The anti-matter vortex is a very dangerous monster to encounter if one lacks disintegration resistance. Any weapon that hits it will be disintegrated, as well as the armor, and eventually the body of anyone who is engulfed by it.
It also exists in Slash'EM Extended, but it's a lot less dangerous in that variant.
If the player does not have disintegration resistance, use Elbereth and teleport away, or use attack spells. Anything you hit it with will be disintegrated, so don't use ranged weapons unless you don't mind them being destroyed.
Swirling clouds of pure elemental energies, the vortices are
thought to be related to the larger elementals. Though the
vortices do no damage when touched, they are noted for being
able to envelop unwary travellers. The hapless fool thus
swallowed by a vortex will soon perish from exposure to the
element the vortex is composed of.