Washington, Sept 18: Astronomers at the Harvard Smithsonian Center for Astrophysics have shown that the Magellanic Clouds are recent arrivals to our galactic neighbourhood.

The Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) are two of the Milky Way's closest neighbouring galaxies. A stunning sight in the southern hemisphere, they were named after Ferdinand Magellan, who explored those waters in the 16th century.

For hundreds of years, these galaxies were considered satellites of the Milky Way, gravitationally bound to our home galaxy.

Now, new research by Gurtina Besla (Harvard-Smithsonian Center for Astrophysics) and her colleagues has revealed that they are recent neighbours to the Milky Way.

As part of their study, the scientists measured the 3-d velocities of the Magellanic Clouds through space with greater accuracy than ever before.

The team observed that the velocities were anomalously high, for which they have now offered two explanations: 1) the Milky Way is more massive than previously thought, or 2) the Magellanic Clouds are not gravitationally bound to the Milky Way.

“We have known about the Clouds since the time of Magellan, and a single measurement has thrown out everything we thought we understood about their history and evolution,” said Besla.

Further analysis by the researchers verified the second explanation. The parabolic orbit they calculated for the Clouds, based on the observed velocities, showed that both are on their first pass by the Milky Way.

Besla said the result carries several implications, including demystifying the Milky Way’s warp.

Earlier, scientists believed gravitational tides due to previous passages of the Magellanic Clouds caused this warp, but since the Clouds arrived only 1-3 billion years ago, they are not likely to be the source of the warp.
 
Another puzzle relates to the Magellanic Clouds themselves.
 
A long trail of hydrogen gas called the Magellanic Stream extends behind the Clouds, spanning 100 degrees of the sky from the earth's viewpoint.
 
Some astronomers have suggested that the Magellanic Stream formed due to tidal interactions between the Clouds and the Milky Way, while others have said that hydrogen was stripped from the Clouds by gas pressure as they plunged through the extremely tenuous gas surrounding our galaxy.
 
But a first-passage scenario rules out both scenarios.
 
“We've been left with a real mystery. One answer has led to many more questions,” said Besla.
 
Besla and her colleagues now intend to focus on the origin of the Magellanic Stream, conducting N-body simulations to puzzle out possible formation mechanisms.
 
“Other astronomers will make direct observations and survey the Stream. The combined power of observational and theoretical research may answer the questions generated by the current work,” Besla said.
 
The paper describing the study is scheduled for publication in the Astrophysical Journal. (With Inputs from ANI)