Mirach's Goblin: Discovery of a dwarf spheroidal galaxy behind the Andromeda galaxy

Understand

It is of broad interest for galaxy formation theory to carry out a full inventory of the numbers and properties of dwarf galaxies in the Local Volume, both satellites and isolated ones.

• Ultra-deep imaging in wide areas of the sky with small amateur telescopes can help to complete the census of these hitherto unknown low surface brightness galaxies, which cannot be detected by the current resolved stellar population and HI surveys.
• We report the discovery of Donatiello I, a dwarf spheroidal galaxy located one degree from the star Mirach (Beta And) in a deep image taken with an amateur telescope.
• The color--magnitude diagram obtained from follow-up observations obtained with the Gran Telescopio Canarias (La Palma, Spain) reveals that this system is beyond the Local Group and is mainly composed of old stars.