March 11, 2014
What Lies Beyond: Astronomer Maps Galaxies Near Our Own
Lee Rannals for redOrbit.com - Your Universe Online
A new paper published in the Monthly Notices of the Royal Astronomical Society has broadened the view of what lies just past our galaxy.
The Milky Way and Andromeda are dominant members of a small group of galaxies. However, not a lot has been known about the smaller galaxies that reside within our neighborhood in the universe. York University Physics & Astronomy Professor Marshall McCall was able to map out the bright galaxies within 35-million light years of the Earth.
"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," McCall said in a statement. "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 by restricting its range of influence."
McCall said twelve of the fourteen larger galaxies located in the Local Sheet are spiral galaxies, while the remaining two are elliptical galaxies. Winds during the earliest phases of the galaxies’ development could have helped build up the disks of the Milky Way and Andromeda galaxies.
"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,” McCall said. “This unusual alignment might have been set up by gravitational torques imposed by the Milky Way and Andromeda when the universe was smaller."
The astronomer says the boundary defined by the Council has helped shed some light on the conditions which led to the formations of the Milky Way. Only a small enhancement in the density of matter in the universe appears to have been required to produce the Local Group.
In order for the arrangement of the galaxies to play out the way they did, nearby galaxies must have developed within a pre-existing sheet-like foundation composed of dark matter, according to the study.
"Recent surveys of the more distant universe have revealed that galaxies lie in sheets and filaments with large regions of empty space called voids in between," says McCall. "The geometry is like that of a sponge. What the new map reveals is that structure akin to that seen on large scales extends down to the smallest."