Testing the presence of a dormant black hole inside HR 6819. (arXiv:2107.08930v2 [astro-ph.SR] UPDATED)

Testing the presence of a dormant black hole inside HR 6819. (arXiv:2107.08930v2 [astro-ph.SR] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Romagnolo_A/0/1/0/all/0/1">A. Romagnolo</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Olejak_A/0/1/0/all/0/1">A. Olejak</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hypki_A/0/1/0/all/0/1">A. Hypki</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wiktorowicz_G/0/1/0/all/0/1">G. Wiktorowicz</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Belczynski_K/0/1/0/all/0/1">K. Belczynski</a>

HR 6819 was reported in Rivinius et al. (2020) to be a triple system with a
non-accreting black hole (BH) in its inner binary. In our study we check if
this inner binary can be reconstructed using the isolated binary formation
channel or the dynamical one within globular star clusters. Our goals are to
understand the formation of the inner binary and to test the presence of a
non-accreting BH. To simulate the inner binary evolution we assumed that the
influence of the third body on the formation of the inner binary is negligible.
We tested various models with different values of physical parameters such as
the mass loss rate during BH formation or the efficiency of orbital energy loss
for common envelope ejection. By comparing the Roche lobe radii with the
respective stellar radii no mass transfer event was shown to happen for more
than 40 Myr after the BH collapse, suggesting that no accretion disk is
supposed to form around the BH during the BH-MS phase. We can therefore
reconstruct the system with isolated binaries, although in our simulations we
had to adopt non-standard parameter values and to assume no asymmetric mass
ejection during the black hole collapse. Out of the whole synthetic Galactic
disk BH population only 0.0001% of the BH-MS binaries fall within the
observational constraints. We expect only few binaries in the Galactic globular
clusters to be potential candidates for the HR 6819 system. Our statistical
analysis suggests that despite the HR 6819 inner binary can be reconstructed
with isolated binary evolution, this evolutionary channel is unlikely to
reproduce its reported parameters. Under the initial assumption that the outer
star doesn’t impact the evolution of its inner binary, we argue that the
absence of a third body proposed by El-Badry & Quataert (2021) and
Bodensteiner, J. et al. (2020) might be a more natural explanation for the
given observational data.

HR 6819 was reported in Rivinius et al. (2020) to be a triple system with a
non-accreting black hole (BH) in its inner binary. In our study we check if
this inner binary can be reconstructed using the isolated binary formation
channel or the dynamical one within globular star clusters. Our goals are to
understand the formation of the inner binary and to test the presence of a
non-accreting BH. To simulate the inner binary evolution we assumed that the
influence of the third body on the formation of the inner binary is negligible.
We tested various models with different values of physical parameters such as
the mass loss rate during BH formation or the efficiency of orbital energy loss
for common envelope ejection. By comparing the Roche lobe radii with the
respective stellar radii no mass transfer event was shown to happen for more
than 40 Myr after the BH collapse, suggesting that no accretion disk is
supposed to form around the BH during the BH-MS phase. We can therefore
reconstruct the system with isolated binaries, although in our simulations we
had to adopt non-standard parameter values and to assume no asymmetric mass
ejection during the black hole collapse. Out of the whole synthetic Galactic
disk BH population only 0.0001% of the BH-MS binaries fall within the
observational constraints. We expect only few binaries in the Galactic globular
clusters to be potential candidates for the HR 6819 system. Our statistical
analysis suggests that despite the HR 6819 inner binary can be reconstructed
with isolated binary evolution, this evolutionary channel is unlikely to
reproduce its reported parameters. Under the initial assumption that the outer
star doesn’t impact the evolution of its inner binary, we argue that the
absence of a third body proposed by El-Badry & Quataert (2021) and
Bodensteiner, J. et al. (2020) might be a more natural explanation for the
given observational data.

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