Cal State Fullerton scientists have helped to identify a second direct detection of gravitational waves from a pair of black holes that collided approximately 1.4 billion years ago.
This second discovery of gravitational waves was observed Dec. 26, 2015 at 03:38:53 Coordinated Universal Time (UTC) — 7:38 p.m. Dec. 25, 2015 (PST) — by both of the twin Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors, located in Livingston, La., and Hanford, Wash.
LIGO scientists announced their latest research in the effort to detect gravitational waves today at the 228th meeting of the American Astronomical Society in San Diego.
The latest discovery, also published today 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 (European) Collaboration using data from the two LIGO detectors.
Cal State Fullerton gravitational-wave faculty researchers are Joshua Smith, associate professor of physics; Jocelyn Read and Geoffrey Lovelace, both assistant professors of physics — all members of the LIGO Scientific Collaboration — and Alfonso Agnew, professor of mathematics.
These CSUF scientists were key contributors to the first detection of gravitational waves, announced Feb. 11 by the National Science Foundation and LIGO Scientific Collaboration, a group of more than 1,000 scientists from universities across the U.S. — including CSUF — and in 14 other countries.
This first groundbreaking discovery was a milestone in physics and astronomy, confirming a major prediction of Albert Einstein’s 1915 general theory of relativity and marking the beginning of the new field of gravitational-wave astronomy. Gravitational waves carry information about their origins and about the nature of gravity that cannot otherwise be obtained.
Second Gravitational-Wave Discovery
For this second discovery, physicists concluded that these gravitational waves were produced during the final moments of the merger of two black holes, in which a quantity of energy roughly equivalent to the mass of the sun was converted into gravitational waves. The detected signal comes from the last 27 orbits of the black holes before their merger.
“With this observation of an unambiguous second binary black-hole merger, LIGO has entered into a phase of gravitational-wave astronomy, where we will now begin to understand how many black holes there are in the universe, what their masses and spins are, and how often they collide with each other to form even larger black holes,” said Smith, CSUF’s Dan Black Director of Gravitational-Wave Physics and Astronomy Center (GWPAC).
What makes this second discovery different from the previous discovery announced in February is that the black holes had much lower masses, Smith explained.
“That means that LIGO could observe those lower mass black holes orbiting around each other many more times before merging, providing more stringent tests of some aspects of Einstein’s general theory of relativity.”
For Lovelace, LIGO’s second observation of gravitational waves from merging black holes was in a way, even more impressive than the first, since the waves were much fainter this time.
“This was only possible thanks to both exquisitely sensitive detectors and to sophisticated software that compared the detectors’ measurements with computer calculations of the black holes and the gravitational waves they created,” said Lovelace, a computational relativist who uses supercomputers to simulate black-hole collisions.
“This triumph doesn’t just show that the first observation was no fluke. LIGO is a new ‘sense’ that lets us learn about the universe while testing Einstein’s theory under the most extreme conditions. This second observation has already given us a better idea about what kinds of black holes are out there and how often they merge. I can’t wait to find out what LIGO observes next.”
For this second discovery, Lovelace and colleagues from the Simulating eXtreme Spacetimes (SXS) collaboration provided numerical relativity calculations of the binary black-hole merger and compared them with the approximate computer models used to find the waves in the detector data. Lovelace and Smith also were reviewers for figures included in the journal article announcing the second discovery, and Lovelace developed some of the software used to create the figures, specifically code that filters the noise from the detector data. CSUF students also performed some of the numerical relativity calculations on the GWPAC supercomputer that helped to build and improve approximate models.
Additionally, Smith was one of the scientists who analyzed data to rule out potential noise sources and confirm that the LIGO observatories detected the second gravitational wave signal from a binary black-hole merger. He also provided comments and input to the editors for several drafts of the article announcing the latest results.
Read, an astrophysicist who works on gravitational waves from binary systems, helped configure the LIGO searches that found the first two gravitational-wave signals. She leads a LIGO group focusing on gravitational waves from binary systems that include neutron stars and is currently preparing a paper describing results from the search for these systems in LIGO’s first observing run.
“Astronomers also expect Advanced LIGO to observe neutron stars crashing together and perhaps neutron stars being torn apart by black holes. That’s particularly exciting because we think those gravitational-wave sources could also be sources of light for traditional telescopes and satellites,” said Read.
The LIGO Observatories are funded by the National Science Foundation and were conceived, built, and are operated by Caltech and MIT. Both discoveries were made possible by the enhanced capabilities of Advanced LIGO, a major upgrade to the LIGO detectors that improved the sensitivity of the instruments, enabling a large increase in the volume of the universe probed.
Advanced LIGO’s next data-taking run will begin in the 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.
“We expect dozens of these detections as we improve our sensitivity in the next few years,” Read added.
For more about the first gravitational wave discovery and CSUF’s role, visit here.