The European Space Agency’s (ESA) Euclid telescope has identified 31 of the oldest known quasars in the early universe, according to a study published in the journal Astronomy & Astrophysics. These extremely distant, luminous objects date back to a period when the universe was in its infancy, providing new data on the growth of supermassive black holes and the evolution of the first galaxies.
Quasars, or quasi-stellar radio sources, are the bright nuclei of distant galaxies powered by supermassive black holes accreting matter. The Euclid mission, which launched in July 2023, uses a wide-field instrument to map the geometry of the dark universe, but its sensitivity to near-infrared light has allowed astronomers to detect these “cosmic monsters” that were previously invisible or overlooked by other surveys.
The discovery of these 31 high-redshift quasars allows researchers to probe the “cosmic dawn,” the era when the first stars and galaxies began to ionize the surrounding hydrogen gas. Because light takes billions of years to travel from these objects to Earth, observing them is effectively looking back in time to the universe’s first billion years.
How did Euclid find these ancient quasars?
Euclid identified these objects by analyzing the specific color signatures of light in the near-infrared spectrum. Because the universe is expanding, light from the most distant objects is "redshifted," shifting from visible light into the infrared range.
The research team filtered through massive datasets to find point-like sources that appeared extremely red, a characteristic typical of quasars at high redshifts. This method allowed them to isolate 31 candidates that represent some of the most distant luminous objects ever recorded. By comparing these findings with existing catalogs, the team confirmed that Euclid can detect these objects more efficiently than previous wide-field surveys.
Why the discovery of early quasars matters for astronomy
The existence of supermassive black holes so shortly after the Big Bang poses a significant challenge to current cosmological models. Quasars are powered by black holes with masses millions or billions of times that of the Sun.
Standard models of accretion suggest black holes grow slowly over time. However, the presence of these 31 ancient quasars suggests either that the “seed” black holes were much larger than previously thought or that they consumed matter at rates far exceeding the theoretical limits. This discovery provides a larger sample size for astronomers to study the relationship between the growth of a galaxy and the growth of its central black hole.
Furthermore, these quasars act as cosmic beacons. As their light travels through the intergalactic medium, it carries a “fingerprint” of the gas it encountered. This allows scientists to map the distribution of matter and the state of ionization in the early universe, helping to determine exactly when the “cosmic fog” of neutral hydrogen cleared.
Comparing Euclid to other space observatories
While the James Webb Space Telescope (JWST) provides deeper, more detailed looks at individual objects, Euclid’s strength lies in its scale. JWST acts like a powerful magnifying glass focusing on a small patch of sky, whereas Euclid acts like a wide-angle lens capturing a panoramic view. This makes Euclid far more effective at finding rare objects like high-redshift quasars across a broad area.
The synergy between these two instruments is critical. Euclid identifies the candidates across the sky, and JWST can then be used to perform detailed spectroscopic analysis on those specific targets to determine their exact chemical composition and age. This “survey-and-follow-up” strategy is currently accelerating the pace of discovery in observational cosmology.
What happens next for the Euclid mission?
This larger census will allow for a statistical analysis of how the early universe was structured.
Do you believe these findings will force a rewrite of early-universe physics? Share your thoughts in the comments below.