UT scientists 'hear' black hole collision; revealing how they may grow

AUSTIN (KXAN) — What happens when black holes collide? In 1971, renowned physicist Stephen Hawking put out a theory that the surface area of black holes never shrink, even during a collision.

New research published this week reveals he was probably right. When two black holes collide they get bigger.

Researched conducted by an international group of scientists, including some from the University of Texas in Austin, looked at the merging of two black holes in January.

The black holes had a surface area of 92,664 square miles before merging. After the collision, a new black hole was born.

This new black hole had a surface area of 154,440 square miles, nearly double that of the original black holes.

Discovering the music of the universe

The team discovered this using a network of gravitational wave detectors, the US National Science Foundation Laser Interferometer Gravitational-Wave Observatory (NSF LIGO). LIGO first discovered the merging of black holes ten years ago this week.

The system detected this by looking at changed in space-time called gravitational waves. These are essentially gravity shockwaves that travel at the speed of light and occur when two objects with high gravity collide, like a black hole.

Since the initial discovery, advancements in LIGO and a partnership with two other detectors in Italy and Japan have led to three hundred black hole mergers discovered.

LIGO has seen several major upgrades, allowing it to see much smaller space-time distortions created by gravitational waves.

In January, LIGO witnessed the black hole collision called GW250114. The collision occurred 1.3 billion light years away. Each black hole was thirty to forty times the size of our sun.

As they collided, a gravitational wave echoed out. LIGO collected the waves, “hearing” them as they passed Earth. As the black holes merged, the waves got louder and then rippled away sort of like when a bell is struck by a hammer.

This ripple makes it hard to measure the surface area of the hole. In the new paper, researchers used improved data provided by LIGO.

This is the second time Hawking’s theory has been observed. The first was in 2021. That observation was not nearly as accurate as the new observation (95% compared to 99.999%), due to the advancements of LIGO.