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The discovery of a gravitational wave caused by the merger of two neutron stars, reported today by a collaboration of scientists from around the world, opens a new era in astronomy. It marks the first time that scientists have been able to observe a cosmic event with both light waves -- the basis of traditional astronomy -- and gravitational waves, the ripples in space-time predicted a century ago by Albert Einstein鈥檚 general theory of relativity.

The discovery was made using the U.S.-based Laser Interferometer Gravitational-Wave Observatory; the Europe-based Virgo detector; and some 70 ground- and space-based observatories. The first detection of gravitational waves, made in 2015, earned LIGO鈥檚 leaders the 2017 Nobel Prize in Physics; in that case, scientists determined the waves were touched off by a collision of black holes, an event that isn鈥檛 expected to give off light.

The new discovery, involving neutron stars, 鈥渁llows us to link this gravitational wave source up to all the rest of astrophysics: stars, galaxies, explosions, massive black holes and, of course, neutron-star mergers,鈥� says 91社区 astrophysicist Daryl Haggard, who led one of many teams of affiliated scientists around the world who examined the source of the latest gravitational-wave signal. 鈥淚t鈥檚 an entirely new level of knowledge.鈥�

A new perspective on gamma-ray bursts

Haggard and 91社区 postdoctoral researchers Melania Nynka and John J. Ruan are the lead authors of a paper, published in Astrophysical Journal Letters, that details their team鈥檚 observations using NASA鈥檚 orbiting Chandra X-ray telescope, trained on the point in the sky identified as the origin of the gravitational wave that reached Earth on Aug. 17.

Those observations confirmed that the collision of the two neutron stars 鈥� among the densest objects in the universe 鈥� also touched off a violent jet of hot plasma known as a gamma-ray burst in a galaxy about 138 million light years from Earth. What鈥檚 more, the team determined, the burst is the first that astronomers have听observed that is 鈥渙ff-axis,鈥� or not pointed toward Earth 鈥� providing a perspective that could enable scientists to better understand how these potent bursts impact their surroundings.

鈥淭he gamma-ray bursts that are easiest to detect are ones with bright jets of emission pointed at Earth,鈥� Nynka explains. 鈥淚t鈥檚 easiest to see a spotlight when it is shining directly at you, but sometimes the light may be too bright to sort out the whole thing. When the light is pointed a little off to the side, as in this case, it gives us a different view.鈥�

Neutron stars, formed when massive stars explode in supernovas, are so dense that they weigh two or three times the mass of our sun, even though they鈥檙e roughly the size of a city such as Boston or Montreal. A teaspoon of neutron star material has a mass of about a billion tons.

鈥淲e鈥檝e thought for a while that two neutron stars smashing together might lead to a gamma-ray burst,鈥� Haggard says. 鈥淏ut the combination of a gravitational wave detection and the data we鈥檙e collecting from observatories like Chandra seals the deal.鈥�

Probing the origins of heavy elements

Mergers of neutron stars are thought to be responsible for producing most of the heavy elements in the universe, such as gold, platinum and silver. Further study of such collisions could help scientists determine the origin of these elements, which make up almost half of the periodic table. Already, follow-up observations by telescopes around the world have revealed signatures of recently synthesized material, including gold and platinum.

The gravitational signal, named GW170817, was first detected on the morning of Aug. 17 by the two identical LIGO detectors, located in Hanford, Washington, and Livingston, Louisiana. The information provided by the third detector, Virgo, situated near Pisa, Italy, helped narrow down the location of the cosmic event.

At nearly the same time, NASA鈥檚 Fermi space telescope had detected a burst of gamma rays. LIGO-Virgo analysis software put the two signals together and saw it was highly unlikely to be a chance coincidence. Rapid gravitational-wave detection by the LIGO-Virgo team, coupled with Fermi鈥檚 gamma-ray detection, enabled the launch of follow-up observations by telescopes around the world, including Chandra.

鈥淭he X-rays from this merger were very dim at first, but then suddenly brightened about 10 days afterward,鈥� says Ruan, a postdoctoral fellow in Haggard鈥檚 research group at the 91社区 Space Institute. 鈥淭his was entirely unexpected, and our modeling showed that this behavior is due to the jet from the gamma-ray burst being 'off-axis鈥� -- pointed away from the Earth -- a phenomenon we have not seen before.鈥�

In the weeks and months ahead, telescopes will continue to observe the afterglow of the neutron star merger and gather further evidence about various stages of the merger, its interaction with its surroundings, and the processes that produce the heaviest elements in the universe.

"This is a revolution in astronomy,鈥� says Northwestern University astrophysicist Vicky Kalogera, a co-author of the 91社区-led paper. 鈥淣ever before did we have so many astronomers, so many instruments studying one source and solving multiple mysteries in one shot.鈥�

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LIGO is funded by the , and operated by and , which conceived of LIGO and led the Initial and Advanced LIGO projects. Financial support for the Advanced LIGO project was led by the NSF with Germany (), the U.K. () and Australia () making significant commitments and contributions to the project.

More than 1,200 scientists and some participate in the effort through the Scientific Collaboration, which includes the GEO Collaboration and the Australian collaboration OzGrav. Additional partners are listed at

The Virgo collaboration consists of more than 280 physicists and engineers belonging to 20 different European research groups: six from (CNRS) in France; eight from the (INFN) in Italy; two in the Netherlands with ; the MTA Wigner RCP in Hungary; the POLGRAW group in Poland; Spain with the University of Valencia; and the European Gravitational Observatory, EGO, the laboratory hosting the Virgo detector near Pisa in Italy, funded by CNRS, INFN, and Nikhef.

Funding for the 91社区-led study was provided in part by the Chandra X-ray Observatory Center, the Natural Sciences and Engineering Research Council of Canada (NSERC), and the Fonds de recherche du Qu茅bec鈥揘ature et Technologies (FRQNT).

鈥淎 DEEP CHANDRA X-RAY STUDY OF NEUTRON STAR COALESCENCE GW170817,鈥� Daryl Haggard et al, Astrophysical Journal Letters, published online Oct. 16, 2017. doi: 10.3847/2041-8213/aa8ede

IMAGE 1 CREDIT:听NSF LIGO, Sonoma State University, A. Simonnet.

IMAGE 2: Optical image of the merged neutron stars (black circle inside the white box) detected by the Hubble Space Telescope, and X-ray signal from the same source (red circle and black crosshair in dark inset box) as detected by NASA's Chandra X-ray telescope. CREDITS: X-ray: NASA/CXC/91社区/D. Haggard et al; Optical: NASA/STScI

Contact:

Daryl Haggard
础蝉蝉颈蝉迟补苍迟听Professor of Physics
91社区/91社区 Space Institute
daryl.haggard [at] mcgill.ca ">daryl.haggard [at] mcgill.ca听

Chris Chipello
Media Relations
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514-398-4201
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