China unveils new gravitational wave research plan "Taiji"

Chinese scientists announced on Tuesday a research program "Taiji" that will study gravitational waves from the merging of binary black holes and other celestial bodies.

Hu Wenrui, chief scientist of the program, announced the launch of three satellites to detect gravitational waves around 2030 and complementary research with the European Space Agency (ESA) laser interferometer space antenna (LISA) project, which plans to launch satellites around 2035.

The discovery of gravitational waves announced by the LIGO Collaboration last week has encouraged scientists worldwide to accelerate their research.

Unlike the LIGO research conducted from a ground-based observatory, Taiji and LISA will observe the waves from space.

As a Chinese term for the "supreme ultimate", taiji is familiar as the black and white circular representing yin and yang.

COSMIC SYMPHONY

Several research teams are working on gravitational waves with different methods and objectives.

Su Meng, a Chinese researcher at the department of physics, Massachusetts Institute of Technology, said the different pitches of ripple-like waves from all around space play the grand symphony of the universe.

Su compared the different frequencies of gravitational waves to the wide range of voice registers in music. For example, he refers to LIGO's newly discovered gravitational waves from a pair of merging black holes as "high-pitched voice."

"The binary star system composed by objects like neutrons and stellar-mass black holes usually radiates gravitational waves of high frequency from tens to thousands hertz," he explains.

The space-based gravitational wave detector developed by Taiji and LISA will be sensitive at much lower frequencies, which Su regarded as the "mid-high notes" of the universe.

"Tianqin," another domestic gravitational wave research plan, which also focuses on finding "notes" like Taiji, was initiated by the Sun Yat-sen University in July 2015 and designed to be carried out in four stages.

Taiji, Tianqin and LISA will launch several satellites to detect the waves.

Then where are the "middle pitched" and the "bass" in the universe? Two other programs in China, "FAST" and "Ali", are looking for the two "voice ranges."

In a valley deep in southwest China's mountainous Guizhou Province, a big sensitive "ear" on earth will soon be completed.

The five-hundred-meter aperture spherical radio telescope, or "FAST", operates in the radio frequency of the electromagnetic spectrum where it can detect and collect a wider range of data on radio sources.

Being able to "hear" more subtle sound from the universe, "FAST" is expected to make breakthroughs in surveying natural hydrogen in distant galaxies, detecting faint pulsars, and also finding the "middle pitched" gravitational wave, which is often released by the merging of supermassive black holes.

Another domestic gravitational wave plan "Ali," named after the Chinese Academy of Sciences (CAS) observatory in Ali, Tibet, has totally different objectives -- detecting the first tremors of the Big Bang, or primordial gravitational waves.

Su dubbed the waves as the "lowest pitch" of cosmic symphony. "It's quite faint and difficult to capture," he said.

Considering weather conditions and small interference, scientists regard only four sites on Earth as ideal places for observation for the primordial waves, including the South Pole and Chile's Atacama Desert in the Southern Hemisphere, and Greenland and Ali on the northern part.

Though Ali Project is still awaiting government approval, Harvard, MIT and the University of Chicago have expressed interest, Su said.

"Whether it is right to understand the birth of the universe based on the known physical law needs to be verified through the research of the primordial gravitational waves," he added.

PRELUDE

"When Galileo turned his telescope to the sky 400 years ago, human beings got their first glance of the beauty of the universe," Su Meng said, "but it is not until the latest discovery of gravitational waves that we heard the first note of the cosmic symphony."

"It's only the beginning," Hu Wenrui echoed with Su, saying that with further detection in space, more questions will be answered.

"Though I might not be able to see the launch of the satellites, I do hope this project will make China one of the most important research bases in the world for gravitational wave detection in space," the 80-year-old academician continued.

With the development of fundamental science research, China could take a substantive leap in other related fields such as space science research, high-end space satellite technology etc, Hu said.

Gravitational wave detection has opened a window for us to observe the mysterious cosmos, so it's necessary for us to master the technology, said Wu Yueliang, vice-president of the University of Chinese Academy of Sciences.

Wu also pointed out that China should establish a long-term investment mechanism and provide stable support for basic research.