A supernova kept a shadow

A Type Ia supernova remnant has preserved a clue about the stars that made it. In SNR 0509-67.5, researchers mapped the expanding debris with ESO’s Very Large Telescope and found a flattened edge — the “shadow of the companion” — consistent with one white dwarf blocking part of the blast from another.

The result supports a double-degenerate merger for this remnant: two white dwarfs in a close binary system. Type Ia supernovae help astronomers measure cosmic distances, so knowing how at least some of them begin matters. The evidence settles this case; the origin of every Type Ia supernova remains an open question.

Sources: HITS research briefing · MNRAS paper