Bengaluru, July 23: An international team of astronomers has carried out an extensive new survey of the Milky Way, revealing previously unseen signatures with unprecedented sensitivity and details that hint at how stars form and die, complex processes that have fascinated researchers for centuries.

The results were published in a series of papers in 'Astronomy & Astrophysics' by the team, which includes scientists from the Indian Institute of Science (IISc) and the Indian Institute of Space Science and Technology (IIST).

(Photo: Brunthaler et al., Sophia Dagnello, NRAO/AUI/NSF)
GLOSTAR image, using data from both the VLA and the Effelsberg radio telescope, shows a segment of the Milky Way's disk, revealing previously unseen tracers of massive star formation. Some of these features are identified in this version of the image.

The data for the survey, which spanned a large part of the Milky Way, was gathered using two powerful radio telescopes: the Karl G Jansky Very Large Array (VLA) at the National Radio Astronomy Observatory, USA, and theEffelsberg100-m radio telescope operated by the Max Planck Institute for Radio Astronomy Germany, as part of the GLOSTAR (Global View on Star formation in the Milky Way) project.

Nirupam Roy, Assistant Professor at the Department of Physics and Rohit Dokara, his former undergraduate student from IISc, as well as Jagadheep D Pandian, Associate Professor at the Department of Earth and Space Sciences in IIST are among the Indian scientists who are part of the GLOSTAR project, Bengaluru-based IISc said in a statement on Friday.

Dokara, now a PhD student at MPIfR, is the first author on one of the papers that reports the detection of new supernova remnants (SNRs) structures born from the explosive death of massive stars in our galaxy.

Previous surveys have detected only about one-third of the expected number of SNRs in the Milky Way (which is nearly 1000), according to the statement.

The GLOSTAR team has now discovered 80 new SNR candidates in the VLA data alone,with more expected to be identified from the combined Effelsberg and VLA data.

They were also able to confirm the presence of 77 previously discovered SNR candidates and reclassify a few that were misidentified.

This is impressive, considering that the northern telescopes utilised by GLOSTAR are able to see only half of the inner regions of the Milky Way, it said.

"This is an important step to solve this long-standing mystery of the missing supernova remnants," said Dokara.

The researchers were also able to detect other traces of star formation.

One of them, for example, is radio emission from methanol molecules in a nearby large star-forming complex 'Cygnus X.'

These are typically emitted from massive stars in very early stages of formation.

The team was also able to detect dense pockets of ionised hydrogen, another tell-tale sign of the presence of massive young stars.

Young stars are usually surrounded by thick clouds of dust and gas.

"Because visible light gets absorbed in this dense cloud around stars, most of the optical telescopes dont reveal much.

What people look for, instead, are radio emissions," explained Roy, who has previously worked at both NRAO and MPIfR.

"Since the GLOSTAR survey detects a wide range of radio emission such as that from methanol molecules to ionised hydrogen, it is able to probe the formation of massive stars from very early to relatively late stages, which is important to get a complete picture of star formation in the Milky Way," added Pandian, who has also previously worked at MPIfR.

The Effelsberg radio telescope is a single large dish spanning 100 m in diameter, capable of detecting large-scale structures, whereas the VLA is a collection of small antennas which work together as an interferometer to capture the details at high resolution.

The data pooled from both telescopes helped the researchers paint a more comprehensive picture of different astrophysical objects in the region.

"This clearly demonstrates that the Effelsberg telescope is still very crucial, even after 50 years of operation," said Andreas Brunthaler of MPIfR, project leader and first author of the survey's overview paper.

Karl Menten, the Director of MPIfR, who initiated GLOSTAR, added: "Its great to see the beautiful science resulting from two of our favourite radio telescopes joining forces."

Both Pandian and Roy currently maintain Max Planck-India Partner Groups with Menten to continue the close collaboration and, in particular, to expand the scope of the GLOSTAR project.

Other members of the research team include scientists from MPIfR and NRAO, and collaborators from institutions in the UK, South Africa, Mexico, France and Australia.

With observations and analysis ongoing, more results are expected to be published over time, it was stated.

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Hong Kong, Oct 25: Amnesty International said Monday it would close its two offices in Hong Kong this year, becoming the latest non-governmental organization to cease its operations amid a crackdown on political dissent in the city.

The human rights group said its local office in Hong Kong would close this month while its regional office will close by the end of the year, with regional operations moved to other offices in the Asia-Pacific region.

This decision, made with a heavy heart, has been driven by Hong Kong's national security law, which has made it effectively impossible for human rights organizations in Hong Kong to work freely and without fear of serious reprisals from the government, Anjhula Mya Singh Bais, chair of Amnesty's board, said in a statement.

Hong Kong implemented a sweeping national security law in 2020 following months of massive anti-government protests. The law outlaws secession, subversion of state power, terrorism and foreign collusion to intervene in the city's affairs. More than 120 people, many of them supporters of the city's democracy movement, have been arrested under the law.

The majority of the city's prominent pro-democracy activists are behind bars for taking part in unauthorized assemblies, and dozens of political organizations and trade unions have ceased operations out of concern for their members' personal safety under the security law.

Bais said the recent targeting of local human rights and trade union groups signaled authorities were intensifying their campaign to rid the city of dissenting voices. It is increasingly difficult for us to keep operating in such an unstable environment, she said.

Critics in Hong Kong say the national security law is an erosion of freedoms, such as those of expression and assembly, that were promised the city for 50 years when the former British colony was handed over to China in 1997.