By Annette Cary

Tri-City Herald

KENNEWICK — The detection of the fiery crash of two neutron stars at the Hanford LIGO and other observatories this summer has upended one theory about the universe.

On Aug. 17, the Laser Interferometer Gravitational-wave Observatory near Richland and two other gravitational-wave observatories detected the gravitational waves, or ripples through space and time, from a neutron star collision for the first time.

Previously, the Hanford LIGO, its twin observatory in Louisiana and a gravitational wave observatory in Italy have detected the merger of black holes. But unlike neutron start collisions, those mergers give off no light.

The gravitational-wave detection of the collision of neutron stars allowed the event to also be observed by telescopes that can detect forms of light, or electromagnetic radiation.

The detection of the neutron star collision was the start of what scientists call multi-messenger astronomy, a new way to learn about the universe by viewing both gravitational waves and light.

As astronomers continue to observe the aftermath of the Aug. 17 detection, they are not seeing what they expected.

A popular theory describing the aftermath of a neutron merger predicts a fast-moving, beam-like jet, thought to be associated with short gamma-ray bursts. It would be expected to weaken with time as the jet lost energy.

Instead, months later scientists at the California Institute of Technology and other institutions are reporting that light with radio wavelengths continues to brighten.

They believe that the jet, launched from the two neutron stars as they collided, is slamming into surrounding material and creating a slower-moving, billowy cocoon.

“We think the jet is dumping its energy into the cocoon,” said Gregg Hallinan, an assistant professor of astronomy at Caltech.

“At first, people thought the material from the collision was coming out in a jet like a firehouse,” he said. “But we are finding that the flow of material is slower and wider, expanding outward like a bubble.”

The neutron star collision was not a typical short gamma ray burst, scientists say now.

Researchers say that more observations of neutron star mergers from the Hanford and Louisiana LIGOs and the Italian gravitational-wave observatory should help them learn more.

Neutron stars are the collapsed cores of large stars and are the smallest, densest stars known to exist.