Black holes are supppsed to be those high density objects that can devour stars around them, and they are called black holes since even light can not escape from them .
Black holes do exist. We have been able to observationally constrain that certain stars exist in a binary with a compact, non-luminous object that is more massive than the Tolman–Oppenheimer–Volkoff limit. Other work has confirmed the existence of supermassive black hole in the centre of many galaxies, including our own. Adaptive optics observations have mapped the orbits of stars right at the Milky Way's centre, and from the speeds and proximity they move around some invisible central object, we infer that it can only be a black hole.
Black holes do not pose danger to their host galaxies. They do not possess some special extra force of "suction" that other bodies lack. They simply operate under the laws of gravity like other bodies in space. Orbiting a 10 solar mass black hole is no more dangerous than orbiting a 10 solar mass star. It's the same mass, only configured with a different density.
The reason that people think that black holes are more dangerous, more forcefully attractive, able to "devour" things in their vicinity, is simply that they are not aware that this only happens at extremely short distances from the black hole. For a 10 solar mass black hole to affect you in that way, you would have to be so close to it that you would be *deep inside* the corresponding 10 solar mass star!
If our Sun was to instantly be replaced by a black hole of the same mass as our Sun, what would happen? Gravitationally, nothing! The Earth and all the other planets would continue to orbit it in the same way. We'd be a lot colder, though!
Massive Black Holes are supposed within every galaxy. Then .... NO PROBLEM!
Both stellar mass and supermassive black holes exist. Most (if not all) large galaxies contain supermassive black holes at or near their center, and large numbers (perhaps measured in the millions or billions in any given galaxy, depending on its overall mass and the number of massive stars that have lived out their lives and died there) are scattered throughout all galaxies, although (since massive stars are not as common as ordinary stars) must more widely scattered than ordinary stars.
However, none of these black holes have any significant effect on the structure or evolution of the galaxies. Collisions between random stars are extremely rare, and since stellar-mass black holes are not as common as ordinary stars, interactions between them and ordinary stars are far rarer. Supermassive black holes can interact with stars or star clusters that happen to pass very close to them, but the vast majority of stars in any galaxy never pass anywhere near the center, even in elliptical galaxies. So there is almost no significant interaction between any of the black holes and any other objects, and other than providing a (presumably small) addition to the amount of 'dark' matter that holds the galaxies together, they cannot significantly affect the structure or future of any normal galaxy.
The Event Horizon Telescope is making an announcement on this in about an hour from now:
https://www.eso.org/public/announcements/ann19018/?lang&fbclid=IwAR2rUwVWiZ-ZpXted9m2z3V1xygjIykKcF8uzk8uvGLMuMD9SBMjclo04BU
You can watch live here:
https://www.eso.org/public/live/
or here:
https://www.youtube.com/watch?reload=9&v=Dr20f19czeE&edufilter=NULL
yes they are!. many of them are already observed through X-ray observations . the last answers cam on the 10th of April. in M37 the Black hole's event horizon is observed as it was predicted before.
one can clasiffy them according to their masses. small ones and supermassive ones and even with atomic size ones. normal size ones are the result of stellar evolution, one form of a dead stars. Supermassive ones could be the aftereffects of galaxy clusters evolution.
ENE: ... in M37 the Black hole's event horizon is observed ...
That should say "... in M87 the Black hole's photon sphere is observed ..."
Observational evidence strongly support that they do exist. Black holes can be catastrophic and supportive as well. It is all related to AGN feedback mechanism. If an AGN approach Eddington Luminosity, the gas resides in the galaxy can be pushed away from the galaxy. But, many people argue that galaxies grow (central star formation) via outflows, i.e. M-sigma relation.
Cheers
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