Studies of galaxies have shown us that they can reveal themselves in different ways. The images presented here by the CRAL were captured by the space telescopes Hubble and Chandra and also by the image slicer MUSE (Multi Unit Spectroscopic Explorer) and concentrate on the signatures of galaxies while also showing that the Universe is in a state of perpetual expansion.

We shall first deal with "mirage"-type galaxies. These can be recognized by their elongated, distorted shape. An unbelievable amount of luck is required to photograph them because they only appear thanks to light being deflected so that they are no longer hidden behind galaxies at the forefront.

The second observable phenomenon is that of "comet" galaxies. This reveals the formation of galaxy clusters when a galaxy plunges into the centre of the cluster producing a trail of stars.

The third set of images were taken by Chandra which captures X-ray sources from galaxy clusters and helps researchers map masses of hot gases by observing how gases are concentrated within the cluster. This leads to the dual conclusion that ordinary matter (which we are made of) does not mix with dark matter and that the two types function differently because they are separate.

The last video highlights an observation made using MUSE of the Hubble Deep Field. It is in some ways a kind of "zoom" made by MUSE of a small part of the sky. This instrument examines spectrum data using imaging (one image per wavelength) and shows that certain galaxies only shine in a certain colour which indicates their distance and enables researchers to study the evolution of galaxies throughout the history of the Universe.

Thanks to Johan Richard for his contribution.

Find out more

• Centre de recherche en astrophysique de Lyon - Observatoire de Lyon (CRAL)
• Une galaxie en pleine transformation : la « galaxie-comète »
• Premiers signes de l'existence d'interactions au sein de la matière noire ? Et si la matière noire n'était pas si noire ?
• VLT – au-delà de Hubble, MUSE dessine l’image tridimensionnelle de l’Univers lointain