Messier 110

Lore & Background

Charles Messier never included M110 in his published list, but he depicted it alongside M32 on his drawing of the Andromeda Galaxy, with a label indicating he first saw the object in 1773. The galaxy was independently discovered by Caroline Herschel on August 27, 1783, and her brother William Herschel described her discovery in 1785. It was not until 1967 that Kenneth Glyn Jones suggested assigning it a Messier number, making it the final entry in the Messier catalog.

The galaxy has a morphological classification of pec dE5, indicating a dwarf elliptical with 50% flattening. It is designated peculiar due to patches of dust and young blue stars near its center—an unusual feature for dwarf ellipticals, the reason for which remains unclear. Unlike M32, M110 lacks evidence for a supermassive black hole at its center. Its interstellar dust has a mass of (1.1–1.8)×10⁴ M☉ at 18–22 K, and its interstellar gas has (4–7)×10⁶ M☉. The inner region shows sweeping deficiencies in its interstellar medium, likely expelled by supernova explosions, and tidal interactions with M31 may have stripped away much of that expelled material.

About half of Andromeda's satellite galaxies orbit in a plane, with 14 of 16 following the same rotation sense. One model proposes that these 16 once belonged to a subhalo surrounding M110, then were broken up by tidal forces during a close encounter with Andromeda.

Reader's Guide

Messier 110 holds a unique place in astronomical history as the last object added to the Messier catalog, despite having been observed and depicted by Charles Messier himself nearly two centuries earlier. Its discovery by Caroline Herschel in 1783 highlights the often-overlooked contributions of early female astronomers. The galaxy's peculiar classification—a dwarf elliptical with central dust patches and young blue stars—challenges the typical view of such galaxies as simple, gas-poor systems, and the reason for this anomaly remains an open question. Its lack of a central supermassive black hole, unlike its companion M32, provides a contrast for studying galaxy evolution. The detection of novae in 1999 and 2002, including one captured by the Sloan Digital Sky Survey, demonstrates ongoing stellar activity. The model suggesting that many of Andromeda's satellites may have originated from a subhalo around M110, later disrupted by tidal forces, gives M110 a potential role in the broader dynamics of the Local Group. As a nearby dwarf elliptical with unusual properties, M110 continues to be a target for studies of interstellar medium processes, tidal stripping, and satellite galaxy formation.

Did You Know?

• It was the last member added to the Messier list, proposed by Kenneth Glyn Jones in 1967.
• Novae were detected in M110 in 1999 and 2002, the latter captured by the Sloan Digital Sky Survey.