The Milky Way Galaxy has long been known to reside within a close family of galaxies, called the Local Group. Our own collection of stars and the Andromeda Galaxy comprise the two largest members of this group, which stretches three million light years from one side to the other.
Marshall McCall from York University decided to map out galaxies slightly further away from our home world. The results were surprising.
"All bright galaxies within 20 million light years, including us, are organized in a 'Local Sheet' 34-million light years across and only 1.5-million light years thick. The Milky Way and Andromeda are encircled by twelve large galaxies arranged in a ring about 24-million light years across - this 'Council of Giants' stands in gravitational judgment of the Local Group," McCall said.
Of the 14 galaxies that make up the ring, 12 are classified as spirals, similar to the Milky Way. The other two are elliptical galaxies, sitting on opposite ends of the rung from one another. Gases from these oddly-shaped collections of stars may have been drawn toward the massive Milky Way and Andromeda galaxies, helping to fuel their growth.
Such order may have been directed in the early Universe by dark matter, which brought the families of stars together.
"Thinking of a galaxy as a screw in a piece of wood, the direction of spin can be described as the direction the screw would move (in or out) if it were turned the same way as the galaxy rotates. Unexpectedly, the spin directions of Council giants are arranged around a small circle on the sky. This unusual alignment might have been set up by gravitational torques imposed by the Milky Way and Andromeda when the universe was smaller," McCall said.
This "small circle" around which the galaxies rotate is located between Andromeda and the Milky Way, an imaginary "balance point" called a barycenter. Think of this like the support between two halves of a see-saw. Each of the two large galaxies is attended by a swarm of smaller stellar families.
Back before astronomers recognized galaxies as vast collections of stars, Edwin Hubble studied the fuzzy patches of light called nebulae. In 1936, he first described a collection of the mysterious objects surrounding our own family of stars. Today, astronomers know of 54 galaxies within our local group.
Throughout the observable Universe, galaxies lay along large bubbles, with vast empty spaces between them.
Details of the study were published in the Monthly Notices of the Royal Astronomical Society.
