Euclid Mission: Unraveling the Mysteries of Galactic Evolution
In just a year since its launch in July 2023, the European Space Agency’s Euclid mission has begun to illuminate the enigmatic processes that dictate the shapes and structures of galaxies. With its advanced capabilities, the Euclid space telescope is set to transform our understanding of how galaxies and their central supermassive black holes evolve together over cosmic time.
Euclid’s first data release, made available in March 2025, showcases the telescope’s remarkable ability to survey the cosmos, having already observed an astonishing 1.2 million galaxies. This is just a fraction of what the mission aims to achieve over its six-year primary operation, which is expected to culminate in the study of tens of millions of galaxies. The implications of this research are profound, as astronomers anticipate significant advancements in our comprehension of galactic evolution.
According to Maximilian Fabricius, a scientist at the Max Planck Institute for Extraterrestrial Physics, “Euclid offers an unprecedented combination of sharpness and sky coverage — it will map the entire extragalactic sky.” This capability allows scientists to systematically investigate the relationship between a galaxy’s shape, its central structures, and its formation history on an expansive scale.
The distinct morphologies of galaxies, from the sprawling spirals like our Milky Way to the smooth ellipticals such as Messier 87, arise from their evolutionary paths. Utilizing Euclid’s data, researchers have constructed a “galactic tuning fork” diagram that illustrates the lifecycle of galaxies. This diagram captures the transition of blue star-forming galaxies as they evolve, depleting their star-forming gas and dust, merging with other galaxies, and ultimately morphing into massive elliptical galaxies.
A key focus of the Euclid mission is the interplay between galaxies and their supermassive black holes. Fabricius and his team have identified galaxies exhibiting potential “secondary nuclei,” which are crucial in the formation of supermassive black hole binaries. These binaries emerge during galactic mergers, where two supermassive black holes, each millions to billions of times the mass of our Sun, begin to orbit one another. This orbital dance generates gravitational waves, which carry away angular momentum, facilitating the black holes’ eventual collision and merger into a larger supermassive black hole.
The merging process is not merely an isolated event; it plays a vital role in the evolution of the host galaxies, particularly in the formation of giant elliptical galaxies. Fabricius elaborates, “The most massive black holes lie at the centers of giant elliptical galaxies and are thought to grow primarily through mergers with other supermassive black holes.” By detecting and analyzing these secondary nuclei, Euclid enables scientists to explore how these colossal black holes continue to grow and how their growth impacts the galaxies that harbor them.
While the first data release from Euclid constitutes only about 0.5% of the total data anticipated from the mission, it has already yielded valuable insights. Notably, Euclid’s sensitivity has uncovered that the most prevalent galaxies in the universe are not the familiar spiral types but rather small, faint dwarf galaxies. These dwarf galaxies, previously too dim for detailed observation, are now recognized as fundamental building blocks for larger galaxies, including our own Milky Way. So far, Euclid has identified 2,674 dwarf galaxies, some of which feature compact blue cores or globular clusters.
As the Euclid mission continues to gather data, our understanding of the galactic tuning fork is becoming increasingly nuanced, allowing for a deeper exploration of galactic structure and evolution. With each new discovery, Euclid is not just mapping the cosmos; it is reshaping our comprehension of the universe’s grand tapestry, revealing the intricate relationships between galaxies and the supermassive black holes that lie at their hearts.