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The first image of a black hole's event horizon. (EHT Collaboration)

LIVE: Scientists Reveal Groundbreaking Results From Event Horizon Telescope

MICHELLE STARR & SIGNE DEAN
10 APR 2019

Folks, you're looking at history. Astronomers have just released the very first direct image, ever, of the event horizon of a black hole.

Stop scrolling and just go back up and look at it for a second.

 

Before this, every image of a black hole was a simulation or an illustration. This 'photo' was taken of the supermassive black hole at the centre of a giant elliptical galaxy called M87, around 55 million light-years away. This thing is humungous - around 6.5 billion times the mass of the Sun. Isn't it just glorious?

It's the first result from the Event Horizon Telescope, a global collaboration that turned radio telescopes around the world into one giant telescope, expressly to find out what a black hole looks like, in real life.

Beautifully, it matches predictions dating back decades. This is it. We now know, for a fact, that the astrophysical objects that were just theory a mere 50 years ago are really what astronomers and physicists thought they were.

"The confrontation of theory with observations is always a dramatic moment for a theorist," said astrophysicist Luciano Rezzolla of Goethe Universität in Germany. "It was a relief and a source of pride to realise that the observations matched our predictions so well."

It looks a bit like a blurry orange coffee stain, but here's what we're looking at. In the middle is the shadow of the black hole. We can't actually see the black hole itself, because its immense gravity doesn't allow any detectable radiation to escape, so it appears as opaque space.

 

Around it is the accretion disc. M87's supermassive black hole is active, which means it's surrounded by a tremendous accretion disc of very hot, swirling gas and dust that is slowly falling into the black hole. That disc gives off a lot of radiation.

Because the disc is rotating, it appears brighter where it is moving towards us, and dimmer where it is moving away. This effect was predicted by Einstein's theory of general relativity.

The image isn't high-enough resolution at this point to measure the rotation speed, but the EHT team could tell that it's rotating in a clockwise direction.

Future analyses of the data - which are all being made publicly available - could reveal more details, such as how closely the image matches predictions of general relativity. It could also help astrophysicists figure out the mechanisms that produce the enormous relativistic jets that shoot from active black holes.

You can read the full news story on the announcement here.

Read our live blog of the press conference unveiling the historic image below.

8:45 am EDT: It's T-minus fifteen minutes until the announcement begins! Make sure to keep refreshing this page for all the updates as they come! Apologies in advance for any typos we make in our excitement. (If you're watching along, best to open the livestream in a new tab.)

8:46 am EDT: Okay, so here's what we're waiting for.

Two black holes have been the focus of the EHT's attention: Sagittarius A*, the supermassive black hole at the centre of the Milky Way galaxy, and the supermassive black hole at the centre of another galaxy called M87.

Sgr A* is about 4 million times the mass of the Sun, with an event horizon 44 million kilometres in diameter (about 30 times the size of the Sun), and 25,640 light-years away.

 

M87's black hole is a lot bigger. It's about 6 billion times the mass of the Sun - around 1,500 times more massive than Sgr A*. But it's also around 2,000 times farther, at a distance of 50 million light-years, so its apparent size should be a little smaller.

Trying to image these targets is like trying to photograph a tennis ball on the Moon, through clouds of dust.

8:48 am EDT: We don't know which black hole we might see, or what it will look like.

French astrophysicist Jean-Pierre Luminet, who gave the world the first visual simulation of a black hole back in 1978, told us last week, "I have not seen the image, but I suspect that the M87* BH image could be better than that of SgrA* because the latter could have more perturbing diffusion effects." In other words, its stronger gravity could produce stronger effects. Neat!

8:50 am EDT: More facts while we wait!

If what we're getting are the pictures, we won't actually see the black hole itself, because the gravitational pull is so strong that no electromagnetic radiation can escape - not even light is fast enough for black hole escape velocity. That point of no return is called the event horizon.

We think we will see the silhouette of that event horizon, backlit by the very hot gas and dust around the black hole, bending and magnifying the spacetime around it.

8:51 am EDT: We are nervously eating snacks.

8:52 am EDT: Here's why we're so certain that it's indeed a black hole we could be seeing shortly.

Theoretical astrophysicist Philip Hopkins of Caltech (who is not involved in the EHT) told us, "I don't think you're going to find astrophysicists who think that the thing in Sgr A* at the centre of the galaxy or at the centre of M87 is anything but a supermassive black hole, because the constraints from dynamics of stars around those systems have ruled out any other kind of compact astrophysical object that we know how to make with present physics."

So if it ain't a black hole, a lot of scientists are going to have... a lot of work to do!

8:55 am EDT: FIVE MINUTES TO GO!

8:56 am EDT: While we wait, let's discuss the Event Horizon Telescope itself. The EHT is a radio telescope, which means it can pick up the long, low-frequency radio wavelengths that penetrate the clouds of dust obscuring black holes.

It's also not just one telescope, but an entire network, spanning the globe. It uses a radio astronomy technique called very-long-baseline interferometry (VLBI), in which multiple telescopes work together as one. So, the EHT is effectively one telescope the size of Earth. It has unprecedented resolution.

08:59 am EDT: One minute! We're not counting, you're counting.

09:00 am EDT: Okay, okay, deep breaths. We are not hyperventilating at all. Here we go!

09:00 am EDT: IT IS DEFINITELY THE PICTURE.

9:02 am EDT: The livestream has commenced, and we're going to have a brief welcome before the simultaneous announcement starts across the globe! Speaking first is Carlos Moedas of the European Research Council. He is very emotional, and can we blame him? No!

"Einstein could not imagine what he discovered… To take a picture of something one man dreamt 100 years ago, you need people from 40 countries."

"If there is a big moment for all of us, it is today."

9:04 am EDT: You can follow along on Twitter with the hashtag #EHTblackhole

09:08 am EDT: Here it is! Everybody, WE HAVE RECEIVED THE PICTURE!

09:10 am EDT: Oh wow. Look at that. Look at it. That's a BLACK HOLE'S SHADOW. That's the accretion disc.

09:13 am EDT: "Even a child knows what a black hole is, and the best description actually came from a child - it's just a hole you cannot fill," says Luciano Rezzolla from Goethe University Frankfurt.

"You may wonder, how do you know it's a black hole? The answer is that it matches extremely well what we predicted in theory."

09:14 am EDT: We have constructed tens of thousands of predictions of black holes, Rezzolla says, and some of these come very close to the image captured by the Event Horizon Telescope.

09:15 am EDT: Eduardo Ros from the University of Granada takes the stage to tell us how the observations were taken. What was really important is that they used telescopes where the atmosphere is very thin and dry, to avoid atmospheric interference. Then they had to pay careful attention to the weather, and be ready to take observations on short notice.

09:17 am EDT: The hard discs from the Antarctica telescope had to sit in storage over winter, because a plane couldn't get in and out easily to transport the data!

09:19 am EDT: Monika Moscibrodzka from Radboud University is explaining what we learned. Over four days' observing time, they saw that the ring didn't change size, and didn't go away. That means it's likely a permanent object.

The change in the light in the ring - it's brighter at the front - indicates rotation. The image is not yet clear enough to measure the rotation, but we do know it's clockwise.

09:22 am EDT: ALL THE DATA is being made public! That is awesome. Six papers are due to appear in The Astrophysical Journal Letters, and they are listed here for you to check out.

09:26 am EDT: The picture is of M87*, but the team is confident they're going to bag Sgr A* soon, so they ask us to "stay tuned".

"This story is not the story of one hero. It is the story of many heroes."

09:29 am EDT: And that's it, that was the announcement! We are now in question time. PHEW, we still can't believe that we're staring at the first-ever image of a black hole. Just... look at it.

09:36 am EDT: The questions are so interesting! Meanwhile, we're gathering up more info about the science behind this huge achievement and will publish a separate article on that soon. Thank you so much to everyone who stayed tuned into our live blog!

We are standing at the dawn of a new age of black hole science.