Where Does Earth Stand Among The Council Of Giants, Milky Way, And Andromeda?
How many times have we stood staring at the night sky and imagined what lies beyond those stars? Well, until recently not much was known about our cosmic neighbors except Andromeda and a few other smaller galaxies. A new paper by York University Physics & Astronomy Professor Marshall McCall, published today in the Monthly Notices of the Royal Astronomical Society, offers a detailed view of several bright galaxies within 35-million light years of the Earth.
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The Earth, and the rest of our solar system, is in the Milky Way galaxy. It contains between 100-400 billion stars, an equal number of planets, and a concentration of gas and dust. Our closest neighbor is the Andromeda galaxy and it, along with the Milky Way, Triangulum Galaxy, and 30 smaller galaxies, forms the Local Group, which is about 3 million light years across.
"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," said McCall, according to a press release Tuesday. "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."
Out of the 14 giant galaxies in the Local Sheet, 12 are "spiral galaxies" and include the Milky Way, Andromeda, and Triangulum galaxies. Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust. The other two are "elliptical galaxies" and are somewhat ellipsoidal and consist of much older stars. The two ellipticals are on opposite sides of the Council. During the formation of the elliptical galaxies, winds that were formed pushed gases towards the Local Group, aiding the formation of disks around the Milky Way and Andromeda.
McCall also has a theory on how galaxies in the Council are spinning. "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," he said.
Studying about the council will also provide new clues about the formation of the Milky Way. It appears that the Local Group was created due to only a small increase in the density of matter in the universe. Also, considering that the Local Sheet and its Council are arranged in a very orderly fashion, it seems that nearby galaxies must have developed within a preexisting sheet-like foundation comprised primarily of dark matter.
"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. 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," McCall said.
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