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Beyond the Milky Way, a galactic wall

The galaxies in the wall cannot be seen, but Dr. Pomarède and his colleagues could observe their gravitational effects by collecting data from telescopes around the world.

In the expanding universe, described in 1929 by astronomer Edwin Hubble and confirmed for nearly a century, distant galaxies fly away from us as if they were dots on an inflating balloon; the longer they are, the faster they return from us according to a relationship called the Hubble Law.

That movement away from the earth causes their light to move to longer, redder wavelengths and lower frequencies, like retiring ambulance sirens. Astronomers use this “redshift”

;, which is easily measured, as a proxy for relative distance in the universe. By measuring galaxy distances independently, the “Cosmicflows” team, such as Dr. Pomarède and his colleagues call themselves, separating the movement caused by the cosmic expansion from movements caused by gravitational irregularities.

As a result, they discovered that the galaxies between the Earth and the South Pole Wall are sailing away from us slightly faster than they otherwise should be, about 30 miles per second, pulled outward by the huge chunk of material in the wall. And galaxies outside the wall move outward more slowly than they otherwise should be, regulated by the gravitational force of the wall.

An astonishing aspect of the wall is how large it is compared to the volume the team examined: a coherent filament of 1.4 billion light years long, packed in a cloud perhaps 600 million in radius. “There is hardly room in the volume for anything bigger!” Dr. Tully said in an email. “We must anticipate that our view of the filament is cut; that it extends beyond our research horizon. “

And yet the South Pole lies in cosmological terms nearby. “One may wonder how such a large and not so distant structure remained unnoticed,” admired Dr. Pomarède in a statement from his university.

But in the expanding universe there is always something more to see.

On the largest scales, cosmologists attest, the universe should expand smoothly and the galaxies should be evenly distributed. But on smaller, more local scales, the universe seems clumsy and cluttered. Astronomers have found that galaxies gather, often by thousands, in giant clouds called clusters and that they are linked to each other in pointed, luminous chains and filaments to form super clusters spanning billions of light years. In between there are large deserts of darkness called voids.

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