Young stars discovered in dwarf spheroidal galaxies confirm their recent infall into the Milky way

Francois Hammer; Piercarlo Bonifacio; Elisabetta Caffau; Yanbin Yang; Frederic Arenou; Carine Babusiaux; Monique Spite; Patrick Francois; Ana Gomez; David Katz; Lorenzo Monaco; Marcel Pawlowski; Jianling Wang

arXiv · 2505.11587

Young stars discovered in dwarf spheroidal galaxies confirm their recent infall into the Milky way

Francois Hammer·Piercarlo Bonifacio·Elisabetta Caffau·Yanbin Yang·Frederic Arenou·Carine Babusiaux·Monique Spite·Patrick Francois·Ana Gomez·David Katz·Lorenzo Monaco·Marcel Pawlowski·Jianling Wang

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Abstract

Recent observations from the ESA Gaia satellite and with the ESO VLT, have identified the presence of a population of young, 0.5 to 2 Gyr old, stars in the halo and in dwarf spheroidal galaxies surrounding the Milky Way. It suggests that MW dwarf galaxies, currently devoid of gas, had, until recent times, enough gas to sustain a burst of star formation. The recent loss of gas coincides with their arrival in the vicinity of the Milky Way, in agreement with orbital predictions from Gaia that indicate that most dwarf galaxies reached the Milky Way halo less than 3 Gyr years ago. This completely changes the interpretation of their dynamics, mass, and dark matter content.

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Francois Hammer, Piercarlo Bonifacio, Elisabetta Caffau, Yanbin Yang, Frederic Arenou, Carine Babusiaux, Monique Spite, Patrick Francois, Ana Gomez, David Katz, Lorenzo Monaco, Marcel Pawlowski, Jianling Wang. 2025-05-16. Young stars discovered in dwarf spheroidal galaxies confirm their recent infall into the Milky way. https://arxiv.org/abs/2505.11587

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