Brute Waves
From Multiversal Omnipedia
Brute Waves are energies contained in moonlight that affect the physiology of Saiyans. Measured in Xeno; Brute Waves can induce a transformation to an Oozaru in Saiyans who retain their tails at 1700 Xeno.
Dragon Ball GT
Even more intense bombardment than 1700 Xeno can turn Saiyans who have lost their tails into Oozaru as well; during his possession of Vegeta, Baby had Bulma construct a device- the Brute Ray Amplifier- that could do just that.
