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Volume 574 Issue 7777, 10 October 2019

Stars colliding

The cover image shows a stage in a modelled sequence of two massive stars merging. The simulation, presented in this week’s issue by Fabian Schneider and his colleagues, looks at how magnetic fields are generated during the merger process. Around 10% of massive stars (those of more than 1.5 solar masses) have a strong surface magnetic field, and it has been suggested that this may be the result of stellar mergers. The researchers used a 3D magnetohydrodynamic simulation to test this hypothesis. In the cover image, a primary, more massive star has just been disrupted as it merges with a secondary star (lighter colours represent stronger magnetic fields). The large black spiral shows the location of gas mainly stemming from the primary star, where no magnetic field is yet present. The black parts in the centre trace the core of the secondary star, where there is also no magnetic field yet (as the merger progresses the magnetic field permeates the whole body). The simulation reveals that such mergers do indeed produce stars with strong fields. The researchers suggest that the merger product leaves behind a magnetar — a highly magnetic neutron star — when it finally explodes as a supernova at the end of its life.

Cover image: Sebastian Ohlmann, Fabian Schneider & Friedrich Röpke

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