Friday Science Trivia: When Two Ultra-Massive Black Holes Collide... What Will Happen, At Earth Distance -- Of 420 Million Light-years?

Together, these two closely circling black holes are about 325 million times more massive than our Sun. Let me repeat that: millions of times. [The last one we observed (in 2019) involved black holes less than 100 times the Sun's mass, but happened nearer to us.]

And the energy released when these ultra-giants collapse into each other will generate a gravity wave of truly cataclysmic proportions. It may be lethal for any star system within about 300,000 light years of the event. . . but we will be comfortably far away, according to all best estimates. We know that energy from these gravity waves propagates, but dissipates, proportional to the square of the distance from the epi-center. And that's a vast, vast amount of. . . distance.

Even so, at our distance. . . tsunamis might occur. It might be equivalent to the energy exerted by the moon's tidal forces, but all within a millisecond. . . so, depending on whether Richard Feynman was right, that all of local space-time will expand and contract in a uniform, and instantaneous fashion, we might see nothing.

But if the wave propagates across the Earth, and is either slowed or accelerated in the interstellar medium around us, we might see an actual ripple in the pond, that is our oceans, since the water would be most easily displaced by it.

In a most extreme scenario, the crystalline structures supporting our crust might fracture, and collapse in places. But only, as I say, if Feynman was. . . wrong. Only if space time doesn't react uniformly to the energy of the gravity wave.

And in any event, this actual merger is likely still some 400 million years ahead, into the future -- as the light of the close approach is just now reaching us, from 420 million years in the past -- far out in the inky black of deep, deep space. So, rest easy. Feynman was almost certainly right about it -- we will be able to detect it at the Ldar facilities in Louisiana and Washington state, assuming we are still here then -- but only the very thinnest fraction of the resulting gravity wave will be converted to energy in the physics of our standard model, based on 2019 observations of smaller, nearer, gravity wave events.

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