The Likelihood of Hosting Undetected Brown Dwarfs in the Solar Vicinity

TL;DR

This study uses the solar neighborhood within $20\ \mathrm{pc}$ and incompleteness corrections to estimate the probability of an undetected brown dwarf near the Sun. By constructing and linearly approximating the cumulative nearest-neighbor distance distribution, it finds a near $51.5\%$ probability of an unseen object within the distance to α Centauri ($\approx 1.346\ \mathrm{pc}$), with about a $25\%$ chance that such an object would be part of a multiple system. The authors discuss why such an object has not been detected, including the possibility of a very faint, potentially Y-class brown dwarf and Gaia/WISE observational limitations, and propose future validation with Euclid surveys. The work provides a framework to constrain the presence of very nearby brown dwarfs and informs observational strategies for confirming or refuting their existence.

Abstract

Based on the spatial distribution of objects in the solar neighbourhood with a radius of 20 parsecs, and after correcting for the incompleteness of observational data, an expression was obtained for estimating the probability of finding an object at a given distance from the Sun. According to these estimates, with a probability of about 0.5, there exists a brown dwarf in the immediate solar vicinity (< 1.2 pc). The possible multiplicity of this hypothetical object is discussed, as well as the reasons why it has not yet been detected.

Figures (7)

• Figure 1: $W2$ magnitudes (left) and $W1-W2$ color indices (right) as a function of parallax for objects from the catalog of Kirkpatrick et al. 2024ApJS..271...55K (red) and the catalog of Best et al. 2021AJ....161...42B (blue).
• Figure 2: Distribution of systems by their distance from the Sun (left), the red curve shows the theoretical dependence $N \varpropto r^2$. Spatial distribution of systems relative to the Sun (right).
• Figure 3: Distribution of systems by their distances to the nearest neighbor. Left: the peak of the distribution is marked with a black dashed line. Right: corrected for incompleteness, red curve shows the Hertz dependence \ref{['equ:hertz']}.
• Figure 4: Correction for incompleteness: exclusion from consideration of systems located at the boundary of the studied region, in a shell of width 1.2 pc. They are marked in blue on the distribution of systems by their distances to the nearest neighbor (left) and on the spatial distribution of systems relative to the Sun (right).
• Figure 5: Left: cumulative distribution of systems by their distances to the nearest neighbor, normalized to unity. Red curve shows the approximating polynomial \ref{['equ:integral']}. Right: fragment of the distribution \ref{['fig:integral']} in the range 1 -- 1.5 pc. Blue line shows the linearized approximating polynomial \ref{['equ:line']} on this segment, black dashed line shows the position of the system $\alpha$ Cen.