Rice astrophysicist discusses historic discovery

For the first time, scientists detect gravity waves and light from colliding stars

In a historic scientific first announced last week, astronomers reported the direct detection of both gravitational waves and light from the same cosmic event, a collision between two massive neutron stars.

Matthew Baring

The observation happened Aug. 17 and was announced in simultaneous press conferences in Europe and the United States Oct. 16.

“This is the first-ever discovery of a merger of two neutron stars, a cataclysmic event that has been predicted to be the origin of short gamma-ray bursts,” said Matthew Baring, professor of physics and astronomy at Rice and a member of the Fermi-Large Area Telescope (LAT) Collaboration that monitored this transient event.

“I have worked on the enigmatic gamma-ray bursts since my Ph.D. thesis,” he said. “They have demonstrated the richness and beauty of Einstein’s special theory of relativity again and again, and in this signature result, they offer a stunning display of his general theory of relativity in action.”

The discovery was made using the U.S.-based Laser Interferometer Gravitational-Wave Observatory (LIGO), the Europe-based gravitational wave detector known as Virgo, as well as about 70 ground- and space-based observatories. Foremost among this large international effort was the Fermi Gamma-Ray Burst Monitor (GBM) detector, which discovered the electromagnetic counterpart about two seconds after the gravitational signal.

Neutron stars are the smallest, densest stars known to exist. They contain more mass than the sun in a sphere that’s less than half the diameter of Harris County, and they are occasionally found in pairs that orbit one another. The Aug. 17 event was the result of such a pair smashing together, a rare occurrence. The collision caused ripples in space-time that were detected by LIGO and Virgo and emitted energy across the electromagnetic spectrum, including visible light, X-rays and radio waves.

Baring said the discovery of both gravitational and electromagnetic radiation from the same event ushers in a new age of astronomy in which scientists can learn more about the makeup of neutron stars, the processes that create heavy elements in the periodic table and the evolution of compact stellar objects in the universe.

“As astrophysicists worldwide had hoped, in anticipation of the LIGO era, this watershed discovery transitions gravitational-wave science into a much broader, richer ‘multi-messenger’ forum, where many astronomical disciplines participate and learn about the exotic constituents of the cosmos,” he said.

Baring said the Aug. 17 discovery helped answer many questions — like how heavy elements such as platinum and gold can be formed, and whether gravity waves do indeed travel at the speed of light. It also may provide insights into research questions that he has studied for more than two decades.

For example, these neutron star collisions are believed to create enormous jets of gamma-ray bursts that spew outward in tight columns. The speed of these outflowing jets has been a central focus of Baring’s research, and he said the Fermi-GBM and Fermi-LAT observations of the collision may provide new clues.

He said early interpretations of the gamma-ray data suggest that the relativistic outflow may not be as fast as most astronomers expected, or that astrophysicists may be viewing the cataclysm from outside the column. “The hope is that the Fermi-GBM data may inform the structure and internal constitution of the progenitor neutron stars. That is a focus of my present research on X-ray signatures from their surfaces and magnetospheres,” Baring said.