Complex sentence: This rapid spinning is thought to be the cause of a gaseous disk that surrounds the star: such stars are known as Be stars, recognizable because the gas radiates emission lines that give a characteristic pattern in the star's spectrum.
Split into simpler sentences: This rapid spinning is thought to be the cause of a gaseous disk that surrounds the star: such stars are known as Be stars. The gas radiates emission lines giving a characteristic pattern in the star's spectrum.