Note: Single-source report; awaiting corroboration.
Neutron stars, the dense remnants of exploded massive stars, are believed to be common throughout the Milky Way but are often invisible due to their faintness and isolation. A new study suggests that NASA’s upcoming Nancy Grace Roman Space Telescope may identify and analyze dozens of these stars by detecting gravitational microlensing when a neutron star passes in front of a background star.
Microlensing occurs when a massive object’s gravity warps spacetime, temporarily brightening and slightly shifting the position of a background star. While many telescopes detect brightness changes, Roman’s advanced instruments can also measure subtle positional shifts, enabling more precise characterization of the lensing object.
Since neutron stars have relatively large masses, they cause more noticeable astrometric shifts than lighter objects. Measuring these shifts lets astronomers directly determine the mass of unseen neutron stars, which photometry alone cannot accomplish. This ability could help scientists test for a possible mass gap between neutron stars and black holes, and improve understanding of neutron star velocities and supernova dynamics.
Study lead Zofia Kaczmarek of Heidelberg University noted the challenge in detecting dim, solitary neutron stars without additional methods. Co-author Peter McGill from Lawrence Livermore National Laboratory emphasized that astrometric measurements make it possible to "directly weigh something that is otherwise unseen." Roman’s observations may transform the search for these elusive objects in our galaxy.