Astronomers have discovered the first "bubble of galaxies," an almost unimaginably huge cosmic structure thought to be a fossilized remnant from just after the Big Bang sitting in our galactic backyard.

The bubble spans a billion light years, making it 10,000 times wider than the Milky Way galaxy.

Yet this giant bubble, which cannot be seen by the naked eye, is a relatively close 820 million light years away from our home galaxy, in what astronomers call the nearby universe.

The bubble can be thought of as "a spherical shell with a heart," Daniel Pomarede, an astrophysicist at France's Atomic Energy Commission, told AFP.

Inside that heart is the Bootes supercluster of galaxies, which is surrounded by a vast void sometimes called "the Great Nothing".

The shell contains several other galaxy superclusters already known to science, including the massive structure known as the Sloan Great Wall.

Pomarede said the discovery of the bubble, which is described in research he co-authored that was published in The Astrophysical Journal this week, was "part of a very long scientific process".

It confirms a phenomenon first described in 1970 by US cosmologist — and future physics Nobel winner — Jim Peebles.

He theorized that in the primordial universe — then a stew of hot plasma — the churning of gravity and radiation created sound waves called baryon acoustic oscillations (BAOs).

As the sound waves rippled through the plasma, they created bubbles.

Around 380,000 years after the Big Bang the process stopped as the universe cooled down, freezing the shape of the bubbles.

The bubbles then grew larger as the universe expanded, similar to other fossilized remnants from the time after the Big Bang.

Astronomers previously detected signals of BAOs in 2005 when looking at data from nearby galaxies.