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Originally Posted by BananaStand
Do I understand correctly that the Universe is expanding in all directions?
Yes.
It is also interesting to note that it is accelerating in the expansion, which is, as of yet, not explained by physics.
Originally Posted by BananaStand
If so, how do we reconcile that with the existence of super massive black holes?
These 2 things are unrelated.
A) SMBH's were formed in the very early universe. For some unknown reason, the cosmic soup that was the big bang was not homogeneous in its density distribution. The variations in density gave rise to the coalescence of matter into some regions and not so much others. Black holes have been present since basically forever.
B) The universal expansion happens at all points in space. The space in between the black holes is expanding. If there is enough distance between a pair of black holes, then the universal acceleration driving them apart is greater than the gravitational acceleration pulling them together.
The expansion of the universe happens over vast distance scales. The Milky Way, our Local Group of galaxies and the greater supercluster of galaxies in which the Milky Way exists are more strongly gravitationally bound than the current rate of acceleration of the universe will affect.
In this respect, the SMBH's are counteracting the universal acceleration within this domain.
Originally Posted by BananaStand
The milky way is getting sucked into one right now, is it not?
It is not. The galaxy is in orbit about Sagittarius A* (the SMBH in the Milky Way), much the same that the planets are in orbit about the sun.
Black holes are a gravity source like any other unless you're "near" the event horizon.
Left alone, black holes are theorized to slowly evaporate in a process known as Hawking Radiation, named after Stephen Hawking, who discovered the physical-mathematical framework which implies this.
Black holes only suck things up when those things get flung into one of their event horizons. The swirling mass of stars that form the Milky Way occasionally leads to near collisions of stars. When stars pass too close to each other, there is a transfer of gravitational energy. This can leave one of the objects with an orbital velocity that is too slow to avoid the galactic nucleus. If so, that object is heading toward the black hole and will get consumed by it.
Merely getting flung "close" to the black hole may be enough, since most black holes have an accretion disk, or a disk of swirling, in-falling material. If a body enters that stuff, there is plenty of friction there to further reduce its orbital velocity and send it into the black hole... well... it'll likely get torn to bits and remain in the accretion disk for quite a while as it is consumed.
Originally Posted by BananaStand
Eventually this galaxy, and all the galaxies around us will be sucked into this thing , correct?
ALL the galaxies? No. (see above)
All the galaxies in our supercluster of galaxies? ... maybe... probably, even... given obscenely long time scales.
Well... either sucked into a black hole or ejected into inter-galactic space... perhaps to be captured by another galaxy, but the odds are against it. The amount of "empty space" out there is truly a rude amount to think about.
Originally Posted by BananaStand
So how can the universe be expanding if there are black holes floating out there condensing entire galaxies into super dense masses?
Both of these processes are happening simultaneously. On "local" scales, gravitational sources win out and bind systems together. On the grandest length scales, though, the space between the isolated pockets of stuff is expanding, driving those pockets ever-further apart.
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