Picture of a Black Hole
Today the Event Horizon Telescope collaboration announced the second image ever of a black hole. The supermassive black hole at the center of our galaxy!
It is an amazing feat and it makes me very happy :) Here it is:
Galaxies have at their center a supermassive black hole. I'm not sure if all of them, but certainly most of them. The one in ours goes by the name of Saggitarius A*, because as seen from earth it is in the direction of the so-called Saggitarius constellation, and in that region there is something that sends a radio signal and got that A* name. Now we know what it is: a black hole with the mass of about 4 million suns, at about 30 thousand light-years from us.
Even if the black hole is huge, it is so far away that it seems like a miracle that we would be able to take an image of it. And when I say “of it”, I really mean its surroundings, since we cannot get light from inside the black hole's event horizon, its gravity being so strong that not even light can escape. On the other hand, things that surround it tend to get hot and emit a lot of radiation, specially if there is matter falling into it. And the gravity is so strong that the light bends around it and we can see things that are actually behind it.
There are so many cool things about this picture, and about this announcement, that I can't possibly give a good account of it. I'll just mention a couple more.
To get an image with such an astonishing resolution, they use a technique called very large baseline interferometry, or VLBI to friends. The idea is that, instead of looking with one single (radio)telescope, there is a cool way of combining the signal arriving at multiple ones. Rather than forming an image by combining the waves that arrive at an antenna, you can time them very precisely and correlate them with the ones from other antennas, obtaining a resolution that is basically as big as if you had a telescope the size of the distance between the telescopes being combined.
These are the locations of the telescopes combined:
Remember in the movie “Contact” when young Ellie says “I'm gonna need a bigger antenna” and the scene cuts to a shot of her next to the Arecibo telescope? Imagine how cool it'd be having a telescope THIS BIG!
This is the second black hole that posed for our earthling cameras. Our first one was:
M87, readers; readers, M87. This “Messier 87” is a black hole in another galaxy that dwarfs our own Saggitarius A*, being about a thousand times more massive. Since it is this big, and looking to it doesn't need to go through all the dust and gas that we find looking towards the center of our galaxy, it was the chosen one for the first picture. It was shown only a few years ago, in 2019. At the time of the announcement I gathered my colleagues at work, to stop working and come see it. This time, it was a friend who warned me (big thank you!).
We have not only one, but two pictures of black holes! In my lifetime. Including the one in the center of our galaxy. How freaking cool is that?