Wind-powered Ultraluminous X-ray Sources
Abstract
Although ultraluminous X-ray sources (ULX) are important for astrophysics because of their extreme apparent super-Eddington luminosities, their nature is still poorly known. Theoretical and observational studies suggest that ULXs could be a diversified group of objects that are composed of low-mass X-ray binaries, high-mass X-ray binaries and marginally also systems containing intermediate-mass black holes. Observational data on the ULX donors could significantly boost our understanding of these systems, but only a few have been detected. There are several candidates, mostly red supergiants (RSGs), but surveys are typically biased toward luminous near-infrared objects. In ULXs harbouring RSGs matter accreted onto the compact body would have to be provided by the stellar wind of the companion because a Roche-lobe overflow could be unstable for relevant mass-ratios. We present a comprehensive study of the evolution and population of wind-fed ULXs, and we provide a theoretical support for the link between RSGs and ULXs. Assuming a minimal model of stellar-wind emission, our estimated upper limit on contribution of wind-fed ULX to the overall ULX population is ~75%-96% for young (<100 Myr) star-forming environments, ~49%-87% for prolonged constant star formation (e.g., disk of Milky Way), and ≲1% for environments in which star formation ceased long time (>2 Gyr) ago. We show also that some wind-fed ULXs (up to 6%) may evolve into merging double compact objects (DCOs). We demonstrate that the exclusion of wind-fed ULXs from population studies of ULXs might have lead to systematic errors in their conclusions.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 2021
- DOI:
- 10.3847/1538-4357/ac0cf7
- arXiv:
- arXiv:2103.02026
- Bibcode:
- 2021ApJ...918...60W
- Keywords:
-
- Black holes;
- Gravitational waves;
- Binary stars;
- X-ray binary stars;
- Astrostatistics;
- Astronomy databases;
- 162;
- 678;
- 154;
- 1811;
- 1882;
- 83;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 14 pages, 9 figures, 2 tables, accepted to ApJ