Publication Date:
2010-10-22
Description:
The X-ray source M33 X-7 in the nearby galaxy Messier 33 is among the most massive X-ray binary stellar systems known, hosting a rapidly spinning, 15.65M(middle dot in circle) black hole orbiting an underluminous, 70M(middle dot in circle) main-sequence companion in a slightly eccentric 3.45-day orbit (M(middle dot in circle), solar mass). Although post-main-sequence mass transfer explains the masses and tight orbit, it leaves unexplained the observed X-ray luminosity, the star's underluminosity, the black hole's spin and the orbital eccentricity. A common envelope phase, or rotational mixing, could explain the orbit, but the former would lead to a merger and the latter to an overluminous companion. A merger would also ensue if mass transfer to the black hole were invoked for its spin-up. Here we report simulations of evolutionary tracks which reveal that if M33 X-7 started as a primary body of 85M(middle dot in circle)-99M(middle dot in circle) and a secondary body of 28M(middle dot in circle)-32M(middle dot in circle), in a 2.8-3.1-d orbit, its observed properties can be consistently explained. In this model, the main-sequence primary transfers part of its envelope to the secondary and loses the rest in a wind; it ends its life as a approximately 16M(middle dot in circle) helium star with an iron-nickel core that collapses to a black hole (with or without an accompanying supernova). The release of binding energy, and possibly collapse asymmetries, 'kick' the nascent black hole into an eccentric orbit. Wind accretion explains the X-ray luminosity, and the black-hole spin can be natal.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Valsecchi, Francesca -- Glebbeek, Evert -- Farr, Will M -- Fragos, Tassos -- Willems, Bart -- Orosz, Jerome A -- Liu, Jifeng -- Kalogera, Vassiliki -- England -- Nature. 2010 Nov 4;468(7320):77-9. doi: 10.1038/nature09463. Epub 2010 Oct 20.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA. francesca@u.northwestern.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20962778" target="_blank"〉PubMed〈/a〉
Print ISSN:
0028-0836
Electronic ISSN:
1476-4687
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
,
Natural Sciences in General
,
Physics
