Collision between Neutron stars and Black holes

Question

When two neutron stars or black-holes come closer and closer, their angular velocity increases with decrease of distance and they start to revolve around a constant center with high relativistic speeds due to the influence of gravity... At last,

• Neutron-stars collide to produce a giant explosion...
• Black-holes collide to form super-massive black-holes...

(Even two neutron stars merge to form black-holes, based on the answer)

So, What are observed during and after this collision..? Magnetic fields & short GRBs only..?

Answer 1

Their angular momentum stays nearly constant. You might be thinking of their angular velocity.

There is a lot of simulation-based work out there on the inspiral of two compact supernova remnants (NSs or BHs), done partly to determine what the gravitational wave signals would look like for the LIGO experiment. Two NSs would merge to form a BH, because their combined mass would be above the threshold for the fermi pressure of the NS to resist gravitational collapse. Part of the NS material would briefly orbit the newly formed BH as an accretion disk, and some of the energy would be beamed out along the rotational axis, visible to us (if we happen to be in the line-of-sight of the axis) as a gamma ray burst.