A Tuning Fork is a device used to tune musical instruments. It vibrates at a single frequency, it is a pure sound of a single note.
The Hubble Diagram not only looks like a Tuning Fork, but is also sounds like it: morphology is a single note, a single parameter, and it is based on a single frequency — the visible wavelengths.
After a century of discoveries and instrumental developments, galaxies appear complex and described by many properties at all wavelengths. Many notes vibrating at several frequencies define a harmonic table. The best example of a harmonic table is a piano. This piano is required to represent the galaxy diversity throughout the Universe from its beginning.
Transforming the Hubble Tuning Fork into a Piano has always been the goal of astrocladistics. We are now ready to tackle this fascinating achievement, and I am fully engaged into this project for the next few years.
To get an overview of the galaxy classification problem, the paths toward a solution and the potential impact of a renewed classification scheme, you can listen to my talk given at the Department of Physics and Astrophysics “Galileo Galilei” in Padova (Italy) on January 29th, 2015.