Not so fast: LB-1 is unlikely to contain a 70 M⊙ black hole

El-Badry, Kareem; Quataert, Eliot

doi:10.1093/mnrasl/slaa004

Cited by 83 publications

(49 citation statements)

References 29 publications

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“…As Liu et al (2019) notes, the Hα line appears to exhibit a low-amplitude, anti-phase motion relative to the primary star, leading the authors to speculate that it originates in an accretion disk around a ≈70 M BH secondary. However, Abdul-Masih et al (2020) and El-Badry & Quataert (2020) have since independently shown that this anti-phase signature can be explained as a spurious result that emerges from the motion of the broad absorption wings of the B-type primary on top of a static Hα line. These results cast doubt on the measurement of the large mass of the secondary from Liu et al (2019).…”

Section: Introductionmentioning

confidence: 99%

The “hidden” companion in LB-1 unveiled by spectral disentangling

Shenar

Bodensteiner

Abdul-Masih

et al. 2020

A&A

127

144

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Context. The intriguing binary LS V +22 25 (LB-1) has drawn much attention following claims of it being a single-lined spectroscopic binary with a 79-day orbit comprising a B-type star and a ≈70 M⊙ black hole – the most massive stellar black hole reported to date. Subsequent studies demonstrated a lack of evidence for a companion of such great mass. Recent analyses have implied that the primary star is a stripped He-rich star with peculiar sub-solar abundances of heavy elements, such as Mg and Fe. However, the nature of the secondary, which was proposed to be a black hole, a neutron star, or a main sequence star, remains unknown. Aims. Based on 26 newly acquired spectroscopic observations secured with the HERMES and FEROS spectrographs covering the orbit of the system, we perform an orbital analysis and spectral disentangling of LB-1 to elucidate the nature of the system. Methods. To derive the radial velocity semi-amplitude K2 of the secondary and extract the spectra of the two components, we used two independent disentangling methods: the shift-and-add technique and Fourier disentangling with FDBinary. We used atmosphere models to constrain the surface properties and abundances. Results. Our disentangling and spectral analysis shows that LB-1 contains two components of comparable brightness in the optical. The narrow-lined primary, which we estimate to contribute ≈55% in the optical, has spectral properties that suggest that it is a stripped star: it has a small spectroscopic mass (≈1 M⊙) for a B-type star and it is He- and N-rich. Unlike previous reports, the abundances of heavy elements are found to be solar. The “hidden” secondary, which contributes about 45% of the optical flux, is a rapidly rotating (vsini ≈ 300 km s−1) B3 V star with a decretion disk – a Be star. As a result of its rapid rotation and dilution, the photospheric absorption lines of the secondary are not readily apparent in the individual observations. We measure a semi-amplitude for this star of K2 = 11.2 ± 1.0 km s−1 and adopting a mass of M2 = 7 ± 2 M⊙ typical for B3 V stars, we derive an orbital mass for the stripped primary of M1 = 1.5 ± 0.4 M⊙. The orbital inclination of 39 ± 4° implies a near-critical rotation for the Be secondary (veq ≈ 470 km s−1). Conclusions. LB-1 does not contain a compact object. Instead, it is a rare Be binary system consisting of a stripped star (the former mass donor) and a Be star rotating at near its critical velocity (the former mass accretor). This system is a clear example that binary interactions play a decisive role in the production of rapid stellar rotators and Be stars.

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Section: Introductionmentioning

confidence: 99%

The “hidden” companion in LB-1 unveiled by spectral disentangling

Shenar

Bodensteiner

Abdul-Masih

et al. 2020

A&A

127

144

View full text Add to dashboard Cite

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“…Both these aspects were, however, challenged by subsequent studies. El-Badry & Quataert (2020a) and Abdul-Masih et al (2020) showed that the anti-phase signature of Hα cannot be readily interpreted as Doppler motion without considering the impact of potential Hα absorption of the B-type component. Simón-Díaz et al (2020) and Irrgang et al (2020) performed spectroscopic studies of the primary and found evidence for processed CNO material in its atmosphere, leading Irrgang et al (2020) to suggest that it is a low-mass stripped helium star.…”

Section: Introductionmentioning

confidence: 99%

Is HR 6819 a triple system containing a black hole?

Bodensteiner

Shenar

Mahy

et al. 2020

A&A

102

106

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Context. HR 6819 was recently proposed to be a triple system consisting of an inner B-type giant plus black hole (BH) binary with an orbital period of 40 d and an outer Be tertiary. This interpretation is mainly based on two inferences: that the emission attributed to the outer Be star is stationary and that the inner star, which is used as mass calibrator for the BH, is a B-type giant. Aims. We re-investigate the properties of HR 6819 to search for a possibly simpler alternative explanation for HR 6819, which does not invoke the presence of a triple system with a BH in the inner binary. Methods. Based on an orbital analysis, the disentangling of the spectra of the two visible components and the atmosphere analysis of the disentangled spectra, we investigate the configuration of the system and the nature of its components. Results. Disentangling implies that the Be component is not a static tertiary, but rather a component of the binary in the 40 d orbit. The inferred radial velocity amplitudes of K1 = 60.4 ± 1.0 km s−1 for the B-type primary and K2 = 4.0 ± 0.8 km s−1 for the Be-type secondary imply an extreme mass ratio of M2/M1 = 15 ± 3. We find that the B-type primary, which we estimate to contribute about 45% to the optical flux, has an effective temperature of Teff = 16 ± 1 kK and a surface gravity of log g = 2.8 ± 0.2 [cgs], while the Be secondary, which contributes about 55% to the optical flux, has Teff = 20 ± 2 kK and log g = 4.0 ± 0.3 [cgs]. We infer spectroscopic masses of 0.4−0.1+0.3and 6−3+5 for the primary and secondary which agree well with the dynamical masses for an inclination of i = 32°. This indicates that the primary might be a stripped star rather than a B-type giant. Evolutionary modelling suggests that a possible progenitor system would be a tight (Pi ≈ 2 d) B+B binary system that experienced conservative mass transfer. While the observed nitrogen enrichment of the primary conforms with the predictions of the evolutionary models, we find no indications for the predicted He enrichment. Conclusions. We suggest that HR 6819 is a binary system consisting of a stripped B-type primary and a rapidly-rotating Be star that formed from a previous mass-transfer event. In the framework of this interpretation, HR 6819 does not contain a BH. Interferometry can distinguish between these two scenarios by providing an independent measurement of the separation between the visible components.

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“…The scatter in velocities at large distances from the Sun is due to the black holes that have wandered into the halo and no longer follow the bulk motion of the disk. from their stellar companions; these black holes tend to have masses ≲20M ⊙ [16,17,74] (with the possible exception of LB-1, which has been claimed to have a mass of 70M ⊙ [75], although this is controversial [76,77]). In contrast, the mass distribution of black holes in merging binaries detected by LIGO and Virgo is consistent with a mass cutoff of approximately M BH ∼ 40M ⊙ and a powerlaw index of around 2 [78][79][80]; however, it is difficult to extrapolate from the properties of the gravitationally detected black holes, as these are found in other Galaxies with unknown star formation histories and metallicities.…”

Section: B Choice Of Mass Distributionmentioning

confidence: 99%

Characterizing the continuous gravitational-wave signal from boson clouds around Galactic isolated black holes

Zhu

Baryakhtar²,

Papa

et al. 2020

Phys. Rev. D

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Ultralight bosons can form large clouds around stellar-mass black holes via the superradiance instability. Through processes such as annihilation, these bosons can source continuous gravitationalwave signals with frequencies within the range of LIGO and Virgo. If boson annihilation occurs, then the Galactic black hole population will give rise to many gravitational signals; we refer to this as the ensemble signal. We characterize the ensemble signal as observed by the gravitational-wave detectors; this is important because the ensemble signal carries the primary signature that a continuous wave signal has a boson annihilation origin. We explore how a broad set of black hole population parameters affects the resulting spin-0 boson annihilation signal and consider its detectability by recent searches for continuous gravitational waves. A population of 10 8 black holes with masses up to 30M ⊙ and a flat dimensionless initial spin distribution between zero and unity produces up to 1000 signals loud enough in principle to be detected by these searches. For a more moderately spinning population, the number of signals drops by about an order of magnitude, still yielding up to 100 detectable signals for some boson masses. A nondetection of annihilation signals at frequencies between 100 and 1200 Hz disfavors the existence of scalar bosons with rest energies between 2 × 10 −13 and 2.5 × 10 −12 eV. Finally, we show that, depending on the black hole population parameters, care must be taken in assuming that the continuous wave upper limits from searches for isolated signals are still valid for signals that are part of a dense ensemble: Between 200 and 300 Hz, we urge caution when interpreting a null result for bosons between 4 × 10 −13 and 6 × 10 −13 eV.

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Not so fast: LB-1 is unlikely to contain a 70 M⊙ black hole

Cited by 83 publications

References 29 publications

The “hidden” companion in LB-1 unveiled by spectral disentangling

The “hidden” companion in LB-1 unveiled by spectral disentangling

Is HR 6819 a triple system containing a black hole?

Characterizing the continuous gravitational-wave signal from boson clouds around Galactic isolated black holes

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