Abstract
Gravitational microlensing is a powerful method to search for and characterize exoplanets, and it was first proposed by Paczyński in 1986. We provide a brief historical excursus of microlensing, especially focused on the discoveries of free-floating planets (FFPs) in the Milky Way. We also emphasize that, thanks to the technological developments, it will allow to estimate the physical parameters (in particular the mass and distance) of FFPs towards the center of our Galaxy, through the measure of the source finite radius, Earth or satellite parallax, and/or astrometric effects.
Highlights
Discovery of the extrasolar planets in our Galaxy is one of the most discussed issues in the scientific community
Based on the results obtained by Sumi et al [23] and the capabilities of different telescopes, which are performing microlensing observations and/or are planned for the near future, we have considered the issue of the free-floating planets (FFPs) detection by gravitational microlensing in the Milky Way
Considering the lower limit of the FFPs per star, we found that by space-based telescopes will be detected about 100 microlensing events caused by FFPs during a month
Summary
Discovery of the extrasolar planets in our Galaxy is one of the most discussed issues in the scientific community. The first attempts to characterize the FFP population in our Galaxy have been conducted by Sumi et al [23] They analyzed the light curves of 474 microlensing events observed during a 2-year survey by the MOAII collaboration towards the Galactic bulge and by analyzing their timescale distribution, which reported the discovery of planetary-mass objects either very distant from their host star (i.e., orbiting at distances larger than 100 AU) or fully unbound. Based on the results obtained by Sumi et al [23] and the capabilities of different telescopes, which are performing microlensing observations and/or are planned for the near future, we have considered the issue of the FFP detection by gravitational microlensing in the Milky Way. We estimate the detection efficiency (that is ratio between the number of events for which each second-order effect is detectable and the number of simulated events) of the finite source effect, orbital or satellite parallax and astrometric effect in microlensing events caused by FFPs towards the Galactic bulge.
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