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Chinese scientists find answer to fast radio bursts

By ZHANG ZHIHAO | CHINA DAILY | Updated: 2021-02-20 07:36

Zhang Shuangnan, a researcher with the Chinese Academy of Sciences, explains a new discovery about the source of fast radio bursts at a news conference in Beijing on Friday. JIN LIWANG/XINHUA

Chinese scientists have confirmed that fast radio bursts-extremely powerful but brief flashes in the cosmos-can come from magnetars, celestial objects with a magnetic strength around 100 trillion times stronger than Earth, according to a study published in the journal Nature Astronomy on Friday.

It was the first confirmation of such a feat, and the findings will be significant for understanding one of the most mysterious events in the universe, said Zhang Shuangnan, a researcher from the Institute of High Energy Physics, Chinese Academy of Sciences.

Since their discovery in 2007, FRBs have fascinated astronomers because they can release a huge amount of energy within thousandths of a second, making them a notoriously elusive phenomenon to study. What is more puzzling is that some FRBs can recur, which fueled many theories ranging from star collisions to activities by alien civilizations.

"There were over 560,000 search results on FRBs and aliens on Chinese search engine Baidu, compared to around 3.5 million results on the actual FRBs itself," he said. "This goes to show that the public is very interested in the mysteries of FRBs, and speculations are very high."

Scientists have hypothesized that FRBs may be emitted by a special class of neutron stars-super-dense remnants of massive stars-called magnetars. However, most of the known FRBs came from distant galaxies billions of light years away, so scientists have been struggling to identify their sources since most telescopes aren't sensitive enough to see them.

A golden opportunity arrived in April last year when an FRB went off in our Milky Way galaxy and was detected by instruments from the United States and Canada, according to studies published in the journal Nature last year.

The FRB occurred about 30,000 light years away, close enough for our telescopes to observe. The FRB was named FRB200428 and scientists believed the culprit was a magnetar called SGR J1935+2154, which was in the general direction of the event.

While more studies were being done to confirm that the magnetar was the source, the discovery of a highly likely origin of FRBs was exciting enough to be listed by the journals Nature and Science as one of the biggest scientific feats last year.

Since an FRB spews out bursts of high energy electromagnetic radiation such as X-rays and gamma rays, Chinese scientists used the country's first X-ray space telescope-the Hard X-ray Modulation Telescope, also known as "Insight"-to study the X-ray bursts emitted from the magnetar.

Zhang, who is also the chief scientist behind Insight, said given the fact that X-rays can penetrate interstellar mediums faster than radio waves, there should be a small gap between the time the X-ray signals and the radio waves from the FRB reach Earth.

Thanks to the state-of-the-art equipment on Insight, which was launched in 2017, scientists discovered the time gap to be 8.62 seconds, which is consistent with the amount of time that the radio wave signal was delayed by the interstellar medium. This confirmed that the X-ray burst and FRB came from the same event.

In addition, with precise measurement of the X-ray burst, Insight established that it came from the magnetar. This discovery, along with results from other telescopes, prove that FRBs can originate from magnetars, thus resolving the long-standing puzzle about the origin of FRBs.

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