Press release GW170817 (2023)

The discovery marks the first cosmic event observed in both gravitational waves and light.

Scientists have for the first time directly detected gravitational waves, ripples in space-time and light from the spectacular collision of two neutron stars. This is the first time a cosmic event has been observed in both gravitational waves and light.

The discovery was made using the US-based Laser Interferometer Gravitational-Wave Observatory (LIGO) and Europe-based Virgo detector; and about 70 ground and space observatories.

Neutron stars are the smallest and densest known stars and are formed when massive stars explode in supernovae. As these neutron stars spiraled toward each other, they emitted gravitational waves that lasted about 100 seconds; When they collided, a flash of light was emitted in the form of gamma rays and seen about two seconds after the gravitational waves hit Earth. In the days and weeks following the crash, other forms of light or electromagnetic radiation were detected, including X-ray, ultraviolet, optical, infrared, and radio waves.

The observations have given astronomers an unprecedented opportunity to study a collision between two neutron stars. For example, observations from the US Gemini Observatory, the European Very Large Telescope and the Hubble Space Telescope are revealing signatures of newly synthesized material, including gold and platinum, and solving a decades-old mystery of where about half of all elements heavier than iron are found. they are produced.

The LIGO-Virgo results are published in the journal todayPhysical Verification Letters; Additional articles from the LIGO and Virgo collaborations and the astronomical community have been submitted or accepted for publication in various journals.

"It is tremendously exciting to witness a rare event that is changing our understanding of how the universe works," said France A. Córdova, director of the National Science Foundation (NSF), which funds LIGO. Goal that many of us had, namely to observe rare cosmic events simultaneously with traditional and gravitational-wave observatories. Only through NSF's four-decade investment in gravitational-wave observatories, along with telescopes observing everything from radio waves to gamma rays, can we expand our ability to discover new cosmic phenomena and piece together a new narrative about the physics of stars in their agony . ”

a zodiac sign

The gravitational signal, named GW170817, was first spotted on August 17 at 8:41 am. M. Easter time; detection was by two identical LIGO detectors in Hanford, Washington and Livingston, Louisiana. Information from the third detector Virgo near Pisa, Italy, allowed us to improve the location of the cosmic event. At the time, LIGO was nearing the end of its second observing run since it was updated in a program called Advanced LIGO, while Virgo had begun its first run, having recently completed an update called Advanced Virgo.

The NSF-funded LIGO observatories were designed, built, and operated by Caltech and MIT. Virgo is funded by the Istituto Nazionale di Fisica Nucleare (INFN) in Italy and the Center National de la Recherche Scientifique (CNRS) in France and operated by the European Gravitational Observatory. About 1,500 scientists from the LIGO Scientific Collaboration and the Virgo Collaboration work together to operate the detectors and to process and understand the gravitational-wave data they collect.

Each observatory consists of two long tunnels arranged in an L-shape, at the intersection of which a laser beam is split in two. Light is sent down the length of each tunnel and then reflected back in the direction it came from by a suspended mirror. In the absence of gravitational waves, the laser light should return to where the beams split at exactly the same time in each tunnel. When a gravitational wave passes through the observatory, it alters the arrival time of each laser beam, causing an almost imperceptible change in the observatory's output signal.

On Aug 17, LIGO's real-time data analysis software picked up a strong gravitational-wave signal from space at one of LIGO's two detectors. At about the same time, NASA's Fermi Space Telescope gamma-ray burst monitor had detected a gamma-ray burst. The LIGO-Virgo analysis software put the two signals together and found that it was highly unlikely that they were a coincidental match, and further automated LIGO analysis showed that there was a matching gravitational-wave signal at the other LIGO detector . The LIGO-Virgo team's rapid detection of gravitational waves, together with Fermi's detection of gamma rays, enabled follow-up launches of telescopes around the world.

The LIGO data showed that two astrophysical objects located a relatively small distance of about 130 million light-years from Earth had spiraled towards each other. It appeared that the objects were not as massive as binary black holes, objects that LIGO and Virgo had previously discovered. Instead, the inspiring objects were estimated to be around 1.1 to 1.6 times the mass of the Sun, which is in the mass range of neutron stars. A neutron star is about 20 kilometers or 12 miles across and so dense that a teaspoon of neutron star material has a mass of about a billion tons.

While binary black holes produce 'chirps' in the sensitive band of the LIGO detector, the chirp of August 17 lasted about 100 seconds and was seen across LIGO's entire frequency range, about the same range as ordinary musical instruments. The scientists were able to identify the source of the chirping as objects much less massive than the black holes observed so far.

"It immediately struck us that the source would likely be neutron stars, the other coveted source we had hoped to see and which promised the world we would see," says David Shoemaker, a LIGO Scientific Collaboration spokesman and lead Researchers Scientists at MIT. Kavli Institute for Astrophysics and Space Research. “From reporting detailed models of the inner workings of neutron stars and the emissions they produce, to more fundamental physics like general relativity, this event is so rich. It is a gift that is passed on.”

"Our background analysis showed that an event of this magnitude happens randomly less than once every 80,000 years, so we immediately recognize it as very reliable evidence and a remarkably close source," adds Laura Cadonati, professor of physics at Georgia Tech deputy spokesperson for the LIGO Scientific Collaboration. "This discovery has really opened the doors to a new kind of astrophysics. I hope it will be remembered as one of the most studied astrophysical events in history."

Theorists have predicted that when neutron stars collide, they should emit gravitational waves and gamma rays, along with powerful jets emitting light across the entire electromagnetic spectrum. The gamma-ray burst detected by Fermi and confirmed shortly thereafter by the European Space Agency's INTEGRAL gamma-ray observatory is called the short gamma-ray burst; The new observations confirm that at least some brief gamma-ray bursts are produced by neutron star mergers, which has only been theorized so far.

"For decades we have suspected that brief gamma-ray bursts were driven by neutron star mergers," says Julie McEnery, Fermi Project scientist at NASA's Goddard Space Flight Center. “Now, with the incredible LIGO and Virgo data for this event, we have the answer. The gravitational waves tell us that the merged objects had masses equivalent to neutron stars, and the gamma-ray flare tells us that the objects are unlikely to be black holes, since a collision with black holes is not expected to cause them to be emit light.

But while one mystery seems to be solved, new mysteries have emerged. The brief gamma-ray burst observed was one of the closest yet, but surprisingly faint for its distance. Scientists are beginning to come up with models for why this might be, says McEnery, adding that new insights are likely to emerge in the coming years.

A speck in the sky

Although LIGO detectors first detected the gravitational wave in the United States, Virgo played a key role in the story in Italy. Due to its orientation with respect to the source at the time of detection, Virgo has regained a small signal; In combination with the signal sizes and timing in the LIGO detectors, this allowed the scientists to accurately triangulate the position in the sky. After doing extensive research to ensure the signals were not an artifact of the instrumentation, the scientists concluded that a gravitational wave was coming from a relatively small speck in the southern sky.

"This event has the most accurate localization of any gravitational wave detected so far in the sky," says Jo van den Brand of Nikhef (the Dutch National Institute for Subatomic Physics) and VU University Amsterdam, who is spokesperson for the Virgo collaboration. "This record-breaking precision enabled the astronomers to conduct follow-up observations that yielded a variety of impressive results."

"This result is a great example of the effectiveness of teamwork, the importance of coordination and the value of scientific collaboration," adds EGO Director Federico Ferrini. "We are pleased to have played our instrumental role in this extraordinary scientific challenge: Without Virgo, locating the source of the gravitational wave would have been very difficult.

Fermi was able to provide a location that was later confirmed and greatly refined using the coordinates of the combined LIGO-Virgo detection. With those coordinates, hours later, a handful of observatories around the world could begin searching for the region of sky where the signal was supposed to be coming from. A new point of light, resembling a new star, has been found for the first time by optical telescopes. Ultimately, about 70 ground and space observatories observed the event at their representative wavelengths.

"This discovery opens the window of a long-awaited 'multi-messenger' astronomy," says Caltech's David H. Reitze, executive director of the LIGO lab. "It's the first time we've observed a catastrophic astrophysical event in both gravitational waves and electromagnetic waves, our cosmic messengers. Gravitational-wave astronomy offers new opportunities to understand the properties of neutron stars in ways that cannot be achieved with electromagnetic astronomy alone.”

A fireball and a glow

Each electromagnetic observatory will publish its own detailed observations of the astrophysical event. A general picture is now emerging from all the observatories involved, further confirming that the initial gravitational-wave signal did indeed come from a pair of inspiring neutron stars.

About 130 million years ago, the two neutron stars were only about 300 kilometers or 200 miles apart in their final moments of orbiting each other, and picked up speed as they closed the distance between them. As the stars spiraled faster and closer together, they stretched and distorted surrounding spacetime, radiating energy in the form of powerful gravitational waves before colliding with each other.

At the moment of the collision, most of the two neutron stars merged into one ultradense object that emitted a "fireball" of gamma rays. The first gamma-ray measurements, combined with the detection of gravitational waves, also confirm Einstein's general theory of relativity, which predicts that gravitational waves should travel at the speed of light.

Theorists have predicted that what follows the initial fireball is a "kilonova," a phenomenon in which material left over from the neutron star's collision, glowing with light, is ejected from the immediate region into space . The new light-based observations show that these collisions create heavy elements such as lead and gold, which are then dispersed throughout the Universe.

Over the coming weeks and months, telescopes around the world will continue to monitor the afterglow of neutron star mergers, collecting more evidence about the various stages of the merger, how it interacts with its environment, and the processes that create the heavier elements of the universe. .

“When we first planned LIGO in the late 1980s, we knew that we would eventually need an international network of gravitational-wave observatories, including Europe, to help locate gravitational-wave sources for light-based telescopes to study the to track and study afterglows of events like this neutron star merger,” says Caltech's Fred Raab, LIGO associate director of observatory operations. "Today we can say that our gravitational-wave network is working brilliantly in tandem with light-based observatories to usher in a new era in astronomy, and it will improve with the planned addition of observatories in Japan and India."

LIGO is funded by theNSF, and operated byCaltechjCON, who designed LIGO and led the Initial and Advanced LIGO projects. Financial support for the Advanced LIGO project was provided by the NSF with Germany (Max-Planck-Gesellschaft), the UK. (Council of Scientific and Technological Institutions) and Australia (Research Council of Australia) make significant commitments and contributions to the project.

More than 1,200 scientists and about 100institutionsfrom around the world join the effort through theLIGO Scientific Cooperation, which includes the GEO collaboration and the Australian OzGrav collaboration. Other partners are listed inhttp://ligo.org/partners.php

The Virgo collaboration consists of more than 280 physicists and engineers belonging to 20 different European research groups: six of themNational Center for Scientific Research(CNRS) in France; eight o'clockNational Institute of Nuclear Physics(INFN) in Italy; two in Holland withNikhef; the MTA Wigner CPR 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.

Written by Jennifer Chu, MIT News Office

RELATED LINKS

Additional LIGO Scientific Collaboration Resources:http://ligo.org/detections/GW170817.php

Additional media assets:http://mediaassets.caltech.edu/nsm

Caltech Story:https://www.caltech.edu/news/caltech-led-teams-strike-cosmic-gold-80074

History of the LIGO laboratory:https://www.ligo.caltech.edu/news/ligo20171016

Documents and related data:https://www.ligo.caltech.edu/page/detection-companion-papers

*MEDIA CONTACTS

Kimberly Allen, MIT
allenkc@mit.edu; +1 617-253-2702

Emily Velasco, Caltech
evelasco@caltech.edu; +1 626-395-6487

Jason Maderer, Georgia-Technology
maderer@gatech.edu; +1 404-385-2966

Severine Perus, Jungfrau-I
severine.perus@ego-gw.it; +39 050 752 325

Aya Collins, National Science Foundation
acollins@nsf.gov; +1 703-292-7737

Pictures

High resolution. Versions of these graphics can be found in our gallery.

GW170817 numbers

Masses of neutron stars and black holes

Current operational installations on the global network include the twin LIGO detectors in Hanford, Washington and Livingston, Louisiana: Virgo in Italy and GEO600 in Germany.

Merging of neutron stars in gravity and matter

Virgo helps locate gravitational wave signals

GW170817: A World Event in Astronomy

Artist's impression of two merging neutron stars.

The LIGO data shows the 'chirping' sound made as the two neutron stars breathe in.

Videos

Neutronensternverschmelzung (Credit: Christopher W. Evans/Georgia Tech)

Jets and debris from colliding neutron stars (Credit: NASA/Goddard Space Flight Center/CI Laboratory)

Last Dance of the Neutron Star Couple (Credits: W. Chestnut/T. Kawamura/B. Giacomazzo/R. Ciolfi/A. Endrizzi)

Gravitational waves, flashes of light (Credit: LIGO/Virgo)

Zooming in on the source of gravitational waves (Credit: LIGO-Virgo)

Last flight of the neutron star pair (Credit: LIGO-Virgo/Aaron Geller/Northwestern University)

Listen to the wave (Credit: Alex Nitz/Max Planck Institute for Gravitational Physics/LIGO)