An international team of astronomers are studying 21 ancient quasi-stellar objects (or "quasars") at the very limits of our observable universe. Each quasar has a supermassive black hole throbbing inside, sucking in the surrounding gas and growing to titanic masses exceeding 100 million suns.

Two of these monsters are located further away than the rest and have been studied by the Spitzer Space Telescope after first being spotted by the Sloan Digital Sky Survey.

"Quasars are a very early stage of galaxies, a sort of baby galaxies," said Marianne Vestergaard, astrophysicist at the Dark Cosmology Center at the Niels Bohr Institute at the University of Copenhagen and co-author of a paper announcing these findings in the March 18 issue of Nature.

"Most galaxies have a massive black hole with a mass of over a million solar masses, but quasars are different. Their black holes are active and growing."

The pair of distant quasars -- named J0005-0006 and J0303-0019 -- are approximately 13 billion light-years away (the light we receive from them is therefore 13 billion years old), meaning they formed less than 800 million years after the Big Bang. This fact makes these specimens pure; they are the "cleanest" quasars ever detected.

"We have found what are likely first-generation quasars, born in a dust-free medium and at the earliest stages of evolution," said Linhua Jiang of the University of Arizona, Tucson and lead author of the study.

During the first few hundred million years after the Big Bang, there was no dust in the universe, just the most basic of gases. Before galaxies formed, it is thought primordial supermassive black holes were ignited as quasars, blasting the universe with intense X-ray radiation, so these earliest quasars wouldn't have contained any dust.

However, this is the first time that observational evidence of dust-free quasars has been confirmed, providing a tantalizing glimpse at how these gargantuan black holes formed.