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Washington DC, Jun 8: Astronomers acting on a hunch have likely resolved a mystery about young, still-forming stars and regions rich in organic molecules closely surrounding some of them.

They used the National Science Foundation's Karl G Jansky Very Large Array (VLA) to reveal one such region that previously had eluded detection and that revelation answered a longstanding question.

The regions around the young protostars contain complex organic molecules which can further combine into prebiotic molecules that are the first steps on the road to life.

The regions, dubbed "hot corinos" by astronomers, are typically about the size of our solar system and are much warmer than their surroundings, though still quite cold by terrestrial standards.

The first hot corino was discovered in 2003 and only about a dozen have been found so far. Most of these are in binary systems, with two protostars forming simultaneously.

Astronomers have been puzzled by the fact that, in some of these binary systems, they found evidence for a hot corino around one of the protostars but not the other.

"Since the two stars are forming from the same molecular cloud and at the same time, it seemed strange that one would be surrounded by a dense region of complex organic molecules and the other wouldn't," said Cecilia Ceccarelli, of the Institute for Planetary Sciences and Astrophysics at the University of Grenoble (IPAG) in France.

The complex organic molecules were found by detecting specific radio frequencies, called spectral lines, emitted by the molecules. Those characteristic radio frequencies serve as "fingerprints" to identify the chemicals.

The astronomers noted that all the chemicals found in hot corinos had been found by detecting these "fingerprints" at radio frequencies corresponding to wavelengths of only a few millimetres.

"We know that dust blocks those wavelengths, so we decided to look for evidence of these chemicals at longer wavelengths that can easily pass through dust," said Claire Chandler of the National Radio Astronomy Observatory, and principal investigator on the project.

"It struck us that dust might be what was preventing us from detecting the molecules in one of the twin protostars," added Chandler.

The astronomers used the VLA to observe a pair of protostars called IRAS 4A, in a star-forming region about 1,000 light-years from Earth. They observed the pair at wavelengths of centimetres.

At those wavelengths, they sought radio emissions from methanol, CH3OH (wood alcohol, not for drinking). This was a pair in which one protostar clearly had a hot corino and the other did not, as seen using the much shorter wavelengths.

The result confirmed their hunch. "With the VLA, both protostars showed strong evidence of methanol surrounding them. This means that both protostars have hot corinos. The reason we did not see the one at shorter wavelengths was because of dust," said Marta de Simone, a graduate student at IPAG who led the data analysis for this object.

The astronomers cautioned that while both hot corinos now are known to contain methanol, there still may be some chemical differences between them. That, they said, can be settled by looking for other molecules at wavelengths not obscured by dust.

"This result tells us that using centimetre radio wavelengths is necessary to properly study hot corinos," Claudio Codella of Arcetri Astrophysical Observatory in Florence, Italy, said.

"In the future, planned new telescopes such as the next-generation VLA and SKA, will be very important to understanding these objects," added Codella.

Beijing, Feb 18: Police in China have arrested a prominent activist who had been a fugitive for weeks and criticised President Xi Jinping's handling of the coronavirus epidemic while in hiding, a rights group said Tuesday.

Anti-corruption activist Xu Zhiyong was arrested on Saturday after being on the run since December, according to Amnesty International.

China's ruling Communist Party has severely curtailed civil liberties since Xi took power in 2012, rounding up rights lawyers, labour activists and even Marxist students.

The death this month of a whistleblowing doctor who was reprimanded by police for raising the alarm about the deadly new virus before dying of it himself triggered rare calls for political reform and freedom of speech.

The "Chinese government's battle against the coronavirus has in no way diverted it from its ongoing general campaign to crush all dissenting voices," said Patrick Poon, China researcher at Amnesty International, in an emailed statement.

Another source, who spoke to news agency on the condition of anonymity, said Xu had been arrested in the southern city of Guangzhou.

Guangzhou police did not respond to requests for comment.

Xu went into hiding after authorities broke up a December gathering of intellectuals discussing political reform in the eastern coastal city of Xiamen in Fujian province, prior to the coronavirus crisis.

Over a dozen lawyers and activists were detained or disappeared after the Xiamen gathering, according to rights groups -- and Xu's detention appears linked to his presence at the meeting, explained Poon.

But while on the run, Xu continued to post information on Twitter about rights issues.

On February 4 Xu released an article calling on Xi to step down and criticised his leadership across a range of issues including the US-China trade war, Hong Kong's pro-democracy protests and the coronavirus epidemic, which has now killed nearly 1,900 people.

"Medical supplies are tight, hospitals are filled with patients, and a large number of infected people have no way to be diagnosed," he wrote. "It's a mess."

"The coronavirus outbreak shows just how important values like freedom of expression and transparency are -- the exact values that Xu has long advocated," Yaqiu Wang, China researcher at Human Rights Watch, told news agency.

But the disappearance of Xu illustrates how the Chinese state "persists in its old ways" by "silencing its critics", she said.

Xu -- who founded a movement calling for greater transparency among high-ranking officials -- previously served a four-year prison sentence from 2013 to 2017 for organising an "illegal gathering".

"That he was a fugitive for so many days while continuing to speak out, that in itself was... a kind of challenge to (Chinese authorities)," said Hua Ze, a long-time friend of Xu who told AFP she lost contact with the Chinese activist on Saturday morning.