Astronomers using NSF’s Laser Interferometer Gravitational-Wave Observatory (LIGO) in the United States and by the Virgo detector in Italy have observed gravitational-wave signals from two compact binary inspirals that are consistent with neutron star-black hole binaries. The two events occurred at least 900 million light-years away; in each case, the neutron star was likely swallowed whole by its black hole partner. An artist’s impression of...