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Astronomy’s ‘discovery of the century’ helps explain ‘cosmic bling’

Updated: 
October 16, 2017 - 8:17pm

HILO — About 130 million years ago, two neutron stars collided, seeding the cosmos with gold and other heavy elements and scattering gravitational waves in all directions.

Those ripples in space were detected Aug. 17 on Earth by sensitive instruments, prompting a worldwide scramble by scientists seeking to confirm an event they knew would launch a new era of astronomy.

There was no shortage of eyes on this patch of sky near the Hydra constellation.

More than 70 telescopes and laboratories participated, including the Subaru Telescope atop Mauna Kea and Pan-STARRS on Haleakala, making it the most well-observed event in the history of astronomy.

Confirmation of the collision, the first ever detected kilonova, was announced Monday following a blitz of science over two months.

Subaru spokeswoman Yuko Kakazu called it the “discovery of the century.”

“This is all we talk about right now,” she said.

The first hint there was something going on came from the Nobel Prize-winning Laser Inteferometer Gravitational Wave-Observatory, which uses lasers to detect subtle changes in space. LIGO, consisting of two mainland locations, made history in 2015 when it detected the first gravitational waves caused by merging black holes.

But to confirm the waves detected in August were from a neutron star collision required the use of observatories in space and on the ground. Astronomers not only witnessed the distant flash, but also captured crucial data from the event, which had been theorized to result in heavy elements like platinum and gold.

As a result, measurements of the light and other energy emanating from the crash have helped scientists explain how planet-killing gamma ray bursts are born and how fast the universe is expanding, in addition to where all that “cosmic bling,” as at least one researcher has called the elements, came from.

“We already knew that iron came from a stellar explosion, the calcium in your bones came from stars, and now we know the gold in your wedding ring came from merging neutron stars,” said University of California Santa Cruz’s Ryan Foley.

Calculations from a telescope measuring ultraviolet light showed that the combined mass of the heavy elements from this explosion is 1,300 times the mass of Earth.

The worldwide alert went out about 2 a.m. Aug. 17 Hawaii time, following detection of the gravitational waves, said Michitoshi Yoshida, Subaru director.

Telescopes have protocol for these types of events that allows them to clear the deck for observing.

But there was little they could do until the next evening.

Yoshida said the collision was only viewable from Hawaii in a 30- to 40-minute window just after sunset.

Subaru — which is part of the Japanese collaboration of Gravitational wave Electro-Magnetic follow-up, or J-GEM — succeeded nonetheless and continued making observations during the next two weeks in optical and infrared light.

He said they found the change in brightness to fit with their theories.

“Everyone thinks the neutron star merger should be the site of gold creation,” Yoshida said. “But no one had observed that kind of phenomenon yet.”

These neutron stars, which are collapsed cores of stars, were so dense that a teaspoon of their matter would weigh 1 billion tons, said Carnegie Institution astronomer Maria Drout. The stars were located in a galaxy called NGC 4993.

Observatories in the southern hemisphere had a slightly better vantage point.

That was fortunate for the Gemini observatory, which has a telescope on Mauna Kea and another in Chile.

The southern telescope spent 25 nights observing the collision.

“We’re seeing processes we were never able to detect before,” Gemini spokesman Peter Michaud said.

What happens to the neutron stars after the collision is up for debate.

Michaud and Yoshida said some think it creates a tiny black hole, while others believe they simply merge into one neutron star.

But there will be more events like this to study after the gravitational wave detectors finish another upgrade next year.

“This is only the first step,” Yoshida said. “We will be very, very super busy.”

Email Tom Callis at tcallis@hawaiitribune-herald.com.

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