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Epoch-making Discovery of Gravitational Waves
On the 11th of last February the US-based Laser Interferometer Gravitational-Wave Observatory (LIGO) formally announced the recent detection of gravitational waves. This was the first time to directly detect gravitational waves—the Holy Grail of physics—and thus represents one of the most significant discoveries in physics over the past century. A research team led by Professor Chao Shiuh of NTHU’s Institute of Photonics Technology has been participating in the LIGO project since 2010 and is the only team from Taiwan involved in the project.
 
On September 14, 2015, at 9:51 UTC, LIGO’s observatories located in Louisiana and Washington both detected gravitational waves; the signals were confirmed by four months of rigorous checking of the data. The gravitational waves were caused by the merger of two black holes, one of which is estimated to have the mass of 29 suns and the other the mass of 36 suns. Based on the observed signals, LIGO scientists estimate that the event took place 1.3 billion years ago. About three 3 times the mass of the sun was converted into gravitational waves in a fraction of a second. By looking at the time of arrival of the signals—the detector in Louisiana recorded the event 7 milliseconds before the detector in Washington—scientists can be certain that the source was located in the Southern Hemisphere.
 
In the press release Prof. Chao Shiuh said that according to Einstein's 1915 theory of general relativity the force of gravity has a distorting effect on space-time, and in 1916 he predicted that the rapid movement of a massive object results in these distortions being transmitted in the form of gravitational waves. But Einstein believed that such gravity waves could not be detected on Earth, due to the tremendous distance involved. However, in 1974 US scientists Russell Hulse and Joseph Taylor discovered a binary system composed of a pulsar in orbit around a neutron star. For the discovery of the pulsar and showing that it could be used to measure gravitational wave, Hulse and Taylor were awarded the Nobel Prize in Physics in 1993. LIGO’s direct observation of gravitational waves fulfills Einstein’s legacy on the 100th anniversary of his general theory of relativity.
 
Prof. Chao points out that this observation of gravitational waves is of great significance for three reasons. First, it provides direct evidence for the existence of gravitational waves. Second, it involved the direct observation of the merger of two black holes. Third, it opens new era for gravitational waves astronomy, thereby expanding our understanding of the nature and evolution of the universe.
 
The team led by Prof. Chao included graduate students Pan Huang-wei, Guo Ling-Chi, Huang Shu-yu, and Cheng Jun, and is the only Taiwanese team in the LIGO Scientific Collaboration (LSC). The NTHU team mainly participated in the research on reducing thermal noise disturbance in the mirrors employed to observe gravitational waves. They are now working on developing the next generation of cryogenic mirrors.
 
Prof. Chao explains that mirrors are one of the key components of LIGO’s observation apparatus, and that at the 100 Hz frequency band the level of noise disturbance must be less than 10-23 meter. His team made use of an ion beam sputter and mechanical loss test equipment to reduce the thermal noise of the mirrors. They also made use of the semiconductor manufacturing process equipments developed by the Taiwan’s National Nano Device Laboratory, and their work has been endorsed by Taiwan’s Ministry of Science and Technology.
 
The report of this discovery has been accepted for publication in the journal Physical Review Letters, which mentions the contributions of the NTHU research team and the Ministry of Science and Technology, thereby highlighting Taiwan’s participation in this international collaborative research.
 
 One of the mirrors at the heart of the LIGO interferometer (courtesy of LIGO)

One of the mirrors at the heart of the LIGO interferometer (courtesy of LIGO)

 The LIGO observatory in Louisiana (courtesy of LIGO)

The LIGO observatory in Louisiana (courtesy of LIGO)

 

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