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Einstein Was Right

The story of how a group of physicists detected a tiny noise from a cosmic event and changed astronomy forever.

ligo director david reitze honored

REITZE WINS 2017 NATIONAL ACADEMY OF SCIENCES AWARD FOR SCIENTIFIC DISCOVERY

On April 20, 2017, David Reitze, UF professor of physics and current director of the Laser Interferometer Gravitational-Waves Observatory (LIGO) at Caltech, will be recognized by the National Academy of Sciences for his leadership at LIGO, which has detected two chirps of gravitational waves from colliding black holes. The discovery is significant because it demonstrates that the fabric of space-time is rippled by enormous outputs of energy, as Albert Einstein predicted in 1916. Learn more about gravitational waves and their detection, below.

Reitze was instrumental in LIGO's growth into a state-of-the-art facility capable of precise detection of faraway, long-ago cosmic events. He built an interdisciplinary team of scientists, several of whom continue to work at UF on its LIGO team. Indeed, the UF LIGO team designed the algorithm that enabled the detection of the gravitational waves.

Dates:

1st chirp: September 14, 2015 (less than 72 hours after beginning operations!)—analyzed and “discovered” on February 11, 2016

2nd chirp: December 26, 2015

Published June 15 in Physical Review Letters, announced in San Diego during a meeting of the American Astronomical Society.

Read UF press release.


Professors Guido Mueller and Bernard Whiting with a scaled-down version of the LIGO optics.

LIGO

The LIGO Scientific Collaboration, which runs the project, is an international and interdisciplinary group of almost 1,000 scientists, including 26 from UF. "It's amazing that Reitze was able to coordinate all these people," says Guido Mueller of the UF LIGO project. "Many of us are not astrophysicists. The strength of the LIGO collaboration is its various enterprises." Because multiple detections of gravitational waves are the only way to confirm the signal, data is corroborated with that of the Virgo Collaboration, a similar project in Europe. As other detectors set up shop, scientists anticipate a steady stream of discoveries through gravitational astronomy. Interferometers around the globe "may give us triggers to look at our data," says David Tanner of UF LIGO. UF's algorithm was 15 years in the making, says Guenakh Mitselmakher of UF LIGO. The algorithm allowed LIGO the unique opportunity to identify the gravitational waves, which arrived at other instruments that did not have sufficient algorithms to pick it up. The program that first detected the waves seen in September 2015, Coherent WaveBurst, was developed in 2004 by the UF LIGO group, a team of faculty, graduate students, and postdocs, and has since undergone continual updating and improvement.

Additional support came through a 17-year umbrella grant from the National Science Foundation. The project is still growing, with a third LIGO detector planned for location in India. In the next five years, LIGO hopes to become sensitive enough to detect individual black holes, not just their mergers. Other gravitational wave detector projects include space-based instruments to detect signals from slower events, such as the acceleration of supermassive black holes. The team's timeline had anticipated these projects to be rolled out by 2034, but Bernard Whiting of UF LIGO says that they now may be operational as soon as 2030 or 2029.

Originally published in Ytori 1(1), the Liberal Arts & Sciences magazine.

A scientist works with a 40-kilogram test mass in the Livingston, La., interferometer’s core optics.
Aerial view of Advanced LIGO Livingston, La.:  The interferometer has precisely aligned mirrors in its two arms, which are each 4 km. long.

how ligo works

The interferometer is a humorous yet accurate name: it involves the use of mirrors to split and reunite a laser beam, then reflect it back onto itself, which cancels out the light beam's waves in a condition known as "anti-phase." Because gravitational waves distort space, the distance between the mirrors changes, and the light goes out of anti-phase. That interference, however small, can be measured, albeit only after intense efforts to detect a tiny event in an enormous instrument. The LIGO detectors are approximately four kilometers wide, and the laser beams must be perfectly aligned to detect the wobble between the mirrors. It is striking that the mirror displacement caused by gravitational waves is 10,000 times smaller than the size of a proton and yet can be measured, says Klimenko.

gravitational waves

Scientists often use the metaphor of the ripples in a pond after a stone falls in to explain the gravitational effects on space-time. Typically, such ripples have been "seen" through radio astronomy, which measures the electromagnetic spectrum; that is, the stone has fallen into the water far from the shore, and astronomers observe the ripples from afar. For the first time, the ripples of gravitational waves have been detected without a telescope, as they arrived at the edge of the cosmic pond.


Advanced LIGO, a recent upgrade of the LIGO instruments in Louisiana and Washington State, had been online for less than 72 hours before the first chirp was detected on September 14, 2015. The team of roughly 1,000 scientists from around the world intended to operate the instruments in "engineering mode" for one month, but the universe had other plans. Two weeks before the "science mode" of the project was set to be deployed, the search algorithm developed at UF discovered a gravitational wave signal detected by twin LIGO interferometers. The finding was so unexpected that only after months of analysis did LIGO researchers confirm the waves produced by two merging black holes; the magnitude was enough that the chirp is very unlikely to be anything else, making the detection a monumental discovery. "I don't think anything like that exists in any other field. This is a miracle," says Sergey Klimenko, a professor of physics at UF who has worked to develop the detection algorithm with Mitselmakher since 1997.

The waves arrived at LIGO's twin detectors within seven-thousandths of a second of each other, just past 4:50 a.m. in Livingston, La., and 2:50 a.m. in Hanford, Wash., showing that the two black holes, 29 and 36 times the mass of our Sun, had merged in a similar time frame after orbiting each other at a speed of approximately 100 orbits per second. While this may seem like current events, cosmically speaking, the collision occurred approximately 1.3 billion years ago.

LIGO's twin detectors heard a second chirp on December 26, 2015; another pair of black holes had combined, creating a mass 21 times that of our sun and warping space-time. One sun's worth of mass was converted into energy and carried away by gravitational waves, which reached Earth over a distance-time of 1.4 billion light-years. Analysis of the signal showed that the pair of black holes had orbited each other for years, producing the waves in the last 55 orbits before their epic merger. In other words, the experience of time and space on Earth is infinitesimal compared with the cosmic magnitude of black hole formation and collision.

uf and ligo

THE UF CONNECTION

By Rachel Wayne

Although LIGO was constructed and is operated by scientists at Caltech and MIT, UF has had an instrumental role (pun intended) in the latest stage, the Advanced LIGO project. From 1996 to present, UF has engineered the "input optics" system, which takes the light from the laser conditions and expands the beam size, and delivers it to the main interferometer, for all of LIGO's projects. After leading UF's input optics (IO) program beginning in 1996, Reitze relocated to Caltech, where he currently serves as executive director of LIGO. "The IO was in such a good shape and the entire IO team at UF was so strong that finishing the $5 million project turned out to be fairly straightforward," said Mueller, who with Tanner has led the team since Reitze's transfer to Caltech in 2011.


UF'S HISTORY WITH LIGO

By Steve Orlando

The University of Florida has been involved with LIGO since its inception. That involvement began with an email message sent in October 1995 to the physics faculty by Guenakh Mitselmakher, who had just joined the physics department as a senior professor. The message was about research opportunities in LIGO and was motivated by Mitselmakher's knowledge of the LIGO project from his work with Barry Barish (then LIGO laboratory director) in high energy physics. A number of faculty responded. The initial group of active participants consisted of Mitselmakher, Bernard Whiting, and physics professors David Reitze and David Tanner. Shortly after this beginning, two other current faculty members joined the UF LIGO group: Sergey Klimenko in 1997 and Guido Mueller in 1998.

Florida's interest was well timed, as the LIGO Laboratory, the consortium managed by Caltech and MIT, was just beginning to design the initial LIGO detector. There were a number of meetings, conferences and lab visits between UF scientists and LIGO scientists.

A critical meeting took place in February 1996, when Mitselmakher, Reitze, Tanner, and Whiting visited the LIGO laboratory to discuss whether and how UF could contribute to the initial LIGO detectors, then beginning their construction. The outcome of this discussion was that the University of Florida took responsibility for the Input Optics (IO) of LIGO, one of the most complex and diverse systems in the entire interferometer. In doing so, Florida was the first institution outside the original Caltech-MIT collaboration to have an essential role in LIGO.

Two black holes are entwined in a gravitational tango in this artist's conception. (Photo courtesy NASA.)