The recent detection of a binary neutron star inspiraling and colliding raises an interesting question in my mind. Type Ia supernovae are believed to be caused by white dwarf/regular star pairs and/or white dwarf pairs. Short gamma ray bursts are now known to be produced by neutron star/neutron star collisions. Black hole/black hole collisions haven't produced any verifiably detected electromagnetic radiation. What about some of the other mixed type collissions? Especially white dwarf/neutron star or neutron star/black hole?

My understanding is that stellar binaries tend to have similar mass, so mixed type remnants will likely be rather rare. Hence, why I didn't ask about white dwarf/black hole binaries. Even so, I'm curious how the large difference in density would affect things. Especially if a neutron star would be tidally shredded into an accretion disk by a black hole before they can collide, making a relatively slow event, or will the process be more rapid and violent, akin to the events we've seen so far?

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    $\begingroup$ EM counterparts to NS+BH mergers are definitely expected. $\endgroup$ – Rob Jeffries Oct 18 '17 at 10:04
  • $\begingroup$ Are you asking about interesting products (elements, high-energy photons, etc) or about the resulting artifact (new star, big black hole, etc)? $\endgroup$ – Carl Witthoft Oct 18 '17 at 13:32
  • $\begingroup$ @CarlWitthoft Mostly observable characteristics of the event, less about element production, or resulting artifact. If there's a black hole involved, for example, I'd expect the result to contain a black hole. While dwarf/neutron star collision seems likely to be like a type Ia supernova and leave behind nothing (?). $\endgroup$ – Sean Lake Oct 18 '17 at 17:33

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