Seeing a Black Hole with a Planet-Sized Telescope | STELLAR

published on July 17, 2020

Thank you to Draper and its Hack the Moon initiative for supporting PBS Digital Studios 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 want to see where I came from, you’ll 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 Joe And if you point enough radio telescopes at the exact same spot, and you have access to a supercomputer, well, you can even see something we once thought was unseeablea black hole 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 supermassive black hole weighing about 65 billion times the mass of our sun, at the center of the M87 galaxy, 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 as a larger telescope, 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 had been hinted at by John Michell as far back as the 18th century Objects that 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 20th century scientists were looking for black holes, but how 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 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 But luckily, space is mostly transparent to radio waves, so that’s what the EHT team chose to look for But that gave astronomers one more problem to solve Radio waves have very long wavelengths, and the longer the wavelength of light you use, the more difficult it is to produce a sharp image Not to mention, as massive as black holes are, its very tiny in the sky From our vantage point on Earth, seeing M87* in the sky is like trying to see a bagel on

The moon The solution? A telescope the size of the Earth Geoff, it's so nice to meet you It's really great to have you here, Joe You have got to tell me how you used those things to take that awesome picture We are using with the Event Horizon Telescope, effectively, a telescope that has a resolution

A thousand times better than the Hubble Space Telescope The way you get finer and finer detail, better angular resolution out of telescopes is you build a bigger diameter aperture So what we do is take telescopes that are located around the world, all radio 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 the telescopes, carefully aligned We can get our clock aligned to more than a picosecond A normal stopwatch goes out to like two places, maybe, and you're going like eleven places beyond that Exactly! Over several nights in April 2017, EHT pointed telescopes at 8 different locations around

The world at the black hole, including the eight antennas here at the Submillimeter Array on Mauna Kea To act as one, they synchronized their observations using an extremely precise clock at each site This clock, called a hydrogen maser, can keep time to within a billionth of a second Then by combining all the data in a supercomputer, 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 supercomputer, 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 its concrete shell, and it sends up its 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 what 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 timestamp it and then we use the hydrogen maser to make sure that on the shortest time scales, everything's aligned just fine This is where our part of the EHT data comes in and we record the light and it gets stopped forever

But this isn’t the end of our story EHT is now trying to take a picture of the supermassive black hole at the center of our very own galaxy in the constellation Sagittarius Thanks to generations of scientists, we’re long past using just our eyes to see the universe With each new discovery, one mystery ends only to reveal ever greater mysteries

For new scientists to uncover, and to keep us all looking out at the stars in wonder If you thought a planet-sized telescope was big, just wait until you find out how big the universe is Check out Matt O’Dowd from Space Time on the next episode Thank you to Draper and their Hack the Moon initiative for supporting PBS Digital Studios You know the story of the astronauts that landed on the moon now you can log on to wehackthemooncom

To discover the story of the male and female engineers who guided them there and back safely Hack The Moon chronicles the engineers and technologies behind the Apollo missions Brought to you by Draper, the site is full of images and videos and stories about the people who hacked the moon PBS is bringing you the universe with the SUMMER OF SPACE, which includes six incredible new science and history shows airing on PBS and streaming on PBSorg and the PBS Video app Watch it all on PBSorg/summerofspace

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