From theory prediction to bold observatory, Chinese researchers help usher in new era in astrophysics

Updated 2017-10-18 08:31:54 Xinhua
A staff worker of the Purple Mountain Observatory displays an image at a press conference at the observatory in Nanjing, east China's Jiangsu Province, Oct. 16, 2017.

A staff worker of the Purple Mountain Observatory displays an image at a press conference at the observatory in Nanjing, east China's Jiangsu Province, Oct. 16, 2017.

Chinese researchers have played a significant role in opening a new era of "Multimessenger astronomy," marked by the first detection of both electromagnetic radiation and gravitational waves and light in the same cosmic collision.

The discovery is also the first verification of a "kilonova" explosion, confirming binary neutron star collisions as one source for the universe's heaviest elements, such as gold and uranium.

THEORY PREDICTION

The story goes back 60 years to the groundbreaking stellar nucleosynthesis paper published in 1957, which offered a successful model of element formation. For decades, however, no one could identify the site of the process and the source of the neutrons.

In the end of the 20th century, astrophysicists were chatting about mergers of neutron stars, which eject a small fraction of matter with a subrelativistic velocity.

Until 20 years ago, a young Chinese called Xin Li and the late pioneering astrophysicist Bohdan Paczynski first presented the model of mergers of neutron stars, and analytical formulae for the associated electromagnetic radiation in the highly cited paper Transient events from neutron star mergers, which was published in 1998.

"Chinese researchers did a remarkable job in the wonderful discovery...Chinese researcher Li has made the first theory prediction," said Suijian Xue, professor and deputy director of the National Astronomical Observatories of China (NAOC) under Chinese Academy of Sciences.

"I am delighted. It is the critical next step to explore in detail the physics involved," Li said after being announced to have for the first time detected the ripples in space and time known as gravitational waves and light from a spectacular collision of two neutron stars.

"However, there is now much more work to be done. We still need more detection like this to prove the model," Li added.

In 2015, detectors from the U.S.-based Laser Interferometer Gravitational-Wave Observatory (LIGO) confirmed the existence of gravitational waves produced during the merger of two black holes, predicted by Albert Einstein's theory of general relativity 100 years ago.

The detection marked the beginning of a new era in observational astronomy, yet no neutron stars had ever been known to have merged until this August.

GLITTERING PROSPECTS AT CHINA'S TELESCOPE

On Aug. 17, the gravitational waves signal, GW170817, was detected by LIGO's twin detectors, respectively located in Livingston, Louisiana, and Hanford, Washington.

The fifth detected source as it was, the source of gravitational waves was historical since a glowing aftermath of the collision of two neutron stars was visible by traditional telescopes.

The Chinese telescope independently observed optical signals resulting from the merger the next day, among some 70 telescopes on the ground or from space across the world.

"While many observatories contributed to the broad set of companion observations, the Chinese observatory, by having half a year of night per year is ideally suited to this challenging task," Gary Sanders, deputy director and project manager of LIGO in 1994-2004, told Xinhua.

Chinese team then conducted immediate follow-up on the gravitational waves source GW170817 in the nearby galaxy NGC4993 all the way from Dome A in Antarctica, using a fully-robotic telescope called AST3.

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