Detecting the Ancient Collision of Two Dead Stars: Embry-Riddle’s LIGO Scientists to Offer Updates on Oct. 20 in Arizona

Assistant Professor of Physics Brennan Hughey and Associate Professor of Physics Michele Zanolin, principal LIGO investigator, will present on “Advanced LIGO at the End of its Second Observing Run,” in room AC1-104 on the Prescott, Ariz., campus, as part of a Science Speaker Series.

The latest detection of gravitational waves, or ripples in space-time as they move around massive objects, thereby confirming Einstein’s theory of general relativity, was announced on Oct. 16 by the National Science Foundation-funded LIGO scientific collaboration as well as VIRGO, a related project hosted by the European Gravitational Observatory.

The collaborators described an intense collision called a kilonova that happens when two fuel-starved neutron stars spiral inward, crash, and collapse, most likely forming a black hole. The smash-up produces gravitational waves as well as an unimaginably bright flash of light.

On Aug. 17, researchers first spotted the signal of wrinkles in space-time, detectable for 100 seconds, caused by the spiraling of two dead stars. Two seconds later, they detected a burst of gamma rays, and finally, the red afterglow caused by a collision of neutron stars that took place long ago, when dinosaurs still roamed the Earth.

More than 30 articles were swiftly published by various peer-reviewed journals.

Embry-Riddle researchers were co-authors on an article in Nature, entitled “A Gravitational-Wave Standard Siren Measurement of the Hubble Constant.” That paper, touted as heralding a new “age of gravitational-wave multi-messenger astronomy,” was co-authored by Embry-Riddle’s Hughey and Zanolin as well as:

• Kellie Ault, graduate student
• Sergio Gaudio, research associate
• Kiranjyot (Jasmine) Gill, undergraduate student
• Andri Gretarsson, associate professor of physics
• Martina Muratore, visiting graduate student
• James Pratt, undergraduate student
• Sophia Schwalbe, undergraduate student
• Kai Staats, research associate
• Marek Szczepançzyk, graduate student

Four prior LIGO announcements have reported the detection of gravitational waves caused by the collision of black holes – an event that generates a telltale chirping sound, but not light.

Capturing data from the space crash of two neutron stars – the smallest and densest of stars, which are heavier than the sun but no larger than a city – was a significant advancement for the LIGO-VIRGO collaborators. “It was the first time we’ve observed light in coincidence with the gravitational wave, and that dramatically increases the amount of physics we’re able to do with the observation,” Hughey noted.

Specifically, for example, the advancement makes it possible to capture a unique measurement of something called the “Hubble constant.” This elusive quantity is fundamentally important to cosmology since it reveals the local expansion rate of the universe.

The discovery also “speaks to the origin of a lot of the heavy metals in the universe,” Hughey noted. That’s because the aftermath of the collision of two dense neutron stars sends gold and other precious metals and heavy elements flying through space.

Of importance to scientists, the research further offers the first direct confirmation that short gamma ray bursts are generated by the collision of neutron stars – a theory that had not yet been verified, Hughey said.

In summarizing the significance of the research overall, astronomer Terry Oswalt, chair of the Department of Physical Sciences on Embry-Riddle’s Daytona Beach, Fla., campus, said: “The detection of the source of gravitational waves from merging neutron stars in the galaxy NGC 4993 across the electromagnetic spectrum ushers in a new era of so-called `multi-messenger astronomy.’ Now we can use the physics of gravity and light together, to pry open a new page in the history book of the universe. Today’s new page tells us where the heaviest elements, like that gold ring on your finger, came from. It also nicely underscores the absolutely critical role of small ground-based telescopes, our constant eyes on the sky.”

For the latest LIGO research, Hughey served on the review committee that helped approve procedures for sending out alerts to telescopes whenever promising signals are detected. Zanolin’s long-standing work also was instrumental for developing key signal-detection codes. Gretarsson has worked for many years in the area of LIGO hardware.

LIGO, a pair of 4-kilometer-long, L-shaped laser rangefinders located in Louisiana and Washington state that detect the single-photon scale disturbances that gravitational waves cause when they hit laser beams, was built in 1994, thanks to research and development funding provided by the NSF to MIT and Caltech.

On Oct. 3, the 2017 Nobel Prize in Physics was awarded to three founding champions of LIGO: physicist Rainer Weiss of the Massachusetts Institute of Technology (MIT), along with theoretical physicist Kip S. Thorne and experimental physicist Barry C. Barish, both of the California Institute of Technology (Caltech) in Pasadena.

In announcing the Nobel Prize in Physics, the award committee explained that “gravitational waves spread at the speed of light, filling the universe. They are always created when a mass accelerates, like when an ice skater pirouettes or a pair of black holes rotate around each other.”

The LIGO-VIRGO collaborators in September described a fourth detection of gravitational waves rippling around black holes located 1.7 billion light-years from Earth.

In June, nine Embry-Riddle researchers on the Prescott Campus were among the co-authors of a paper in Physical Review Letters that described the third detection of gravitational waves resulting from the collision of two massive black holes.

General background on Embry-Riddle’s participation in the LIGO collaboration can be found in the spring 2017 edition of ResearchER magazine.