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Kilonovae, short gamma-ray bursts & neutron star mergers
This Collection of research and comment from Nature Research focuses on the electromagnetic counterparts to the gravitational wave event GW 170817 from the merger of two neutron stars. LIGO’s first three gravitational wave detections, and LIGO-Virgo’s first, all originated from mergers of black holes. These momentous black-hole clashes produced gravitational waves that were audible to LIGO-Virgo but there was nothing to see. But a neutron star merger is different. Following GW 170817, a short gamma ray burst and kilonova occurred, releasing photons across a wide electromagnetic spectrum: from radio waves to infrared to visible to X-rays to gamma rays. The Research papers published in Nature and Nature Astronomy cover some of these counterpart signals. Welcome to the era of gravitational wave astrophysics.
The astronomical event GW170817, detected in gravitational and electromagnetic waves, is used to determine the expansion rate of the Universe, which is consistent with and independent of existing measurements.
The LIGO Scientific Collaboration and The Virgo Collaboration
A stochastic background of gravitational waves is expected to arise from a superposition of a large number of unresolved gravitational-wave sources and should carry unique signatures from the earliest epochs of the Universe. Limits on the amplitude of the stochastic gravitational-wave background are now reported using the data from a two-year science run of the Laser Interferometer Gravitational-wave Observatory. These limits rule out certain models of early Universe evolution.
The LIGO Scientific Collaboration & The Virgo Collaboration
Black holes and spacetime singularities are fundamental in science. While observational proof for black holes is hard to come by, alternatives can be ruled out or confirmed to exist through precision gravitational wave observations.
Black holes present a profound challenge to our current foundations of physics, and an exciting era of astronomy is just opening in which gravitational-wave observation and very-long-baseline interferometry may provide important hints about the new principles of physics needed.