UWM scientists help in detection of violent collision of neutron stars

Scientists around the world, including a team at the University of Wisconsin-Milwaukee, have now observed the violent collision of two neutron stars — a cosmic event that occurred 130 million years ago and may shed light on the universe's future.

Neutron stars, among the most exotic objects in the universe, form from the cores of giant stars that have exploded.

Their collision, detected on Aug. 17 by the billion-dollar, international project known as LIGO, gave off enormous energy — about 40 times the amount of energy our sun will emit in its lifetime.

"We think that these type of collisions are responsible for most of the heavy elements we see on earth, including gold and uranium," explained UWM associate professor David Kaplan, who was involved in the discovery. "We think this collision produced 100 times the mass of the Earth in gold." 

The same technology allowed scientist two years ago to detect the collision of two black holes, confirming the existence of gravitational waves. The neutron star collision, however, produced something the black hole discovery did not: a visible image, seen eventually by some 70 telescopes around the world.

What they saw was a bright blue dot, fading rapidly. What the LIGO detectors picked up registered as a series of numbers that computers hunting for tell-tale patterns seized on.

Just two weeks ago, three scientists with LIGO were awarded the 2017 Nobel Prize in physics for observation of the black hole collision. That discovery confirmed the existence of gravitational waves, predicted a century earlier by Albert Einstein. 

The role UWM scientists played in the latest discovery was two-fold. They established the complex system that calibrates all of the data from two enormous L-shaped detectors in Hanford, Wash., and Livingston, La. It was these detectors that confirmed the existence of gravitational waves and detected the neutron star collision.

UWM scientists also coordinated the viewing and data collection by dozens of powerful telescopes around the world.

Patrick Brady, director of UWM's Leonard E. Parker Center for Gravitation, Cosmology and Astrophysics, said he was strolling around Amsterdam with his wife when news of the neutron star discovery arrived in a text message.

"Oh, my God! Oh, my God!" he shouted. 

The neutron star discovery "helps us understand how elements that make up planets were enriched over billions of years," said Kaplan. "In the Milky Way, probably one of these events has happened every million years."

The new discovery will also help scientists studying how fast our universe is expanding, work that may someday tell us how and when the universe will end.

Previously, scientists have calculated how fast galaxies are moving away from us by observing changes in brightness of the light from certain cosmic events as that travels from its origin to earth.

A similar technique will now allow scientists to measure the speed galaxies are moving away from Earth by measuring changes in the gravitation waves, which are much bigger at the site of collisions and much smaller when they reach Earth.

Although the exact details of their composition are yet to be discovered, scientists believe neutron stars are composed mostly of neutrons, charge-less, sub-atomic particles found in the nucleus of atoms.