UH Discovery Changes Understanding of Universe

Courtesy photo

University of Hawai‘i researchers played a major role in one of the most significant astronomical discoveries in decades—the first observations of a binary neutron star merger and resulting kilonova explosion.

The discovery fundamentally affects our understanding of the origin of many of the elements common on Earth and in our bodies.

UH astronomers, together with their international collaborators, announced the discovery in articles published in Science, Nature and The Astrophysical Journal. They were part of the largest armada of telescopes, researchers and astronomers ever mobilized after the gravitational waves from a binary neutron star merger were detected for the first time.

Two neutron stars (the leftover remnants of massive stars that used up all of their fuel) were orbiting each other in a death spiral, emitting gravitational waves until they finally collided and merged. The cataclysmic coalescence ejected a few percent of the neutron stars’ material into space at about one-quarter the speed of light.

This rare neutron-rich material produced new and highly radioactive atomic nuclei, which rapidly decayed in an eerie glow called a kilonova. The study of this event shows that at least some of the elements heavier than iron were originally created in binary neutron star mergers like this one.

This reflected astronomers’ understanding that much of the material in our bodies and in the Earth, originated in stars. For decades, it was thought that some of the elements heavier than iron, such as silver, came from the dying explosions of massive stars.

Now, UH astronomers together with their international collaborators have seen for the first time a different way that such elements are created and dispersed in the universe.

“A new astronomical object fading this fast is unheard of, and the Pan-STARRS Team alerted the worldwide community to the unique nature of SSS17a,” said Ken Chambers, director of the Pan-STARRS Observatory. “This was the signature of a kilonova.”

The picture that emerged over the following two weeks was that the initially bluish object changed into a redder and strangely colorful object the likes of which has never been seen before. The final piece of the puzzle came from spectra taken by the UH astronomers and their international collaborators on a variety of telescopes.

The neutron-rich material ejected from the merger is a fertile environment for the kind of nuclear reactions that build larger and larger nuclei from smaller ones and some of these were seen. “We see fingerprints of key elements that are heavier than iron,” said Chambers.

The result is a fundamental change in our understanding of the origin of at least some of the heavier elements, many of which are common on Earth and are even in our bodies.