Using data from the Gaia space telescope, a team led by researchers at Lund
University in Sweden has shown that large parts of the Milky Way's outer
disk vibrate. The ripples are caused by a dwarf galaxy, now seen in the
constellation Sagittarius, that shook our galaxy as it passed by hundreds of
millions of years ago.
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 composed of hydrogen and helium. Over
billions of years, the gas then collected in a rotating disk where the
stars, such as our sun, were formed.
In a new study published in Monthly Notices of the Royal Astronomical
Society, the research team presents their findings about 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. When the dwarf galaxy Sagittarius passed the Milky Way, it created
wave motions in our galaxy, a little bit like when a stone is dropped into a
pond," Paul McMillan, the astronomy researcher at Lund Observatory who led
the study, explains.
By using data from the European space telescope Gaia, 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 ripples are in different parts of the
disk, the researchers have begun to piece together a complex puzzle,
providing clues about Sagittarius' history and orbit around our home galaxy.
"At the moment, Sagittarius is slowly being torn apart, but 1–2 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 by how much of the Milky Way they could study
using the data from Gaia. To date the telescope, which has been in operation
since 2013, has measured the movement across 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 travel through it. This type of 'galactic seismology'
will teach us a lot about our home galaxy and its evolution," Paul McMillan
concludes.
Reference:
Paul J McMillan et al, The disturbed outer Milky Way disc, Monthly Notices
of the Royal Astronomical Society (2022).
DOI: 10.1093/mnras/stac2571
Tags:
Space & Astrophysics