Nanjing University’s astronomy and space science team participated in the detection and theoretical explanation by scientists from multiple countries that led to the discovery of gravitational waves (GWs) from the merging of two neutron stars and electromagnetic counterparts to GW transients, a breakthrough jointly announced at 22:00 Beijing Time on October 16, 2017.
By using the funds from China’s 985 Project, Nanjing University contributed to the construction of the three wide-field Antarctic Schmidt Telescopes (AST3) and carried out the GW 170817 observation with these telescopes.
These telescopes are located at Antarctic Dome A (80°22′S 77°21′E), the highest point of the Antarctic Plateau. They are the world’s first completely remote-controlled telescopes in Antarctica.
This was a joint project of many institutions in China led by the Center for Antarctic Astronomy of the Zijinshan Astronomical Observatory.
The observation started from 21:00 Beijing Time on August 18 and did not cease until August 28.
Participating in the observation were Associate Professor Zhang Hui and doctoral candidate Liang Ensi, members of Zhou Jilin’s research team from School of Astronomy and Space Science, Nanjing University.
Other team members, Professor Dai Zigao, doctoral candidates Liu Liangduan and Xiao Di, and research fellow Wu Xuefeng, who is from the Zijinshan Astronomical Observatory, analyzed the data observed from AST3 with a semi-analytical model of kilonova and made important findings.
They found that the merging of these two neutron stars ejected high-speed materials which are travelling at the speed of 30% of the velocity of light and weighing about 1% of the masses of the Sun or the masses of neutron-rich materials of over 3,000 Earths.
These materials became heavy elements and even some super-heavy elements – heavier than iron – through the processes of fast neutron capture and nucleosynthesis.
The data observed from AST3, together with the data from other telescope observations in the world, have provided very important information for humankind to understand the physical merging of two neutron stars.
AST3 on Antarctica Plateau, constructed with Nanjing University’s 985 Project funds
With AST3, the Nanjing University team has also conducted research on extrasolar planets.
By observations made in 2008, 2016, and 2017 with Chinese Small Telescope ARray (CSTAR) (diameter: 14.5 cm) at the Kunlun Station and the second telescope of AST3 (AST3-2), Associate Professor Zhang Hui and Dr. Wang Songhu (2012) succeeded in discovering more than 100 extrasolar planet candidates with high fidelity, of which six have been largely confirmed.
This was the first time in the world for humankind to find large quantities of extrasolar planet candidates in Antarctica, and it has greatly elevated the international influence of China in the observation of extrasolar planets.
The scanning and observation of the TESS Antarctic field with AST3-2.
In the TESS field, the precision of AST3-2 is up to the magnitude of 0.001, and this telescope has enabled researchers to find more than 100 extrasolar planet candidates.
At present, with the support of the Double First-Rate Construction Project, the school of astronomy and space science is setting up a “Time-Domain Observatory of Nanjing University (TiDO)” in the Ali Prefecture of Tibet.
TiDO will be put into use at the end of 2017 and will be used to carry out cutting-edge observations of optical counterparts to GWs, new extrasolar planets, supernova explosion, and the Tidal Disruption Event (TDE).
A diagram of the signal of a transiting extrasolar planet candidate discovered by the Nanjing University team, and its size as compared with and distance from a fixed star