A new type of giant star that fades away and newly born stars that increase their brightness up to 300 times are part of the discovery published in the Monthly Notices of the Royal Astronomical Society. The study is part of the Milky Way VVV survey and had the participation of astronomers from the Center for Astrophysics and Related Technologies (CATA).
Mysterious objects lie at the center of our Milky Way and have been revealed through 10 years of nighttime sky observation. One of these objects is nicknamed “old smokers,” a new type of red giant star that can fade away to become almost invisible, and proto-stars that significantly increase their brightness, up to 300 times.
The study is part of the mapping of stars in our galaxy called “VISTA Variables in the Via Lactea” or VVV, which analyzed the 222 stars showing the greatest changes in brightness, selected from among hundreds of millions of stars. They used the VISTA infrared telescope located at the Cerro Paranal Observatory in Chile, which can see through the layers of dust that hide the stars in the center of our galaxy. Additionally, the Very Large Telescope (VLT), also located in our country, was essential in this analysis. The VLT was used to obtain spectra of some of these stars, which are representations of the amount of light they emit at different wavelengths, providing key information about their composition and behavior.
The team, led by Professor Philip Lucas from the University of Hertfordshire in the United Kingdom, included astronomers such as Dante Minniti from the Andrés Bello University in Chile and the founder of the VVV project, Márcio Catelan from the Pontificia Universidad Católica de Chile, and Amelia Bayo, an astronomer from the European Southern Observatory (ESO), all of them researchers from the Center of Astronomy and Related Technologies (CATA).
They look very dim and red for several years, to the point that sometimes we can’t see them at all.
One of the key discoveries was the identification of 32 proto-stars experiencing large eruptions, that increased their brightness from 40 to 300 times. Dr. Zhen Guo, a researcher from the Institute of Physics and Astronomy at the Universidad de Valparaíso and leader of the spectroscopic follow-up, explained that the main objective was to find rarely-seen newborn stars as they go through these large outbursts, which can last from months to decades.
Buried deep inside the dark cloud of gas and dust that fills the picture, this star gradually brightened 40-fold over the course of two years and has remained bright since 2015. The cause of such events is not clearly understood. This infrared image shows what we would see if our eyes were sensitive to wavelengths three times longer than visible light.
But the most surprising discovery was that of red stars that changed their brightness in an unexpected way over the 10 years of observation. Through the analysis of their spectra, the team concluded that they were a new type of red giant star. Dr. Dante Minniti 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.”
Infrared images of a red giant star about 30,000 light years away, near the centre of our Milky Way galaxy, which faded away and then reappeared over the course of several years.
Why had not we seen this type of stars until now? A clue to answer this question lies in the fact that these stars are located in the nuclear disk of the Milky Way, a region where stars tend to have a higher abundance of heavy elements. Although this suggests that it should be easier for dust to form and cool in the outer layers of these red giant stars, the exact mechanism by which they expel these dust clouds remains a mystery. This discovery opens up new lines of research in astronomy regarding how these processes affect the distribution of elements in the universe.
Artículos del estudio publicado en Monthly Notices of the Royal Astronomical Society