The Olhar Espacial program will feature two fascinating astronomy topics this Friday (the 31st): Be stars and multiple star systems. Although these concepts may seem complex, the program promises a complete explanation of the material.
The Olhar Espacial program will feature two fascinating astronomy topics this Friday (the 31st): Be stars and multiple star systems. Although these concepts may seem complex, the program promises a complete explanation of the material.
Be stars are characterized by being very hot, massive, and rapidly rotating. Their distinguishing feature is the presence of emission lines in their spectra, caused by a gas disk formed around them. Despite being known for over a century, their origin and evolution still raise many questions.
Multiple star systems, consisting of two or more gravitationally bound stars, serve as a natural laboratory for studying the processes of star formation, evolution, and interaction between stars. In many cases, such interaction directly influences the formation of Be star disks, altering their rotation and behavior.
Studying these systems helps to gain a deeper understanding of stellar evolution and the dynamics of objects that shape the structure of our galaxy.
Danilo Ferreira is a postdoctoral researcher at the National Astrophysics Laboratory (LNA). He holds a doctorate in astronomy from the National Observatory and has completed an internship at the Paris Observatory. His scientific research focuses on massive stars, particularly Be stars and multiple systems, as well as exoplanets and observational methods.
Danilo participates in national and international projects covering photometry, spectroscopy, and interferometry. Furthermore, he is actively involved in science popularization and student training, with a special focus on the Brazilian Olympiad in Astronomy and Aeronautics (OBA), where he served as a judge at IOAA 2024.
The host of Olhar Espacial is Marcelo Zurita, an astronomer and columnist for OD. The program airs at 9:00 PM Brazilian time on their social media channels.
The Milky Way may have undergone a drastic transformation in its orientation due to a significant collision that occurred approximately ten to eleven billion years ago. This hypothesis was recently proposed by astronomers from the University of Durham during the Royal Astronomical Society's National Astronomy Meeting, held in Birmingham.
The conclusion was reached through the analysis of cosmological simulations involving galaxies similar to ours, which were compared with data obtained by the Gaia mission, belonging to the European Space Agency. The main objective of this study is to elucidate why the stellar halo of the Milky Way exhibits a rotation rate considerably slower than predicted by researchers.
If this interpretation is validated, it will add a new segment to the narrative of galaxy formation and may provide clues about the evolution of dark matter. Furthermore, it suggests that the location of the Solar System within the Milky Way has not maintained a constant orientation over time.
To investigate the cause of the slow rotation of the stellar halo, scientists monitored the evolution of twenty-five galaxies with characteristics similar to the Milky Way using supercomputers over billions of years. The goal was to determine which events could result in a configuration similar to what is currently observed.
The comparison showed that galaxies whose stellar halos rotate more slowly possessed two notable characteristics: they had suffered a head-on impact with another galaxy and subsequently experienced an orientation change greater than 90 degrees in their disks, an event termed by astronomers as a 'disc flip.'
Kirill Batrakov, the researcher responsible for the study, pointed out that the history of the Milky Way itself points to the possibility of this process having occurred in our galaxy. He stated during the presentation at the Royal Astronomical Society's National Astronomy Meeting: 'We already know that the Milky Way underwent a massive head-on collision with a galaxy known as Gaia-Sausage-Enceladus. Therefore, we believe that the Milky Way's disk probably also changed orientation in the past.'
The researchers recall that Gaia-Sausage-Enceladus, nicknamed the 'Sausage Galaxy,' was a dwarf galaxy incorporated into the Milky Way between ten and eleven billion years ago. This encounter is considered the largest merger event in the early phase of our galaxy, leaving behind billions of stars in extremely elongated orbits.
According to the authors, identifying this ancient disk inversion expands the possibilities for understanding the behavior of the dark matter halo, as the findings indicate a strong correlation between the rotation of this invisible structure and that of the stellar halo.
Batrakov emphasizes that a modification of this magnitude would have altered the path of most stars in the Milky Way. He stated: 'A disk flip means that most stars in the Milky Way have traveled very different paths than those currently observed, possibly even our Sun, which indicates that our seemingly stable position in the galaxy may not have been the case throughout the entire existence of the Solar System.'
The astronomer also emphasizes that reconstructing such remote episodes aids in comparing the evolution of the Milky Way with that of other galaxies. Batrakov concluded during the dissemination of the study: 'Since we live inside the Milky Way, we can study it with a level of detail impossible in any other galaxy. Discovering that its disk changed orientation adds a new chapter to its history and shows that it is possible to reconstruct this complex past from current observations.'
