Data from ESA’s Gaia mission is re-writing the history of our galaxy, the Milky Way. What had...
Data from ESA's Gaia mission is re-writing the history of our galaxy, the Milky Way.
What had traditionally been thought of as satellite galaxies to the Milky Way are now revealed to be mostly newcomers to our galactic environment.
For decades it has been widely believed that the dwarf galaxies that surround the Milky Way are satellites, meaning that they are caught in orbit around our galaxy, and have been our constant companions for many billions of years.
François Hammer, Observatoire de Paris - Université Paris Sciences et Lettres, France, and colleagues from across Europe and China, used the Gaia data to calculate the movements of 40 dwarf galaxies around the Milky Way.
In the case of the dwarf galaxies in the new study, which represents the majority of the dwarf galaxies around the Milky Way, their energies are higher still.
"The Milky Way is a big galaxy, so its tidal force is simply gigantic and it's very easy to destroy a dwarf galaxy after maybe one or two passages," says François.
In other words, becoming a companion to the Milky Way is a death sentence for dwarf galaxies.
In the traditional view that the Milky Way's dwarfs were satellite galaxies that had been in orbit for many billions of years, it was assumed that they must be dominated by dark matter to balance the Milky Way's tidal force and keep them intact.
The fact that Gaia has revealed that most of the dwarf galaxies are circling the Milky Way for the first time means that they do not necessarily need to include any dark matter at all, and we must re-assess whether these systems are in balance or rather in the process of destruction.
"Thanks in large part to Gaia, it is now obvious that the history of the Milky Way is far more storied than astronomers had previously understood. By investigating these tantalising clues, we hope to further tease out the fascinating chapters in our galaxy's past," says Timo Prusti, Gaia Project Scientist, ESA. Notes for editors "Gaia EDR3 proper motions of Milky Way Dwarfs. II: Velocities, Total Energy and Angular Momentum" by Francois Hammer et al.