For the first time, scientists have observed ripples in the fabric of spacetime, called gravitational waves, arriving at Earth from a cataclysmic event in the distant universe. This observation confirms a major prediction of Albert Einstein’s general theory of relativity, published in 1916, and opens an unprecedented new window onto the cosmos.

Gravitational waves carry information about their dramatic origins and about the nature of gravity that cannot otherwise be obtained. Physicists have concluded that the detected gravitational waves were produced during the final fraction of a second of the merger of two black holes to produce a single, more massive spinning black hole. This collision of two black holes had been predicted but never observed. 

The gravitational waves were detected on September 14, 2015 at 5:51 a.m. Eastern Daylight Time (9:51 a.m. UTC) by both of the twin Laser Interferometer Gravitational-wave Observatory (LIGO) detectors, located in Livingston, Louisiana, and Hanford, Washington, USA. The LIGO Observatories are funded by the National Science Foundation (NSF), and were conceived, built, and are operated by Caltech and MIT. The discovery, accepted for publication in the journal Physical Review Letters, was made by the LIGO Scientific Collaboration (which includes the GEO Collaboration and the Australian Consortium for Interferometric Gravitational Astronomy) and the Virgo Collaboration using data from the two LIGO detectors.

"This first direct detection of gravitational waves is a breathtaking discovery that will stand out among the major achievements of the 21st-century science because it opens the door to many discoveries that I believe will be made in the coming decade," said Abhay Ashtekar, Director of the Institute for Gravitation and the Cosmos at Penn State University and Holder of the Eberly Family Chair in Physics at the University. "This first detection by LIGO originated in a collision of two black holes orbiting each other, which we call binary pairs. It has already resolved the long debated issue of the existence of binary pairs with masses tens of times greater than that of our Sun," Ashtekar said.

"Gravitational waves are quite literally ripples in the fabric of our universe," said LIGO scientist Chad Hanna, an assistant professor of physics at Penn State affiliated with the Institute for Gravitation and the Cosmos. "This new way of discovering how the universe functions gives us the ability to begin to understand the universe in a way that simply has been impossible before. Just as Galileo with his small telescope could not have predicted what the Hubble Space Telescope has been able to show us now, it is almost impossible to predict how our new ability to detect gravitational waves will change our fundamental understanding of the universe." 

Hanna, who is co-chair of one of LIGO’s largest astrophysics working groups, the Compact Binary Coalescence group, said "We can expect, because of this fundamentally new way of observing the universe, that in one hundred years what our children's children will know will be profoundly different from what we now are able to know."

Penn State's Institute for Gravitation and the Cosmos has had an important role in developing gravitational-wave science for two decades. In 2001 National Science Foundation awarded the Penn State founding group the designation as a National Science Foundation Physics Frontier Center for Gravitational Wave Science. "Our center has promoted and sustained a lively exchange of ideas between experts in diverse areas that previously had remained distinct -- resulting in the creation of a collaborative gravitational-wave-research community," said Ashtekar, who has led the Institute since its beginnings. "The resulting contributions to the development of gravitational-wave science include our mathematical and numerical analyses concerning general relativity, our interface with relativistic astrophysics, and our innovative contributions to data analysis."

Adding to the excitement of LIGO's historic first detection of a gravitational wave was the scramble by scientists controlling other types of astronomical detectors to quickly look for other signals from the wave that LIGO was not designed to detect. "We had been planning for these observations for several years," said Penn State Professor of Astronomy and Astrophysics David Burrows, who leads the instrument team for the X-ray Telescope on the Swift observatory. "In order to try to find an X-ray or ultraviolet counterpart for a gravitational wave, we had to rapidly point NASA’s orbiting Swift observatory to search for the precise location where the wave had originated." The science and flight operations of the Swift satellite are controlled by Penn State from the Mission Operations Center on the University Park campus.

Swift Mission Director and Penn State Professor of Astronomy and Astrophysics John Nousek added "Among space telescopes, Swift is uniquely capable of rapidly responding to unpredictable events like this, which are a challenge to capture because the evidence they produce lasts such a short time. Swift's astronomical follow-ups will play a crucial role in advancing the understanding of LIGO's detections." Results of the Swift observations now are being prepared for publication.

More information from Penn State about LIGO is at ligo.psu.edu. More information from the LIGO Scientific Collaboration is at https://www.ligo.caltech.edu/. LIGO research is carried out by the LIGO Scientific Collaboration (LSC), a group of more than 1000 scientists from universities around the United States and in 14 other countries. More than 90 universities and research institutes in the LSC develop detector technology and analyze data; approximately 250 students are strong contributing members of the collaboration.