Milky Way disc flipped 90 degrees after dwarf galaxy collision 10bn years ago
10 reported
Astronomers at Durham University have presented evidence that the Milky Way was flipped on its side following a head-on collision with a dwarf galaxy about 10 billion years ago. The event, which occurred long before the solar system formed, involved a dwarf galaxy known as the Gaia Sausage. The Milky Way tore the interloper apart and absorbed its stars, but the collision likely flipped the entire disc of the Milky Way by more than 90 degrees into its current orientation. The researchers used supercomputer simulations of Milky Way-like galaxies to show that such head-on collisions with the Gaia Sausage could cause a “disc flip” that slowly reorients the galaxy over at least a few hundred million years. The discovery was made while investigating the slow rotation of stars in the Milky Way’s halo, which orbit the galactic center at about 25km per second, compared to 220km per second for stars in the disc. The findings are being presented this week at the Royal Astronomical Society’s National Astronomy Meeting in Birmingham.
What’s reported
The collision took place about 10 billion years ago.
The dwarf galaxy involved is called the Gaia Sausage.
The Milky Way tore the dwarf galaxy apart and absorbed its stars.
The collision likely flipped the Milky Way’s disc by more than 90 degrees.
Durham University researchers used supercomputer simulations to model the event.
The disc flip probably took at least a few hundred million years, according to lead researcher Kirill Batrakov.
Stars in the Milky Way’s halo rotate at about 25km per second, while disc stars orbit at about 220km per second.
The ancient collision was first identified in 2018 using data from the European Space Agency’s Gaia mission.
The Gaia Sausage contained stars, gas, and dark matter amounting to more than 10 billion times the mass of the sun.
The collision is recognized as the galaxy’s last major merger and a defining event in Milky Way history.
Key figures
Kirill Batrakov, lead researcher at Durham University.
Sources: The Guardian
