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Elliptical galaxies “refuse” to form stars!

The observation by a scientific collective of a thousand far away "elliptical" galaxies is shaking up our knowledge of galaxies. How can they be rich in gas without producing any stars?
Published on 30 January 2018

The observation of our closest galaxies led the astrophysicists to distinguish disk-shaped galaxies, such as the Milky Way, which are abundant in gas and produce stars, and elliptical (or spheroidal) galaxies, which are lacking in gas and new stars. Quite naturally, they have correlated the presence of large gas reservoirs with the formation of stars.

An international collaboration involving the Irfu has analyzed a set of infrared and radiofrequency readings covering a set of nearly one thousand elliptical galaxies, more than ten billion light years away. They were surprised to measure a mass of cold dust one hundred times greater than expected, indicating the massive presence of gas. However, these atypical galaxies from the early universe do not form stars like their closest counterparts.

Why is this so? Scientists have very few leads to explain this paradox. According to certain simulations, the gas could be more likely to "feel" the gravitational attraction of stars in spherical galaxies than in disks. The large-scale morphology of the galaxy would thus influence the highly localized formation of stars.

Other simulations will follow, and the researchers are preparing to directly detect the gas of these galaxies using the large ALMA (Atacama Large Millimeter/submillimeter Array) radio interferometer now operational in Chile.

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