Requestioning the History of the Magellanic Stream. Star formations found leading the charge.

For decades, astronomers and scientists have believed the Magellanic clouds to be a closely related companions to our Milky Way galaxy, having orbited the galaxy several times the last billions of years. Evidence from 2002 and 2005 suggested that this was not the case, and that the clouds were moving much faster than can be explained by a bound orbit with the Milky Way. They concluded that the system was only making its first pass into our Milky Way.

However, recent discoveries have added more to the confusion of history of the Magellanic stream. An international team of researchers led by Dana Casetti-Dinescu of Southern Connecticut State University have, for the first time, discovered young stars that are enveloped in the Leading arm of the stream. The wide and irregular feature of the stream once again suggests that the cloud has had long interaction with the Milky Way.

Observation of the leading arm verified 19 young giant stars. Similar radial velocities between several of the stars suggests formation of the stars together. One star is so young (only about 1-2 million years old), that it could not have possibly been ejected from the Milky Way or the Magellanic Clouds. Finding such stars have helped scientists to determine distances to the system much more easily than before when diffuse gases had to be observed. Observations show that these clouds are extremely close to the Milky Way disk (about 40,000 light years closer than we previously thought!).

Stars form as a consequence of tidal interactions of gaseous materials and the compression of them into dense and heated systems. The travelling cloud making its collision into the diffuse gases of the Milky Way's exterior halo has created the irregularity in the leading arm, and forced the clouds of gases to compress into each other as they travel. The presence of such hot and young stars so close to the Milky Way means that the clouds of gases are moving slow enough to gravitate together and condense.  If the interaction was too violent, gases would be stripped away, and kinetic energy of the system would be too great for the potential energy to be enough to form stars. 

All of the star formation and new observations of the cloud are throwing researchers into disagreement about the past of the Magellanic stream, and to really be able to model and understand its history requires the discovery of more young stars from the system. 

http://www.skyandtelescope.com/news/Young-Stars-Lead-the-Magellanic-Stream-250790851.html

http://www.skyandtelescope.com/news/Finding-the-Source-of-the-Magellanic-Stream-220688101.html