How a black hole and neutron star might form and merge

Two stars orbit each other 900m light years from Earth

The more massive star explodes as a supernova and becomes a black hole

The second star increases in volume until it incorporates the black hole in a so-called common envelope

The second star explodes as a supernova and becomes a neutron star

Black hole and neutron star spin faster and closer until they start to merge

The last extremely violent cycles and merger last a few tens of seconds, sending gravitational waves out into the universe

The black hole swallows the neutron star

Two stars orbit each other 900m light years from Earth

The more massive star explodes as a supernova and becomes a black hole

The second star increases in volume until it incorporates the black hole in a so-called common envelope

The second star explodes as a supernova and becomes a neutron star

Black hole and neutron star spin faster and closer until they start to merge

The last extremely violent cycles and merger last a few tens of seconds, sending gravitational waves out into the universe

The black hole swallows the neutron star