For those who have yet to see "Dragon Ball Super" episodes 128-131, this article contains spoilers; so read at your own peril. Anyway, so after watching "Dragon Ball Super" finally unveil Goku’s mastered ultra instinct in episode 129, I had some theories about the swirling mass of energy that surrounded Goku.  The “ki” was so huge that it resembled a galaxy; something intergalactic and somewhat spiritual.  

So we all know how the whole Ultra Instinct thing got started, right? Goku tried to hit Jiren with a Spirit Bomb and ended up getting the attack deflected back at him; forcing him to take the full brunt of it at close range.  This somehow awakens a new level of power in Goku that the Gods of Destruction dub Ultra Instinct.  Regardless, the point is, this all started with a Spirit Bomb. 

Goku and the Spirit Bomb

Goku has used the Spirit Bomb on many separate occasions before we get to the timeline in Super; some instances were in the "DBZ" timeline, while others were in "DBZ" movies that were independent of the timeline.

As far as being used in the actual "DBZ" timeline, the first was against Vegeta, the second was in his fight with Frieza on Namek, and the third was with Kid Buu.  Other targets include characters like Lord Slug, Dr. Wheelo, Turles, Android 13, and that's just to name a few. Check out DBZFusion405's look back at Goku's use of the Spirit Bomb on YouTube to get a full list of Goku's Spirit Bomb victims and take a little trip down memory lane:

In each instance, Goku gathered spiritual energy from all nearby beings; and with Frieza, gathered energy from the entire universe. That energy flowed through him until he compressed it into a huge energy attack; basically making him a conduit or a temporary container that could store all that energy before being redistributed as an attack.  But what if that temporary container isn’t so temporary?

My Ultra Instinct theory

Let’s say hypothetically, that Goku as a Saiyan, known for being able to take huge amounts of energy without being harmed, is channeling Spirit Bomb energy through his body.  As that’s happening, his S-cells are soaking in the energy; storing it like a plant does in photosynthesis.  That would mean that even after using a Spirit Bomb attack, Goku would still have spiritual energy residing in him; laying dormant and possibly simply merging with his own energy, and in turn, making him stronger. 

Now fast forward back to the present, where Jiren struck Goku with his own Spirit Bomb at close range.  Not only is Goku  actually hit with his own Spirit Bomb for the first time, but he’s in Super Saiyan Blue form when it happens. 

This is very significant, because up until this point, Goku had never been Super Saiyan Blue while using a Spirit Bomb (and definitely has never done so while being hit by one) and the SSB form is something that he incorporated into the Super Saiyan arsenal after reaching the Super Saiyan God level.  The keyword here being God.  

So all this energy he's gathered is just as condensed and massive as a normal Spirit Bomb, and then he gets hit with it; fully soaking him in energy, while he's already at the precipice of a godly level with SSB.

This is my theory: getting hit with this Spirit Bomb while in Super Saiyan Blue awakened all that latent residual spiritual energy that Goku accumulated over time from every attempt to use the Spirit Bomb. This alone tipped Goku's Super Saiyan God power over the edge into a vast, new level of energy; like an overflowing cup of water under a faucet.  That is what brings Goku to Ultra Instinct. 

Have you noticed that when Goku is in Ultra Instinct, the aura that shimmers around him resembles the congregating spirit energy on the outside edges of a Spirit Bomb?  I speculate that it is more than likely all the spirit energy Goku has absorbed; now resting comfortably on the surface, instead of laying dormant inside and waiting to be utilized. 

When Goku finally masters Ultra Instinct and powers up, releasing all that energy in the air like he usually does, he shows us the true amount of his energy; which is so vast that it is literally the size of a galaxy.

Once again, I believe this "galaxy energy" is the accumulation of all the spiritual energy that Goku gathered over time; combined with his own energy that expands every time he gets stronger or reaches a new level of power -- especially now that he has reached a level that has surpassed the Gods of Destruction. 

Once again, this is all just speculation and I'm sure the fandom has already discussed this idea at length.  We'll see what happens if Toyotaro further explores the world of the Gods and Ultra Instinct after the much anticipated "Dragon Ball Super" movie -- slated for a December release -- hits theaters, and the "Dragon Ball Super" series returns for its next season.  

All episodes of "Dragon Ball Super" can currently be seen on Funimation, Crunchyroll, and Hulu streaming services