Our home in the cosmos, the Milky Way, contains between 100 and 400 billion stars. Astronomers believe that the galaxy was born about 13.6 billion years ago , emerging from a colossal swirling cloud of gas composed of hydrogen and helium. Over billions of years, the gas built up into a spinning disk where stars formed.
Now, using data from the Gaia space telescope, a team led by researchers at Lund University in Sweden has shown that much of the Milky Way’s outer disk vibrates, wobbles, ripples.
What are these ripples due to?
Astronomers have discovered that the ripples are caused by a dwarf galaxy, now seen in the constellation Sagittarius, that rocked our galaxy in its wake hundreds of millions of years ago.
“We can see these stars wobble and move up and down at different speeds. When the Sagittarius dwarf galaxy passed through the Milky Way, it created wave motions in our galaxy , a bit like dropping a stone into a pond,” explains Paul McMillan, an astronomical researcher at the Lund Observatory who led the study published in the journal Monthly . Notices of the Royal Astronomical Society.
According to a process similar to “galactic seismology”, the scientists modeled a wave pattern that would be able to explain this domino effect behavior that unbalances the position of the stars in the galaxy. They concluded that the ripples were likely released hundreds of millions of years ago, when the Sagittarius Dwarf Galaxy last passed through our galaxy.
Data from the European space telescope Gaia allowed them to study a much larger area of the Milky Way’s disk than was previously possible and have allowed them to predict the outcome of this complex puzzle about the history of Sagittarius and its orbit around our planet. home galaxy. Astronomers suspect that Sagittarius, a very small dwarf galaxy compared to the estimated mass of the Milky Way, was once a much larger galaxy:
“Right now, Sagittarius is slowly tearing itself apart, but 1 to 2 billion years ago it was significantly larger , probably about 20 percent the mass of the Milky Way’s disk,” McMillan said.
Collisions between our galaxy and the Sagittarius galaxy would have occurred at various times throughout history and probably changed the shape and size of our galaxy through cosmic collisions.
“With this new discovery, we can study the Milky Way in the same way that geologists draw conclusions about the structure of the Earth from seismic waves passing through it. This type of “galactic seismology” will teach us a lot about our home. galaxy and its evolution”, concludes Paul McMillan.
Referencia: Paul J McMillan, Jonathan Petersson, Thor Tepper-Garcia, Joss Bland-Hawthorn, Teresa Antoja, Laurent Chemin, Francesca Figueras, Shourya Khanna, Georges Kordopatis, Pau Ramos, Merce Romero-Gómez, George Seabroke. The disturbed outer Milky Way disc. Monthly Notices of the Royal Astronomical Society, 2022; DOI: 10.1093/mnras/stac2571
