Photographing the invisible

The world’s been abuzz this week with a very exciting event … the first ever photo of a black hole. But what’s so impressive about taking a photo of something we were pretty sure was up there in space anyway?

The problem with black holes is that they’re pretty black, i.e. they emit absolutely no light or radiation, making them absolutely, 100% invisible.

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The Oxford English Dictionary definition of the word black- the entire absence of light.

 

This cool feature of black holes is due to the fact that they have such a huge gravitational pull that they actually trap light rays inside their event horizon.

The longer explanation is that black holes are very dense- they have a huge mass in a very tiny volume. Because of the huge mass, they have a strong gravitational pull on everything around them. The comparatively small volume means that they can keep pulling all the things around inside and trap them inside permanently. The area around the black hole where things will get pulled inside, never to be seen again, is known as the event horizon. So if any matter, or even light, crosses over the event horizon, it’s pulled way into the depths of the black hole and held so strongly by the gravitational force that the black hole exerts that it can’t ever cross back out again.

So that means that no light can escape, be emitted, or reflected from the black hole. And the way that we see things is when light is emitted or reflected from the surface. So until recently, astronomers thought that made black holes absolutely invisible.

But as science is often known for, some new people with big ideas came along and turned science fiction into reality.

A group of 200 researchers collaborated on this project, gathering data from an array of telescopes to effectively create a massive Earth-sized telescope capable of imaging a black hole in the distant Messier 87 galaxy. In fact, they gathered so much data that it couldn’t be sent online and had to be actually stored on hard disks and transported physically … creating a significant time delay in obtaining the South Pole data as observations were conducted during winter when there is no plane access!

Anyway, to cut a long story short, the team led by Dr Katie Bouman devised an algorithm to turn their massive collections of data into the world’s first black hole photo, an image that shows the super-heated gases and dust surrounding a dark centre.

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The very exciting photo! Image from Wikimedia Commons

The project involved taking multiple images over several days, showing differences that indicate activity in the gas surrounding the black hole (meaning that there are fairly violent reactions occurring, a result of the huge gravity pulling neighbouring material in) and most importantly, a distinctive round centre. This visual confirmation of the circular centre is evidence to support current theories (like Einstein’s Relativity) and furthering our understanding of space.

 

And now that we have a picture of a black hole, it’s making great rounds on the internet in many memes as the world becomes excited that we can finally see what this popular science-fiction body actually looks like!


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