On the Origin of Black Hole Spin in High-mass X-Ray Binaries

Abstract

Black hole (BH) spins in low-mass X-ray binaries (LMXBs) cover a range of values that can be explained by accretion after BH birth. In contrast, the three BH spin measurements in high-mass X-ray binaries (HMXBs) show only values near the maximum and likely have a different origin connected to the BH stellar progenitor. We explore here two possible scenarios to explain the high spins of BHs in HMXBs: formation in binaries that undergo mass transfer (MT) during the main sequence (MS; Case-A MT), and very close binaries undergoing chemically homogeneous evolution (CHE). We find that both scenarios are able to produce high-spin BHs if internal angular momentum (AM) transport in the progenitor star after its MS evolution is not too strong (i.e., weak coupling between the stellar core and its envelope). If instead efficient AM transport is assumed, we find that the resulting BH spins are always too low with respect to observations. The Case-A MT model provides a good fit for the BH spins, the masses of the two components, and the final orbital periods for two of the three BHs in HMXBs with measured spins. For one of them, the mass predicted for the BH companion is significantly lower than observed, but this depends strongly on the assumed efficiency of mass transfer. The CHE models predict orbital periods that are too large for all three cases considered here. We expect the Case-A MT to be much more frequent at the metallicities involved, so we conclude that the Case-A MT scenario is preferred. Finally, we predict that the stellar companions of HMXBs formed through the Case-A MT have enhanced nitrogen surface abundances, which can be tested by future observations.

Binary Black Hole Population Properties Inferred from the First and Second Observing Runs of Advanced LIGO and Advanced Virgo

“…Once a BH is formed, however, changing the spin magnitude is more difficult owing to limitations on mass accretion rates affecting how much a BH can be spun up (Thorne 1974;Valsecchi et al 2010;Wong et al 2012;Qin et al 2019). Once the BBH system is formed, the spin magnitudes do not change appreciably over the inspiral (Farr et al 2014).…”

GW190412: Observation of a binary-black-hole coalescence with asymmetric masses

“…Recent work modeling the core-envelope interaction in massive stars finds angular momentum transport to be highly efficient, leading to stellar cores with extremely slow rotation prior to collapse, hence BHs with low spins (χ ∼ 0.01, e.g., [232][233][234]). Though particular phases of mass transfer early in the evolution of the primary star can potentially lead to significant spin at birth [235], modeling of this evolutionary pathway finds that it does not lead to systems that can merge as BBHs [235,236]. Binary interactions following the formation of the first-born BH, such as mass transfer from the companion star to the BH, are also inefficient at spinning up BHs significantly [237][238][239][240][241].…”

The black hole spin in coalescing binary black holes and high-mass X-ray binaries

“…This formation channel was for the first time proposed by Valsecchi et al (2010) to explain the formation of M33 X-7. More specifically, a systematic study for this formation channel was carried out by Qin et al (2019).…”

“…Fast rotating BH can be formed via the two channels, and the Case-A MT channel could explain well the current observed 3 systems with close orbits. More details about the two channels for explaining the current observed 3 HMXBs are given in Qin et al (2019).…”

“…Such formation channel has been extensively studied recently Marchant et al, 2016;Song et al, 2016). In addition, CHE is also considered to be an alternative approach to predicting BH with high spin a * in HMXBs (Qin et al, 2019). However, this model predicts orbit periods that are too large for currently three observed systems and more studies in detail are presented in chapter 4.…”