February 26, 2024

Astronomers have discovered a mysterious group of giant, aged stars at the heart of the Milky Way, emitting solar system-sized clouds of dust and gas.

The stars, which were called “old smokers”, sat still for many years, fading almost to invisibility, before suddenly blowing out huge clouds of smoke. The discovery was made while monitoring nearly a billion stars in infrared light during a 10-year survey of the night sky.

“They sit there and just suddenly throw matter off,” says Prof Philip Lucas of the University of Hertfordshire, who led the observations. “This is a new kind of star and they all seem to be clustered together in the same part of the sky, very close to the center of our Milky Way galaxy.”

The astronomers began to capture rarely seen newborn stars – known as protostars – as they underwent the equivalent of a stellar growth spurt. During these periods, young stars rapidly gain mass by feeding on surrounding star-forming gas, leading to a sudden increase in brightness.

The team tracked hundreds of millions of stars and identified 32 erupting protostars that increased in brightness at least 40-fold and in some cases more than 300-fold.

However, another group of red giant stars near the center of the Milky Way turned up unexpectedly in the analysis. When studied in more detail with the European Southern Observatory’s Very Large Telescope, seven of the stars were found to be a new type of red giant star, which the researchers called “old smokers”. Convection currents and instabilities within the star could cause the release of enormous plumes of smoke, Lucas suggested.

“These are solar system-sized clouds,” Lucas said. “Our guess is that these are dust clouds in one direction, possibly from one spot on the surface of the star.”

The findings have wider significance because material released by dying stars into interstellar space seeds the next generation of stars.

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“The discovery of a new type of star that ejects matter may have greater significance for the distribution of heavy elements in the core disk and metal-rich regions of other galaxies,” Lucas said.

The findings are published in the Monthly Notices of the Royal Astronomical Society.

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