On April 10, 2019, the Event Horizon Telescope project released an image that to this point had been believed to be impossible: we had captured an image of a black hole.
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This image flooded the news and social media, and despite some criticising the so called "blurriness" of the image, many were in awe of this image of an object that captures so many of our imaginations. But just what is this object, and how did we manage to pull off this stunt?
The black hole in question lies at the centre of a supergiant galaxy known as Messier 87 (or M87), one of the largest galaxies in the observable universe.
The black hole itself is also massive: known as a "supermassive black hole", it has a mass equivalent to 7 billion Suns - a huge monster! In fact, we believe that most galaxies have a supermassive black hole in the centre of them. Our Milky Way galaxy has one named Sagittarius A*, with a mass of 4 million Suns, and we are hoping to get an image of this black hole soon.
However, what is almost more impressive is how we managed to take an image of the centre of M87. The black hole is a tiny imprint on the sky - the equivalent of someone in Canberra seeing the width of a grain of sand in Perth.
Here's to hoping that radio interferometers will be able to capture stunning images that capture our imaginations far into the future.
Even for astronomers, to see something this small is difficult. In order to see past the dust that surrounds the black hole, astronomers needed to observe the microwaves coming off it, and so to see something this small with microwaves we would require a telescope the size of the planet!! Impossible, right?
Well, using a technique known as very-long-baseline interferometry (VLBI), researchers can use a handful of smaller telescopes and combine their light, effectively "simulating" a telescope with a diameter equivalent to the distance they are apart.
This is exactly what the Event Horizon Telescope is: a bunch of radio telescopes spanning from Greenland to the South Pole that looked at the same part of the sky at the exact same time. When the light from all these telescopes was combined, we managed to get the beautiful black hole image!
Radio interferometry was in fact developed in Australia by prominent astronomers Ruby Payne-Scott and Joseph Pawsey in the 1940s, and is still going strong today in Australia with the Australian Telescope Compact Array (ATCA) in Narrabri, NSW and the Australian Square Kilometre Array Pathfinder (ASKAP) in the outback of WA.
Here's to hoping that radio interferometers will be able to capture stunning images that capture our imaginations far into the future.
- Jonah Hansen is a PhD student specialising in space interferometry at Mount Stromlo Observatory, at the Australian National University.
