Properties of Dark Matter: Astronomers Say, Close to Reveal it

Researchers are busy in exploring about the dark matter and the dark energy. In such astronomers have recently reached one step closer to revealing the properties of dark matter enveloping our Milky Way galaxy. They have viewed a new map of twelve streams of stars orbiting within our galactic halo.

Astronomers say that the stream of stars is very important for them as they not only reveal the dark matter that holds the stars in their orbits, they also tell us about the formation history of the Milky Way, making it clear that the Milky Way has steadily grown over billions of years by shredding and consuming smaller stellar systems.

Ting Li, Professor of University of Toronto and the lead author of the paper said that they were seeing those streams being disrupted by the Milky Way’s gravitational pull, and eventually becoming part of the Milky Way”. Prof. Li added, “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 her team are the first group of scientists to study such a rich collection of stellar streams, measuring the speeds of stars using the Anglo-Australian Telescope (AAT), a 4-meter optical telescope in Australia. The team used the Doppler shift of light — the same property used by radar guns to catch speeding drivers — to find out how fast individual stars are moving.

On the way to exploring dark matter, he international team of collaborators initiated a dedicated program — the Southern Stellar Stream Spectroscopic Survey (S5) — to measure the properties of stellar streams: the shredded remains of neighboring small galaxies and star clusters that are being torn apart by our own Milky Way.

Previous studies have focused on one stream at a time, whereas, “S5 is dedicated to measuring as many streams as possible, which we can do very efficiently with the unique capabilities of the AAT,” agencies have reported comments of co-author Professor Daniel Zucker of Macquarie University.

According to the researchers, the properties of stellar streams reveal the presence of the invisible dark matter of the Milky Way.
They say that we see the Christmas lights on a dark night, but not the tree they are wrapped around. But the shape of the lights reveals the shape of the tree. And it is the same with stellar streams — their orbits reveal the properties of the dark matter.

As mentioned in reports, the astronomers can use these observations to work out the chemical compositions of the stars, as well as measuring their speeds, and telling us where they were born.

Professor Alex Ji at the University of Chicago, a co-author on the study said, “These two types of streams provide different insights into the nature of dark matter”.

The researchers have claimed that those new observations are essential for determining how our Milky Way arose from the featureless universe after the Big Bang. Prof. Li added, “For me, this is one of the most intriguing questions, a question about our ultimate origins”.

Quoting to Dr. Sergey Koposov, reader in observational astronomy in the University of Edinburgh and a co-author of the study as saying, reports said, “Gaia provided us with exquisite measurements of positions and motions of stars, essential for identifying members of the stellar streams”. It is said that a crucial ingredient for the success of S5 were observations from the European Gaia space mission.

The team of astronomers plans to produce more measurements on stellar streams in the Milky Way. Taking these results as a starting point, they expect that there will be a lot of dedicated studies looking at stellar streams over the next decade. Being much excited, Prof. Li said that they were trail-blazers and pathfinders on the journey of exploring properties of the dark matter, and the journey was going to be very exciting.