Decades of work behind black hole image

The technical feat of combining data from eight different telescopes around the world to make a single image is extraordinarily difficult, and was 10 years in the making, writes the University of Auckland's Dr JJ Eldridge

Since yesterday, a fuzzy red/yellow blob with a dark shadow has been posted around the world on all news platforms - the first ever image of a black hole. Why is this a big deal?

Well for a start, general relativity is one of the most amazing theories in physics today. Since its publication in 1915 many researchers around the world have built upon it and tested it to ever greater detail and precision. The shadow in the centre of the black hole is the latest, and arguably, simplest test.

General relativity predicts that black holes exist when the density of an object becomes so high that not even light can escape it. The shadow we see is the event horizon, in some ways it is an edge of the Universe, it is a one-way door, anything crossing it cannot return.

It is strange to think that we have studied black holes for decades, and even in 2015 detected the gravitational waves released by two merging black holes but we have never seen this edge before. And now we have. It’s an old saying but, “seeing is believing”.

It should also be noted that this result is the work of a huge number of people building up to our current understanding of these objects. While Albert Einstein created General Relativity, it was Karl Schwarzschild who used it to mathematically describe the most basic type of non-rotating black hole.

However, this black hole in M87 is a rotating black hole, the mathematical description of which is fiendishly complex. It was New Zealander Roy Kerr who created the Kerr metric, the severely warped spacetime around such a black hole.

And then what might these black holes look like? These initial calculations were made by researcher Jean-Pierre Luminet some 40 years ago. They bear a strong resemblance to the images we saw today.

At the same time, the technical feat of combining data from eight different telescopes around the world to synthesise a single image is extraordinarily difficult. It required a huge team of over 200 people from 20 different countries to come together, work together and form the Event Horizon Telescope.

But it’s funny to think, out of all these large number of people, over so many years it still came down to a single person pushing “run” on their code to combine the data. While there were several teams who made versions of the images, the most widely publicised has been Assistant Professor Katie Bouman who made the first images.

For me, it’s the human story of so much effort, over so many years to make a simple test to look at a black hole for the first time that is so amazing. However, the scale of this black hole is almost as exciting – and it is because it’s such a monster that we are able to see it.

It is 6.5 billion times the mass of our Sun, it is 100 billion kilometres wide, almost the same distance as Voyager has travelled and it is 53 million light-years away at the core of a galaxy called M87.

Of course, now we have many more questions that we could ask… and that is also what is exciting – where this new observation and technique will lead next.

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