Satellite galaxies can carry on forming stars when they pass close to their parent galaxies

Most scientists believed that star formation would cease once a satellite galaxies passed close to its parent galaxy of higher mass. This was because the bigger galaxy would remove any gas from the galaxy, which would leave it without the material it needed to make new stars. Arianna di Cintio (Instituto de Astrofsica de Canarias) led the team that discovered this using numerical simulations. The study's results were published in the Monthly Notices of the Royal Astronomical Society. The researchers used sophisticated simulations to simulate the entire Local Group of galaxies including the Milky Way and the Andromeda galaxies. They found that satellites can not only retain their gas, but also can experience new episodes of starformation when passing close enough to their parent galaxy's pericentre (the minimum distance they can reach from its centre). Satellite galaxies belonging to the Local Group have a variety of star formation histories. Their origin is not fully understood. The authors used hydrodynamic simulations in the Constrained Local UniversE project (CLUES), to study the star formation histories for satellite galaxies that are similar to the Milky Way, within a cosmological setting. Although the majority of cases see the gas from the satellite being sucked out of the parent galaxy by gravitational action, and then transfers to the larger galaxy, this process is known as accretion. However, 25% of the sample showed that the interactive process clearly enhanced star formation. These results showed that star formation peak times are associated with close passes of satellites around parent galaxies, as well as the interaction of satellites. Two key characteristics of star formation were identified by the researchers: The satellite must pass close to the parent galaxy with large amounts of cold gas and not be too far away, in order to allow for the compression of the gas to form stars. Galaxies that pass too close to their parent galaxy or with less gas are not allowed to form new stars. Arianna di Cintio is the lead author of the paper. She adds that this is crucial when trying to understand star formation in smaller dwarf galaxies within our Local Group. This is an unsolved problem. This discovery will provide a fascinating explanation for the star formation episodes observed in dwarf galaxies belonging to the Local Group. This finding requires revisions to the theoretical models that explain the formation stars in dwarf galaxies. ###

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