36 November/December 2021

Physics

8

// B Y C A R O L I N E D E L B E R T //

SIMULATING EXTREME SPACETIMES (SXS) PROJECT/ COURTESY OF LIGO

What

Happens

When Two

Black Holes

Collide?

F

OR THE FIRST TIME, WE’VE OBSERVED A 50-YEAR-OLD

theorem from Stephen Hawking in the natural world. Scien-

tists from the Massachusetts Institute of Technolog y (MIT),

California Institute of Technology, Cornell University, and

Stony Brook Universit y analyzed the gravitational wave data

of two inspiraling black holes. What they found in the col-

lision proved Hawking’s Area Theorem: The area of a black

hole’s event horizon cannot shrink.

When a binary black hole system inspirals, the orbits of the two

black holes shrink, and the system begins emitting gravitational waves.

The emission rate increases as the orbits shrink further and gain speed,

and when a merger finally occurs, wave emission peaks. The two black

holes become a single, new black hole, and according to Hawking’s

The total area

of the two

inspiraling black

hole horizons was

r o u g h l y 9 0 , 7 3 4

square miles.