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superclusters rule the tiny collection of galaxies

superclusters

superclusters
superclusters ESA/Hubble & NASA

The cosmic bullies next door

How vast superclusters rule the tiny collection of galaxies we call the Local Group  by Liz Kruesi

IN 1994 astronomer Renée Kraan-Korteweg spotted some 600 galaxies lying the same distance away from us, all clustered around the constellations Hydra and Vela. These findings hinted that the region might harbor an enormous structure, perhaps a supercluster, though learning more about it would not be easy. These galaxies sit behind the Milky Way’s dense disk, which holds billions of stars and enormous clouds of dust, materials that obscure background light signals. To study what lies behind this region, aptly named the “Zone of Avoidance” (ZOA), you need to find a way to subtract the dust from observations and use instruments advanced enough to separate foreground stars from background light. It’s a lot of work, it takes a lot of time, and scientists in charge of those high-end instruments aren’t always keen to allot time to difficult projects with no guarantee of discovery. But over the next couple of decades, Kraan-Korteweg chipped away at the problem. In 2000, she persuaded the 6-degree Field Galaxy Survey team to use commissioning time to study the region. After analyzing the data, she learned that practically all the thousands of galaxies over the 12° of sky she studied lie at that same distance. She used radio surveys to study the hydrogen in galaxies behind the ZOA. She used infrared telescopes to peer through the Milky Way’s dust. And with each project, time after time, she kept returning to the unexplained conglomeration of galaxies. “It all seemed limitless [for it] to come together,” she says. But last year, Kraan-Korteweg and her team confirmed that

Galaxy cluster Abell 3627 lies at the heart of the Great Attractor — a massive collection of several large clusters that tugs the Milky Way and all nearby galaxies toward a spot in the constellations Norma and Triangulum Australe. The Great Attractor escaped notice until the 1980s because it lies behind the Milky Way’s obscuring disk. ESO

The 2,000 galaxies of the Virgo Cluster reside 55 million light-years from Earth. This cluster marks the center of the Local Supercluster, a region that spans some 150 million light-years. Our Local Group of several dozen galaxies lies on this supercluster’s outskirts. ESO/DSS2