The growth of the black hole is causing debate.

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The growth of the black hole is causing debate. 

Proving the growth of the black hole is very difficult because the observations about the black hole itself are hard to get. So the thing, that astronomers must do with that kind of thing is starting to find an extremely small-size black hole, what is alone in the universe. 

And then they should observe the change in the size of Einstein's loop, which means the area where gravity is affecting the route of the photons. So if that area is growing that means the size of the black hole is growing. The growing mass causes the size of the gravity field is increasing because the gravity would get stronger. 

But the fact is that normally the disk of material, that surrounds the black hole denies sharp observations about the area, what is near the black hole. If we are thinking of the supermassive black holes, what are the center of the galaxy, we must remember that the mass of those black holes is extremely high. And that makes it difficult to find the difference in the size of the gravity field of those objects. So everything is relative. 

If we want to compare supermassive black holes with something, what we know, we can take the sandpit, what weight is tons of sand as an example. The thing in the case of supermassive black holes is that they are like that pile of sand and the material that is dropping in the black hole is like the bucket of sand that we fall on the sandpit. 

Even we feel that the sand that we fall to the sandpile feels heavy, we cannot detect the change of the mass. We must remember that the weight of a supermassive black hole is 10⁵-10⁹ times of the Sun and that means the increase of the mass when the material drops in the black hole are hard to measure. 

https://www.quantamagazine.org/astronomers-debate-how-forbidden-black-holes-grow-20201103/