The picture of the black hole looked really cool, like absolutely amazing, but is it just a cool picture?
What’s the point of taking a picture of a black hole?
And how can you even take a picture of something that emits no light?
From the image we can see if general relativity behaves how we think it should behave. We have tried many ways to disprove general relativity and this is one more method, with this image we are trying looking at how light acts when it is near something really heavy (because black holes are really, really heavy).
So what does general relativity predict we’ll see?
The black hole is so massive that it warps the space around it so that light no longer takes a straight path about the black hole, So we’ll see a little bit of a smugged incomplete circle that is brighter on one side. (I’m not going to go into the maths behind it, just the main ideas)
So where is the light actually coming from if a black hole doesn’t actually emit light?
When we’re looking at the black hole the light we actually see is from the accretion disk, this is the matter that feeds the black hole. The matter in this disk is traveling fast (Near the event horizon it is traveling a significant percentage of the speed of light, like 90,000 kilometres per second!) Since this matter is going so fast it has a lot of energy, and this energy is released in the form of light, this is the light you see in the picture. The image being brighter on one side is because the Accretion disk is rotating it will look like the side that is coming toward us is brighter.
The accretion disc doesn’t go straight to the edge of the black hole, Schwarzschild radius it sits at a stable orbit at about 3 times Schwarzschild radius. But there is something that can orbit much closer, because it can travel much faster, light. Light can orbit around a black hole twice as close as matter can (1.5 times the Schwarzschild radius) but this is not a stable orbit
Personally I find that knowing a bit of information about an image helps me to appreciate it more, and the image of the supermassive black hole in the middle of M87 is so astounding.
Post by Izzy Donaldson