Some stars lose their shine in the late stages of their existence, becoming no longer visible, before releasing a cloud of gas and dust, which earned them the description "smoking old stars," according to astronomers who reported discovering these stars in the heart of the Milky Way galaxy.

Dante Minitti from Andres Bello University in Chile explained in a statement that "these old stars remain quiet for years or decades before suddenly releasing clouds of smoke in a completely unexpected way."

The professor, who participated in preparing the study published in "Monthly Notices" issued by the British Royal Astronomical Society, noted that these stars are pale and red in color "to the extent that seeing them is sometimes almost impossible," according to the Agence France-Presse the day before yesterday.

The principal author of the study, astrophysicist and professor at the University of Hertfordshire, Philip Lucas, told the French agency that their "unique" behavior had not been observed before.

The multinational team of astronomers were initially searching for young stars within a decade-long observation program which enabled them to discover a large number of primordial stars (i.e., newly born stars).
But the program also provided them with a "pleasant surprise," according to Professor Lucas, consisting of the discovery of at least 21 "smoking old stars."

These stars are located in the center of the Milky Way galaxy, in a region known as the nuclear stellar disc, which contains a large concentration of stars.

The "smoking old stars" are believed to be a new type of red giant stars, which are stars at the end of their life that gain a large size and have a low surface temperature.

Professor Lucas viewed that "what is surprising about this discovery is observing stars that are quiet and do nothing, then suddenly, their apparent brightness drops by 40 to 100 times, to the extent that observing them becomes almost impossible with telescopes. After a few years, without any warning, they regain their original brightness."

Professor Lucas added: "All we managed to learn about these stars indicates that they emit clouds of smoke for reasons we do not know."

It is believed that these clouds composed of gas and dust are the reason for the star's brightness decrease, as they obscure it from observers’ sight.

Their activity occurs in a region of the galaxy rich in heavy elements which these stars may contribute to.