The multiple faces of today’s galaxies: their morphologies tell their evolution

(© Image: Unsplash) - The large morphological classes of galaxies have fascinated astronomers since their discovery. A new analysis led by Louis Quilley, PhD student (Sorbonne University), and Valérie de Lapparent, researcher at the Institut d'Astrophysique de Paris (IAP), establishes a physical link between the order of the different types of the famous Hubble sequence, and the systematic evolution of galaxies. This analysis shows for the first time that the trajectory of galaxies across the green plain, the transition zone through which galaxies evolve from forming many new stars to a quiescent state, is closely related to morphological types, making the Hubble sequence an inverse evolutionary sequence. These results were published on October 27, 2022 in Astronomy and Astrophysics . Less than a century earlier, in 1926, the American astronomer Edwin Hubble published a morphological classification of galaxies that grouped together the different objects he had observed according to their shape and the details they contained. An order is chosen and constitutes a sequence ranging from elliptical galaxies, to lenticular, spiral and irregular. Later enriched by Gérard de Vaucouleurs and Allan Sandage, the Hubble sequence remains a reference tool for classifying galaxies, still used today by astronomers.