LB-1 Is Inconsistent with the X-Ray Source Population and Pulsar-Black Hole Binary Searches in the Milky Way

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  • Mohammadtaher Safarzadeh
  • Enrico Ramirez-Ruiz
  • Charles Kilpatrick

If confirmed, a wide binary system consisting of a 70Mblack hole (BH) and an 8Mmain-sequence star (LB-1) is observed to reside in the Milky Way (MW). While we remain agnostic about the nature of LB-1, we show that long-term evolution of an 8Mstar around a BH with mass between 5 and 70Mmakes them visible as ultraluminous X-ray (ULX) sources in the sky. Given the expected ULX phase lifetime (0.1 Myr) and their lack of detection in the MW, we conclude that the frequency of an 8-20Mstar to be in binary around a stellar mass BH should be less (f <4 x 10(-3)). This is in tension with Liu et al., who claimed the detection frequency of an LB-1-like system to be around 8-20Mstars (f 3 x 10(-2)). Moreover, the 8Mstar is likely to end as a neutron star (NS) born with a very small kick from an electron-capture supernova (ECSN), leaving behind a wide NS-BH binary. So far, less than 1% of all the detectable pulsars in the MW have been mapped and there has been no detection of any pulsars in binary systems around BHs, which sets an upper bound of about 100 possible pulsar-BH systems in the MW. We show whether the NS is born from ECSN, a frequency upper limit of (f 10(-3)) for stars with masses 8-20Min the MW to have a BH companion. The rate discrepancy will further increase as more pulsars are mapped in the MW, yet these searches would not be able to rule out the Liu et al. detection frequency if NSs are instead born in core collapse SNe with the commonly inferred high kick velocities.

Original languageEnglish
Article number116
JournalAstrophysical Journal
Volume901
Issue number2
Number of pages6
ISSN0004-637X
DOIs
Publication statusPublished - 1 Oct 2020

    Research areas

  • Astrophysical black holes, Pulsars, Binary stars, Common envelope binary stars, Interstellar dust extinction, MASS, LUMINOSITY, SUPERNOVAE, STAR

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