Rare Collision of Two Uneven Black Holes Detected at LIGO

By Marty Kaufman -

Until recently, scientists believed the colliding black holes tend to be evenly matched in size. But now, a new detection at LIGO (Laser Interferometer Gravitational-Wave Observatory) pushes that hypothesis aside. On April 12th, 2019, the gravitational wave detectors in the observatory picked up another space-time ripple signal that originated from two colliding black holes. However, upon closer look, the scientists found out that the new detection didn't match the signals they got from other such collisions.

The Merging Black Holes Were Detected at LIGO

Rare Collision of Two Uneven Black Holes Detected at LIGO

Instead of showing two evenly matched black holes, the new signal was triggered by a merger in which one black hole is way bigger than the other, three or four times bigger, to be exact. Maya Fishbach — a doctoral candidate at the University of Chicago who presented the finding — said that it is an unlikely observation that no one on the team was expecting.

Previous Black Hole Mergers Involved Same-Size Objects

Rare Collision of Two Uneven Black Holes Detected at LIGO

The previous ten mergers of black holes that LIGO detected in its first two observing runs were between objects that were about the same size. Regardless of the size of the collision, one of the black holes was never much larger than the other. Now, the new signal is turning that trend on its head.

LIGO had a shorter third observing run, which produced more than 50 detections. The data is enough to have scientists busy for a while, and they're still analyzing those observations. This means that more unbalanced mergers could be discovered in the near future. One thing is certain though — such an asymmetric merger will definitely expand the range of black hole pairs scientists can expect to see.

The detection will also give scientists a better understanding of the processes that lead to a black holes pair and how rare such unbalanced pairs may be. The new discovery involves objects that existed around 2.4 billion light-years away from our solar system, and while the small black hole was roughly eight times the mass of the sun, the other was nearly thirty solar masses.