Wednesday, May 1, 2019

Speaking of Science: The grown-up era of gravitational waves

Speaking of Science
Talk nerdy to us

An artist's impression of gravitational waves generated by binary neutron stars. (R. Hurt/Caltech-JPL)

The era of gravitational wave astrophysics was born in 2015, when the twin LIGO facilities in Louisiana and Washington state picked up the very first ripples in space time caused by merging black holes. The detection confirmed Albert Einstein's century-old theory that cosmic cataclysms would ruffle the fabric of the universe, and gave scientists a new way to observe some of the darkest and most mysterious objects in space.

Two years later, LIGO and a partner observatory in Italy called Virgo spotted the gravitational wave signal of two neutron stars colliding, while astronomers at dozens of telescopes around the world and in space hustled to capture light bursts from the same event. That's when this new era "came of age," NASA astrophysicist Julie McInery told me. "We're able to combine dramatically different ways of viewing the universe," she said, "and I think our level of understanding is going to leap forward as a result."

And now the era of gravitational wave astrophysics has finally gotten a job, purchased a pant suit, and started bringing home the bacon. Since LIGO and Virgo resumed operations this April after undergoing upgrades to improve their sensitivity, they have recorded five candidate gravitational wave events — as many as were spotted in LIGO's first two years of observing.


Before this latest observing run, LIGO and Virgo detections were kept secret until the results could be analyzed, peer reviewed, and published in a journal. But now candidate events are posted online as they happen, and the world can watch in real time as astronomers scramble to pinpoint their sources.

One of the April events appeared to come from a second neutron star collision -- a phenomenon called a kilonova. Unlike black hole mergers, these events produce light, making them especially interesting to researchers who want to study the universe using the two "messengers" of gravity and electromagnetism.

The latest detection, on April 26, may even be from a never-before-seen event: the collision of a neutron star with a black hole. Provisionally labeled S190426c, the signal appears to come from 1.2 billion light-years away, in the northern hemisphere of the sky. That distance makes it difficult to pinpoint, and there is a relatively high chance of it being a false alarm, but astronomers have spent much of the past week trying to track this strange signal down.

Some scientists created a channel on Slack, the instant messaging service, to discuss their findings. Others were already together, at a conference called Enabling Multi-Messenger Astrophysics (EMMA) in Baltimore. The researchers who would normally race against one another for a result instead tweeted pictures of themselves gathered in the same room as they coordinated optical telescope follow-ups.

Already, more than four dozen follow up observations of S190426c have been posted to NASA's online coordinates network. None appears to have pinpointed the signal's exact source. But astronomers will keep looking. The grown-up era of gravitational wave astrophysics has just begun.

-- Sarah Kaplan

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