UAH researcher part of second gravitational wave detection

UAH Center for Space Plasma and Aeronautic Research (CSPAR) research scientist Dr. Tyson Littenberg says the LIGO detections herald the age of gravitational wave astronomy.

Michael Mercier | UAH

A University of Alabama in Huntsville researcher had an integral role again as scientists with the LIGO Scientific Collaboration observed gravitational waves - ripples in the fabric of spacetime - for the second time.

The gravitational waves were detected by both of the twin Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors, located in Livingston, La., and Hanford, Wash., on Dec. 26, 2015, at 03:38:53 UTC.

Research scientist Dr. Tyson Littenberg at UAH's Center for Space Plasma and Aeronomic Research (CSPAR) helped the LIGO team develop computer algorithms that comb through data.

"These first few months of observing with LIGO were surprisingly fruitful - everyone was prepared for it to take much longer before we discovered anything - and we are already putting the finishing touches on preparations for the next observing run. Welcome to the age of gravitational wave astronomy!" says Dr. Littenberg.

A Laser Interferometer Gravitational-wave Observatory (LIGO) detector facility.

LIGO

"Here in Huntsville, we are part of the team that develops sophisticated computer algorithms to analyze the data and accurately tease out as much information as we can about each candidate signal," he says. "We also perform exhaustive analyses of all the collected data searching for instrumental artifacts that might fool those computer algorithms, in order to measure how confident we are in each detection. In addition, we run large-scale simulations to determine how sensitive our experiment is to a zoo of different gravitational wave signals."

During the merger, which occurred approximately 1.4 billion years ago, a quantity of energy roughly equivalent to the mass of the sun was converted into gravitational waves. The detected signal comes from the last 55 orbits of the black holes before their merger. Based on the arrival time of the signals - with the Livingston detector measuring the waves 1.1 milliseconds before the Hanford detector - the position of the source in the sky can be roughly determined. This second observation proves the LIGO detectors are doing their job well.

"Detecting another black hole merger is a good thing because it means that LIGO has already reached the sensitivity where it is operating as a routine observatory, and we are uncovering a population of black hole mergers in the universe - systems that had been theoretically predicted but never before observed," says Dr. Littenberg, who has been involved in LIGO-related research since 2007 and applied for UAH's 2015 acceptance as a member of the LIGO Scientific Collaboration. "By using the gravitational waves from these systems as laboratories, we will learn new things about the universe that would otherwise be inaccessible to us if we only had telescopes."

Gravitational waves carry information about their origins and about the nature of gravity that cannot otherwise be obtained, and physicists have concluded that these gravitational waves were produced during the final moments of the merger of two black holes - 14 and eight times the mass of the sun-to produce a single, more massive spinning black hole that is 21 times the mass of the sun.

A representative graphic shows two black holes merging.

LIGO/SXS

LIGO's first black hole merger detection occurred in early September during the final "shakedown" of the observatories just a few days before the official start of the observing period. Both discoveries were 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.

"The observatories continued to operate through mid-January at roughly the same sensitivity," Dr. Littenberg says. "In that time we had a marginal candidate in October which was probably a gravitational wave, but not loud enough for us to be confident beyond any reasonable doubt, and a second clear-as-a-bell signal on Dec. 26."

Since then, scientists have been hard at work improving the instruments and methods used to analyze the data, and learning from the first observations.

Advanced LIGO's next data-taking run will begin this fall. By then, further improvements in detector sensitivity are expected to allow LIGO to reach as much as 1.5 to 2 times more of the volume of the universe. The Virgo detector is expected to join in the latter half of the upcoming observing run.

"At that time, we will resume collecting data with more sensitive observatories knowing that we can look forward to several more black hole mergers along with anything else the universe has in store for us," he says.

Three major scientific themes are emerging from LIGO observations, according to Dr. Littenberg:

• "Through what mechanism, or mechanisms, do binary black holes form? Divulging this information will teach us about the formation of black holes, and about the environment in which they are born. GW150914, the September event, and GW151226, the December event, have very different mass properties. Does that imply that there are multiple ways binary black holes form, or that they can be created with a broad range of outcomes? Subsequent observations of similar systems will allow us to accurately test different hypotheses."
• "We also use the gravitational wave signals as a way of testing our theoretical understanding of gravity, which is encapsulated in Einstein's General Theory of Relativity. So far, Einstein's theory has passed each gravitational wave test. Each observation is a new opportunity to test our most basic physical theories in novel ways, which will ultimately lead to deeper understanding of how the universe works at the most fundamental level."
• "In the months and years to come we will continue to measure mergers of binary black holes which, in its own right, is very exciting stuff. However, there is much more that we expect the universe has to say. As LIGO's sensitivity continues to improve, and as other observatories start collecting data, different sources of gravitational waves will reveal themselves. What is the next gravitational wave source going to be? Will it be a signal that was predicted, as were black hole mergers, or will it be something totally unexpected? We are exploring the universe in a brand new way and incredible surprises could be lurking around the next bend."

The LIGO Observatories are funded by the National Science Foundation (NSF), and were conceived, built and are operated by Caltech and MIT. This 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.

LIGO research is carried out by the LIGO Scientific Collaboration (LSC), a group of more than 1,000 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.

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.

The NSF 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, the ARCCA cluster at Cardiff University, the University of Wisconsin-Milwaukee, and the Open Science Grid. Several universities designed, built, and tested key components and techniques for Advanced LIGO: The Australian National University, the University of Adelaide, the University of Western Australia, the University of Florida, Stanford University, Columbia University in the City of New York, and Louisiana State University. 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 Germany, and the University of the Balearic Islands in Spain.