It Takes A Village To See A Black Hole

Imagine for a moment that I'm a beam of light, far outside the visible range, traveling from a star in a distant part of the universe.

If you wanna see where I came from, you're gonna need two things; a series of radio telescopes like the Submillimeter Array behind me and one of the most accurate clocks in the world.

I've traveled a long way to get here so when I arrive on Earth, I'm an extremely faint signal.

To see me, you'll need to point multiple antennas at the same point in the sky.

Antennas like these.

But my faint signal will arrive at each telescope at ever so slightly different points in time.

Using our incredibly precise clock, we can synchronize these signals and combine those faint images to make a much more vivid me.

And if you point enough radio telescopes at the exact same spot and you have access to a super computer, well you can even see something we once thought was unseeable, a black hole.

(digital music) On April 10, 2019, astrophysicists from the Event Horizon Telescope Collaboration electrified the world with the first ever image of a black hole.

This astronomical donut smothered in orange frosting is a super massive black hole.

It weighs about 6.5 billion times the mass of our own sun at the center of the M87 Galaxy.

It's about 55 million light years away in the constellation Virgo.

The orange ring that we see are photons produced by hot, swirling gas orbiting around the edge of the black hole.

The inner edge of that ring is the event horizon, a precipice of no return.

The EHT is not just one telescope, it's many telescopes including these here working together in concert and it let us see something we used to think was impossible.

The idea of dark massive objects in space dense enough to capture light itself have been hinted at by John Mitchell as far back as the 18th century.

These objects came to be called dark stars.

But the first modern hints about black holes arrived as an abstract mathematical idea inside Einstein's Theory of General Relativity.

Over the rest of the 20th century, scientists started looking for black holes.

But how to do you observe the absence of light?

Creating an image of a light swallowing cosmic abyss is not unlike tuning in to hear your favorite song on the radio, except imagine that this is your receiver.

Black holes may not produce any light waves in the visible spectrum but those hot clouds of swirling gas at their edge produce light in other parts of the electromagnetic spectrum that we can detect.

Luckily, space is mostly transparent to radio waves so that's what the EHT team chose to look for.

That gave astronomers another problem to solve.

Radio waves have very long wavelengths and the longer the wavelength of light that you use to produce an image, the more difficult it is to produce a sharp image.

And not to mention as massive as a black hole is, it's very tiny in the sky.

From our vantage point on Earth, M87 is like trying to see a bagel on the moon.

The solution, build a telescope the size of the Earth.

Geoff, so nice to meet you.

- Really great to have you here Jeff.

- You have got to tell me how you use those things to take that awesome picture that I've seen.

- We are using with the Event Horizon Telescope, effectively a telescope that has a resolution 1,000 times better than the Hubble Space Telescope.

The way you get finer and finer detail, better angular resolution out of telescopes is you build bigger diameter apertures.

So what we do is we take telescopes that are located around the world, that already exist, and we connect them together and we use them to build a single telescope.

It's a mirror the size of the whole planet, but most of the mirror is missing.

In order to make that mirror, we have to have the clocks between these telescopes carefully, carefully aligned.

We get our clock aligned to better than a pico-second.

- A normal stopwatch goes out to like two places maybe and you're going 11 places beyond that.

- [Geoff] Exactly, exactly.

- Now over several nights in April 2017, EHT pointed telescopes at eight different locations around the world at the black hole including the eight antennas here at the Submillimeter Array on Mauna Kea.

And to act as one, they synchronized their observation using extremely precise clock at each site.

This clock called a Hydrogen Maser can keep time to within a billionth of a second.

And then, by combining all the data in a super computer, they created the first ever radio image of a black hole.

We're in a very big science room, what happens in here?

- So, it's a big super computer, specially designed for the purpose of combining the signals together from all of our different telescopes and also to take the combined signal and format it in a way that we can use for the Event Horizon Telescope.

- This is where you saved the black hole.

- Exactly, light stopped right here.

At the other end of this lab is where the clock signals come in.

So the Hydrogen Maser is in the bunker that's underneath here, in it's concrete shell.

And it sends up it's reference tone 10 megahertz signal.

And that signal gets distributed to all the different clocks that are used throughout the system.

We're interfering waves together.

That's where interferometry means.

And so if those waves move back and forth a little bit, when you interfere them, they destructively interfere and you lose your signal.

We use GPS to time stamp it and then we use the Hydrogen Maser to make sure that on the shortest timescales, everything's aligned just finely.

This is where our part of the EHT data comes in and we record the light and get stopped forever.

- This is not the end of our story.

EHT is now trying to take a picture of the super massive black hole at the center of our very own galaxy, in the constellation Sagittarius.

But thanks to generations of scientists, we're long past just using our eyes to see the universe.

With each new discovery, one mystery ends only to reveal even greater mysteries for new scientists to discover and to keep us all looking out at the stars in wonder.

(digital music) If you thought a planet-sized telescope was big, just wait until you find out how big the universe is.