An international team of astronomers has announced the discovery of the oldest quasars ever observed, deepening a longstanding cosmic mystery about the early universe. Using data from the European Space Agency’s Euclid space telescope, which orbits at a stable point approximately 1.5 million kilometers from Earth, the researchers identified 31 quasars, including two that date back to roughly 670 million years after the Big Bang. This era corresponds to about five percent of the universe's current age of 13.8 billion years.
Quasars are extremely luminous objects powered by supermassive black holes at the centers of distant galaxies, where vast amounts of surrounding matter are rapidly consumed in energetic feeding processes. Their extraordinary brightness allows scientists to observe them across vast cosmic distances, effectively looking back in time to probe the infancy of the universe.
The two oldest quasars discovered surpass the previous record held since 2021 by around 20 million years, setting a new benchmark in the study of the early cosmos. Prior searches for ancient quasars primarily relied on ground-based telescopes, but the launch of the Euclid telescope in 2023 has significantly advanced this field. According to Daming Yang, the lead author of the study and a PhD student at Leiden University in the Netherlands, Euclid has doubled the number of known ancient quasars within just two years.
These newly uncovered quasars originate from the epoch of reionization, a pivotal period when the first stars and galaxies began to form, ending the so-called cosmic dark ages. Researchers use quasars as "cosmic lighthouses" to analyze the gas lying between the Earth and these distant objects, helping to trace the process through which the universe became reionized.
Despite these advancements, the discoveries have raised challenging questions. The quasars contain supermassive black holes with masses billions of times that of the Sun, existing at a time when the universe was still very young. This finding complicates existing models of cosmic evolution, as scientists do not yet fully understand how such massive objects could have formed so rapidly after the Big Bang.
"Every step further back in time makes the puzzle more perplexing," said Joseph Hennawi, co-author of the study, highlighting the difficulty in explaining the rapid growth of these early supermassive black holes. Researchers are now continuing their search for even older quasars in hopes of gaining deeper insight into the formation of the first cosmic structures and the early growth mechanisms of black holes.