Life cycle of stars [Image from the Internet]

On April 11, 2019, an international team led by Professor Xue Yongquan from the University of Science and Technology of China (USTC) announced their observation of a unique X-ray signal from 6.6 billion light years away, which is highly likely powered by a magnetar, the aftermath of a binary neutron star merger. This discovery was published in Nature.

A portrait of Xue Yongquan. The background panels show his research interests: mysterious magnetars, the active galactic nucleus and the 7Ms Chandra Deep Field-South survey. [Image by Sheng Zhenfeng]

Neutron stars are some of the most miraculous objects in the universe, yet our grasp of their physics is still fuzzy. For years, astronomers wondered about what is the ending of a binary neutron star merger system. Many advocated for its becoming a black hole, while some believed that a magnetar would be formed.

The answer was finally revealed by the universe itself. The X-ray transient captured by the group, lasting for 7 hours, gave researchers evidence about the formation of magnetar. Duration is the key -- if the transient were powered by a resulting black hole, it could shine for only seconds.

The group also observed that the X-ray transient lies in the outskirts of its host galaxy, like binary neutron star systems usually do, since they are usually kicked away from the center after supernova explosions. This can be taken as supporting evidence that the X-ray transient is indeed powered by a binary neutron star merger.

Meanwhile, researchers calculated the event rate density of similar X-ray transients. The result is consistent with the neutron star merger event rate density robustly inferred from the gravitational wave detection of a binary neutron star merger in 2017.

“The discovery of this new X-ray transient is highly intriguing. Particularly exciting, due to the discovery being made by Chandra with its excellent spatial resolution, is the ability to identify the host galaxy,” one reviewer of this paper said.

This discovery has profound implications for understanding the state of extremely dense nuclear matter. It helps rule out a series of theoretical nuclear matter models which are inconsistent with the observations, thus providing new insights into the physics of neutron stars.

(Written by Wu Qiran, edited by Shi Xiao, Hu Dongyin, USTC News Center)

For more information, please contact:

Dr. & Prof. Xue Yongquan

Department of Astronomy, University of Science and Technology of China

Source: News Center, University of Science and Technology of China


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