The origin of OB runaways and the Astronomical Multipurpose Software Environment

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• Simon Portegies Zwart (Leiden)
• Thursday 15 March 2012, 16:30-17:30
• Sackler Lecture Theatre, IoA (tea at 4:00 pm).

If you have a question about this talk, please contact Mark Gieles.

More than 20\% of all massive stars in the Milky-way Galaxy have an unusual high velocity of $>30$\,km/s. The origin of this population of runaway OB stars has been puzzling astronomers for more than half a century. In one of the favorite explanations a star is launched from a binary system when its companion explodes in a core-collapse supernova. This mechanism fails to explain the high proportion of runaway stars that ware ejected from clusters, because the ejection occurred well before any star experienced a supernova explosion. We demonstrate that the observed runaways are explained by stellar ejections mediated by strong three-body interactions with a binary star. Such a binary forms during the core collapse of a young ($\aplt 1$\,Myr) and rather low mass ($ 5000-10000$\,\Msun) star cluster. This model reproduces the key characteristics of OB runaways in the Milky-way Galaxy and it explains the $\apgt 100$\,\Msun\, runaway stars around young star clusters, e.g. R136 and Westerlund 2. The high proportion and the distribution in mass of OB runaway stars in the Milky-way Galaxy can be explained if the vast majority of massive stars are born in dense and relatively low mass clusters.

This talk is part of the Institute of Astronomy Colloquia series.

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