Ω particles, otherwise known as 'Primordium Omega', is a dark, chaotic substance that is dangerous to touch. Many voids purely consist of this matter. If surrounded by, anything can be absorbed into Primordium Omega, and gain it's energy, this is how the Shadow is able to eat; he is purely made from it.
If mixed with its opposite: Primordium Alpha with the right amount, it can destroy galaxies, adding Primordium Delta to it as well can destroy from multiverses to even some small realities.