Segue 3

Segue 3 is a faint star cluster of the Milky Way galaxy discovered in 2010 in data obtained by Sloan Digital Sky Survey.^[1] It is located in the Pegasus constellation about 17 kpc from the Sun and is moving away from it at 167.1 ± 1.5 km/s.^[2]

Segue 3
Observation data (J2000 epoch)
Constellation	Pegasus
Right ascension	21h 21m 31s[1]
Declination	19° 07′ 02″[1]
Distance	55.1 ± 2.3 kly (16.9 ± 0.7 kpc[2])
Apparent magnitude (V)	14.9[1]
Apparent dimensions (V)	52 ± 10″ (half-light diameter)[2]
Physical characteristics
Radius	6.8 ± 1.3 ly (2.1 ± 0.4 pc)[2]
Other designations	Segue 3
See also: Globular cluster, List of globular clusters

Segue 3 is extremely faint—its visible absolute magnitude is estimated at −1.2^[1] or even at about 0.0 ± 0.8,^[2] which means that the cluster is only 100 to 250 times brighter than the Sun. Its small radius—of about 2.1 pc—is typical for galactic globular clusters.^[2] The cluster has a slightly flattened shape and shows some evidence of tidal disruption.^[2]

The metallicity of Segue's 3 stars is [Fe/H] ≈ −1.7, which means that they contain 70 times less heavy elements than the Sun. These stars are more than 12 billion year old.^[2] Segue 3 appears to be one of the faintest globular clusters of the Milky Way.