First off, not a stupid question at all! In fact, it is a very good one that many astronomers have dedicated their lives to researching! I think I’ll start with our galaxy and the general case of galaxies.
Here is an image of the center of our milky way (we can only get this side-on view because we are viewing it from within):
In this photo, a supermassive black hole resides in the bright white area, right of the center. The black hole has been calculated to be about 4 million solar masses. Yes. You heard correctly, there is a supermassive black hole at the center of our galaxy. However, don’t panic.
The supermassive black hole is about 27 kilolightyears away and we are a long way from any harm it could cause us. This is actually a very normal thing about the universe we live in. It is theorized that there are supermassive black holes at the center of almost every large galaxy! Everywhere we look we find evidence of them in the orbits of stars around the centers of galaxies.
Some galaxies have special cases of black holes, known as quasars, at their center. Here is an artists impression of a quasar:
Quasar’s and supermassive black holes, when viewed relative to galaxies, are members of objects known as active galactic nucleus (or AGN for short). AGN’s are the super dense regions at the center of galaxies that have abnormal luminosity (meaning they are super bright), and often emit light/radiation in all wavelengths of the electromagnetic spectrum. Galaxies with AGN’s are known as Active Galaxies. Our galaxy is considered an active Galaxy.
Here is a hubble image of an AGN at the center of Galaxy M87. Electromagnetic radiation is seen being emitted from a jet:
There is still very little known about the causes of these AGN’s, how they are formed from supermassive black holes and the intermediate stages of AGN’s and black holes. There are even galaxies that have no AGN’s and the stability of galaxies has been a big mystery for the past few years. There is still much that we can learn in this area.
Science doesn’t have all of the answers, and it may never have all of them. But Science has a way to figure out those answers. Someone once told me that younger scientists are able to make breakthrough discoveries because they don’t yet know what is impossible.
So I would like to tell you again, this was not a dumb question! I encourage you to continue to ask these questions! Thanks for the great ask.
"To find the truth, we need imagination and skepticism" - Carl Sagan, Cosmos: A Personal Voyage
There are a couple of inaccuracies in the answer that the astronomer in me can’t quite let go (AGN were my thing, back when this was my day job).
Supermassive black holes (SMBHs) in themselves are not considered AGN. The SMBH at the centre of the Milky Way is not currently accreting matter at any appreciable rate, so the Milky Way is not presently considered an AGN. It occasionally gobbles up a star, but there’s no evidence to suggest the presence of an accretion disc with associated radiative activity.
It’s more true to say that ‘every AGN has an SMBH’, because the current model for AGN requires one. The present model (which has a lot of evidence in its favour, although as with all extragalactic models there’s a lot of scatter), basically states that all AGN have fundamentally the same structure (SMBH, accretion disc, some more distant non-stellar material) and that the differences between the different types (quasar, Seyfert 1, Seyfert 2, etc) is due to accretion rate and viewing angle.
As far as ‘some galaxies not having AGN’ goes, at the moment the evidence is in favour of every galaxy with a bulge component having an SMBH, and therefore likely having been an AGN in the past if they are not currently. Galaxies with only disk components do not show evidence of SMBH, so current thinking is that the processes that shape the galactic bulge also strongly influence SMBH formation.
The babiest SMBH that we* know of is in NGC 4395, with a mass of a mere ~10^5 solar masses. NGC 4395 has an extremely small bulge component. I could go on about this AGN for days.
*that I know of, really. I only read astro-ph in my spare time these days.
To add a quick, fun addendum to theformerastronomer’s great additions/corrections, there’s debate at the moment as to whether AGNs trigger or suppress star formation in the rest of the host galaxy. To be brief, the radiation pressure/winds/unicorns coming from the super massive black hole is thought to have an effect on the rest of the galaxy but is it pushing gas and dust together to trigger star formation, or is it blowing all the material out of the galaxy (or something else) or is there no appreciable effect at all? This is one of those current big unknowns and can cause debates at the pub if you get people talking about it, like the (non-)existence of the “galactic main sequence” hohoho.