Is the discovery of a "mass gap" black hole by this tiny telescope just plain luck/serendipity or could it be the first of many similar discoveries?

Question

The Kilodegree Extremely Little Telescope is a pair of modest lenses with high quality medium format CCDs attached sitting on oversized mounts in Arizona and Sutherland.

These very modest instruments have discovered several exoplanets (by choosing a niche magnitude range) and have now seemed to have discovered a particularly interesting 3 $M_{\odot}$ black hole + red giant binary.

Jayasinghe et al. (2021) A Unicorn in Monoceros: the 3M⊙ dark companion to the bright, nearby red giant V723 Mon is a non-interacting, mass-gap black hole candidate

Question: Is the discovery of this "mass gap" black hole by this tiny telescope just plain luck or serendipity, or could this be the first of many similar discoveries? How likely is it that there are more nearby "mass gap black holes" that just got missed due to the parameter space sampled by time domain based surveys?

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From keltsurvey.org/telescopes

This picture (KN) shows the KELT-North telescope at Winer.

This picture shows the KELT-South telescope at Sutherland.

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click for larger

Figure 13. The right panels show the template subtracted H𝛼 (red dot-dashed), H𝛽 (blue dashed) and Ca i 𝜆6439 (black) line profiles at various orbital configurations illustrated in the left panels. The size of the compact object is simply chosen to make it easily visible.

Answer 1

Section 2 of Jayasinghe et al. (2021) explains why this system was studied. It wasn't discovered by KELT it was a known, single-lined spectroscopic binary, with radial velocity variations and an inferred mass-function suggesting an unseen companion of at least 1.6 solar masses. This was followed up as part of a programme to find non-interacting compact binaries.

Whether there are mass-gap black holes is still open, since it appears that the status of this candidate as a black hole is questioned (El Badry et al. 2023) and therefore how likely there is to be a population of such objects can't be answered at present (e.g., Yong 2022). It could well be that observational selection effects lead to them not being found as part of interacting binary systems, which is how almost all Galactic black holes have so far been found.

The prospects for systematically finding non-interacting, nearby black-hole binary systems en masse has been made eminently possible with the advent of the Gaia satellite. The reflex motion of a seen companion to a more massive black hole can be observed in the astrometry and radial velocities provided by Gaia.

A very recent example is presented by El Badry et al. (2023), who find a $>5M_\odot$ unseen object as a companion to a solar-type star; almost certainly a black hole. This object was independently studied by Chakrabarti et al. (2022) who also present evidence for a $\sim 12 M_\odot$ unseen object.