Helping to understand the origin of the universe, the key evidence for the existence of gravitational waves detected by the Chinese celestial eye is the universe | mass | gravitational waves
In 1916, Einstein made a prediction that there were gravitational waves in the universe, which were ripples caused by accelerating objects disturbing the surrounding spacetime. However, due to the fact that gravitational waves propagate at the speed of light and gravitational interactions are extremely weak, Einstein himself stated that humans may not be able to detect gravitational waves.
100 years later, the Laser Interferometric Gravitational Wave Observatory in the United States announced the detection of gravitational waves generated by the merger of stellar mass double black holes in the 100Hz frequency band, and thus won the 2017 Nobel Prize in Physics.
Due to its extremely low frequency and period of several years, the detection of nanohertz gravitational waves can reach wavelengths of several light years, making it even more challenging. Recently, the Chinese pulsar time array research team, which is composed of scientific researchers from the National Astronomical Observatory of the Chinese Academy of Sciences and other institutions, used the Chinese Celestial Eye Telescope to detect the key evidence of the existence of nano Hertz gravitational waves, and China's research on nano Hertz gravitational waves has reached the leading level in synchronization with the international level. The relevant papers are published online in the Journal of Astronomy and Astrophysics in China.
The United States, Europe, and Australia have been conducting searches for about 20 years
Larger celestial bodies generate lower frequencies of gravitational waves. For example, the gravitational waves generated by the supermassive double black hole system at the center of the galaxy, which is the largest celestial body in the universe, are mainly concentrated in the nanohertz frequency band.
Detecting gravitational waves with frequencies as low as nanohertz will help astronomers understand the origin of the universe's structure, and explore the growth, evolution, and merging processes of supermassive black holes, the largest celestial body in the universe; It also helps physicists to gain insight into the fundamental physical principles of spacetime.
The long-term observation of a group of millisecond pulsars with extremely regular rotation using a large radio telescope is currently the only known detection method for nanohertz gravitational waves. The discovery of nanohertz gravitational waves is one of the focal points of international competitions in the fields of physics and astronomy. Internationally, the United States, Europe, and Australia have each conducted a 20-year search for nanohertz gravitational waves using their respective large radio telescopes. Recently, some emerging forces have gradually joined this field, including China, India, and South Africa.
In June 2016, the Chinese Academy of Sciences carried out a prospective layout of the research on the detection of the gravitational waves of the Nahertz, and formed a research team of the China Pulsar Time Array in conjunction with Peking University, the Chinese Academy of Sciences Xinjiang Observatory, Yunnan Observatory, Shanghai Observatory, the National Time Service Center, Guangzhou University, etc. In September 2019, China's Tianyan was still in the debugging stage, and the research team collaborated with the China Tianyan Debugging Working Group to conduct a trial observation.
[Will open a new window for gravitational wave astrophysics]
In this study, the Chinese pulsar timing array research team used the Chinese celestial eye to conduct long-term systematic monitoring of 57 millisecond pulsars, and formed these millisecond pulsars into gravitational wave detectors on the scale of the Milky Way to search for nanohertz gravitational waves. The team analyzed and studied data collected by the Chinese Tianyan based on independently developed software, with a time span of 3 years and 5 months. At a confidence level of 4.6 sigma, relevant signal evidence with nanohertz gravitational wave characteristics was discovered. The sensitivity of China's nanohertz gravitational wave detection has reached a level comparable to that of the United States, Europe, and Australia, thus independently achieving this major scientific breakthrough.
"This research result is consistent with the theoretical expectation of the supermassive double black hole system," said Cai Ronggen, an academician of the CAS Member.
He Zishan, an academician of the American Academy of Arts and Sciences and a professor at Peking University, said, "The generation of nanohertz gravitational waves is a unique prophecy for the merger of supermassive black holes. This long-awaited prophecy has finally been observed by the Chinese pulsar timing array research team using the Chinese celestial eye. It not only has a profound impact on the extensive fields of galaxy evolution and supermassive black hole research, but also will open a new window for gravitational wave astrophysics."
Due to the short time span of current observation data, the research team of the Chinese pulsar timing array is currently unable to determine the main physical source of gravitational waves in the nanohertz band. However, this will be resolved as the time span of subsequent observation data increases.
