Council of Giants: Our Intergalactic Neighborhood

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We orbit a yellow dwarf star called The Sun that orbits the center of The Milky Way — a large 100,000 light-year wide spiral galaxy. The Milky Way contains around 400 billion stars and at least as many alien worlds. Beyond our galaxy, as we look into intergalactic space, we know that we share a region known as the “Local Group” — 54 galaxies (including dwarf galaxies) that are contained within a volume approximately 3 million light-years across. The Milky Way and Andromeda, another spiral galaxy, are King and Queen of this realm, the largest two galaxies in the Local Group.

Beyond the Local Group, however, there has been some ambiguity as to its make-up and distribution.

PHOTOS: Hubble’s Sexiest Spiral Galaxies

In a new paper published in the journal Monthly Notices of the Royal Astronomical Society, astronomer Marshall McCall, of York University in Toronto, has mapped out the bright galaxies within 35 million light-years from the Milky Way, expanding our intergalactic horizons.

“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 in a York University press release. “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.”

In the video shown above, McCall graphically illustrates the Local Sheet in a simple 3-D model that clearly shows the intergalactic structure of the ‘Council of Giants’ — the largest galaxies, including the Milky Way and Andromeda — and beyond.

ANALYSIS: When Did Galaxies Get Their Spirals?

Some information about the possible evolution of the galaxies (and the stars contained within) can be gleaned from this map argues McCall. Twelve of the 14 giant galaxies in the Local Sheet are spirals; flattened disks with spiral arms rotating around a central core. The others are puffed-up elliptical galaxies that lack any kind of disk or spiral structure.

Interestingly, two ellipticals are located at either end of the Council of Giants — these two galaxies, early in their evolution, would have blasted out powerful stellar winds that may have pushed gas toward the Local Group that helped build the massive spirals of the Milky Way and Andromeda. Also, the spin directions of the Council giants are arranged around a small circle in the sky, that “might have been set up by gravitational torques imposed by the Milky Way and Andromeda when the universe was smaller,” said McCall. In other words, the modern large-scale structure and spin direction of the galaxies contained within the Council have been shaped from the earliest evolution of the Local Sheet’s existence.

ANALYSIS: Vast Rivers of Hydrogen Flow into Galaxies

What’s more, the modern orderly arrangement of the galaxies contained within the Sheet is indicative of the structure of dark matter in the earliest epochs of galactic formation. The large scale structure of dark matter, which is thought to make up 85 percent of the mass of the Universe, is believed to be arranged in a huge web with filaments connecting, creating discrete regions of gravitational anchors around which the galaxies (and clusters of galaxies) formed.

“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,” said 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.”

Marshall McCall / York University
Marshall McCall / York University

Source: York University

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