a separation of about 4.5 AU. Its orbital period is currently estimated to be around 16 years. This would explain why the GG Tauri Ab's spectrum suggests an unusually low-mass star instead of the higher mass that was measured. Because of interactions with GG Tauri A, the outer pair GG Tauri Ba and Bb are not very stable. The internal orbit of GG Tauri Ba and Bb must be retrograde relative to its whole orbit around GG Tauri A, in order to be stable. Circumstellar disks T Tauri stars are usually surrounded by circumstellar disks of gas and dust. These disks coalesce into protoplanets and then into planets. The subsystem GG Tauri A has a large, circumbinary (technically circumtrinary) disk. Within the disk, GG Tauri Aa also has a disk, and furthermore, at least one of the Ab stars must have a disk as well. The latter is inferred from the presence of a "gap" in the largest disk, detected at the three-o'clock position, at a position angle of about 268°. First seen in 2002, it is interpreted as a shadow because it does not rotate with the disk. Interstellar material blocks the light from part of the disk, causing this shadow. The Aa and Ab rings are coplanar to each other. The disk around GG Tauri Aa has a mass of about , or about the mass of Jupiter, at a temperature of about 20 to 30 K. GG Tauri Aa appears to have a jet coming out from the poles, as evidenced by forbidden Fe II lines. Mass is currently accreting from the inner disks into the stars themselves. Because the disks have not been consumed yet, the larger, circumbinary disk must be supplying mass into the smaller disks. Several lines of evidence point to this. Firstly, a search for diatomic hydrogen gas (H2) could be found up to 100 AU away from the center of the system, but significant emission was also detected 30 au away. This emission was detected where a previous survey found gas streaming from the outer disk to the inner disk, so it was assumed that the emission resulted from mass falling from the inner disk to the outer disk. Observations taken in 2014 showed similar results. Secondly, near-infrared polarimetry of the area showed the same structure connecting the inner and outer disks. The stars of GG Tauri A are closer to the