Euclid telescope discovers oldest quasars ever observed

Euclid telescope discovers oldest quasars ever observed

An international team of astronomers has identified 31 ancient quasars, including the two oldest ever observed, using the European Space Agency’s Euclid space telescope. These objects, the brightest in the universe, date back to when the universe was roughly 670 million years old, representing only 5 per cent of its current age of 13.8 billion years.

The discovery, published Monday, July 6, in Astronomy & Astrophysics, beats the team's own previous record for the most distant quasar set in 2021 by approximately 20 million years. The two most distant objects, designated EUCL J172902.75+641018.1 and EUCL J125308.55+705432.3, have redshifts of 7.77 and 7.69 respectively and are located more than 13 billion light-years from Earth.

Quasars are the intensely luminous cores of distant galaxies powered by supermassive black holes. As gas and dust spiral into these black holes, gravitational energy is converted into radiation, causing some to shine with the light of a trillion suns. Because of this extreme luminosity, they act as cosmic beacons or lighthouses that allow researchers to study the gas and conditions of the early universe.

Technological Shift in Quasar Hunting

For decades, astronomers relied primarily on ground-based telescopes to find these rare objects. However, the launch of Euclid in 2023 has fundamentally altered the field. Daming Yang, lead author of the study and a PhD student at Leiden University, stated that Euclid has doubled the number of known ancient quasars in just two years.

Finding these objects from the ground is described as nearly impossible because their light is stretched into near-infrared wavelengths by cosmic expansion. This redshift causes the signals to fall into a range where the Earth's atmosphere glows brightly, masking the faint light of the quasars. Furthermore, ancient quasars are easily mistaken for stars in the Milky Way. Euclid overcomes these hurdles by operating from a stable position 1.5 million kilometres from Earth, combining wide-area sky coverage with high-resolution infrared imaging.

The discoveries were made via the Euclid Wide Survey, which aims to map more than one-third of the sky. The efficiency of the new telescope is stark: while previous surveys took over a decade to identify about ten quasars at comparable distances, Euclid surpassed that number in roughly one year of observations.

The Mystery of Rapid Growth

The existence of these objects deepens a perplexing cosmic mystery regarding how supermassive black holes grew so massive so quickly. Some of these monsters weigh billions of times the mass of the sun, yet they existed during the universe's infancy.

"We don’t yet have a good understanding of how they grew so massive, so fast."

Joseph Hennawi, physics professor, via the study

Standard cosmological models suggest that the earliest quasars should form in the highest-density regions of a dark matter cosmic web, surrounded by many smaller galaxies. However, a separate MIT-led study using the James Webb Space Telescope (JWST) found a surprising variety of environments. While some quasars were surrounded by more than 50 galaxies, others appeared to be sitting in the middle of nowhere with only a few stray galaxies nearby.

Anna-Christina Eilers, assistant professor of physics at MIT, noted that it is difficult to explain how these quasars grew so large if they appear to have nothing to feed from. One possibility is that these "lonely" quasars are actually surrounded by galaxies hidden by cosmic dust.

Insights into the Cosmic Dawn

These quasars date back to the epoch of reionisation, the period when the first stars and galaxies formed and ended the cosmic dark ages. Follow-up observations of one newly discovered quasar revealed it resides in a gas- and dust-rich galaxy undergoing intense star formation.

Other research has focused on the structure of these early black holes. Astronomers detected the earliest known flickering quasar, dating to 850 million years after the Big Bang. The flicker revealed that the black hole's accretion disk was thin and flat, resembling mature black holes seen in the nearby universe rather than the puffy, chaotic disks expected in the early universe.

Next Steps

The research team is now working toward several goals:

• Searching for the first quasar beyond redshift 8, which would place it within the first 630 million years of the universe.
• Sifting through JWST data to measure black hole masses and probe the chemistry of surrounding gas.
• Using the Atacama Large Millimeter Array to target glowing cosmic dust in host galaxies.
• Developing a complete quasar chronicle of the first billion years to understand the timeline of early cosmic evolution.