They release clouds of dark material that prevent light from escaping.

A recent study observing nearly a billion stars in infrared light has unveiled numerous stars previously hidden from our view, a new category termed “old smokers,” which are aging red giants that suddenly emit clouds of dark material, obscuring their light.

The study, published in the Monthly Notices of the Royal Astronomical Society, says that while dust blocks the view of the galactic center in visible light, infrared wavelengths can penetrate this barrier.

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As Earth’s atmosphere blocks infrared light, telescopes like the James Webb Space Telescope (JWST) and the Visible and Infrared Survey Telescope (VISTA) in Chile, located above much of the atmosphere, have successfully studied the galactic core in the infrared and near-infrared light.

An international research team analyzing VISTA’s data observed for years the formation of protostars initiating fusion, focusing on stars with the greatest brightness variations. They underwent massive outbursts lasting months to decades; in the case of 32 protostars brightness increased by a factor of 40 or more over 9.5 years of observation, with some becoming 30,000 percent brighter. Of these stars with mysterious brightness changes, 21 were red stars.

Detailed investigation of seven red giants revealed they are older stars of a previously unknown type.

“These elderly stars sit quietly for years or decades before emitting clouds of smoke in a totally unexpected manner,” said Professor Dante Minniti of Andrés Bello University. “They appear very dim and red for several years, sometimes becoming invisible.”

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These “old smokers” are concentrated in the Milky Way’s central Nuclear Disc, explaining their prior elusiveness. Closer to the galactic center, stars have higher metal concentrations due to multiple generations of supernovae enriching the region with heavy elements. This metallic abundance likely facilitates the condensation of dust particles around stars or in their cooler outer layers, yet the exact cause of these erratic emissions remains unclear.

As galaxies evolve, supernovae and kilonovae influence their outer regions, expanding high-metal areas. Eventually, old smokers might become a common feature in our own stellar neighborhood.

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