Noninteracting Black Hole Binaries with Gaia and LAMOST

Abstract

Until recently, black holes (BHs) could be discovered only through accretion from other stars in X-ray binaries, or in merging double compact objects. Improvements in astrometric and spectroscopic measurements have made it possible to detect BHs also in noninteracting BH binaries (nBHBs) through a precise analysis of the companion’s motion. In this study, using an updated version of the StarTrack binary-star population modeling code and a detailed model of the Milky Way (MW) galaxy, we calculate the expected number of detections for Gaia and LAMOST surveys. We develop a formalism to convolve the binary population synthesis output with a realistic stellar density distribution, star formation history (SFH), and chemical evolution for the MW, which produces a probability distribution function of the predicted compact-binary population over the MW. This avoids the additional statistical uncertainty that is introduced by methods that Monte Carlo sample from binary population synthesis output to produce one potential specific realization of the MW compact-binary distribution, and our method is also comparatively fast to such Monte Carlo realizations. Specifically, we predict ∼41–340 nBHBs to be observed by Gaia, although the numbers may drop to ∼10–70 if the recent (≲100 Myr) star formation is low (∼1 M ⊙ yr−1). For LAMOST we predict ≲14 detectable nBHBs, which is lower partially because its field of view covers just ∼6% of the Galaxy.

Population Synthesis of Black Hole Binaries with Normal-star Companions. I. Detached Systems

“…Whether there is the mass gap or not can shed light on supernova mechanisms for the formation of NSs and BHs. Although Gaia astrometry was already claimed to be able to discover invisible BHs with optical companions (e.g., Gould & Salim 2002;Mashian & Loeb 2017;Breivik et al 2017;Yalinewich et al 2018;Yamaguchi et al 2018;Breivik et al 2019;Shao & Li 2019;Andrews et al 2019;Wiktorowicz et al 2020), merging BH-CS binaries that appear as GW sources are alternatively potential objects to test the mass gap and relevant supernova mechanisms.…”

Predicting the self-lensing population in optical surveys

“…We have shown that observations of repeating SL flares are a promising way of detecting non-interacting compact object binaries. Using the comprehensive model of the Milky Way galaxy developed in Wiktorowicz et al (2020) and the database of BHs in stellar populations (Wiktorowicz et al 2019) extended for systems in which the compact object is a NS, we have calculated realistic predictions for three ongoing or planned large-area optical surveys: ZTF GPS, TESS, and the Vera Rubin-LSST. Our results indicate that such current or future optical surveys may have the ability to detect hundreds to thousands of SL binary systems.…”

“…To account for the stellar mass distribution in the Galaxy, we use the Milky Way model of Robin et al (2003), modified as described in Wiktorowicz et al (2020). Following the procedure introduced in Wiktorowicz et al (2020), which improves on the traditional Monte Carlo-based sampling methods, we calculated the fraction of the Galactic mass within a distance 𝑑, observable from the Earth for the 1 https://universeathome.pl/universe/bhdb.php instruments under consideration (Figure 2). To calculate bolometrically corrected absolute magnitude (𝑚 abs ) we use the YBC database (Chen et al 2019, see also Sec 2.4).…”

“…Whilst X-ray binaries in the Galaxy number in the ∼thousands (e.g. van Haaften et al 2015), this is orders of magnitude less than should be present in the form of non-interacting binaries with large orbital separations (Wiktorowicz et al 2020). As non-accreting systems contain relatively pristine compact objects (having never accreted any material since their formation) they offer profound insights into the nature of the formation process and of the evolution of the binary itself.…”

“…The former two have been discussed at length in relation to high precision surveys such as GAIA or LAMOST (e.g. Wiktorowicz et al 2020, and references ★ E-mail:gwiktoro@gmail.com therein), whilst here we focus on the self-lensing signature of wide and non-accreting binaries in our Galaxy.…”