Galactic supercluster found hiding behind Milky Way

The Zone of Avoidance. It sounds like a no-fly zone, but it’s actually a swathe of the sky rendered invisible to astronomers, thanks to the Milky Way galaxy’s dust and stars in the way.

But now, astronomers from South Africa, Europe and Australia, led by Renee Kraan-Korteweg from the University of Cape Town, have discovered a giant collection of galaxies – called the Vela Supercluster – concealed by the Milky Way, some 800 million light-years away.

The so-called Vela supercluster was unveiled in the Monthly Notices of the Royal Astronomical Society Letters.

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Superclusters are the biggest and most massive known structures in the universe. The can stretch hundreds of millions of light-years end to end.

The most famous, the Shapley Supercluster, is thought to be the largest of its kind in our corner of the cosmos. It’s around 650 million light-years away.

Now another, though more distant, supercluster has been seen – sort of. Kraan-Korteweg and her crew examined thousands of galaxies partly within the Zone of Avoidance (that is, partially masked by the Milky Way) with the Southern African Large Telescope in 2012.

They found eight new clusters in the area of the Vela constellation. Observations with the Anglo-Australian Telescope measured their redshift to track their movements – and it turned out they were all part of the one supercluster.

Looking up in the sky, with the Milky Way a streak overhead, the Vela Supercluster would look perpendicular behind it, if it were visible. 

“I could not believe such a major structure would pop up so prominently,” Kraan-Korteweg says.

Follow-up observations will uncover the supercluster’s extent, mass and gravitational influence. New telescopes and surveys, such as the MeerKAT in South Africa, which saw first light this year, and the Taipan galaxy survey in Australia will help out.