In an unexpected discovery that shifts how scientists think about the early days of the universe, astronomers have detected a supermassive black hole that they say is the most distant ever observed.

The colossal black hole is so far away that light from the quasar in which it is located was emitted just 690 million years after the Big Bang, which took place 13.8 billion years ago. Quasars are star-like celestial objects made up of a supermassive black hole and surrounding gas, which shines with incredible brilliance as it falls into the black hole.

The newfound object certainly lives up to the supermassive moniker; it’s about 800 million times as massive as the sun. In comparison, the supermassive black hole at the center of our Milky Way galaxy, Sagittarius A*, is about 4.6 million times as massive as the sun.

That stupendous size has astronomers scratching their heads.

“Now that we are seeing it, we have to explain it,” Dr. Eduardo Banados, an astrophysicist with the Carnegie Institution for Science in Pasadena, California, and the lead author of a paper about the discovery, told the Los Angeles Times. “And that is a big challenge for theorists right now.”

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The paper was published online Dec. 6, 2017 in the journal Nature.

Larger supermassive black holes have been discovered, Dr. Robert Simcoe, a professor at MIT’s Kavli Institute for Astrophysics and Space Research and co-author of the paper, told NBC News MACH in an email. “What’s unprecedented is the combination of large size so early in the history of the universe.”