Using data from the Gaia space telescope, a team led by researchers from Lund University in Sweden has shown that large parts of the Milky Way’s outer disk are vibrating. The ripples are being caused by a dwarf galaxy, now visible in the constellation Sagittarius, that shook our galaxy as it passed hundreds of millions of years ago.
Our cosmic home, the Milky Way, contains between 100 and 400 billion stars. Astronomers believe the galaxy formed 13.6 billion years ago from a rotating cloud of hydrogen and helium gas. Over billions of years, the gas then accumulated in a rotating disk where stars, like our sun, were formed.
In a new study published in Monthly Bulletins of the Royal Astronomical Societythe research team presents its findings on the stars in the outer regions of the galactic disk.
“We can see that these stars wobble and move up and down at different speeds. As the dwarf galaxy Sagittarius passed through the Milky Way, it created ripples in our galaxy, a bit like throwing a rock into a pond,” says Paul McMillan, the astronomy researcher at Lund Observatory who led the study.
Using data from Europe’s 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 the strength of the waves in different parts of the disk, the researchers have begun to piece together a complex puzzle that provides clues to Sagittarius’ history and its orbit around our home galaxy.
“Right now Sagittarius is slowly being torn apart, but 1-2 billion years ago it was significantly larger, probably about 20 percent the mass of the Milky Way disk,” says Paul McMillan.
The researchers were surprised at how much of the Milky Way they were able to study with the data from Gaia. To date, the telescope, which has been in operation since 2013, has measured the movement of about two billion stars across the sky and the movement of 33 million towards and away from us.
“This new discovery will allow us to study the Milky Way in the same way that geologists infer the structure of the Earth from the seismic waves that pass through it. This type of “galactic seismology” will teach us much about our home galaxy and its evolution,” concludes Paul McMillan.
Materials provided by Lund University. Note: Content can be edited for style and length.