Andromeda XXI

Andromeda XXI, also known as And 21 or And XXI, is a moderately bright dwarf spheroidal galaxy located about 859,000 to 920,000 light-years from the Sun in the constellation Andromeda. It is the fourth largest dwarf spheroidal galaxy in the Local Group of galaxies, which includes our own Milky Way and the Andromeda Galaxy.

This galaxy was discovered using data from the first year of the Pan-Andromeda Archaeological Survey (PAndAS). This survey used the Megaprime/MegaCam wide-field camera on the Canada-France-Hawaii Telescope to study the areas around the Andromeda Galaxy (M31) and the Triangulum Galaxy (M33).

Andromeda XXI is a satellite of the larger Andromeda Galaxy. It appears as a group of stars in space and does not show any new stars being born today. Most of its stars formed about 5.8 billion years ago. Scientists think it may have lost a lot of its mass in the past due to gravitational effects from the Andromeda Galaxy.