Segue 3 is a faint

star cluster Star clusters are large groups of stars. Two main types of star clusters can be distinguished: globular clusters are tight groups of ten thousand to millions of old stars which are gravitationally bound, while open clusters are more loosely clust ...

of the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye ...

galaxy discovered in 2010 in the data obtained by

Sloan Digital Sky Survey The Sloan Digital Sky Survey or SDSS is a major multi-spectral imaging and spectroscopic redshift survey using a dedicated 2.5-m wide-angle optical telescope at Apache Point Observatory in New Mexico, United States. The project began in 2000 a ...

. It is located in the

Pegasus constellation Pegasus is a constellation in the northern sky, named after the winged horse Pegasus in Greek mythology. It was one of the 48 constellations listed by the 2nd-century astronomer Ptolemy, and is one of the 88 constellations recognised today. Wit ...

at the distance of about 17 kpc from the Sun and moves away from it with the velocity of . Segue 3 is extremely faint—its visible

absolute magnitude Absolute magnitude () is a measure of the luminosity of a celestial object on an inverse Logarithmic scale, logarithmic Magnitude (astronomy), astronomical magnitude scale. An object's absolute magnitude is defined to be equal to the apparent mag ...

is estimated at −1.2 or even at about , 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 the galactic globular clusters. The cluster has a slightly flattened shape and shows some evidence of the tidal disruption. The metallicity of Segue's 3 stars is , which means that they contain 70 times less heavy elements than the Sun. These stars are more than 12 billion year old. Segue 3 appears to be one of the faintest globular clusters of the Milky Way.

References

{{Milky Way Milky Way Globular clusters ?