Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.
Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month. However, black hole mergers are not expected to produce any electromagnetic radiation (light), meaning they cannot be detected by conventional telescopes.
Artist's concept of the explosive collision of two neutron stars. This material relates to a paper that appeared in the Oct. 16, 2017, online issue of Science, published by AAAS. The paper, by D.A. Coulter at University of California, Santa Cruz in Santa Cruz, CA, and colleagues was titled, "Swope Supernova Survey 2017a (SSS17a), the optical counterpart to a gravitational wave source."
Credit: Illustration by Robin Dienel courtesy of the Carnegie Institution for Science
Please cite the owner of the material when publishing. This material may be freely used by reporters as part of news coverage, with proper attribution. Non-reporters must contact Science for permission.
In contrast, binary neutron star (NS-NS) mergers have long been expected to produce an energetic explosion and a plume of radioactive material, generating light, but have never previously been detected. These mergers provide important clues as to how matter behaves under these extreme conditions.
The papers published online in Science on 16 October describe how light from the NS-NS merger was precisely located, subsequent observations at X-ray, ultraviolet (UV), optical, infrared (IR) and radio wavelengths, and theoretical analysis of the event.
First, a study by David Coulter et al. describes how a team of astronomers pinpointed the location of the merger during the critical few hours following detection of the gravitational waves. The team used the Swope 1-meter telescope in Chile to search for light emitted by the merger, searching the area of the sky that the gravitational waves could have come from.
Using a catalog of known nearby galaxies, they created a prioritized list of likely locations and began snapping images of them. In just their ninth image, they spotted a new source and identified the location of the event: within a galaxy called NGC 4993, about 130 million light years away. As the first team to locate the source, they dubbed it Swope Supernova Survey 2017a (SSS17a).
Immediately after SSS17a was identified, Maria Drout and colleagues began monitoring its brightness with the Swope and Magellan telescopes. Combining their observations with data from other facilities, they analyzed the UV, optical and IR brightness of the event from 11 hours to 18 days after the merger. The source quickly faded and changed from a blue to a red color - a sign that the material was expanding rapidly and cooling as it went.
They interpret the emission as a "kilonova," an ejection of newly-produced heavy elements, whose radioactive decay powers the emission of UV, optical and infrared light. They estimate that the merger ejected material with a mass of 5% of our Sun, containing heavy chemical elements such as lanthanides.
A separate study by Phil Evans et al. describes how the Swift and NuSTAR space telescopes swung into action to observe the event at UV and X-ray wavelengths. The Swift satellite quickly detected a UV source at the location of the event, but it rapidly faded and had disappeared two days later.
The UV observations imply that material was ejected at a velocity that is a substantial fraction of the speed of light, and that it was hotter at early times than theoretical models of kilonovae had predicted. Neither Swift nor NuSTAR detected X-ray emission from the merger, but the authors were able to use its absence to determine the angle at which the binary system was tilted, estimating it to be 30 degrees from our line of sight.
Benjamin Shappee et al. studied the optical and near-infrared spectrum emitted by SSS17a between 12 hours and 18 days after the merger. They show that it behaves unlike any previously-known class of astronomical transient, such as supernovae or gamma-ray bursts. Their earliest observations show that the material ejected from the merging neutron stars was expanding at about 30% of the speed of light, much faster than a supernova.
As the material expands and cools, the spectrum becomes more complicated. They conclude that the ejecta contain two different components: one hot, blue and short-lived, whilst the other is cooler, redder and produces light for longer. There are no absorption lines due to the host galaxy in the spectrum. They note that no single previously-existing model can fully explain the spectroscopic changes they observed.
Gregg Hallinan, Alessandra Corsi, and colleagues monitored the event using numerous radio telescopes around the world. Sixteen days after the gravitational waves reached Earth, they detected the first radio waves from the event. They interpret the radio emission as produced when the expanding material slams into the surrounding gas within NGC 4993, which has a surprisingly low density.
The lack of radio emission at earlier times indicates that the relativistic jet, required to produce the observed gamma rays, cannot be aligned with the line of sight to Earth. They produce two different models that can explain the radio brightness whilst being consistent with observations at other wavelengths, and show how the two models make different predictions for how the radio emission will change over the next few months.
A study by Charles Kilpatrick et al. combines optical to near-infrared brightness and spectroscopy data with modeling, to determine the nature of the event independently of the gravitational wave signal. The observations of SSS17a match what scientists have previously predicted for kilonova events, but only if there are two distinct components with different masses, velocities and fractions of lanthanide elements.
These properties indicate that at least one of the merging objects must have been a neutron star, and the other one probably was too, thereby confirming the result found from the gravitational waves. They also calculate the amount of heavy elements produced in the SSS17a merger, estimate how frequently those events occur, and show that NS-NS mergers can be a major source of the lanthanide elements throughout the Universe, including those on Earth.
A paper by Mansi Kasliwal and colleagues brings together observations at X-ray, UV, optical, IR and radio wavelengths to produce a detailed theoretical model of the merger. Using data from 24 telescopes on seven continents, they reconstruct the total energy emitted by the event at each stage, then seek to simultaneously explain the observations at all wavelengths.
In their preferred model, a jet of material is produced that expands at close to the speed of light, but is directed away from our line of sight. Instead, we see emission from a "cocoon" of shocked material surrounding the jet, which expands over a wider angle.
They confirm this model with detailed simulations, and predict that about 30% of future NS-NS mergers will produce bright gamma rays that will reach Earth. Finally, they estimate the mass of heavy elements produced in the event and use that to calculate the rate of NS-NS mergers, showing both that they can be a major source of those elements and that many more detections can be expected.
These ground-breaking results are put into a broader context in a related Perspective by Joshua Bloom and Steinn Sigurdsson.
Science Press Package | EurekAlert!
NASA investigates invisible magnetic bubbles in outer solar system
02.11.2017 | NASA/Goddard Space Flight Center
Ions in the spotlight
02.11.2017 | Albert-Ludwigs-Universität Freiburg im Breisgau
The Fraunhofer Institute for Laser Technology ILT and Rapid Shape GmbH are working together to further develop resin-based 3D printing. The new “TwoCure” process requires no support structures and is significantly more efficient and productive than conventional 3D printing techniques for plastic components. Experts from Fraunhofer ILT will be presenting the state-funded joint development that makes use of the interaction of light and cold in forming the components at formnext 2017 from November 14 to 17 in Frankfurt am Main.
Much like stereolithography, one of the best-known processes for printing 3D plastic components works using photolithographic light exposure that causes liquid...
A team of researchers led by Prof. Wolfram Pernice from the Institute of Physics at Münster University has developed a miniature abacus on a microchip which calculates using light signals. With it they are paving the way to the development of new types of computer in which, as in the human brain, the computing and storage functions are combined in one element.
Researchers at the universities of Münster, Exeter and Oxford have developed a miniature “abacus” which can be used for calculating with light signals. With it...
Extremely short electron bunches are key to many new applications including ultrafast electron microscopy and table-top free-electron lasers. A german team of physicists from Rostock University, the Max Born Institute in Berlin, the Ludwig-Maxmilians-Universität Munich, and the Max Planck Institute of Quantum Optics in Garching has now shown how electrons can be accelerated in an extreme and well-controlled way with laser light, while crossing a silver particle of just a few nanometers.
Of particular importance for potential applications is the ability to manipulate the acceleration process, known as a swing-by maneuver from space travel, with...
Cancer cells can reactivate a cellular process that is an essential part of embryonic development. This allows them to leave the primary tumor, penetrate the surrounding tissue and form metastases in peripheral organs. In the journal Nature Communications, researchers from the University of Basel’s Department of Biomedicine provide an insight into the molecular networks that regulate this process.
During an embryo’s development, epithelial cells can break away from the cell cluster, modify their cell type-specific properties, and migrate into other...
For the second time, Dr. Samuel Sánchez from the Max Planck Institute for Intelligent Systems in Stuttgart receives the Guinness World Record for the smallest nanotube travelling through fluid like a jet engine.
Dr. Samuel Sánchez is thrilled, just like last time he received a Guinness World Record for the smallest jet engine ever created. Sánchez is a Research Group...
30.10.2017 | Event News
23.10.2017 | Event News
17.10.2017 | Event News
02.11.2017 | Physics and Astronomy
02.11.2017 | Physics and Astronomy
02.11.2017 | Trade Fair News