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Abstract We resolve the multiple images of the binary-lens microlensing event ASASSN-22av using the GRAVITY instrument of the Very Large Telescope Interferometer (VLTI). The light curves show weak binary-lens perturbations, complicating the analysis, but the joint modeling with the VLTI data breaks several degeneracies, arriving at a strongly favored solution. Thanks to precise measurements of the angular Einstein radiusθE= 0.724 ± 0.002 mas and microlens parallax, we determine that the lens system consists of two M dwarfs with masses ofM1= 0.258 ± 0.008M⊙andM2= 0.130 ± 0.007M⊙, a projected separation ofr⊥= 6.83 ± 0.31 au, and a distance ofDL= 2.29 ± 0.08 kpc. The successful VLTI observations of ASASSN-22av open up a new path for studying intermediate-separation (i.e., a few astronomical units) stellar-mass binaries, including those containing dark compact objects such as neutron stars and stellar-mass black holes.
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This content will become publicly available on February 1, 2026
Uncovering the invisible: A study of Gaia18ajz, a candidate black hole revealed by microlensing
Context.Identifying black holes is essential for our understanding of the development of stars and can reveal novel principles of physics. Gravitational microlensing provides an exceptional opportunity to examine an undetectable population of black holes in the Milky Way. In particular, long-lasting events are likely to be associated with massive lenses, including black holes. Aims.We present an analysis of the Gaia18ajz microlensing event reported by the Gaia Science Alerts system. Gaia18ajz is a long-timescale event exhibiting features indicative of the annual microlensing parallax effect. Our objective is to estimate its lens parameters based on the best-fitting model. Methods.We used photometric data obtained from the Gaia satellite and terrestrial observatories to investigate a variety of microlensing models and calculate the most probable mass and distance to the lens, taking into consideration a Galactic model as a prior. Subsequently, we applied a mass–brightness relation to evaluate the likelihood that the lens is a main sequence star. We also describe theDarkLensCode(DLC), an open-source routine that computes the distribution of probable lens mass, distance, and luminosity employing the Galaxy priors on stellar density and velocity for microlensing events with detected microlensing parallax. Results.We modelled the Gaia18ajz event and found its two possible models, the most probable Einstein timescales for which are 316−30+36days and 299−22+25days. Applying Galaxy priors for stellar density and motion, we calculated a most probable lens mass of 4.9−2.3+5.4 M⊙located at 1.14−0.57+0.75 kpc, and a less probably mass of 11.1−4.7+10.3 M⊙located at 1.31−0.60+0.80 kpc. Our analysis of the blended light suggests that the lens is likely a dark remnant of stellar evolution rather than a main sequence star.
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- Award ID(s):
- 2206828
- PAR ID:
- 10610708
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- Astronomy & Astrophysics
- Date Published:
- Journal Name:
- Astronomy & Astrophysics
- Volume:
- 694
- ISSN:
- 0004-6361
- Page Range / eLocation ID:
- A94
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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