"No Man's Sky"'s vast galaxies of randomness mean that there are important rare resources to be found all over. None of them are rarer than Omegon, colloquially referred to as "Om," which players are going to need to help upgrade some of the necessary in-game items they have, namely the ship, exosuit, and jetpack. Things you will need in your interplanetary jaunts.
What is Omegon, though? All we know about it is that it is a really, really rare element in the "No Man's Sky" universe that might be similar to dark matter. It's powerful, for sure, but other than there's not much information on it, and due to its rarity, it fetches a lot of money in the marketplace, should players choose to buy it instead of mining it. There are ways to mine it, however.
Here's the thing about Omegon: you can't reliably find it anywhere. Meaning you won't be able to pinpoint a vein and keep coming back to it, because it's invisible on your radar and you're going to have to stumble it when you explore a planet. It's more often found on planets that are radioactive, and "No Man's Sky" even makes the mere act of mining it ridiculously hard.
How hard, you ask? Well, you're going to have to make a hole below it using explosives, like the grenade launcher, because if you simply mine it as it is, it's going to break into two parts and roll away from you even if the ground beneath it is flat. That's how much "No Man's Sky" wants to make it hard for you.
So even if you do find sources of Omegon in "No Man's Sky," you shouldn't expect to come back for them again. The best chances you have of reliably finding them is by going to a farther, higher-tier star system and exploring there, but that's still a gamble in itself. Good luck!