We present the results of spectrophotometry and BVR CCD photometry , as well as integrated H i radio measurements of a new blue compact galaxy ( BCG ) HS 0822+3542 with extremely low oxygen abundance : 12 + log ( O/H ) = 7.35 , or 1/36 of solar value .
The galaxy is the third most metal-deficient BCG after I Zw 18 and SBS 0335–052 .
Its very high mass fraction of gas ( \approx 95 % of all visible mass ) and blue colours of underlying nebulosity are also similar to those of SBS 0335–052 .
This suggests that HS 0822+3542 is one of the nearest and dimmest galaxies experiencing a recently-started first star formation ( SF ) episode .
Its properties imply that for such galaxies there is a linear scaling of the main parameters , at least for the baryon mass range ( 0.3–20 ) \times 10 ^ { 8 } M _ { \odot } .
The total mass estimate indicates that the galaxy is dynamically dominated by a dark matter ( DM ) halo , which itself is one of the least massive for galaxies .