Another real amazing series of NOVA is about the discovery of a black hole at the centre of our galaxy. It a 7 part series called ‘Monster of the Milky Way' and it can be found here.
I loved watching this, especially the part where Andrea Ghez talks very enthusiastic about how they discovered that stars were accelerating to phenomenal speeds around a mysterious invisible object.
The only conclusion that could follow from that, was that they were obitting a black hole in the middle of our galaxy, that had to be 3 million times heavier than our sun.
Andrea Ghez: A decade ago, you couldn't look at the center of our galaxy with high resolution, so you couldn't distinguish stars from one another.
Narrator: Ghez was able to correct the blurring effects of the atmosphere with a revolutionary new technology called "adaptive optics."
Andrea Ghez: So this little animation shows you the benefit of adaptive optics. You see the stars without adaptive optics; you turn the adaptive optics on, and all of a sudden, you see stars. And in particular, you see stars near the center of the galaxy. Without adaptive optics, you would only see one big blob. And those stars are, in fact, the most important for us to track. We track all of them, but these are the ones that are the key to the problem.
Narrator: Thanks to the new technology, the team could peer into the heart of the Milky Way with amazing precision.
Andrea Ghez: Our view to the center of the galaxy is absolutely superb. And our ability to position stars at the center of the galaxy is like somebody in Los Angeles seeing somebody in New York be able to move their fingers, like this, okay? Just two centimeters. That's the precision with which we can measure something that is 26,000 light years away from us.
Narrator: Once the view was clear, Ghez could start the hunt. If there were a black hole at the center of the galaxy, its paw print would be found in the rapid orbits of nearby stars.
Eric Becklin: The conclusive experiment to be done, that really demonstrated that there was a black hole, was to follow the orbits of individual stars in the galactic center very, very accurately and with the highest precision possible.
Narrator: When an object like a star approaches another, more massive object, the pull of gravity will make the star speed up. If it's orbiting close to a massive black hole, the star should accelerate to enormous speed and then whip around the black hole, like a slingshot.
Eric Becklin: Okay, so we have the black hole, here. The more massive it is, the more pull there is. The more pull there is, as it gets closer to the black hole, the faster it goes. And we are measuring the speed of these stars. That's the key to getting the mass, is measuring the speed of those stars.
Andrea Ghez: This is our road map, and that's the center of our galaxy. There's a large cluster of stars that are orbiting the center of our galaxy. And by measuring the motion of stars, and in particular, their orbits, we can figure out whether or not there's a central black hole. That environment in there, it's a crowded party.
Narrator: Ghez set out to monitor the partygoers, to track every movement of the central stars.
Andrea Ghez: Basically, the way this experiment works is you take an image; you see where all the stars are. And then you come back, some time later, and you take another image, and you look to see if they've moved. And so the second time we took an image, we knew we were golden. Those stars had clearly moved. This one moved to here, this one moved to here, this one moved to here, and so on.
Narrator: As Ghez continued to track the stars, she found some making dramatic hairpin turns.
Andrea Ghez: It made a huge jump to over here. So it went, whoop, all the way around. And it's moving on order 10,000,000 miles per hour. So it is just speeding away.
Narrator: Other astronomers clocked the stars with similar results. Not only were the stars accelerating to phenomenal speeds, their orbits were perfectly smooth. Ghez knew that they had to be circling a single massive object. Most black holes are thought to be about 10-times more massive than our Sun, but the object at the center of the Milky Way was roughly 3,000,000 times as massive. For Ghez and Becklin, that could mean only one thing.
Eric Becklin: All other physical explanations of what was at the very center were gone. The only thing left was a black hole.
Narrator: Not only was this black hole supermassive, it was millions of miles wide. Astronomers around the world admitted the evidence was impressive.
Brian McNamara: I have to say, when I first saw Andrea's video, I was stunned, when I saw that star come out of the left side of the frame and go zipping around, and go shooting off into the other end of the frame. And it moved around a point in space, and nothing was there.
Steven Ritz: That we could, with our instruments, effectively travel to the center of the galaxy, 26,000 light years away, and collect the evidence for such an incredible object, was really an amazing achievement.
Narrator: It seemed undeniable: a giant black hole and at the center of our Milky Way. But how could such a monstrosity come to be?