Starship Asterisk*

Through a series of simulations, an international team of researchers has determined that some mergers of neutron stars produce radiation that should be detectible from Earth. When neutron stars of unequal mass merge, the smaller star is ripped apart by tidal forces from its massive companion (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). Credit: S Bernuzzi et al, MNRAS 2020

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When two neutron stars slam together, the result is sometimes a black hole that swallows all but the gravitational evidence of the collision. However, in a series of simulations, an international team of researchers ... determined that these typically quiet—at least in terms of radiation we can detect on Earth—collisions can sometimes be far noisier.

“When two incredibly dense collapsed neutron stars combine to form a black hole, strong gravitational waves emerge from the impact,” said David Radice ... “We can now pick up these waves using detectors like LIGO in the United States and Virgo in Italy. A black hole typically swallows any other radiation that could have come out of the merger that we would be able to detect on Earth, but through our simulations, we found that this may not always be the case.”

The research team found that when the masses of the two colliding neutron stars are different enough, the larger companion tears the smaller apart. This causes a slower merger that allows an electromagnetic “bang” to escape. Astronomers should be able to detect this electromagnetic signal, and the simulations provide signatures of these noisy collisions that astronomers could look for from Earth. ...

• Monthly Notices of the RAS (online 27 Jun 2020) DOI: 10.1093/mnras/staa1860
• arXiv.org > astro-ph > arXiv:2003.06015 > 12 Mar 2020