The Euclid space telescope has discovered 31 quasars dating from the early universe. Two of them set a new record, as their light was emitted when the cosmos was only 670 million years old, about 5% of its current age.
A quasar corresponds to a very bright phase in the evolution of a galaxy. At its center, a considerable amount of matter falls toward a supermassive black hole. As it accelerates and heats up, the gas releases so much energy that the nucleus can outshine the luminosity of its entire galaxy.
The central point of this artist's interpretation is a blazing reddish-orange disk composed of spiraling matter. The matter swirls toward a brilliant white-yellow center, from which a thin beam-like jet of matter emerges to the left, directed toward the upper center of the frame.
Credit: ESA under CC BY-SA 3.0
The two oldest objects bear the designations EUCL J172902.75+641018.1 and EUCL J125308.55+705432.3. Their light traveled for more than 13 billion years before reaching astronomers' instruments.
Euclid's observations also add twelve quasars dating back to the first 770 million years of cosmic history.
The researchers identified these quasars thanks to their redshift. The expansion of the Universe stretches light during its journey. The farther an object is, the greater this shift, allowing the estimation of the epoch when its light was emitted.
Until now, astronomers mostly observed very bright quasars, which were easier to spot. This selection probably represented only a small fraction of the actual population. The vast coverage of the Euclid telescope now makes it possible to search for fainter objects over a much larger area of the sky.
This new population provides information on the rapid growth of the first supermassive black holes. Their existence so early after the Big Bang remains difficult to explain, as models must produce a considerable mass in a few hundred million years.
The observed quasars belong to the epoch of reionization. During this period, the light from the first stars and galaxies gradually transformed the intergalactic gas. Euclid's data should help link this transition to the formation of the first cosmic structures.