Getting Closer To Solving... "The Final Parsec Problem"? The Math Doesn't Work, When Two Super Massive Galaxies Collide -- So, How Do Their Black Holes... Merge?

If one envisions this as a simple rubber sheet, around a center pole in which two very, very heavy steel marbles are rolling toward one another (and thus, the rubber sheet itself increasingly sags -- toward the center pole), we can easily imagine that -- at some point, as the two are "whirlpooling" around each other, closer and closer and picking up speed -- eventually they will bump into each other at the bottom -- and in the language of astrophysics. . . that's the moment of merger. And we "hear" the blip -- as a gravity wave -- even across hundreds of millions of lightyears, here.

At least, that is how middle schoolers are taught it might happen. But out there, across billions of light-years in scale. . . the observed reality seems a little different. The black holes often reach a sort of. . . equilibruim point -- and don't fall in any further, for the last three or so light years of separated distance [the so called Final Parsec]. Or so all the mathematical models hold.

But in point of fact, over billions of years (as light from thousands of galaxies reaches us). . . we can observe that the pairs of two do, indeed. . . merge into one ultra super massive black hole, forever changing the shapes and orbits of the galaxies that host them. So what gives? Let's listen to the Beeb, here (for a plain English tour through the high math problems):

. . .[A]stronomers encounter [a mathematical contradiction] when they try to model exactly how [super massive black holes merge]. In order to spiral towards one another, the two black holes must first shed energy. To start with, that energy is transferred to surrounding material, including gas and dust. Except when the galactic black holes get within a parsec of each other – just over three lightyears – it seems there’s no longer enough ‘stuff’ to shed energy to. . . .

There must be solution to this "Final Parsec Problem", and recent experiments such as NANOGrav have picked up a lot of gravitational waves that look like they come from colliding supermassive black holes.

There’s clearly something we are missing in our models.

That could be the influence of a third black hole, but that’s unlikely to account for all cases. . . .

Perhaps the black holes interact with their environment in some other way that causes them to lose orbital energy, spiral in and collide.

Perhaps the black holes interact with their environment in some other way that causes them to lose orbital energy, spiral in and collide.

For now, the Final Parsec Problem remains one of the biggest mysteries in black hole and galactic astronomy. . . .

Perhaps your own super bright young mathematician / offspring will solve this for us, in a few years' time. Smiling. . . perhaps.

नमस्ते