On November 7, 2023, the Monthly Notices of the Royal Astronomical Society (MNRAS) published online the results of astrometric microlensing events prediction research by SU Jie, WANG Jiancheng and others of the Yunnan Observatories.

Gravitational lensing describes the deflection and magnification of background sources when a massive object (lens) passes in front of them. When the lens is a stellar-mass object, the deflection is less than a few microarcseconds (mas) and the effect is referred to as microlensing. Microlensing describes the positional deflection (astrometric microlensing) and magnification (photometric microlensing) of a background source over time.  Astrometric microlensing makes it possible to measure the mass of a single star directly. It can also detect faint and compact lenses such as isolated neutron stars and black holes, because the luminosity of the lens is not necessarily measured. Microlensing events are intrinsically rare occurrences which depend on the alignments of source star and lens star. So predicting when and where they will occur is highly advantageous for the collection of data throughout an event.

The study searched for microlensing events using Gaia DR3, and selected potential lens stars from the three types of stars: high-proper-motion stars, nearby stars and high-mass stars. It predicts 4500 astrometric microlensing events caused by 3558 lens stars during J2010.0 and J2070.0, where 1664 events are different from those found previously. There are 293 lens stars that can cause two or more events, and five lens stars will cause more than 50 events. In the events researchers find that 116 events have the distances of background stars from the proper motion path of lens stars more than 8 arcsec in the reference epoch, where the maximum distance is 16.6 arcsec.

In the future, Gaia Data Release 4 will provide the epoch astrometry, which can be used to measure the shift of a handful of events. The predicted events are expected to be followed up using space devices such as Hubble Space Telescope, James Webb Space Telescope, or the Chinese Space Station Telescope that will be launched in the near future.

Contact:
WANG Jiancheng, SU Jie
Yunnan Observatories, CAS
E-mail: jcwang@ynao.ac.cn, sujie1@ynao.ac.cn