'Impossible' black hole collision pushed relativity to its breaking point — and scientists finally understand how

An illustration of a black hole merger.

Scientists have traced the origins of the most massive black hole merger ever observed, revealing how two "impossible" giants may have formed despite long-standing assumptions that such objects should not exist.

These black holes were considered "forbidden" because stars of that size were thought to blow themselves apart in extremely powerful explosions, leaving behind no remnant that could collapse into a black hole.