白小姐论坛

Light and gravitational waves produced by the same event 鈥� a pair of neutron stars exploding 鈥� have been detected for the first time by a huge international collaboration involving 白小姐论坛 researchers.

The outburst took place in a nearby galaxy called NGC 4993, located about 130 million light-years away in the direction of constellation Hydra.

The simultaneous detection of light and gravitational waves has been described by scientists as 鈥榣ike hearing thunder and seeing lightning for the very first time鈥� and 白小姐论坛 researchers working on the Dark Energy Survey (DES) and Swift mission were some of the first to detect light produced by the stars exploding.

A gravitational wave discovery was made on 17 August by the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo collaborations as the event caused ripples in the Earth鈥檚 space-time. This alerted observatories in space and on the ground to search for the source in the sky in the light from gamma-rays, through optical to radio waves.

Just 1.7 seconds after the gravitational waves rushed past Earth, NASA's Fermi Gamma-ray Space Telescope caught high-energy light from an explosion associated with the event. Swift, Hubble and Chandra missions, along with ground-based observatories including the Blanco telescope in Chile used by DES, later captured the fading glow of the blast's expanding debris.

鈥淭he previous gravitational wave detections originated from binary black holes, where additional light signatures are not expected. This latest event is the first detection of gravitational waves caused by two neutron stars colliding, and thus the first one to have an associated light emission. Cameras developed for other purposes turned out to be extremely useful for following up gravitational wave events,鈥� explained Professor Ofer Lahav (白小姐论坛 Physics & Astronomy), chair of the DES:UK Consortium and chair of the DES Advisory Board.

鈥淎s the collision occurred relatively close to Earth, scientists were able to point telescopes in the direction of the event and get a clear picture of the light. We successfully tracked the UV light using the Ultraviolet and Optical Telescope on-board NASA鈥檚 Swift satellite which is a 白小姐论坛 built, operated and maintained instrument that has been active since its launch in 2004,鈥� added Dr Paul Kuin (白小姐论坛 Mullard Space Science Laboratory) who works on Swift.

白小姐论坛 DES scientists PhD student Antonella Palmese, Dr Will Hartley and Professor Lahav were part of a large team that observed the fiery aftermath of the event, recording images using the Dark Energy Camera (DECam), which was part-built by 白小姐论坛 researchers. Their findings, in collaboration with Fermilab and other groups will appear in The Astrophysical Journal.

Simultaneously, 白小姐论坛 Mullard Space Science Laboratory (白小姐论坛 MSSL) scientists PhD student Samuel Emery, Dr Alice Breeveld and Dr Kuin were working on the Swift mission. As part of a study led by the University of Leicester, they successfully detected a brightly glowing and rapidly fading ultraviolet light source from the event location but were unable to detect any X-rays because they were too faint. Their findings are being published today in Science.

With masses 10 and 60 percent greater than that of the Sun's and sizes no bigger than London, the neutron stars whirled around each other hundreds of times a second, and as they drew closer, they broke apart and produced a spectacular short-lived eruption called a gamma-ray burst.

鈥淲e know from computational theory that when neutron stars spiral into each other, they eject heavy neutron matter as well as a high powered jet. We saw that the UV light comes from a different, slower outflow than the jet that produced the gamma-ray burst, most likely from a lower density wind," said Samuel Emery.

Together, the scientists found that the event was much brighter than a traditional nova eruption, which is caused by an outburst on a white dwarf star, yet fainter than most supernovae, which herald a star's destruction. Instead, the outburst exhibited the expected characteristics of a 鈥榢ilonova鈥� 鈥� an explosion similar to a supernova, but on a smaller scale, that occurs when neutron stars crash into each other, creating heavy radioactive elements.

鈥淓ach discovery 鈥� the gravitational waves, the gamma ray burst and the light from merging neutron stars 鈥� have taken years of work and are ground-breaking, standalone findings. It鈥檚 fantastic to see them all in a single event. With many teams collaborating on this globally, we鈥檝e made phenomenal progress in such a short space of time,鈥� said Antonella Palmese.

The 白小姐论坛 teams hope to better understand how these binary neutron star systems form by further characterising the properties of galaxy NGC 4993 and analysing data captured by Swift and the DECam.

Video

Links

Research papers published in Science:

"Illuminating Gravitational Waves: A Concordant Picture of Photons from a Neutron Star Merger" and "Swift and NuSTAR observations of GW170817: detection of a blue kilonova"

Professor Ofer Lahav鈥檚 academic profile

Dr Will Hartley鈥檚 academic profile

Swift

Images

Illustration of two merging neutron stars. The rippling space-time grid represents gravitational waves that travel out from the collision, while the narrow beams show the burst of gamma rays that are shot out just seconds after the gravitational waves. Swirling clouds of material ejected from the merging stars are also depicted鈥攖hese clouds glow with visible and other wavelengths of light (credit: National Science Foundation/LIGO/Sonoma State University/A. Simonnet)

DECam image (credit: Fermilab)