Why can't we see Planet Nine. Why is it hiding? The latest idea is that it is invisible. A black hole lurking in the outer reaches of our solar system. This one is a primeval black hole – and one of those missing black holes (small to medium). The new study is on the arxiv pre printer server – see https://phys.org/news/2019-09-planet-primodial-black-hole.html … and https://arxiv.org/abs/1909.11090
Meanwhile, at https://phys.org/news/2019-09-sharper-black-holes-host-galaxies.html … the special relationship between supermassive black holes and their hosts, the galaxies, can be understood as a connection that began at galaxy formation. A black hole is a point in space where matter has been compressed so tightly it creates intense gravity. This gravity is so strong even light can't escape – a main tenet of the theory. The existence of black holes was entirely theoretical until astronomers, back in the 1960s, are said to have seen 'observational hints' of their existence. This year astronomers released an image of a silhouette of a black hole – or what they think is a black hole. A team at Yale have now made a 'sophisticated' simulation to make a new discovery. The Romulus simulation (computer generated) seeks to trace the evolution of a black hole beginning at Big Bang and evolving through the history of the universe. It therefore includes thousands of simulated galaxies that reside in a variety of different cosmic environments, a massive task. The simulation is said to provide a snap shot of black hole growth. They, predictably, show black holes growing in size as the galaxies expand and grow. What else.