Is there a nearby microlensing stellar remnant hiding in Gaia DR3 astrometry?

TL;DR

This study investigates a potential nearby stellar remnant, possibly a white dwarf, by analyzing Gaia DR3 astrometry for signs of unmodeled microlensing effects that could reveal its presence.

Contribution

The paper demonstrates how incorporating astrometric microlensing modeling explains Gaia DR3 astrometric anomalies, suggesting the detection of a nearby stellar remnant.

Findings

Estimated lens mass around 1 solar mass

Lens distance approximately 0.9 kpc

Consistent microlensing signal with Gaia data

Abstract

Massive galactic lenses with large Einstein Radii should cause a measurable astrometric microlensing effect, i.e. the light centroid shift due to the motion of the two images. Such a shift in the position of a background star due to microlensing was not included in the $Gaia$ astrometric model, therefore significant deviation should cause $Gaia$'s astrometric parameters to be determined incorrectly. Here we studied one of the photometric microlensing events reported in the $Gaia$ DR3, GaiaDR3-ULENS-001, for which poor goodness of $Gaia$ fit and erroneous parallax could indicate the presence of the astrometric microlensing signal. Based on the photometric microlensing model, we simulated $Gaia$ astrometric time-series with the astrometric microlensing effect added. We found that including microlensing with the angular Einstein Radius of $\theta_{\rm E}$ = $2.60^{+0.21}_{-0.24}$ mas ($2.47^{+0.28}_{-0.24}$ mas) assuming positive (negative) impact parameter $u_0$ reproduces well the astrometric quantitie reported by $Gaia$. We estimate the mass of the lens to $1.00^{+0.23}_{-0.18}$ $M_\odot$ ($0.70^{+0.17}_{-0.13}$ $M_\odot$) and its distance to $0.90^{+0.14}_{-0.11}$ kpc ($0.69^{+0.13}_{-0.09}$ kpc), proposing the lens could be a nearby isolated white dwarf.