83 quasars discovered in the early universe

5 articles published in the journals “The Astrophysical Journal Letters“, “The Astrophysical Journal” (here and here), “The Astrophysical Journal Supplement Series” (paiwalled, available here) and “Publications of the Astronomical Society of Japan” describe various aspects of the discovery of 83 new quasars dating back to about 13 billion years ago, studied together with 17 other quasars from that era that were already known. A team of researchers led by Yoshiki Matsuoka, now at the Japanese Ehime University, used the Hyper Suprime-Cam (HSC), an instrument mounted on the Subaru Telescope of the National Astronomical Observatory of Japan (NAOJ) in Hawaii. Those quasars are powered by supermassive black holes and their study will help perfect our cosmological models.

Today we know that it’s normal for galaxies to have supermassive black holes at their center and that sometimes they’re surrounded by enormous amounts of gas and dust that get very hot as they approach it, resulting in strong electromagnetic emissions that make them so bright that they’re visible even from billions of light years away. The timeline and modes of those supermassive black holes’ formation are still the subject of discussion, especially following the discovery of some so distant that we see them as they were when the universe was less than a billion years old.

Increasingly sophisticated instruments made it possible to discover more distant and therefore more ancient objects and HSC is at a cutting-edge one with its field of vision, seven times the area of ​​the full Moon mounted on one of the largest telescopes in the world. For this project, called Subaru High-Exploration of Low-Luminosity Quasars (SHELLQs), the researchers scanned the sky during more than 300 nights of telescope time over more than five years.

The analysis of the collected data made it possible to identify many quasar candidates that were examined not only with the Subaru telescope but also with the Gran Canarias on the island of La Palma and with the Gemini South in Chile. The result was the discovery of 83 very distant new quasars, added to the 17 already known in the examined area.

The top image (courtesy National Astronomical Observatory of Japan. All rights reserved), obtained with HSC, shows one of the quasars discovered in this study. The bottom image (courtesy National Astronomical Observatory of Japan. All rights reserved) shows a composition that includes all the 100 quasars observed with HSC.

This study is important among other things to look for new information on what is known as the reionization period, when hydrogen got separated into protons and electrons. One of the hypotheses to explain that event is that the early universe was full of quasars that emitted the radiations that caused it. However, even after these new discoveries the known quasars remain too few to explain the reionization.

The authors of this study will continue their search for very distant supermassive black holes to gather more information on those primordial objects and understand when they first appeared in the universe. These are important researches to understand why the universe evolved in a certain way with the reionization and the formation of galaxies.

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