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In the cave
From the visible to the invisible to find out more about galaxies

Imagine you are in your car trying to tune into a radio station by pressing buttons to change the frequency. Certain stations will come through with static so you can't hear them properly while others will sound perfectly clear. It is similar for astronomers when they work on defining an "identity card" for galaxies giving all their characteristics.

A series of images showing the NGC 4650A galaxy obtained using the MUSE instrument developed by the CRAL and installed at the Very Large Telescope unit in Paranal, Chile. Credits: © ESO / MUSE consortium / R. Bacon L. Calçada

This work was carried out by researchers from the Lyon Centre for Astrophysics Research (CRAL) and covers the whole spectrum ranging from blue to infra-red. In the same way as a radio broadcast can be heard when we are on the right frequency, the gases which make up this galaxy become visible when observed using the right wavelength! This technique has been applied to the galaxy NGC 4650A which is portrayed in the place of honour in the images presented here. NGC 4650A is located in the southern hemisphere in the constellation Centaurus 115 light years away from the Milky Way. It is one of the family of polar-ring galaxies which explains its rather distinctive shape as it is made up of a ring of stars and gas.

To obtain this kind of image, the CRAL researchers based their work on data from MUSE (Multi Unit Spectroscopic Explorer). This is a unique and very high-performance integral-field spectrograph capable of slicing space images which took nearly ten years to develop. MUSE is located on the Nasmyth platform of the Very Large Telescope (VLT) at Paranal in the Chilean desert and is used by researchers to study the mechanisms which led to the formation of galaxies. This instrument is capable of obtaining the spectrum of each object in all the elements of an image and thus of characterizing numerous faraway galaxies while even discovering new ones!

Thanks to Emmanuel Pecontal for his contribution.

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