The Missing Link between Black Holes in High-mass X-Ray Binaries and Gravitational-wave Sources: Observational Selection Effects

Abstract

There are few observed high-mass X-ray binaries (HMXBs) that harbor massive black holes (BHs), and none are likely to result in a binary black hole (BBH) that merges within a Hubble time; however, we know that massive merging BBHs exist from gravitational-wave (GW) observations. We investigate the role that X-ray and GW observational selection effects play in determining the properties of their respective detected binary populations. We find that, as a result of selection effects, detectable HMXBs and detectable BBHs form at different redshifts and metallicities, with detectable HMXBs forming at much lower redshifts and higher metallicities than detectable BBHs. We also find disparities in the mass distributions of these populations, with detectable merging BBH progenitors pulling to higher component masses relative to the full detectable HMXB population. Fewer than 3% of detectable HMXBs host BHs >35M ⊙ in our simulated populations. Furthermore, we find the probability that a detectable HMXB will merge as a BBH system within a Hubble time is ≃0.6%. Thus, it is unsurprising that no currently observed HMXB is predicted to form a merging BBH with high probability.

An Extreme Black Hole in the Recurrent X-Ray Transient XTE J2012+381

“…While high-mass X-ray binary (HMXB) systems are ideal candidates to link the population of XBs to that of BBHs, as they contain a BH and a massive star that could also evolve to produce a secondary BH, Gallegos-Garcia et al (2022) find that only up to 11% of HMXBs that experience an accretion episode while both stars are still on the main sequence (case A mass transfer) can evolve to eventually form a merging BBH system, and that at most 20% of merging BBH systems originate from case A HMXBs. Additionally, Liotine et al (2023) find that observational selection effects can further divide the link between HMXBs and BBHs through the fact that only around 0.6% of detectable HMXBs could produce a BBH system that would merge in a Hubble time. Therefore, independently understanding the different BH spin distributions is imperative, and the most pragmatic way to expand the spin distribution in XBs is to continue to measure the spins of as many BHs as possible.…”

Disentangling the Black Hole Mass Spectrum with Photometric Microlensing Surveys

“…Massive, extragalactic BHs can be detected through a strong gravitational interaction with another object causing gravitational radiation (e.g., Abbott et al 2016Abbott et al , 2023a or through accretion causing electromagnetic (EM) radiation (e.g., Fabbiano 2006;Akiyama et al 2019;Event Horizon Telescope Collaboration et al 2022). Studies using gravitational-wave (GW) emission and EM observation can be effective for understanding the extragalactic BH population (e.g., Roulet & Zaldarriaga 2019;Abbott et al 2021bAbbott et al , 2023bEdelman et al 2023), provided that detection bias from observational selection effects is mitigated (Liotine et al 2023).…”

The High-mass X-Ray Binary Luminosity Functions of Dwarf Galaxies

“…In addition, there is growing evidence suggesting that HMXBs in dwarf galaxies in the early Universe may have contributed significantly to the ionizing radiation during the preheating of the intergalactic medium leading up to the epoch of reionization (Warszawski et al 2009;Madau & Fragos 2017;Eide et al 2018). The study of HMXBs also provides an important constraint on binary star and compact object evolution, with important implications for gravitational wave sources (Podsiadlowski et al 2003;Abbott et al 2016;Liotine et al 2023).…”