The most massive progenitors of neutron stars: CXO J164710.2-455216

Abstract

The evolution leading to the formation of a neutron star in the very young Westerlund 1 star cluster is investigated. The turnoff mass has been estimated to be 35 Msun, indicating a cluster age ~ 3-5 Myr. The brightest X-ray source in the cluster, CXO J164710.2-455216, is a slowly spinning (10 s) single neutron star and potentially a magnetar. Since this source was argued to be a member of the cluster, the neutron star progenitor must have been very massive (M_zams > 40 Msun) as noted by Muno et al. (2006). Since such massive stars are generally believed to form black holes (rather than neutron stars), the existence of this object poses a challenge for understanding massive star evolution. We point out while single star progenitors below M_zams < 20 Msun form neutron stars, binary evolution completely changes the progenitor mass range. In particular, we demonstrate that mass loss in Roche lobe overflow enables stars as massive as 50-80 Msun, under favorable conditions, to form neutron stars. If the very high observed binary fraction of massive stars in Westerlund 1 (> 70 percent) is considered, it is natural that CXO J164710.2-455216 was formed in a binary which was disrupted in a supernova explosion such that it is now found as a single neutron star. Hence, the existence of a neutron star in a given stellar population does not necessarily place stringent constraints on progenitor mass when binary interactions are considered. It is concluded that the existence of a neutron star in Westerlund 1 cluster is fully consistent with the generally accepted framework of stellar evolution.

5 pages of text and 4 figures (submitted to Astrophysical Journal)

References in corpus (7)

• A 15.65 solar mass black hole in an eclipsing binary in the nearby spiral galaxy Messier 33
• A census of the Wolf-Rayet content in Westerlund 1 from near-infrared imaging and spectroscopy
• On IC 10 X-1, the Most Massive Known Stellar-Mass Black Hole
• The Orbital Period of the Wolf-Rayet Binary IC 10 X-1; Dynamic Evidence that the Compact Object is a Black Hole
• Intermediate to low-mass stellar content of Westerlund 1
• The WR population predicted by massive single star and by massive binary evolution
• Exciting the Magnetosphere of the Magnetar CXOU J164710.2-455216 in Westerlund 1

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