
Originally Posted by
Xaeden
That's with Asgard hyperdrives. Goa'uld motherships prior to the end of the season 1 finale could only go 10 times the speed of light:
CARTER: Teal'c, how fast can this ship go?
TEAL'C: The Goa'uld Ha'tak vessel can travel at 10 times the speed of light.
CARTER: Okay, if we are heading to Earth, then we have along time.
O'NEILL: Based on what?
CARTER: Based on the coordinates of the planets we gated to.
O'NEILL: We didn't gate to a plant, we gated to a ship!
CARTER: But that ship had to be in orbit around, or on the surface of a planet, in order for those gate coordinates to work. So based on the location of those coordinates, even if we were traveling at 10 times the speed of light, it would take at least a year to get to Earth. Probably more.
This is a large part of the reason why the Goa'uld abandoned so many planets after human rebellions. Why send ships on missions that kept them occupied for years when you could simply gate to a new world and seed a new population of slaves there? You basically have to wipe out a good chunk, if not all, of the existing population on a rebellious world anyway, and by doing this you're removing ships from defensive/offensive positions, so you're making yourself a weaker/more appealing target for your enemies in order to reclaim a world that may not be worth the effort.
The big reveal at the end of the episode was that in the year since Teal'c left, the Goa'uld figured out how to significantly upgrade their hyperdrive engines...
JACKSON: I thought you said we couldn't be there for at least a year. Jack gets up and walks beside Danny.
CARTER: I guess this ship can go way faster then 10 times the speed of light. Colonel, we saw the Death gliders. They're preparing for launch, sir.
Also be mindful that when Apophis lost those two ships it severely weakened his position among the other Goa'uld, while later in the series we are made aware of there being hundreds of motherships spread throughout the Milky Way with individual system lords commanding fleets large enough for them to shrug off the loss of one, two, or even a handful of motherships. This suggests that they may have engaged in a significant ship building effort in the early seasons of Sg-1. It makes sense that they would do that following the development of faster hyperdrives as that would have made ships a viable alternative to gate travel for the first time in Goa'uld history.
Given all this, it would have been horribly painstaking and resource heavy to try to send ships to other galaxies prior to the events of Sg-1. The Pegasus galaxy is three million light years away. At 10 times the speed of light, that would have taken the Goa'uld not hundreds of years, but hundreds of thousands. The Goa'uld lack an ability to preserve a living being for that long so we're talking about an automated mission, and, even if the ship could remain functional after 300,000 years on its own, there's then the very long wait period for the hope of any sort of return message. Further, if Goa'uld motherships were faster than the smaller Goa'uld craft (which makes sense), that means they would either have to send a smaller ship on a much longer mission or give up what was a very valuable resource before they went on a building spree.
Our real world prospects for sending a probe 4.3 light years to the nearest solar system are not that bad and we still haven't done it yet. With current technologies it's likely to take tens of thousands of years for any craft to reach Alpha Centauri. The exact time frame depends on how much we spend, but no matter how much money we pour into it, new technologies are going to emerge in the next decades, never mind tens of thousands of years, that will significantly shorten travel time, so it's a complete waste of time, resources, and money to try to send probes now because they'll be beaten to Alpha Centauri by probes we develop in the intervening years.
Same with the Goa'uld. Per "Exodius," it would have taken them 125 years to travel 4 million light years in a Goa'uld mothership, but that was at maximum hyperdrive speed, which likely isn't something that they could have maintained for the whole journey. Thus, with their post season 1 hyperdrive capabilities, it's a 94 year trip to Pegasus at max speed, but realistically it's probably a 100-300 year journey. This means if they launched today they'd beat any ship sent out there prior to season 1 by... still hundreds of thousands of years. Even the Goa'uld would have had the foresight to realize it's better to devote resources to trying to develop faster travel than to send out ships on impossibly long journeys into the unknown.
As for launching today. Again, they know that better technology exists. If you're a Goa'uld would you lock yourself away in a sarcophagus for possibly hundreds of years without any knowledge of if you will make it to your destination and, if you did, whether there would be anything there for you to establish what you desire (a base of power) or, if there is, whether you'd have the resources on hand to conquer and/or carve out a sphere of influence?
Even if you're one of the Goa'uld who knows about Pegasus and you're leaving the Milky Way for the express purpose of trying to get there, you're likely to need a lot of ships to contend with whatever is there ~100 years from now. Certainly more than the lesser Goa'uld in hiding today can martial. You'd probably need the entire resources of a system lord (or two) prior to their fall, but no system lord would give up their power for a long sojourn to Pegasus. Especially when they know that the technology to get there in days, weeks, or months is out there waiting to be discovered or reinvented. Hell, for all they know, by the time they get there, the Goa'uld will have already conquered the whole galaxy and advanced their technology to such a level that this explorer Goa'uld's own antiquated ships wouldn't stand a fraction of a chance in battle.
For your fan fiction, rather than sending Goa'uld into the dark of space for such long periods, what I'd suggest is that you use the gate. If a Goa'uld found a ZPM and learned how to dial Pegasus with it, he or she likely would have sent some Jaffa through as scouts. Teal'c explained that it was standard procedure to send Jaffa scouts and write off a world as too dangerous/inaccessible if they didn't return (that appears to be what happened with Apophis' serpent guards who came through the Beta gate and died in Antarctica).
This hypothetical Goa'uld may have had reason to believe his Jaffa would have found a way to establish a connection back, but when that very obviously didn't happen, you'd have Jaffa potentially mingling with Pegasus humans who their larvae could take as hosts when they mature. There would be no system lords to stop them from doing this as is usually the case in the Milky Way (the Goa'uld kill most of their offspring before they are mature enough to take a host to limit the competition), but these Goa'uld would also have limited resources and likely no access to a Queen.
Consequently, you'd have a small population of Goa'uld trapped in the Pegasus galaxy who would have to work to try to gain power and resources, all while trying to remain under the Wraith's radar. By the time your story starts, they may, for example, have a small fiefdom and access to middling technology that they stole/recovered from the Wraith, Ancients, and advanced human inhabitants of the galaxy, or they may have access to some very powerful Ancient hardware (along with ATA humans or a workaround to the ATA gene lockout) and be about to enter the galactic stage with a very big splash.
Alternatively, maybe a rogue Wraith scientist found and have been experimenting on them or the Goa'uld have started trying to infiltrate the Wraith. Also don't forget that cloning can be used to create more larvae Goa'uld, which can in turn be used to create Jaffa in Pegasus.
Lead poisoning (for example) can be passed to a child, either while in the womb or through breast milk, so I see no reason why the same also wouldn't be true of naquadah. On the other hand, I doubt naquadah in one's blood stream would block any sort of gene therapy.