Scientists look at Milky Way’s dark matter

Astronomers think they are one step closer to revealing the properties of dark matter enveloping the Milky Way.

Stellar streams are long filaments of stars produced by the stretching action of tidal forces.

In a new study, experts have mapped 12 streams of stars, which they think creates a more accurate picture of how the Milky Way galaxy, which includes our Earth, was created.

The Milky Way has steadily grown over billions of years by consuming or “eating” smaller stellar systems.

University of Toronto Professor Ting Li, lead author of the new research, said: “We are seeing these streams being disrupted by the Milky Way’s gravitational pull, and eventually becoming part of the Milky Way.

“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 Li and an international team embarked on the Southern Stellar Stream Spectroscopic Survey (S5) to measure the properties of stellar streams.

The properties of stellar streams help reveal the presence of the invisible dark matter of the Milky Way.

Study co-author Professor Geraint Lewis, of the University of Sydney, said: “Think of a Christmas tree.

“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 stellar streams – orbits reveal the matter.”

As well as measuring speeds, the astronomers can use these observations to work out the chemical compositions of the stars to get 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.