WASHINGTON: A supernova — the explosive death of a star — is always violent, blasting material into space while typically leaving behind a compact stellar remnant like a neutron star or black hole. But some supernovas involving the largest stars in the cosmos may be so immensely powerful they leave absolutely nothing behind. Scientists since the 1960s have theorised the existence of these ultra-powerful supernovas, and have now come up with evidence for them — albeit indirect — in research invol...