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The Jellyfish Shape of a Galaxy Gives Hints on its Past

An international team, including a researcher from IRFU, has discovered an elliptical galaxy with an unexpected jellyfish shape, within a galaxy cluster about one billion light-years away. The completely atypical presence of long "tails" of gas and areas of star formation could be explained by a recent merger with a companion gas-rich galaxy.
Published on 4 December 2017

A young galaxy such as the Milky Way still contains large amounts of gas, and by "falling" towards the center of its cluster, it is strongly deformed, creating "tails" of gas and stars in formation. This phenomenon is not found in elliptical galaxies (more ancient) which have consumed all of their initial gas.

In this context, the galaxy discovered in cluster Arbell 2670 comes as quite the surprise: it is both elliptical and has "tails" of gas and young stars. More precisely, observations recorded in Chile with the new multi-wavelength spectrograph of the VLT European Observatory reveal long stripped "tails" of stars and gases towards the back of the galaxy in motion. This pattern is explained by the action of the ionized gas of the cluster, which tends to push the gas of the galaxy in the direction opposite from its movement, whereas the stars, not very sensitive to its action, are found in the head.

The origin of the gas in the galaxy remains unsolved. It could be explained by the recent merger of the galaxy with another one that was rich in gas. Much of this gas would have been in the center of the galaxy, leading to multiple-star formations... The jellyfish puzzle is still missing a few pieces.

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