Beyond the Milky Way, a Galactic Wall

Beyond the Milky Way, a Galactic Wall


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

On the largest scales, cosmologists attest, the universe should be expanding smoothly, and the galaxies should be evenly distributed. But on smaller, more local scales, the universe appears lumpy and gnarled. Astronomers have found that galaxies are gathered, often by the thousands, in giant clouds called clusters and that these are connected to one another in lacy, luminous chains and filaments to form superclusters extending across billions of light-years. In between are vast deserts of darkness called voids.

From all of this has emerged what some astronomers call our “long address”: We live on Earth, which is in the solar system, which is in the Milky Way galaxy. The Milky Way is part of a small cluster of galaxies called the Local Group, which is on the edge of the Virgo cluster, a conglomeration of several thousand galaxies.

In 2014, Dr. Tully suggested that these features were all connected, as part of a giant conglomeration he called Laniakea — Hawaiian for “open skies” or “immense heaven.” It consists of 100,000 galaxies spread across 500 million light-years.

All this lumpiness has distorted the expansion of the universe. In 1986, a group of astronomers who called themselves the Seven Samurai announced that the galaxies in a huge swath of the sky in the direction of the constellation Centaurus were flying away much faster than the Hubble law predicted, as if being pulled toward something — something the astronomers called the Great Attractor. It was the beginning of something big.

“We now see the Great Attractor as the downtown region of the supercluster that we live in — an overall entity that our team has called the Laniakea Supercluster,” Dr. Tully said. All the different parts of this supercluster are tugging on us, he added.

As a result, the Great Attractor and its relatives are shedding light on another enduring cosmic mystery — namely, where we are headed.

Astronomers discovered in 1965 that space is suffused with microwave radiation, a bath of heat — with a temperature of 2.7 degrees Kelvin, or minus 455 degrees Fahrenheit — left over from the birth of the universe 14 billion years ago. Subsequent observations revealed that this bath is not uniform: It is slightly warmer in one direction, suggesting that we — Earth, our galaxy and the Local Group — are moving through the microwaves, like a goldfish in a fishbowl, at about 400 miles per second in the approximate direction of Centaurus, but aiming far beyond.



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