Local Sheet

Lore & Background

The Local Sheet was identified and described in 1987 by astronomer Brent Tully with colleague Richard Fisher in his book The Nearby Galaxies Atlas as Cloud 14. It is a huge 10 Mpc (33 Mly) prolate filament and is mostly host to late-type galaxies, in contrast to the Virgo Cluster, where more than half of the giant galaxies are early-type galaxies. Tully maintains that the Coma-Sculptor Cloud and the Local Sheet do not quite overlap, as the Local Sheet comprises only the co-moving part of the Coma-Sculptor Cloud, while McCall considers the two terms synonymous, referring to one and the same region.

The Local Sheet is part of the Local Volume and lies within the Virgo Supercluster (Local Supercluster). A significant component of the mean velocity of its galaxies results from the gravitational attraction of the Virgo Cluster, producing a peculiar motion of about 185 km⋅s⁻¹ toward the cluster. A second component is directed away from the center of the Local Void, an expanding region spanning an estimated 45 Mpc (150 Mly) that is only sparsely populated with galaxies, with a velocity of 259 km⋅s⁻¹.

The so-called Council of Giants is a ring of twelve large galaxies surrounding the Local Group in the Local Sheet, with a radius of 3.746 Mpc (12.22 Mly) and its center located 810 kpc (2.6 Mly) away from the Sun. Ten of these are spirals, while the remaining two are ellipticals (Maffei 1 and Centaurus A), which lie on opposite sides of the Local Group.

Reader's Guide

The Local Sheet is significant as the co-moving region of the Coma-Sculptor Cloud that contains the Milky Way and nearly all nearby bright galaxies, providing a local reference frame for studying galaxy motions. Its peculiar velocity components—185 km⋅s⁻¹ toward the Virgo Cluster and 259 km⋅s⁻¹ away from the Local Void—reveal the gravitational influences shaping our cosmic neighborhood. The Council of Giants, a ring of twelve large galaxies surrounding the Local Group, highlights the structure within the Sheet. The dispute between Tully and McCall over whether the Local Sheet and Coma-Sculptor Cloud are synonymous underscores ongoing refinement in mapping nearby large-scale structure. The Sheet's inclination of 8° from the Virgo Supercluster and its role as a wall bordering the Local Void make it a key feature in understanding the distribution of matter and voids in the local universe.

Did You Know?

• The Local Sheet has a diameter of about 10.4 megaparsecs (34 million light-years) and a thickness of 465 kiloparsecs (1.52 million light-years).
• The Local Group has a peculiar velocity of only 66 km⋅s⁻¹ with respect to the Local Sheet.
• The Council of Giants is a ring of twelve large galaxies surrounding the Local Group, with two ellipticals (Maffei 1 and Centaurus A) on opposite sides.

Architecture of a Galactic Wall

The Local Sheet is a vast, prolate filament of space stretching roughly 10.4 megaparsecs across its broadest dimension while remaining only 465 kiloparsecs thick — a structure so flat and extended that it reads almost like a sheet of paper laid across the cosmos. Nearly every bright galaxy in our immediate neighbourhood finds a home within its boundaries, and beyond that 10.4-megaparsec rim, galactic velocities shift dramatically, marking a clear demarcation line. Unlike the dense Virgo Cluster, where more than half the giant members are early-type ellipticals, the Local Sheet is dominated by late-type spirals, giving it a distinctly different galactic character. It sits within the Local Volume and the broader Virgo Supercluster, and it plays a structural role as one wall delineating the boundary of the Local Void, a vast underpopulated region stretching an estimated 45 megaparsecs. The sheet is inclined just 8 degrees relative to the plane of the Local Supercluster, a slight tilt that hints at the complex gravitational choreography shaping this corner of the universe.

A Tug-of-War in Velocity Space

The motion of galaxies within the Local Sheet is governed by two competing gravitational influences that together sculpt the sheet's characteristic peculiar velocity. The first and dominant pull comes from the massive Virgo Cluster, whose gravitational attraction drags the entire sheet at roughly 185 kilometres per second toward that dense concentration of galaxies. The second component points in the opposite direction: away from the centre of the Local Void, a sparsely populated expanse spanning an estimated 45 megaparsecs. This repulsive-looking component carries a velocity of 259 kilometres per second, a signature of the void's expansion pushing surrounding matter outward. Despite these large-scale flows, individual galaxies within the sheet exhibit remarkably low internal scatter, with a typical radial velocity dispersion of only 40 kilometres per second. The Milky Way's own Local Group, for its part, moves with a modest peculiar velocity of just 66 kilometres per second relative to the sheet as a whole, underscoring how tightly the sheet's members are bound to a shared co-moving frame.

The Council of Giants

Encircling the Local Group within the broader Local Sheet is a remarkable ring of twelve large galaxies known as the Council of Giants. This ring has a radius of approximately 3.746 megaparsecs — about 12.22 million light-years — and its geometric centre sits roughly 810 kiloparsecs, or 2.6 million light-years, from the Sun. The composition of the council is strikingly uniform: ten of the twelve members are spiral galaxies, while the remaining two are ellipticals. Those two ellipticals, Maffei 1 and Centaurus A, occupy positions on directly opposite sides of the Local Group, creating a kind of gravitational bookend around our neighbourhood. The council's existence within the Local Sheet underscores how the sheet functions not merely as a diffuse background of faint objects but as a structured environment in which even the most massive nearby galaxies are arranged in coherent, ring-like geometries. It is a reminder that on scales of millions of light-years, the universe still favours order and symmetry over random scattering.

Naming, Discovery, and the Coordinate Framework

The region we now call the Local Sheet was first formally identified and described in 1987 by astronomer Brent Tully together with colleague Richard Fisher, who catalogued it as Cloud 14 in their work The Nearby Galaxies Atlas. Tully and Fisher characterised it as a roughly 10-megaparsec prolate filament, the co-moving portion of the broader Coma-Sculptor Cloud. Tully himself has maintained that the Coma-Sculptor Cloud and the Local Sheet do not perfectly overlap, insisting that the Local Sheet comprises only the co-moving subset. Other researchers, such as McCall, treat the two names as fully synonymous, referring to one and the same region. The Local Sheet's importance extends beyond mere classification: it serves as the foundational reference plane for the Supergalactic coordinate system, where the sheet, also called the Supergalactic Plane, defines the X–Y axes. This makes the Local Sheet not just a physical structure but a cornerstone of how astronomers orient themselves in the extragalactic sky, anchoring an entire coordinate framework to the motion and geometry of our immediate cosmic neighbourhood.