With the sharp focus on Nuka-World proper and the gangs that occupy it, you might not take notice of a small encampment in the southwest corner of the map with a small cult-like group of people called Hubologists clearly patterned after Scientology. But you should make the trek, as the quest you get there rewards you with Hub's Alien Blaster, the best gun in Nuka-World. Here's how you get Hub's Alien Blaster.
Shortly after making it to Nuka-Town USA, you'll hear whispers of people called Hubologists camped out to the southwest, which will mark it on your map. Head that way until you come across a man called Cleansed. Follow him to the Hubologist's Camp and talk to Dara Hubbell, who will hire you to hunt down five spacesuits in exchange for 200 Caps.
Go to the Galactic Zone and enter the Vault-Tec: Among The Stars exhibit. Follow the guide path and you'll find the suits on animatronic people. Some of them are in plain sight along the path, while others are in rooms just off it. Once you have all five, return to Dara and claim your Caps. She'll then ask you to lead the Hubologists into battle to liberate the Nuka-World Junkyard and claim the wrecked UFO there.
Follow Dara to the junkyard and clear out all the robots there. Look for a tunnel entrance in the center mound of junk and follow it until you emerge again. Defeat the Annihilator Sentry Bot Mk. II and secure the UFO for the Hubologists. Dara will then give you Hub's Alien Blaster as a reward.
At this point, you can continue helping the Hubologists by repairing the UFO using three fusion cores and a power distributor, the latter which you can find in a nearby shed. Doing so will net you more Alien Blaster ammo, which you're going to want because it's pretty rare. If you want to get long-term usefulness out of Hub's Alien Blaster, though, you need to modify it with a Fusion Mag, which will let it use Fusion Cells as ammo.
Now you're ready to vaporize some aliens!