The Virgo Cluster is still assembling itself from merging galaxy clumps
Some 53.8 million light-years away, roughly 1,300 galaxies, perhaps as many as 2,000, crowd together in the Virgo Cluster. It is not a settled city but a young one: three main clumps are merging, and surrounding clouds of spiral galaxies are falling in to join them, pulled by a combined mass of about a thousand trillion suns.
Charles Messier logged many of its brighter members in the late 1770s and early 1780s, listing them among fuzzy objects that were not comets and describing them as nebulae without stars. Their true identity as galaxies emerged only in the 1920s. The cluster spans about 8 degrees of sky, and a 6-inch telescope can pick out around 160 of its galaxies on a clear night; the brightest is the elliptical Messier 49.
The dominant clump, Virgo A, centres on the giant elliptical M87, whose supermassive black hole had its event horizon imaged by the Event Horizon Telescope in 2019. Virgo A is roughly ten times as massive as the clumps around M86 and M49. Elliptical galaxies crowd toward the core, while spirals string out in a filament about four times longer than it is wide, pointing along our line of sight. The first known ultra-diffuse galaxy turned up in the core in 1984.
Life inside is harsh. The space between galaxies is filled with thin plasma at 30 million kelvin that glows in X-rays, and as galaxies plough through it, the pressure strips away their gas and can shut down star formation. Galaxies race around at up to 1,600 km per second relative to the centre, a sign of the cluster's enormous mass. Up to a tenth of its stars drift between galaxies, probably flung out by encounters.
The cluster sits at the heart of the Virgo Supercluster, which includes our own Local Group. Its gravity reaches us: it slows the Local Group's retreat from it by about ten percent, a pull astronomers call the Virgocentric flow.
Source: Virgo Cluster
