An upper limit on the frequency of short-period black hole companions to Sun-like stars [@greenUpperLimitFrequency2025]

Abstract

Seeking to narrow the uncertainty regarding the survival rate in the formation of stellar-mass BHs.
This uncertainty is most extreme in LMXB systems
Defines `close’ systems as $P_{or b} ≲ 3 d$
Searching through for AFGK-type stars in TESS (I wonder why TESS was picked). These are the non-accreting companion and progenitors of LMXBs
Detecting the BHs via the deformation of the main star via the light curves
Found a selection of 457 candidates from a sample of $4.7 \times 1 0^{6}$
However, after spectra follow-up on 200 of the sample, none showed spectra consistent with a BH companion (Very curious what “spectra consistent with a BH companion” means, especially as these are non accreting. Is this using a radial velocity method?…)
On the basis on non-detection they conclude that fewer than one in $1 0^{5}$ sun-type stars host a close BH companion
This upper limit is in tension with that some models predict ( $\sim 1 0^{4 - 5}$ ), but congruent with other models that predict on in $1 0^{7 - 8}$

Isolated stars with mass greater than $≳ 15 - 25 M_{⊙}$ are believed to end their lives as BHs, suggesting that there are $\sim 1 0^{8}$ stellar mass BHs in our galaxy. The majority of which are believed to evolve with a stellar companion, half of which will interact with said companion at some point during their lifespan.
A very small number (7) BH-LS systems have been detected
Because of the scarcity of these systems, it’s useful to try and set an upper limit on their distribution