Slower and Noisier

Aug. 3, 2020

It seems strange to talk about “quiet” versus “noisy” collisions of neutron stars. But many such impacts form a black hole that swallows all but the gravitational evidence. A series of simulations using PSC’s Bridges platform and other supercomputers by a Penn State scientist suggested that, when the neutron stars’ masses are different enough, the result is far noisier. The model predicts an electromagnetic “bang,” which isn’t present when the merging stars’ masses are similar, that astronomers should be able to detect.

Above: a neutron star is ripped apart by tidal forces from its massive companion in an unequal-mass binary neutron star merger (left). Most of the smaller partner’s mass falls onto the massive star, causing it to collapse and to form a black hole (middle). But some of the material is ejected into space; the rest falls back to form a massive accretion disk around the black hole (right). From Figure 4 in Accretion-induced prompt black hole formation in asymmetric neutron star mergers, dynamical ejecta and kilonova signals. Bernuzzi S et al., Monthly Notices of the Royal Astronomical Society, online June 2020.