Starship Asterisk*

Artist’s illustration of two colliding neutron stars. (Image: NASA/Swift/Dana Berry)

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On April 25, 2019, the National Science Foundation's Laser Interferometer Gravitational-Wave Observatory (LIGO) and the European-based Virgo detector registered gravitational waves from what appears likely to be a crash between two neutron stars—the dense remnants of massive stars that previously exploded. One day later, on April 26, the LIGO-Virgo network spotted another candidate source with a potentially interesting twist: it may in fact have resulted from the collision of a neutron star and black hole, an event never before witnessed. ...

The discoveries come just weeks after LIGO and Virgo turned back on. The twin detectors of LIGO — one in Washington and one in Louisiana — along with Virgo, located at the European Gravitational Observatory (EGO) in Italy, resumed operations April 1, after undergoing a series of upgrades to increase their sensitivities to gravitational waves — ripples in space and time. Each detector now surveys larger volumes of the universe than before, searching for extreme events such as smash-ups between black holes and neutron stars. ...

In addition to the two new candidates involving neutron stars, the LIGO-Virgo network has, in this latest run, spotted three likely black hole mergers. In total, since making history with the first-ever direct detection of gravitational waves in 2015, the network has spotted evidence for two neutron star mergers, 13 black hole mergers, and one possible black hole-neutron star merger. ...