Scientific American - 11.2019

ENRICO SACCHETTI

November 2019, ScientificAmerican.com 63

ASTROPHYSICS

The first major gravitational-

wave observatory to be

built under Earth’s surface—

KAGRA in Japan—is set

to turn on

By Lee Billings

Gravitational waves— ripples in spacetime

produced by merging black holes, colliding neutron stars,

detonating supernovae and other cosmic cataclysms—

have sparked a revolution in astrophysics. First observed

in 2015, a century after Albert Einstein predicted their

existence, these elusive whispers in the fabric of reality

are already revealing otherwise hidden details of the exot-

ic objects that produce them. Studies of gravitational

waves have provided researchers with the first direct evi-

dence that black holes exist, produced new estimates of

the cosmic expansion rate, and shown that neutron stars

are the main sources of the universe’s supply of gold, plat-

inum and other heavy elements. Eventually they could

allow researchers to glimpse the universe as it was in the

first fractions of a second after the big bang.

CENTER

OF

GRAVITY

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