Unknown stars stream discovered in the Milky Way

Surveying the Star Speed ​​finds new remnants of a neighboring galaxy in our home galaxy

Visualization of the Aquarius stream and its location in the Milky Way. © Arman Khalatyan, AIP
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An international team of astronomers has discovered a previously unknown star stream in our Milky Way: the "Aquarius Stream". The Star Stream is the remnant of a smaller galaxy in our neighborhood that was torn apart by the Milky Way's gravity 700 million years ago. The find now presented in the "Astrophysical Journal" is the result of surveying the speeds of 250, 000 stars.

"I have a stream": with these words, the 33-year-old New Zealand scientist Mary Williams of the Astrophysical Institute Potsdam enthusiastically presented her discovery to the expert audience of an international conference. Because she had discovered a previously unknown star stream in the Milky Way. The Aquarius stream, named after the constellation of Aquarius, was anything but easy to find.

Unlike almost all known currents, it is inside the galactic disk. There the high concentration of stars of the Milky Way blocks the view. The stream as a localized, geometric shape is not recognizable in the overall picture. "The electricity is right on our doorstep, and yet we could not see it, " Williams says.

Speed ​​measurement revealed "strange" stars

The Aquarius stream first appeared when the astronomer first surveyed the radial velocities of 12, 000 stars in the region, using the RAVE Survey at the Australian Astronomical Observatory. So she found out that 15 stars differ in their speed pattern from the others and shoot at relative speeds of up to 15, 000 kilometers per hour through the rotating disc of the Milky Way.

The comparison of stellar parameters with simulations showed that the stars originally came from a neighboring galaxy as part of a larger stellar stream. The latter, attracted by the gravity of the Milky Way, hit the Milky Way about 700 million years ago, was torn apart and finally formed a stellar stream due to the dynamics. This makes the Aquarius stream a special and relatively young stream. Other known streams are billions of years old and located in the outskirts of the Milky Way. display

Measuring one million stars as a target

The special method, which led to the discovery of the stellar current with the help of the RAVE Survey, allows astronomers to hope for many more discoveries of this kind. By 2012 RAVE should have measured the characteristics of up to one million stars of our Milky Way. Williams has been a member of the team since the project started; Since 2007, she has been responsible for data processing at the AIP.

With RAVE we want to understand the genesis of our Milky Way explains Matthias Steinmetz, the project leader of the multinational RAVE collaboration at the Astrophysical Institute Potsdam. We want to know how often such mergers with neighboring galaxies have happened in the past and what we can expect in the future. One thing is certain: in about three billion years, the Milky Way is the n The closest major collision with the Andromeda galaxy before if you do not even anticipate one of the dwarf galaxies discovered in recent years in the closest cosmic neighborhood. (Astrophysical Journal, 2011; doi: 10.1088 / 0004-637X / 728/2/102)

(Astrophysical Institute Potsdam, 03.02.2011 - NPO)