“Old smokers”: Research team finds new type of stars in the heart of the Milky Way

They emit dense clouds of dust and were therefore called Old Smokers by astronomers. The ejected dust could play an important role in the formation of new stars and planets in some parts of the Milky Way, the scientists report in the journal ‘Monthly Notices of the Royal Astronomical Society’.

“Our real goal was to discover so-called protostars, which exhibit huge bursts of brightness that last for months or even many years,” explains Zhen Guo of Valparaiso University in Chile. “These outbursts occur in the rotating disk of gas and dust surrounding the newly born stars – and could complicate planet formation.” So far, astronomers don’t know what causes the outbursts. That’s why Guo and his colleagues wanted to record as many such outbreaks as possible and track them as they progressed.

In their search, the researchers used data from an observation project running since 2010 at the European Southern Observatory’s Vista telescope in Chile, which measures the brightness of about a billion stars in the central bulge of the Milky Way. Vista detects infrared radiation and is therefore particularly suitable for detecting newborn stars. These are often hidden behind dust clouds and therefore invisible to optical telescopes – but infrared radiation can penetrate the dust.

The team was successful: Guo and his colleagues identified 32 protostars with flares that increased their brightness by up to three hundred times. Many of these eruptions are still ongoing, giving researchers the first opportunity to track the mysterious phenomena throughout their trajectory.

But in addition to what they were actually looking for, the team also discovered something completely unexpected in the Vista data: old red stars at the heart of the Milky Way that mysteriously changed their brightness over the years. The researchers identified a total of 21 of these celestial bodies. They initially had no explanation for the fact that these stars were barely visible at first, but then became brighter. Further observations of seven of these objects eventually provided an explanation: apparently the stars had ejected huge clouds of dense dust that reduced their brightness.

These Old Smokers, as astronomers have called the new type of star, are all located in a disk-shaped structure at the center of the Milky Way. The astronomers write that stars in this disk contain a higher proportion of heavy elements than further away in the Milky Way. And that could also be an explanation for the phenomenon, according to Guo and his colleagues. If more heavy elements are present, more dust can form in the cool outer layers of the stars.

But why the ancient smokers glow quietly for a long time and then suddenly emit their dust in large bursts remains a mystery. With the help of further observations of the new stars, the researchers want to determine the cause of the dust eruptions. The dust emitted by the old stars in the central part of the Milky Way and other galaxies could play an important role in the redistribution of heavy elements in space. These heavy elements in turn influence the formation of new stars and planets, especially rocky planets like our Earth. (sda/dpa)