Stellar streams are long filaments of stars produced by the stretching action of gravitational forces.
The Milky Way has steadily grown over billions of years by “eating” smaller star systems.
“We are seeing these streams being disrupted by the Milky Way’s gravitational pull, and eventually becoming part of the Milky Way," said the University of Toronto's Prof Ting Li, the lead author of the research.
“This study gives us a snapshot of the Milky Way’s feeding habits, such as what kinds of smaller stellar systems it ‘eats’. As our galaxy is getting older, it is getting fatter.”
Prof Ting and an international team embarked on the Southern Stellar Stream Spectroscopic Survey (S5) to measure the properties of stellar streams.
As part of the study, they looked at the speeds of stars using the Anglo-Australian Telescope, an optical telescope in Australia.
Co-author, Prof Daniel Zucker of Macquarie University in Sydney, said that unlike previous studies that have focused on one stream at a time, “S5 is dedicated to measuring as many streams as possible, which we can do very efficiently with the unique capabilities of the AAT”.
The properties of stellar streams help to reveal the presence of the invisible dark matter of the Milky Way.
“Think of a Christmas tree," said Prof Geraint Lewis of the University of Sydney, another co-author.
“On a dark night, we see the Christmas lights but not the tree they are wrapped around. But the shape of the lights reveals the shape of the tree.
“It is the same with stellar streams. Their orbits reveal the dark matter.”
As well as measuring speeds, the astronomers can use these observations to work out the chemical compositions of the stars for clues as to when they were born.
The team now plans to produce more measurements on stellar streams in the Milky Way. The study will be published in the American Astronomical Society’s Astrophysical Journal.