Class T nebula

A class T nebula was a type of small nebula, around a thousand kilometers in diameter, composed of hydrogen, helium, and argon.

The USS Voyager passed a T-class nebula in 2376. A Hierarchy assault starship was hidden inside the cloud. 

A T-class nebula was located within three light years of the planet Dinaal. It contained a planetoid with a mining colony. 

Tクラス星雲 Klasse T nevel T-Klasse-Nebel