Global Network Catches Fleeting Kilonova for the First Time

Las Cumbres Observatory astronomers were part of an international group of scientists who discovered and made some of the first observations of a kilonova, a new type of explosion in space. This marks the first time in history that an astronomical phenomenon has been first sensed through gravitational waves and then seen with telescopes.

On August 17th, NASA’s Fermi satellite detected a burst of gamma rays and, at the same time, the miles-long laser detector at the Laser Interferometer Gravitational-wave Observatory (LIGO) facility in Washington found microscopic distortions in space caused by gravitational waves passing through the Earth. Additional gravitational wave detectors in Louisiana and Italy were analyzed and astronomers calculated that the signal was coming from about 130 million light-years away, approximately in the direction of the constellation Hydra. Such a signal had never been seen before, but was unmistakably generated by two neutron stars spiraling together. These are stars composed entirely of neutrons and are more massive than the Sun, but only ten miles in diameter. They are in-between normal stars and black holes in size and density — just a teaspoon of neutron star material would weigh 1 billion tons.

Astronomers at Las Cumbres Observatory received the neutron star merger alert and activated their robotic network of 20 telescopes around the world. They searched the region of the sky around the constellation Hydra and were one of six groups to discover a new source of light near the galaxy NGC 4993. The LCO telescopes in Chile first saw the kilonova, and as the Earth rotated and night moved around the globe, it was picked up again with LCO telescopes in Australia, and then again in South Africa. Thanks to their global network, Las Cumbres Observatory was the only facility to observe it every few hours for five consecutive days. During that time, the light from the explosion dimmed by a factor of more than 20, fading at an unprecedented rate for something so luminous.

These explosions from merging neutron stars had long been theorized, though never conclusively observed. They are thought to be the primary source of all the elements heavier than iron in the universe. For example, most of the gold on Earth may have been created in a kilonova. The origin of the name is that these explosions were predicted to be a thousand times brighter than a nova, though dimmer than a supernova. We now know that one reason they had been so elusive is that they fade too quickly for conventional astronomical facilities to detect.

Iair Arcavi, a NASA Einstein postdoctoral fellow at the University of California, Santa Barbara, led the Las Cumbres Observatory gravitational-wave follow-up effort and the study published today in Nature [http://www.nature.com] describing the results. He said, “For years we’ve heard theorists predict how a kilonova should look. I couldn’t believe we were finally seeing one for the first time!”

Curtis McCully, a postdoctoral researcher at LCO and coauthor on the study said, “Thanks to knowing where to look and then having telescopes networked together all around the world, we were able to watch this new type of cosmic explosion rise and fade in real time. This is a remarkable story of the advent of gravitational-wave astronomy combined with robotic internet-based optical astronomy.”

At conventional observatories, astronomers travel to the telescope and stay up all night to operate them. Las Cumbres Observatory is unique — the telescopes are robotic — so they have the ability to drive themselves. They are also unique in the way they are networked together — observations can be triggered at any of the observatory’s facilities around the world within minutes and the telescopes can hand off observations to obtain continuous 24-hour coverage.

Las Cumbres Observatory was founded in 2005 by technologist Wayne Rosing, who retired as Vice President of Engineering at Google to start the observatory. Rosing said, “From 2005, the team has been building LCO with the goal of doing time-domain science. Our goal is now a reality.”

Las Cumbres astronomers used their and other facilities around the world, including the 8-meter Gemini telescope in Chile, to split the light of the kilonova into its chromatic components — a rainbow. Postdoctoral researcher Curtis McCully led that study, published in Astrophysical Journal Letters [http://apjl.aas.org]. It found that only a tiny amount of material was ejected in the explosion — only about 1% of the total matter in the system. The material was also flung out at an extraordinary speed, as much as 30% of the speed of light.

The LCO group also contributed to a study measuring the Hubble constant, which characterizes the expansion rate of the universe. This study uses the inspiraling neutron stars as “standard sirens” to determine their distance from Earth and compares it to the redshift (or how much light has been stretched by the expansion of the universe).

Astronomer Andy Howell, who leads the supernova group at LCO and is a coauthor on the studies, said, “This is a game-changer for astrophysics. A hundred years after Einstein theorized gravitational waves, we’ve seen them and traced them back to their source to find an explosion with new physics of the kind we only dreamed about before.”