Gravitational waves help reveal our violent universe

Neutron Star merger photo
Image: University of Warwick | Mark Garlick

It took over a century to find gravitational waves after they were first theorized by Albert Einstein in 1916. Now, less than two years after that initial observation in February 2016, the ability to detect gravitational waves has led to the discovery of merging neutron stars. Not only can we detect this otherworldly event, we can also see it.

On August 17th, 2017 the detection of the gravitational waves from this event sent astronomers around the world into a frenzy. After over a month of analyzing the event and synthesizing the abundance of data collected, many of these research teams have finally published their discoveries.

The first breakthrough came hours after the Laser Interferometer Gravitational-Wave Observatory (LIGO) detected the gravitational waves from the neutron star merger. David Coulter and his team, utilizing the Swope 1-meter Telescope in Chile, were able to locate the source of the gravitational waves. This marked the first-ever detection of a gravitational wave-inducing event on the electromagnetic spectrum.

Typically events that are massive enough to cause the ripples in the fabric of space-time that we call gravitational waves involve the interaction of black holes. While black holes are detectable using LIGO and other gravitational-wave interferometers, the inability of light to escape black holes prevents these gargantuan events from being detected on the electromagnetic spectrum. This limits our ability to collect data from such events, and in turn limits astronomers abilities to create the models necessary for us to learn how these events have shaped our universe.

Following the location of the event, named Swope Supernova Survey 2017a (SSS17a) after the telescope used to find it, a swarm of researchers and their teams pointed their astronomical instruments 130 million light-years away towards its source.

One of the most comprehensive studies of the event came from Mansi Kasliwal, an assistant professor of astronomy at the California Institute of Technology (Caltech). Utilizing 24 telescopes across 7 continents her and her team was able to use measurements from a variety of wavelengths to build a model of the event at various stages.

As theorized, it was discovered that these neutron star (NS-NS) mergers result in a remarkably violent explosion that scatters light and ejects newly formed heavy elements in a radioactive plume.

The study concluded that the plume ejected from the neutron star merger expanded at close to the speed of light and produced an abundance of heavy elements, including the lanthanide series of “rare earth metals”. Furthermore, by combining the data collected from the gravitational waves with the electromagnetic observations the research team was able to identify hallmark emission signatures that could help us find similar NS-NS mergers throughout our universe.

Finally, the researchers at Caltech were able to use the mass of heavy elements created by the merger to calculate the approximate frequency of these events. The results show that neutron star mergers are most likely a major contributor to the existence of these elements in the universe, including here on Earth.

It cannot be overstated how thrilling this is for astronomers around the world. Just two years after the first gravitational wave was measured, these ripples in space-time have now given us a glance at how some of the heaviest elements on our planet came into existence. This discovery marks one of many to come as gravitational wave detection allows us to unlock the mysteries of our universe.

Author: Skylar Knight

Skylar is currently in the MSc Science Communication program at Imperial College London. He has years of experience working in science museums, academic publishing, writing, filmmaking, and science education.