A new study developed by the Ohio State University (United States) and the University of Birmingham (United Kingdom) has defined in detail the exact moment in which the Milky Way integrated with the satellite galaxy Gaia-Enceladus and how it did so . An event that took place 10,000 million years ago, when it already had most of its stars.
The work, published in the journal Nature Astronomy , puts on the table that the Milky Way, as we know it today, was formed after the collision with a dwarf galaxy about 10 billion years ago but most of the galaxy was already formed even at this very early moment; that is, “the Milky Way had already been built long before this great merger occurred,” the authors state.
A history of cosmic violence
According to this new evidence , the Milky Way would have grown much faster than astronomers expected.
Like other giant spiral galaxies in the universe, our galaxy would have accumulated its mass by colliding and merging with smaller galaxies over time. The stars of those unfortunate devoured galaxies mixed with the Milky Way ; something that makes it difficult to discover what galaxies were like before merging.
Using relatively new methods in the astronomical field (astroeismology), the researchers were able to identify the most precise ages possible for a sample of around a hundred red giant stars in the galaxy .
” Astroseismology is the only way we have to access the inner part of the stars, ” says Josefina Montalbán, from the Faculty of Physics and Astronomy at the University of Birmingham in the United Kingdom and leader of the project.
The study also used a spectroscopic study, called APOGEE, which provides the chemical composition of stars. “We have demonstrated the great potential of astroseismology, in combination with spectroscopy, to determine the age of individual stars,” he clarifies.
With these and other data, they were able to show what was happening when the Milky Way merged with an orbiting satellite galaxy, known as Gaia-Enceladus, about 10 billion years ago.
“The Gaia-Enceladus fusion event is believed to be one of the most important in the history of the Milky Way, shaping how we observe it today,” continues Montalbán.
The results allowed them to conclude that a large percentage of the stellar composition of our galaxy was already in place before the merger. The ages of the stars from the “intruder” galaxy were very similar to those of the Milky Way stars themselves at the time of the massive collision, although they were somewhat younger.
In addition to confirming the date of the merger , the discovery could open up new research into the initial conformation of the Milky Way, which could have developed much faster than previously thought.
“We now intend to apply this approach to larger samples of stars and include even more subtle features of the frequency spectra,” the authors conclude. Little by little, we are approaching a much clearer view of the history, evolution and assembly of the Milky Way.
Referencia: Josefina Montalbán, J. Ted Mackereth, Andrea Miglio, Fiorenzo Vincenzo, Cristina Chiappini, Gael Buldgen, Benoît Mosser, Arlette Noels, Richard Scuflaire, Mathieu Vrard, Emma Willett, Guy R. Davies, Oliver J. Hall, Martin Bo Nielsen, Saniya Khan, Ben M. Rendle, Walter E. van Rossem, Jason W. Ferguson, William J. Chaplin. Chronologically dating the early assembly of the Milky Way. Nature Astronomy, 2021; DOI: 10.1038/s41550-021-01347-7
