Question: why do explosions happen on neutron stars?

Alice Harpole answered on 17 Mar 2016:

The explosions I look at happen on neutron stars that are in orbit around stars like our Sun. Because neutron stars have such strong gravity, they pull matter off the surface of the star. This matter then eventually makes its way to the surface of the neutron star, where it forms a liquid layer we call an ocean (though it’s only about 10m thick). As this is happening continuously, more and more matter will end up in the ocean, squashing the stuff beneath it. This causes the temperature and density in the ocean to increase, until it reaches a point where nuclear fusion burning begins. This process is a runaway reaction, and so although the burning starts at a single point, it very quickly spreads across the entire ocean (hence why I call it an explosion – it covers the whole star in about a second!). Lots of energy is released, so we see these explosions as very bright bursts of X-ray radiation.