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New type of star - nicknamed 'old smokers' - discovered at the heart of the Milky Way

Scientists say they have discovered a new type of star deep at the heart of our galaxy.

The stars have been given the nickname "old smokers" by scientists because they have been observed "puffing" out clouds of gas.

They are a type of red giant, which are formed during the dying stages of medium sized stars - like our Sun - after they have run out of hydrogen for nuclear fusion.

The "old smokers" were discovered by an international team of scientists led by Professor Philip Lucas, of the University of Hertfordshire.

Researchers made their ground-breaking discovery after monitoring almost a billion stars in infrared light during a 10-year survey of the night sky.

The work was carried out as part of a long-term survey called 'VISTA Variables in the Via Lactea', or VVV.

As part of the study, researchers found 21 red stars near the centre of the Milky Way that showed ambiguous changes in brightness.

Professor Lucas explained: "We weren't sure if these 21 stars were protostars starting an eruption, squalling newborns if you will, or recovering from a dip in brightness caused by a disc or shell of dust in front of the star.

"A third option was that they were older giant stars throwing off matter in the late stages of their life, puffing out gas like old smokers."

However, after analysis, researchers concluded that these stars were a new type of red giant.

Professor Dante Minniti at Andrrs Bello University, Chile, founder of the VVV survey, said: "These elderly stars sit quietly for years or decades and then puff out clouds of smoke in a totally unexpected way.

"They look very dim and red for several years, to the point that sometimes we can't see them at all."

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The stars were heavily concentrated in the innermost part of the Milky Way, known as the Nuclear Disc, a region where stars tend to be richer in heavy elements than anywhere else.

This should, scientists say, make it easier for dust particles to condense out of gas in the relatively cool outer layers of red giant stars.

However, how this leads to the ejection of puffs of dense smoke that the team observed remains a mystery.

Researchers believe the discovery could change what we know about the way that elements are distributed across Nuclear Disc and metal-rich regions of other galaxies.

The project involved astronomers from the UK, Chile, South Korea, Brazil, Germany, and Italy, who carried out their research with the help of the Visible and Infrared Survey Telescope (VISTA) - a British-built telescope high in the Chilean Andes at Cerro Paranal Observatory.

As well as the "old smokers", the team also detected dozens of rarely-seen newborn stars, known as protostars, which undergo extreme outbursts for months, years, or decades, as part of the formation of a new solar system.

Most of these newly-spotted stars are hidden from view in visible light by large amounts of dust and gas in the Milky Way - but infrared light can get through, allowing scientists to see them for the first time.

The team discovered 32 erupting protostars that increased in brightness at least 40-fold, and in some cases over 300-fold.

The findings, which also involved work led by Dr Zhen Guo, formerly of the University of Hertfordshire and now based at the University of Valparaiso in Chile, have been published in the Monthly Notices Of The Royal Astronomical Society.