Scientists have used a gravitational wave detector to "hear" two black holes getting bigger as they merged into a single, gigantic entity.

The detection, made by the Laser Interferometer Gravitational-wave Observatory (LIGO) on Jan. 14, provides the best evidence yet for a theory put forth by famed physicist Stephen Hawking more than half a century ago, but which was never proven in his lifetime.

Now with a decade of experience under their belts, LIGO collaborators have made many improvements to the detectors — such that black hole mergers are now spotted about once every three days instead of once a month, according to a statement from Caltech, which jointly operates LIGO along with MIT.

During the event detected Jan. 14, LIGO witnessed two black holes merging, with the resulting black hole measuring significantly bigger than the two objects entering into the collision.

Before the merger, the combined surface area of the two black holes was about 93,700 square miles (243,000 square kilometers) — roughly the size of Oregon. After the merger, by contrast, the newly formed and single black hole had a surface area of roughly 154,500 square miles (400,000 square km) — about the size of California. In other words, the newly merged black hole was larger than the sum of its parts.