International Gemini Observatory and Subaru Combine Forces to Discover First Ever Pair of Merging Quasars at Cosmic Dawn

This illustration depicts two quasars in the process of merging. the quasars are shown with a small blue circle at the center and then white fading to yellow fading to orange and then red. Jets, shown as translucent blue, stream from the centers above and below the quasars. — *This illustration depicts two quasars in the process of merging. Credit: International Gemini Observatory/NOIRLab/NSF/AURA/M. Garlick*

Since the very first instant after the Big Bang the Universe has been expanding. This means that the early Universe was considerably smaller and early-formed galaxies were more likely to interact and merge. Galaxy mergers fuel the formation of quasars — extremely luminous galactic cores where gas and dust falling into a central supermassive black hole emit enormous amounts of light. So when looking back at the early Universe astronomers would expect to find numerous pairs of quasars in close proximity to each other as their host galaxies undergo mergers. However, they have been surprised to find exactly none — until now.

With the aid of the Gemini North telescope, one half of the International Gemini Observatory, which is supported in part by the U.S. National Science Foundation and operated by NSF NOIRLab, a team of astronomers have discovered a pair of merging quasars seen only 900 million years after the Big Bang. Not only is this the most distant pair of merging quasars ever found, but also the first confirmed pair in the period of the Universe’s history known as Cosmic Dawn.

Cosmic Dawn spanned from about 50 million years to one billion years after the Big Bang. During this period the first stars and galaxies began appearing, filling the dark Universe with light for the first time. The arrival of the first stars and galaxies kicked off a new era in the formation of the cosmos known as the Epoch of Reionization.

The Epoch of Reionization, which took place within Cosmic Dawn, was a period of cosmological transition. Beginning roughly 400 million years after the Big Bang, ultraviolet light from the first stars, galaxies and quasars spread throughout the cosmos, interacting with the intergalactic medium and stripping the Universe’s primordial hydrogen atoms of their electrons in a process known as ionization. The Epoch of Reionization was a critical epoch in the history of the Universe that marked the end of the cosmic dark ages and seeded the large structures we observe in our local Universe today.