Is there a supermassive black hole in the center of every single galaxy? I've read that there's a supermassive black hole in the center of every single galaxy, as we confirmed theres for example one in the center of ours, and in the andromeda galaxy, but does that confirm theres one in every single galaxy? And if so, why? Was it born at the beginning of the galaxys birth?
 A: Brief answer until someone with more knowledge adds details.
The answer is about evidence, theoretical models of galaxy formation, and the balance of probability. As I understand it, the evidence and knowledge acquired to date is such that it would be reasonable to hold that most galaxies have a black hole at their centre. I would not go so far as to say "every" but I am not ruling that out as a possibility.
The evidence includes the observations of, and models of, quasars. We can't really claim to know for sure what quasars are, but processes associated with black holes seem to be the only viable candidate.
A: Observational evidences indicate that almost every large galaxy has a supermassive black hole at its center.
https://en.wikipedia.org/wiki/Supermassive_black_hole
Can we safely say that every galaxy has a black hole at its center?
No
Can we safely say that almost every galaxy has a black hole at its center?
Yes
A: At least, it's a good guess that spiral galaxies should have a black hole in the core, according to a correlation noticed between spiral arms pitch angle and black hole mass located in the spiral galaxy core,- from the research of 140 local volume-limited spiral galaxies sample:
$$ M_{_{SMBH}} \propto 10^{-0.062~~|~P~|} ,$$
where $P$ is spiral arms pitch angle.
Of course correlation was extracted from a local spiral galaxies,- not all of spiral galaxies in a visible universe. But again, many laws were extrapolated using observational data available at hand (Hubble law also was not produced from all galaxies redshift in the universe). It's impossible to observe everything and in every time moment.
Anyway it's a good guess that each spiral galaxy should have a black hole in the center, less or more massive.
Other types of galaxies are less likely having black holes in the center, due to the fact that they are too small or of irregular shape, not rotating, etc.
A: The fact that we have a supermassive black hole at the center of our galaxy of course is not sufficient in order to state that there is one black hole in every single galaxy out there. You could never have a conclusive and certain confirmation unless you're able to identify all black holes and all galaxies present in the universe, which is not so easy to do.
Nevertheless, astronomers do believe that supermassive black holes lie at the center of all large galaxies, as in our own Milky Way. If we focus for example on stellar black holes, they are very difficult to detect and judging from the number of stars large enough to produce them, scientists have estimated that there are as many as ten million to a billion in the Milky Way alone. This could be interpreted as a strong suggestion that every galaxy has at the center a black hole, but it's not a conclusive proof.
Another possible explanation of this hypothesis relies on the fact that one possible mechanism (not the only one of course) for the formation of supermassive black holes involves a chain reaction of collisions of stars in compact star clusters that results in extremely massive stars, which then collapse to form intermediate-mass black holes. The star clusters then sink to the center of the galaxy, where the intermediate-mass black holes merge to form a supermassive black hole.
