ESA's Euclid Space Telescope Discovers Distant Quasars at Record Distances

The ESA's Euclid space telescope has embarked on a groundbreaking journey in the study of early quasars and their host galaxies. New research led by Silvia Belladitta from the Max Planck Institute for Astronomy (MPIA) and her colleagues has followed up on one of Euclid's discoveries, delving deeper into the host galaxy of one of the earliest known supermassive black holes in the universe.

Bright Objects with a Dark Center

Active galactic nuclei, particularly known as quasars, are responsible for some of the brightest phenomena observed in the night sky. Their immense brightness is driven by matter falling into a central supermassive black hole, which can have millions or even billions of solar masses. These supermassive black holes are found in nearly all galaxies. The energy output from these black holes significantly influences star formation within their host galaxies—an effect that is particularly pronounced in the most massive galaxies. The active galactic nucleus can suppress star formation by heating the gas that serves as the raw material for new stars, but it can also contribute to gas compression, thereby fostering star formation.

The formation of the first galaxies and their central black holes is a highly active area of research. A crucial aspect of this puzzle involves the search for the first quasars and the investigation of their host galaxies. However, peering into the past presents challenges: we observe objects as they were in the early universe when their light has taken an exceptionally long time to reach us. If the light reaching our telescopes today shows us a quasar as it was 13.4 billion years ago, it means that light has traveled for 13.4 billion years from that quasar to our telescopes.

Searching for 'Ordinary' Quasars

Over such vast distances, even inherently bright objects like quasars appear relatively dim. Naturally, the easiest quasars to observe are the particularly bright examples; however, the extreme brightness of a quasar suggests it may not represent the overall population of quasars. Here, the ESA's Euclid telescope showcases its strengths as an exceptional 'quasar finder' in the early universe—a remarkable capability confirmed through follow-up observations with ground-based telescopes.

Eduardo Banados, group leader at MPIA and co-leader of the Euclid quasar group from 2022 to 2025, remarked, “Seeing Euclid unleash its potential is incredibly satisfying. But it gets even better: for the first time, we can study ordinary, typical quasars in the early universe, not just extraordinarily bright ones. This provides insights into how most early black holes have grown—and how these black holes have influenced their host galaxies.”

In just 1.5 years of observation, Euclid has more than doubled the number of known early quasars from nine to 21. This includes quasars with redshift z > 7, which we see as they were less than 800 million years after the Big Bang. Within just a few months, Euclid broke the redshift record for quasars not once, but twice!

Characteristics of an Early Host Galaxy

For one of those ordinary early quasars, Belladitta and her team were able to scrutinize its host galaxy more closely. This quasar is designated EUCL J125308.55+705432.3, a name derived from its position in the sky. The light we receive from this quasar today was emitted 13 billion years ago, just 800 million years after the Big Bang (at redshift z=7.7). In the ultraviolet spectrum, this quasar is only about 15% as bright as earlier quasars that held the redshift record.

To study the host galaxy, the researchers utilized the NOEMA antenna array (Northern Extended Millimeter Array) located on the Plateau de Bure in the French Alps. The twelve 15-meter antennas of NOEMA are combined to function as a single, significantly larger telescope. With this array, astronomers observed the host galaxy at two carefully selected submillimeter wavelengths.

Using Submillimeter Light to Assess Star Formation and Dust Content

The first type of light analyzed is the II line. This light arises in molecular clouds where new stars are forming. The brightness of this line allows astronomers to infer the star formation rate of a galaxy.

This light also enables mass estimation: most of us have experienced how the sound of an emergency vehicle changes as it passes by. Movement affects the wavelength of waves. In a similar manner, astronomers can reconstruct how gas moves within the galaxy from the shape of the II line, allowing for an estimation of the galaxy's mass.

The second type of submillimeter light studied by Belladitta and her colleagues is the thermal radiation from cold dust within a galaxy. The intensity of this light provides insights into the amount of dust present in the galaxy. Typically, the amount of dust correlates with the amount of molecular hydrogen in a galaxy, which serves as the raw material for star formation. Observations indicate that this galaxy possesses a significant amount of dust and, consequently, molecular hydrogen!

Reconstructing the Star Formation Rate

From their observations, Belladitta and her colleagues reconstructed key characteristics of the galaxy hosting the quasar. This galaxy appears to be forming new stars at a rate exceeding 250 solar masses per year. In contrast, our Milky Way forms roughly one solar mass of new stars annually. This high star formation rate aligns with earlier observations of less distant quasars. The mass of the galaxy is estimated to be around ten billion solar masses, which is about one-tenth the mass of our Milky Way and consistent with an early galaxy that has much of its growth yet to come.

Silvia Belladitta, a postdoctoral researcher at MPIA and the lead author of the study, stated, “We have found a galaxy that possesses all the ingredients to become a truly large exemplar: it is as massive as the host galaxies of the brightest early quasars, and it contains a vast reservoir of molecular gas that enables intense star formation. This opens up a fascinating possibility: UV-faint quasars like EUCL J125308.55+705432.3 may be in a different stage of development than their more luminous relatives. Either the black hole is growing more slowly than in the brightest quasars, or much of its activity is hidden behind dense clouds of dust. We now need to determine which of these possibilities holds true with future observations.”

Future Plans

These individual findings represent important puzzle pieces in our overall understanding of galaxy development, guiding astronomers on what to investigate next. The comprehensive sky survey planned for six years with Euclid is expected to discover hundreds more early quasars of this kind. Follow-up observations like those from Belladitta and her colleagues will provide information about star formation rates and galaxy masses. Gradually, a more complete picture of the earliest galaxies and supermassive black holes in the universe will emerge, enriching our understanding of the formation and evolution of these primordial galaxies—a critical prerequisite for our own existence.

Background Information

The results described here were published as Belladitta et al. “Euclid: A UV-faint quasar in a highly luminous star-forming host galaxy at z≈7.7” in the journal Astronomy & Astrophysics. The results of the Euclid quasar search were published as D. Yang et al., “Euclid: Discovery of 31 new quasars at 6.6 < z < 7.8” in the journal Astronomy & Astrophysics.

The scientists involved from MPIA include Silvia Belladitta, Eduardo Banados, Fabian Walter, Knud Jahnke, Sarah Bosman, Julien Wolf, and Mischa Schirmer, in collaboration with Roberto Decarli (INAF Observatory, Bologna), Daming Yang (Leiden Observatory), Francesco Guarneri (University of Hamburg), and the rest of the Euclid collaboration.

Euclid is an ESA mission aimed at measuring the properties of dark energy and dark matter throughout the entire cosmic history. Since its launch in 2023, Euclid has been surveying about one-third of the sky, capturing images of two billion galaxies and determining the precise distances of around 50 million galaxies. The first major data release from Euclid, DR1, will provide the international scientific community with data covering an area of nearly 2000 square degrees in November 2026. The Max Planck Institute for Astronomy (MPIA) is a founding member of the Euclid consortium, which now comprises more than 150 institutions across Europe, Canada, Japan, and the USA. During the construction phase, MPIA contributed hardware for the near-infrared instrument aboard Euclid. Currently, MPIA scientists are involved in the operation of the space telescope and lead the calibration efforts for Euclid.