LIGO and Virgo Detect Gravitational Waves from Neutron Star Collision for the First Time 60 Observatories Join To Solve Cosmic Puzzles


October 2017


Image: Artist's conception of the Golden Binary which produced gravity and light and heavy elements like gold (via LIGO). Thanks to this discovery, we finally know where all the elements of the periodic table get made.


On August 17 of this year the two LIGO and the Virgo gravitational-wave observatories detected for the first time gravitational waves from the merger of two neutron stars. The merger occurred about 120 million light years from Earth, closer than scientists’ previous expectations.


The discovery was almost simultaneous with a sharp burst of gamma rays observed by two orbiting satellites, Fermi and INTEGRAL. LIGO's alert, sent to about a hundred observatories around the world, initiated a successful hunt for light and other emission from the event. A broad range of so-called cosmic messengers (gravitational waves, gamma-rays, X-rays, light, radio waves) have been recorded from the collision, marking the beginning of what astronomers refer to as “multimessenger astronomy.”


Gravitational waves are ripples in the fabric of space-time traveling at the speed of light. Their existence was predicted by Albert Einstein over 100 years ago, but their first discovery was achieved by LIGO in 2015. They carry information on the acceleration of heavy objects, such as during the merger of two neutron stars or black holes.


This year’s Physics Nobel Prize was awarded to three scientists who were instrumental in the construction of LIGO and the first direct observation of gravitational waves, published last year. This award, heralded as the beginning of gravitational-wave astronomy, was given independently of the discovery of the neutron star collision.


Neutron stars are dead stars, born from the catastrophic collapse of very heavy stars under their own gravity. They represent the densest known form of matter, with a teaspoon of neutron star matter weighing a billion tons. Neutron star mergers were one of the original motivations for constructing the LIGO detectors, an endeavor that began half a century ago, and which became the biggest project the National Science Foundation ever funded.


Scientists in the LIGO Scientific Collaboration and elsewhere are using the observations of the neutron star merger to study the Universe as well as the fundamental laws of Nature. UF has made key contributions to these studies across the entire scope of the project. We now better understand how extremely energetic photons are produced in outer space. We are also able to study the expansion of the Universe in unprecedented ways by comparing the observed gravitational waves to what we know about the distant galaxy in which the merger happened more than a 100 million years ago. We are also making steps towards understanding how matter behaves at densities greater than that of the atomic nucleus.


UF made seminal contributions to infrared and optical observations of emission from the debris around the merged neutron stars. Lead by Steve Eikenberry, UF built the FLAMINGOS-2 instrument, a near-infrared imaging spectrograph installed in the Gemini-South 8-meter telescope. FLAMINGOS-2 detected the infrared emission 12 hours after the merger took place. In addition, newly appointed UF faculty Imre Bartos plays a leading role in searches for neutrinos from the merger, probing emission mechanisms at extreme energies. "Neutrinos are notoriously hard to detect, so we use IceCube, a billion-ton detector deep in the ice under the South Pole in Antarctica" said Bartos. "No extra neutrinos were seen, from this event, but even this allow us to set limits on what happened following the merger."


UF is a founding member of the LIGO Scientific Collaboration. UF became the third university to join LIGO after Caltech and MIT. Currently, gravitational-wave detectors have 232 institutions and about 1600 scientists as members. UF has led the design and construction of critical components of the LIGO observatories, being responsible for the input optics of both the initial and the Advanced LIGO detector. This is one of the most complex parts of the detector, and many key components were fabricated at UF. Florida also made critical contributions to the optical design of the main interferometer. (Guido Mueller, David Reitze, David Tanner, Paul Fulda, John Conklin). UF also leads the computational effort to reduce thermal noise in the detector. (Hai-Ping Cheng)


UF led the development of the algorithm that discovered the first gravitational wave signal in LIGO data on September 14, 2015. The UF algorithm is being used to study the fate of the neutron stars after they merged. (Sergey Klimenko, Guenakh Mitselmakher).


UF researchers are looking forward to the identification of the chorus of many distant mergers of neutron stars and black holes which are too far to be individually identifiable. This new discovery indicates that the choir of neutron stars will stand out of the crowd. (Bernard Whiting) The list of UF senior LIGO members is Guenakh Mitselmakher (PI), David Tanner, David Reitze (LIGO Executive Director), Sergey Klimenko, Guido Guido Mueller, Bernard Whiting, Steve Eikenberry, Hai-Ping Cheng, John Conklin, Imre Bartos.


LIGO is funded by the NSF, and operated by Caltech and MIT, which conceived of LIGO and led the Initial and Advanced LIGO projects. Financial support for the Advanced LIGO project was led by NSF with Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council) and Australia (Australian Research Council) making significant commitments and contributions to the project. More than 1,200 scientists from around the world participate in the effort through the LIGO Scientific Collaboration, which includes the GEO Collaboration. 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 Centre National de la Recherche Scientifique (CNRS) in France; eight from the Istituto Nazionale di Fisica Nucleare (INFN) in Italy; two in The Netherlands with Nikhef; 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.