Brazilians integrate consortium that detected gravitational waves and black holes

Discoveries open up new prospects for the study of the universe. Brazilian researchers' participation in the international collaboration is supported by FAPESP.

By Elton Alisson  |  Agência FAPESP – After a series of rumors in recent months, an international consortium of scientists that includes researchers from Brazil confirmed on February 11 the first direct detection of gravitational waves, created by two black holes as they collided and merged. Gravitational waves are ripples in the fabric of spacetime that were predicted by Albert Einstein (1879-1955) a century ago.

The announcement was made by scientists from the Laser Interferometer Gravitational-Wave Observatory (LIGO) at a press conference hosted by the US National Science Foundation (NSF) in Washington, DC, and in an article published by the journal Physical Review Letters.

More than 1,000 scientists affiliated with 90 universities and research institutions in 15 countries in addition to the United States are involved in the LIGO Scientific Collaboration (LSC).

The participants include Odylio Denys de Aguiar, Marcio Constâncio Júnior, César Augusto Costa, Allan Douglas dos Santos Silva, Elvis Camilo Ferreira and Marcos André Okada, all six of whom are affiliated with Brazil’s National Space Research Institute (INPE), and Riccardo Sturani, a researcher at São Paulo State University’s Institute of Theoretical Physics (IFT-UNESP).

The researchers from Brazil participate in the LSC through projects supported by FAPESP.

“Ladies and gentlemen, we have detected gravitational waves. We did it,” announced David Reitze, LIGO’s executive director, at the press conference.

Using LIGO’s two widely separated identical detector sites working in unison as a single “observatory”, one in Livingston, Louisiana, and the other 3,000 km away in Hanford, Washington state, the researchers said they observed gravitational waves produced by a cataclysmic event, named GW 150914, in a galaxy more than 1 billion light years from Earth.

The gravitational waves were detected on September 14, 2015, at 5:51 a.m. EDT (6:51 Brasília time).

The scientists concluded that the detected gravitational waves were produced during the final fraction of a second of the merger of two black holes spinning around each other like tops. The collision and merger created a single more massive black hole, irradiating energy as gravitational waves.

The disturbance the antennas picked up was converted by LIGO researchers into sound waves, producing a now famous “chirp”. The shape of such signals created by the rise and fall in frequency and amplitude of the waveforms can be used to discern the size and mass of black holes, helping to determine how strong the event was at its source.

During the final milliseconds of the black hole merger, the researchers estimated that the peak energy radiated by the gravitational waves was 10 times greater than the combined power of the light radiated by all the stars in the observable universe.

“It's the first time the universe has spoken to us through gravitational waves,” Reitze said, adding that the two black holes were only about 150 km across and had similar masses, weighing at 36 times and 29 times the mass of the Sun. “As they get closer and closer together, they merge, and there’s this burst of gravitational waves that travels for 1.3 billion years.”

Detection system

Gravitational waves are caused by some of the most violent phenomena in the cosmos, such as collisions and mergers of massive compact stars. Their existence was predicted by Albert Einstein in 1916 on the basis of his theory of general relativity.

Einstein postulated that accelerating massive objects would shake spacetime so much that waves of distorted space would radiate from the source. These ripples in the gravitational field, or gravitational waves, travel through the universe at the speed of light, bearing information about their origins as well as valuable clues to the nature of gravity itself.

To detect gravitational waves directly as they arrive here on Earth, however, the scientists measured a distance between detector observations equivalent to about one-thousandth the diameter of a proton.

Laser interferometry, the technique they used to detect the gravitational waves and locate their sources, measures the difference between observations by detectors placed very far apart. LIGO’s detectors were developed and are operated by the Massachusetts Institute of Technology (MIT) and the California Institute of Technology (Caltech), both in the US.

“This first detection of gravitational waves opens up a new window for observation of the universe and marks the onset of a new era of research in astronomy and astrophysics,” said César Augusto Costa, a researcher at INPE.

Aguiar’s research group at INPE is working on upgrades to LIGO’s seismic isolation system using chilled mirrors to counter the effect of vibrations and on characterization of the detectors to identify and exclude sources of noise.

Sturani’s group at IFT-UNESP is modeling and analyzing signal data from coalescing binary systems. This work is important because gravitational waves interact very weakly with matter, so that effective analytical techniques and precise theoretical modeling of signals are required in addition to high-performance detectors, Sturani explained.

“This first detection of gravitational waves by LIGO is the result of observations made between August and September of last year,” he said. “Collection of the last set of data was completed in January, and the full analysis will be published in April.”

In addition to the article in Physical Review Letters, the researchers expect to publish 12 other papers with results of the collaboration in the coming months.

The article “Observation of Gravitational Waves from a Binary Black Hole Merger” (doi: http://dx.doi.org/10.1103/PhysRevLett.116.061102) by LIGO Scientific Collaboration & Virgo Collaboration can be read at http://link.aps.org/doi/10.1103/PhysRevLett.116.061102.

 

Numerical simulations of the gravitational waves emitted by the inspiral and merger of two black holes. The colored contours around each black hole represent the amplitude of the gravitational radiation; the blue lines represent the orbits of the black holes; the green arrows represent their spins (image: NASA Ames Research Center/PRL)

Aerial view of LIGO detector in Hanford, Washington (photo: NSF)