Cygnus X-1 must have a mass of about 7 solar masses or else it would not exert enough gravitational pull to cause the wobble in the spectral lines of HDE 226868.

• 天鹅座X则必须有7个太阳大小的质量，否则它将不会有足够的引力来引起HDE226868谱线的来回波动。