Our cosmic home, the Milky Way, contains between 100 and 400 billion stars. Astronomers believe that the galaxy was born 13.6 billion years ago, emerging from a rotating cloud of gas made up of hydrogen and helium. Over billions of years, the gas built up into a spinning disk where stars, like our sun, formed.
“We can see these stars wobble and move up and down at different speeds. When the Sagittarius dwarf galaxy passed by the Milky Way, it created wave motions in our galaxy, a bit like when a stone is dropped into a pond. Paul McMillan, the astronomy researcher at Lund Observatory who led the study, explains in a statement.
By using data from the European Gaia space telescope, the research team was able to study a much larger area of the Milky Way’s disk than was previously possible. By measuring how strong the waves are in different parts of the disk, researchers have begun to piece together a complex puzzle, providing clues about the history of Sagittarius and its orbit around our home galaxy.
“Right now Sagittarius is slowly tearing itself apart, but 1 or 2 billion years ago it was significantly larger, probably around 20% of the mass of the Milky Way’s disk,” says Paul McMillan.
The researchers were surprised at how much of the Milky Way they were able to study using the Gaia data. To date, the telescope, which has been in operation since 2013, has measured the movement in the sky of approximately two billion stars and the movement towards or away from us of 33 million.
“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 the seismic waves that pass through it. This type of ‘galactic seismology’ will teach us a lot about our home galaxy and its evolution”, concludes Paul McMillan.