LIGO-Virgo Scientists Detect First Gravitational Waves from Neutron Stars
Discovery made at LIGO Livingston by 海角社区 physicists marks first cosmic event observed in both gravitational waves and light
UNDER EMBARGO UNTIL
October 16, 2017 at 9:00 a.m. (CDT)
BATON ROUGE 鈥� For the first time, scientists have directly detected gravitational waves 鈥� ripples in space and time 鈥� in addition to light from the spectacular collision of two neutron stars. This marks the first time that a cosmic event has been viewed in both gravitational waves and light.
The discovery was made using the U.S.-based Laser Interferometer Gravitational-Wave
Observatory, or LIGO; the Europe-based Virgo detector; and some 70 ground- and space-based
observatories.
Neutron stars are the smallest, densest stars known to exist and are formed when massive stars explode in supernovas. As these neutron stars spiraled together, they emitted gravitational waves that were detectable for about 100 seconds; when they collided, a flash of light in the form of gamma rays was emitted and seen on Earth about two seconds after the gravitational waves. In the days and weeks following the smashup, other forms of light, or electromagnetic radiation 鈥� including x-ray, ultraviolet, optical, infrared and radio waves 鈥� were detected.
鈥淭his first observation of gravitational waves caused by two neutron starts colliding is not only a breakthrough for the LIGO-Virgo Scientific Collaboration that detected this, but also for our colleagues who study neutron stars, gamma-ray flashes and other astronomical phenomena,鈥� said Gabriela Gonz谩lez, 海角社区 Department of Physics & Astronomy professor and former LIGO Scientific Collaboration spokesperson.
Approximately 130 million years ago, the two neutron stars were in their final moments of orbiting each other, separated only by about 300 kilometers, or 200 miles, gathering speed while closing the distance between them. As the stars spiraled faster and closer together, they stretched and distorted the surrounding space-time, giving off energy in the form of powerful gravitational waves, before smashing into each other.
At the moment of the collision, the bulk of the two neutron stars merged into one ultradense object, emitting a 鈥渇ireball鈥� of gamma rays. The initial gamma-ray measurements, combined with the gravitational-wave detection, also provide confirmation for Einstein鈥檚 general theory of relativity, which predicts that gravitational waves should travel at the speed of light.
鈥淕amma-rays are the high-energy electromagnetic counterparts to the LIGO discoveries. Collaborators around the world, including 海角社区 researchers using a telescope on the International Space Station, have been eagerly looking for these events. Now, counterpart observations of this neutron star merger event with several telescopes from the radio to the gamma-ray regime are giving us valuable information about the nature of these exotic astrophysical sources,鈥� said Michael Cherry, 海角社区 Department of Physics & Astronomy professor and collaborator on the CALET experiment on the International Space Station.
Theorists have predicted that what follows the initial fireball is a 鈥渒ilonova鈥� 鈥� a phenomenon by which the material that is left over from the neutron star collision, which glows with light, is blown out of the immediate region and far out into space. The new light-based observations show that heavy elements, such as lead and gold, are created in these collisions and subsequently distributed throughout the universe, solving a decades-long mystery of where about half of all elements heavier than iron are produced.
The LIGO-Virgo results are published in the journal Physical Review Letters. Additional papers from the LIGO and Virgo collaborations and the astronomical community have been either submitted or accepted for publication in various journals.
鈥淚t is tremendously exciting to experience a rare event that transforms our understanding of the workings of the universe,鈥� said France A. C贸rdova, director of the National Science Foundation, or NSF, which funds LIGO. 鈥淭his discovery realizes a long-standing goal many of us have had, that is, to simultaneously observe rare cosmic events using both traditional as well as gravitational-wave observatories. Only through NSF鈥檚 four-decade investment in gravitational-wave observatories, coupled with telescopes that observe from radio to gamma-ray wavelengths, are we able to expand our opportunities to detect new cosmic phenomena and piece together a fresh narrative of the physics of stars in their death throes.鈥�
A stellar sign
The gravitational signal, named GW170817, was first detected on Aug. 17 at 7:47 a.m. Central Daylight Time; the detection was made by the two identical LIGO detectors, located in Hanford, Wash., and Livingston, La. The LIGO Livingston observatory is located on 海角社区 property, and 海角社区 faculty, students and research staff are major contributors to the international scientific collaboration.
The information provided by the third detector, Virgo, situated near Pisa, Italy, enabled an improvement in localizing the cosmic event. At the time, LIGO was nearing the end of its second observing run since being upgraded in a program called Advanced LIGO, while Virgo had begun its first run after recently completing an upgrade known as Advanced Virgo.
Each observatory consists of two long tunnels arranged in an 鈥淟鈥� shape, at the joint of which a laser beam is split in two. Light is sent down the length of each tunnel, then reflected back in the direction it came from by a suspended mirror. In the absence of gravitational waves, the laser light in each tunnel should return to the location, where the beams were split at precisely the same time. If a gravitational wave passes through the observatory, it will alter each laser beam鈥檚 arrival time, creating an almost imperceptible change in the observatory鈥檚 output signal.
鈥淭he staff of the LIGO Livingston Observatory, together with students and scholars in residence, and including many from 海角社区, have worked hard for many years to operate and improve the detector, making it capable of participating in this discovery,鈥� said Joe Giaime, head of LIGO Livingston and 海角社区 professor of physics and astronomy. 鈥淭he gravitational-wave and other astronomical observations reported today mark LIGO鈥檚 full involvement in multi messenger astronomy. Today鈥檚 scientific harvest has been sown and labored over for decades by colleagues around the world.鈥�
On Aug. 17, LIGO鈥檚 real-time data analysis software caught a strong signal of gravitational waves from space in one of the two LIGO detectors. At nearly the same time, the Gamma-ray Burst Monitor on 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, and another automated LIGO analysis indicated that there was a coincident gravitational wave signal in the other LIGO detector. Rapid gravitational-wave detection by the LIGO-Virgo team, coupled with Fermi鈥檚 gamma-ray detection, enabled the launch of follow-up by telescopes around the world.
The LIGO data indicated that two astrophysical objects located at the relatively close distance of 130 million light-years from Earth had been spiraling in toward each other. The two objects were estimated to be in a range from around 1.1 and 1.6 times the mass of the sun, in the mass range of neutron stars. A neutron star is about 20 kilometers, or 12 miles, in diameter and is so dense that a teaspoon of neutron star material has a mass of about a billion tons.
While binary black holes produce 鈥渃hirps鈥� lasting a fraction of a second in the LIGO detector鈥檚 sensitive band, the Aug. 17 chirp lasted approximately 100 seconds and was seen through the entire frequency range of LIGO 鈥� about the same range as common musical instruments. Scientists could identify the chirp source as objects that were much less massive than the black holes seen to date.
About the LIGO-Virgo Scientific Collaboration
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 100 from around the world participate in the effort through the , 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.
Additional Link:
GW170817: Observation of gravitational waves from a binary neutron star merger, Physical Review Letters:
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