The first attempt at imaging the black hole
at the center of our own galaxy was made in 2006,
using instruments in Arizona and Hawaii.
It was not successful, but researchers learned a lot.
Realizing more telescopes were required.
By 2009, an international collaboration
between eight different telescopes had coalesced.
They aim to capture an image of the super-massive black hole
at the center of Messier 87.
So for this experiment it was clear
that we need expertise from completely different areas.
And so we needed someone with imaging capabilities.
We needed someone with numerical relativity capabilities.
And in my case, we needed someone who can try
to find this additional information via pulsars.
And so just being part of this team
means you work completely differently.
The project was named
The Event Horizon Telescope.
Instruments in North and South America, Europe,
Hawaii and even in Antarctica
would unite to form a telescope
with a virtual diameter equal to the Earth.
None of these facilities was designed to work
as part of such a large array and the technical difficulties
facing the team were immense.
Signals from all the sites
would have to be processed at a central location.
Yet the distances that separated them were so great
that a direct line linking them was impractical.
Data transfer would take place via computer hard drives
that were moved from the place of acquisition
to two locations, the Max Planck Institute in Bonn
and the MIT Haystack Observatory in Massachusetts.
The Event Horizon Telescope collaboration
is a collaboration of more than 200 scientists
with different backgrounds.
They all come from different parts of the world.
They have different experiences, different set of skills.
There are engineers, observers, theoreticians,
and they all work together,
not only to image the event horizon of a black hole,
but also to understand what we're seeing.
Theoreticians already understood
that while a black hole could only ever appear
as a silhouette it's influence upon light
emanating from surrounding matter would be dramatic.
By using mathematical simulation, NASA came up
with a moving image of what they thought
the EHT project would reveal.
Viewed from above the swirling accretion disk
appears without distortion.
The smooth inner circle is the photon ring,
light in orbit just outside the event horizon.
When viewed from the side, the black hole's gravitation
bends light from the accretion disk
so it can be seen from several angles at the same time.
But no one really knew what they would see.
For decades evidence had accumulated
that a black hole at the center of galaxy M 87
was consuming huge amounts of material.
Unusually high emissions across the electromagnetic spectrum
were detected in this region and images
from the Hubble Space Telescope revealed
a huge jet of matter extending out light years.
In April 2017, the EHT was scheduled to make a series
of coordinated observations of the heart of the M 87 galaxy.
Each observatory had been equipped
with its own atomic clock
as all data had to be meticulously timestamped.
Good weather had to happen simultaneously at each site
and a go/no-go decision was made several hours
before each observation.
April the 5th, 6th and 7th had good conditions
with data being collected.
Observations were suspended on the 8th and 9th
due to strong winds at the sites in Mexico and Arizona
with the final nights observations
made on the 10th and 11th of April.
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.
During the observation period,
five petabytes, that's 5,000 terabytes of data was recorded.
The hard drives upon which it was stored weighed half a ton.
They were transported to correlators
in Westford, Massachusetts, and to Bonn in Germany.
While this was relatively simple for most sites,
limited access to the South Pole telescope
delayed its data for several months.
Interpreting radio data as a picture
relies upon the black hole's gravitation
bending passing electromagnetic waves.
The EHT will only be able to see the individual points
from rays that are bent toward the Earth.
It is the correlation of all these points
that builds them into a recognizable image.
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.
In April 2019, the Event Horizon Telescope team
released their image of the active center of the M87 galaxy.
At its heart was the silhouette
of one of the largest black holes we know.
It's roughly 38 billion kilometers across,
the diameter of our solar system.
Its mass is 6.6 billion times greater than our sun.
After predictions flowing from the general theory
of relativity more than 100 years ago,
the world finally has proof that black holes do exist.
But this is not the end for the EHT team.
Expanding the number of telescopes in the network
will enhance resolution and there are plans to investigate
the black hole at the center of our own galaxy.
The future of this project is amazing.
We have done something extraordinary.
We've made the first picture of a black hole,
but now we want to do even more.
Now we want to make the first movie.
Now we want to understand how space time
rotates around the black hole.
We'll do that by putting more telescopes around the world
to make our virtual lens even better.
Investigation into black holes
is not restricted to radio astronomy.
The New Technology Telescope at La Sille in Chile,
the first instrument equipped with active optics,
began long-term observation of the stars
at the center of our own galaxy in 1992.
The NTT observed in the infrared part of the spectrum
because only that light was able to penetrate
the heavy clouds of gas and dust
shrouding the central regions of the Milky way.
A team from the Max Planck Institute
plotted the positions of the stars,
building up an image of the way they moved.
They began using the larger telescopes
of the European Southern Observatory at Paranal
when they came online.
Over 16 years, they mapped the paths of 28 stars.
The Milky Way center is one of the most important
laboratories we have to study in very great detail
What's happening in centers of galaxies
in much more detail than we can ever hope to do
in all other galaxies.
Yet, here we are.
We can study whether there is a central black hole,
what happens around it and so forth,
all very general issues,
which you would like to explore and which you cannot
really study that much in detail in other galactic nuclei.
Results show that the stars
are orbiting an invisible point,
which must be our own galaxy's black hole.
Analysis of their highly eccentric paths
suggest the Milky Way's black hole is slightly greater
than 4 million times the mass of our sun.
Of particular interest is the star S2,
which is in a 16 year orbit of the black hole.
It's elliptical path was due to take it to its closest pass
and it's highest speed, in April 2018.
We want to use it as a tool to test
whether general relativity, the theory of Einstein,
is actually wrong or right.
General relativity predicts
that the black hole's influence would distort
S2's light toward the infrared as it reached 3%
of the speed of light, which happened,
yet another vindication for Einstein.
This test is important to researchers
because general relativity predicts that time stops
inside a black hole's event horizon.
And they want to know if the laws of physics
break down approaching these extremes.
Since Copernicus proposed that the planets orbited the sun
astronomers have speculated
about planets orbiting other stars.
Advances in telescope technology allowed researchers
to see dips in the brightness of stars
that could only be caused by a transiting planet.
These fluctuations in intensity gave astronomers clues
about the planet size and its orbit.
A different method monitored the spectral shifts
in a star's light caused
by a consistent change in its position.
Again, only explicable by an orbiting planet.
Using these systems, telescopes around the world
began cataloging exoplanets,
but the methods used were biased toward finding large
planets, similar in size to Jupiter
that had an easily detectable influence on their star.
And of all the planetary systems out there
researchers could only use these methods
for planetary systems that were edge on to the Earth.
Even so the number of exoplanets
we knew about continued to grow.
There were surprises.
In 2012, a French team discovered an orphan planet
wandering across our galaxy. It had no star.
It was detected by its emissions in the infrared.
It's difficult to predict the orphan planet's size,
but it certainly still, at the very least,
several times the mass of Jupiter.
Naturally researchers were keen to see Earth-sized planets,
planets that could possibly nurture life.
When a new and highly accurate spectrometer
called HARPS was installed at ESO's La Sille
three and a half meter telescope this became possible.
Among its discoveries are two planets orbiting Gliese 667C
about 20 light years from Earth.
The star is a red dwarf,
about one third the mass of our sun.
Of particular interest is Gliese 667 Cc,
a planet about five times the mass of the Earth
and at a distance from its star
that puts it in the habitable zone.
Statements about conditions on Gliese 667Cc
have such a large margin of error
that much more work needs to be done before it could
be declared a possible venue for life as we know it.
Another star 40 light years away
has a greater range of possibilities.
TRAPPIST-1 is an ultra cool red dwarf star orbited
by seven planets, all of them close to Earth in size.
To date this is the largest number of exoplanets
detected orbiting an individual star.
At least three of the planets
are considered in the habitable zone.
Many different observatories have been gathering data
about the TRAPPIST-1 system,
but we still know so little about what kind of environments
the different planets might have.
However, the coming generation of telescopes
should be able to analyze the atmospheres
of the TRAPPIST's planets.
So they will remain a region of close study into the future.
At the moment around 3,800 exoplanets have been cataloged,
and that number continues to grow.
In 2018 the satellite TESS was launched
to search for more exoplanets.
To have a clear view of both the Northern and Southern skies
TESS was placed in a 14 day orbit around the earth,
at a 40 degree angle to the plane of the moon's orbit.
It will systematically map 26 segments of the sky,
recording fluctuations in the brightness
of nearby stars that reveal exoplanets.
During its close passes of the Earth,
The planet hunter downlinks its data to sites
across the United States.
Ground-based observatories will then follow up leads
in a more detailed way.
This type of collaboration between orbiting
and terrestrial telescopes is becoming common.
An interesting discovery
came from the young star Beta Pictoris.
Fluctuations in its light did not bear
the rhythmic signature of an orbiting planet.
Further investigation by the European Southern Observatory
revealed three comets orbiting the young star.
Beta Pictoris is only around 20 million years old
and still displays a proto-planetary ring of dust.
In TESS's first year of operations,
at least 29 new exoplanets were confirmed.
With a further 1000 objects of interest
listed in publicly accessible databases.
During its two year life
TESS will image 200,000 celestial bodies,
including 1,000 of the closest red dwarf stars.
And there will soon be a new planet hunter in orbit,
the Wide Field Infrared Survey Telescope, WFIRST,
will use a different technique
known as gravitational microlensing
to detect much smaller exoplanets.
As one star passes in front of another
it's gravitation distorts the distant stars light.
By monitoring the light over time,
a spike in what should be a regular curve
reveals an exoplanet orbiting the lensing star.
But that's not WFIRST's only objective.
There's a gap in knowledge
that some cosmologists find embarrassing.
When quantifying the speed at which galaxies rotate
and the amount of mass they contain
there's a baffling mismatch.
Our laws of physics say that spinning galaxies
do not contain enough matter
and therefore enough gravitation
to prevent them from flying apart, and yet they don't.
Astrophysicists came up with the dark matter hypothesis.
This is not just matter that doesn't glow.
It is matter that interacts with nothing else.
The only influence it has is via gravitation.
Halos of dark matter surrounding galaxies is the current
method to explain why they move the way they do.
Estimates say there is five times more dark matter
than matter, yet no one can explain it.
Another fascinating anomaly is that early galaxies,
galaxies whose light has taken more than 10 billion years
to reach us, rotate at a slower rate.
The influence of dark matter is not as pronounced.
New generations of telescope are being built
to help researchers answer some fundamental questions
about the laws governing the universe,
but it seems that cosmology has reached a stage
where it is just discovering how little we know
about what lies beyond the solar system.
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