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January/February 2018^ DISCOVER^13
TOP: ROBERT HURT (CALTECH/IPAC), MANSI KASLIWAL (CALTECH), GREGG HALLINAN (CALTECH), PHIL EVANS (NASA) AND THE GROWTH COLLABORATION; NSF/LIGO/SONOMA STATE UNIVERSITY/A. SIMONNET
ASTRONOMERS
SEE AND HEAR
THE COSMOS
❯
FOR HUNDREDS OF MILLIONS OF YEARS, two city-sized
stars — each outweighing our sun — circled one
another in a fatal dance. They were neutron stars, the
collapsed cores left behind after giant stars explode into
supernovas. Then, 130 million years ago, the dance ended.
Their collision was fast and violent, likely spawning a black
hole. And a shudder — a gravitational wave — rippled across
the fabric of space-time. Light from the cataclysm followed
seconds later.
The space-time distortion and the light reached Earth
together on Aug. 17, making astronomical history.
Astronomers announced the finding Oct. 16.
The gravitational wave first reached Italy’s just-finished
detector, Advanced Virgo, before stretching and squeezing
the two LIGO observatories in the United States. Orbiting
space telescopes and instruments on all seven continents
turned to watch the cosmic collision play out in all manner of
light: radio, infrared, optical, ultraviolet, X-rays, gamma rays.
“It was extremely close to us, and so it was an extremely
strong signal,” says LIGO scientist Jolien Creighton of the
University of Wisconsin-Milwaukee.
In 2016, LIGO (short for Laser Interferometer Gravitational-
Wave Observatory) announced it had detected gravitational
waves for the first time, confirming Albert Einstein’s
predictions in general relativity. Astronomers compared it
to finally hearing the cosmos. But the real breakthroughs
would come from hearing and seeing the cosmos
simultaneously, or so-called “multi-messenger astronomy.”
That’s now happened.
This one event produced dozens of research papers
boasting thousands of scientists as co-authors. And it
uncorked a jug of other scientific feats, like a new direct
measurement of the expansion of our universe, and the best
evidence yet that gravitons — gravity-carrying particles —
have no mass, just like photons (light particles). Astronomers
even caught the collision’s chemical fingerprints, revealing the
creation of 10 to 100 Earths’ worth of gold and other heavy
elements, ending decades of debate on their cosmic origins.
“We’ve created a new field of astronomy,” says Ryan
Foley of the University of California, Santa Cruz, who led the
optical discovery team. “We’ve been walking around for all
of humanity being able to see the universe but not being
able to hear it. Now we get both.”
He adds: “It’s even hard to predict where this field will go,
but I can tell you now it’s going to be exceptional.” ERIC BETZ
Astronomers captured the
merging of neutron stars
in various types of light,
including ultraviolet, infrared
and radio waves (above),
as well as via gravitational
waves — a first.