Gravitational Waves Detected 100 Years After Einstein’s Prediction

11 February 2016

Two Black Holes Merge Into One 

Northfield, Minn.—For the first time, scientists have observed ripples in the fabric of spacetime called gravitational waves, arriving at the earth from a cataclysmic event in the distant universe. This confirms a major prediction of Albert Einstein’s 1915 general theory of relativity 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 (09:51 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.

Carleton College Professor, Students Contribute to Discovery

Carleton College is a key contributor to the first direct detection of gravitational waves, led by Nelson Christensen, the George H. and Marjorie F. Dixon Professor of Physics at Carleton. He leads a research team that includes two current Carleton students, while five Carleton alumni joined Christensen and the current students as co-authors on the LIGO discovery paper and numerous associated companion papers that were released today.

“This detection has been a long time coming, but it was worth it. It is a spectacular observation of two black holes spiraling into one another to form an even more massive black hole. This will likely be one of the most important physics observations in a generation,” Christensen said.

“We now have a new way to observe the universe. Gravitational-wave astronomy is born. We have been able to peer into the blackness of the universe, but still see two black holes collide and create a new black hole. We have seen the birth of a black hole.”

“This is one of the most powerful astrophysical events ever witnessed. If you think of Einstein’s relationship between mass and energy, E=mc2, this merger of two black holes resulted in three solar masses of energy being released as gravitational wave. That is a phenomenal amount of energy released,” Christensen said. “With this discovery we begin a new era of astronomy. Who knows what we will see next? Since Galileo pointed a telescope at Jupiter, every time a new method to observe the heavens has been created new and unexpected objects have been seen.”

Christensen explains his initial LIGO research project at Carleton. “In 1999 when Carleton first joined the LIGO Scientific Collaboration I proposed a research program that would allow us to extract the physical parameters from the system that created a gravitational-wave signal. Through that research, we have been able to extract the masses of the black holes that created this signal, as well as the distance to the source, and information on how fast the final black hole is spinning. Many Carleton students have contributed to this effort over the years.”

“The masses of these black holes adds much new information to what we know about them in the universe. They were the equivalent of 29- and 36-times the mass of our sun. It was not known that there would be black holes in this mass range, but now we have seen them.”

The Carleton team is also actively involved in efforts to identify noise and clean the LIGO data. “Many Carleton students have made significant contributions to developing methods to improve LIGO’s data quality. Multiple students have published this work, even as first authors,” Christensen explained. “We have a team of students now who are actively engaged in the effort to address noise issues in the data from LIGO’s recent observing run. Their efforts are greatly appreciated by the collaboration.”

The observations by LIGO are only one part of the ongoing gravitational-wave research at Carleton. Joel Weisberg, the Herman and Gertrude Mosier Stark Professor of Physics and Astronomy and the Natural Sciences, has been part of the team that demonstrated the existence of gravitational waves in 1982. Weisberg, along with noted astrophysicist Joseph Taylor, have been using radio telescopes to observe the decay of the orbit of a binary neutron star system. The rate at which the orbit is decaying matches exactly with what one would predict for the energy loss through the emission of gravitational waves. The results of Taylor and Weisberg are considered to be the first experimental proof that gravitational waves exist.

Many Carleton students have contributed to Weisberg’s observations of the binary neutron star system. In fact, Weisberg and current Carleton junior Yuping Huang ’17 (Shantou, Guangdong, China) just submitted a paper that gives the most recent update on the orbital decay of the binary neutron star. And once again, these results fully support general relativity and the existence of gravitational waves.

With respect to the detection of gravitational waves by LIGO, Weisberg said, “We have moved from proof of the existence of gravitational waves via our observations of the first binary pulsar, to LIGO’s detection of the waves on Earth, in some 35 years. This is a testament both to the extreme difficulty in measuring gravitational waves, and to the careful work of the LIGO team members.”

The discovery was made possible by the enhanced capabilities of Advanced LIGO, a major upgrade that increases the sensitivity of the instruments compared to the first generation LIGO detectors, enabling a large increase in the volume of the universe probed—and the discovery of gravitational waves during its first observation run. The US National Science Foundation leads in financial support for Advanced LIGO. Funding organizations in Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council, STFC) and Australia (Australian Research Council) also have made significant commitments to the project. Several of the key technologies that made

Advanced LIGO so much more sensitive have been developed and tested by the German UK GEO collaboration. Significant computer resources have been contributed by the AEI Hannover Atlas Cluster, the LIGO Laboratory, Syracuse University, and the University of Wisconsin-Milwaukee. Several universities designed, built, and tested key components for Advanced LIGO: The Australian National University, the University of Adelaide, the University of Florida, Stanford University, Columbia University of the City of New York, and Louisiana State University.

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. The LSC detector network includes the LIGO interferometers and the GEO600 detector. The GEO team includes scientists at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute, AEI), Leibniz Universität Hannover, along with partners at the University of Glasgow, Cardiff University, the University of Birmingham, other universities in the United Kingdom, and the University of the Balearic Islands in Spain.

LIGO was originally proposed as a means of detecting these gravitational waves in the 1980s by Rainer Weiss, professor of physics, emeritus, from MIT; Kip Thorne, Caltech’s Richard P. Feynman Professor of Theoretical Physics, emeritus; and Ronald Drever, professor of physics, emeritus, also from Caltech.

Virgo research is carried out by the Virgo Collaboration, consisting of more than 250 physicists and engineers belonging to 19 different European research groups: 6 from Centre National de la Recherche Scientifique (CNRS) in France; 8 from the Istituto Nazionale di Fisica Nucleare (INFN) in Italy; 2 in The Netherlands with Nikhef; the Wigner RCP in Hungary; the POLGRAW group in Poland; and the European Gravitational Observatory (EGO), the laboratory hosting the Virgo detector near Pisa in Italy. 

Carleton College Gravitational-Wave Research Members

Professor Nelson Christensen joined Carleton College in 1999. Since that time his primary research activity has been in gravitational-wave detection with LIGO. His research, funded by the National Science Foundation continuously since 2000, has involved the development of parameter estimation techniques, methods to detect gravitational waves from the Big Bang, and methods to identify and remove sources of noise in the LIGO detectors.

Professor Joel Weisberg’s research at Carleton College pertaining to the binary pulsar has been funded continuously from the National Science Foundation since 1987.

“We have continued to monitor the binary pulsar from the time I came to Carleton into the present. This research has included Carleton students. Their contributions have been essential right up to a recent joint submission of a paper my student Yuping Huang ‘17.”

Over the last 17 years a number of Carleton College students have participated in LIGO’s effort to observe gravitational waves. Currently five of these alums are members of the LIGO Scientific Collaboration, and appear as co-authors on this important discovery paper.

Adam Libson ’04 is currently a post-doctoral scholar at the Massachusetts Institute of Technology. Libson is a co-author on the LIGO discovery paper. One of his research efforts has evolved over the years, and was applied in LIGO’s discovery, “My first experience with original research was working on data analysis for LIGO at Carleton. Guided by Prof. Christensen, I worked to develop techniques to estimate the parameters of compact binary inspirals detected by LIGO. These techniques are now being used by groups around the world and were even used in the analysis of the announced gravitational wave event. I am extremely proud to have contributed to this effort.” Libson’s still contributing to LIGO’s science effort: “I am now working as a postdoc at MIT on an experiment looking at the fundamental quantum noise that should eventually limit the Advanced LIGO detectors. My time at Carleton provided excellent preparation for this work. While my research at Carleton concerned data analysis, I was exposed to a fantastic array of experimental techniques in my lab classes. Additionally, working on my comprehensive project allowed me to broaden my knowledge and to explore the physics of gravitational wave detection.”

Michael Coughlin ’12 is presently a pursuing a PhD in physics at Harvard University, and is also a co-author on the LIGO discovery paper. Coughlin noted, “Working on LIGO has given me the opportunity to not only contribute to one of the most important discoveries there will ever be in gravitational physics but also work together with scientists across all disciplines to do so.” And with respect to his education at Carleton, he added, “Carleton fosters a broad and collaborative learning environment that makes for a successful transition to performing real science in a world that requires a breadth of knowledge. In addition, Carleton’s emphasis on undergraduate research early in their college career gives students an opportunity to be successful from early on.”

Tom Callister ’13 is presently a PhD student in physics at the California Institute of Technology. He is also a co-author on LIGO’s discovery paper. Callister observed, “I feel incredibly fortunate to be a part of LIGO in this exciting time. Along with many others from Carleton, I am working to detect the gravitational wave “stochastic background,” the combination of all sources too distant to observe individually. In the coming years, I expect that the continued observation of gravitational waves will yield many new (hopefully unexpected!) insights about our Universe.” Speaking about the training he received at Carleton he noted, “My experiences at Carleton, particularly the instruction and mentorship I received in the Physics & Astronomy department, have definitely given me a huge head start both as a graduate student and as a scientific researcher. Carleton’s liberal arts curriculum not only gave me a solid grounding in physics, but taught me to communicate effectively, solve problems creatively, and work collaboratively with my peers. The emphasis placed on independent student research also went a long way in preparing me for my current research as a graduate student.”

Santiago Caride ’08 is a post-doctoral scholar at Texas Tech University, and a co-author on the LIGO discovery paper. Caride explained his contributions to LIGO, “I have worked on improving our search programs. I have integrated a new algorithm (barycentric resampling) that has made searches for continuous gravitational waves (from pulsars) over an order of magnitude faster, computationally; it will be used extensively in such searches in Advanced LIGO data. I am using this method in a search in LIGO data for gravitational waves from a nearby globular cluster.” When asked about his scientific training at Carleton, Caride replied, “Carleton gave me my foundations in LIGO specifically and in being a scientist in general. Graduate school has made me a good scientist, but at Carleton I learned both how to be a scientist and what it was like to be a scientist.”

Tomoki Isogai ’10 is currently finishing his PhD in physics at MIT. Tomoki is also a co-author on the LIGO discovery paper. Isogai explained his contributions to LIGO science, “I was involved in data analysis to exclude noises in the signal data at Carleton, and has been developing a technology to improve the gravitational-wave detector sensitivity at MIT. I am very excited that I have involved with a big milestone in physics, and am thankful that Prof. Christensen gave me the opportunity.” When asked about his training at Carleton, Isogai replied, “ At Carleton, I had first-hand experiences of physics using real gravitational-wave data, and also had opportunities to go to the actual gravitational-wave observatory for research. Those hands-on experiences showed me the excitement and motivation of actual physics outside of classroom, and taught me how science is carried out in real world.”

Nathaniel Strauss ’16 (Holmen, Wisconsin) is a senior physics major at Carleton College, and has been conducting gravitational wave research with Prof. Christensen for the last three years; he is a co-author on the paper announcing the observation of gravitational waves. Strauss reflected on the detection: “Every time humanity finds a new way to look up, we see things we never expected, which can lead us down intellectual paths we never knew existed. This detection is our first step down one of those paths, and I’m very excited to find out where this path might lead in the coming years.” When asked about his contributions to LIGO’s continuing observational efforts, Strauss responded, “After I hunt down noise in the LIGO data, I post my results to the online logbook for the whole collaboration to see, and it is rewarding to see that my results can generate meaningful discussion about how to reduce this noise.”

Jialun Luo ’16 (Guangzhou, China) is a senior physics major at Carleton, and a co-author on the discovery paper. He observes, “The detection of gravitational wave shows a new way of observing our universe. Personally I am very excited about what will be discovered about our universe with the new tool available. I was involved in a few projects in LIGO, which taught me lessons of contributing in a big collaboration.”