Black holes keep 'burping up' stars they destroyed years earlier, and astronomers don't know why

Many black holes that consume a star seem to ‘burp up’ energy long after the fact. When the star is ripped apart, some the stellar material forms a swirling accretion disk that orbits the hole. Sometimes, material is flung out from this disk, which is detectable as a wash of radio waves. Astronomers observed 24 star-destroying black holes and were surprised to find radio signals indicating that 10 of them emitted these outflows years after the initial event — although we don’t yet know why.