Charles Messier never included the galaxy in his list, but it was depicted by him, together with M32, on his drawing of "Nébuleuse D'Andromède", later known as the Andromeda Galaxy. A label of the drawing indicates that Messier first saw the object in 1773.[a][10] M110 was independently discovered by Caroline Herschel on August 27, 1783; her brother William Herschel described her discovery in 1785.[b][10][11] The suggestion to assign the galaxy a Messier number was made by Kenneth Glyn Jones in 1967,[12] making it the last member of the Messier List.
Properties
This galaxy has a morphological classification of pec dE5, indicating a dwarf elliptical galaxy with a flattening of 50%. It is designated peculiar (pec) due to patches of dust and young blue stars near its center.[13] This is unusual for dwarf elliptical galaxies in general,[9] and the reason is unclear.[13] Unlike M32, M110 lacks evidence for a supermassive black hole at its center.[14]
The interstellar dust in M110 has a mass of (1.1–1.8)×104M☉ with a temperature of 18–22 K, and the interstellar gas has (4–7)×106M☉. The inner region has sweeping deficiencies in its interstellar medium IM, most likely expelled by supernova explosions. Tidal interactions with M31 may have stripped away a significant fraction of the expelled gas and dust, leaving the galaxy as a whole, as it presents, deficient in its IM density.[15]
Novae have been detected in this galaxy, including one discovered in 1999,[16] and another in 2002. The latter, designated EQ J004015.8+414420, had also been captured in images taken by the Sloan Digital Sky Survey (SDSS) that October.[17]
Local context
About half of the Andromeda's satellite galaxies are orbiting it along a highly flattened plane, with 14 out of 16 following the same sense of rotation. One theory proposes that these 16 once belonged to a subhalo surrounding M110, then the group was broken up by tidal forces during a close encounter with Andromeda.[18]
^Herschel, William (1785). "On the construction of the heavens". Philosophical Transactions of the Royal Society of London. 75: 213–266. From p. 262: "There is a very considerable, broad, pretty faint, small nebula near it [the Andromeda galaxy, M31]; my Sister [Caroline] discovered it August 27, 1783, with a Newtonian 2-feet sweeper. It shews the same faint colour with the great one, and is, no doubt, in the neighborhood of it. It is not [M32] … ; but this is about two-thirds of a degree north preceding it, in a line parallel to β [Beta] and ν [Nu] Andromedae."
^ abFord, Holland C.; et al. (July 1973), "Planetary Nebulae in Local-Group Galaxies. I. Identifications in NGC 185, NGC 205, and NGC 221", Astrophysical Journal, 183: L73, Bibcode:1973ApJ...183L..73F, doi:10.1086/181255